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July 31, 2006

Heat index this week: 110-115

With daytime highs headed for triple digits, and humidities high enough to slice, heat index readings are likely to bubble up above 110 degrees this week, and perhaps as high as 115. That's more than enough to trigger Excessive Heat Warnings for the region, and those were hoisted this afternoon by the forecasters at Sterling.

Some readers scoff at the heat index readings. And it's easy for the tool to be misused.  It surely means nothing to shout about a heat index of 93 when the actual temperature is just 91 or 92.

But when the temperatures rise above normal body temperature - 98.6 or so - cooling off becomes a real problem. And when humidities are so high they impair the evaporation of sweat from the skin - the body's chief cooling mechanism - people can get into serious trouble.  So when it's 100 degrees, and the heat index is 110, it's time to pay attention.

There are dozens of dead people out west this week whose demise stands in silent testimony to the hazards of ignoring the stress that high temperatures and humidities place on the human body. So be cool.

In the meantime, here's AccuWeather's take on this heat wave.

Posted by Frank Roylance at 4:37 PM | | Comments (0)
Categories: Forecasts

Nasty heat ahead

The good news is that the fierce heat and humidity we're facing this week already has an end - sort of - in sight. The bad news is that we're looking at five or six days of ferocious weather before we finally break out of it.

The forecast speaks for itself. Daytime highs will climb to near 100 degrees, and there will be some measure of relief overnight, with lows near 75 degrees. Even if you can escape the heat by huddling in your air-conditioned house, or car, or workplace, BGE will own your wallet this week as we spin our fans and churn our air conditioners to stay ahead of this blast furnace outside.

Excessive heat warnings were posted for Tuesday through Thursday across Central Maryland. That means heat index readings could top 110 degrees.

We could easily break daily heat records Tuesday and Wednesday. Here are the records for August as they stand now.

You can blame the same high-pressure system that stalled over the west coast last week, sending thermometers to record highs all up and down the Pacific states. The Great Plains caught it over the weekend, and now it's headed our way

Relief could be as near as the weekend. The forecasters in Sterling are posting expected highs near 85 degrees for Saturday and Sunday, which is actually a shade below normal for this time of year. But they seem to have some doubt about whether the cold front they're counting on to deliver the cooler weather will actually make it this far south. Here's a snippet from their forecast discussion, in their somewhat archaic telegraph English:


Posted by Frank Roylance at 10:46 AM | | Comments (1)
Categories: Forecasts

July 27, 2006

Heat kills

There is just an amazing amount of bad heat-wave news out there today. California, St. Louis, England, France ... it goes on and on. People are overheating, even catching fire. What's it all mean? Maybe nothing. But lots of people are wondering.

Posted by Frank Roylance at 2:55 PM | | Comments (3)
Categories: Events

Showery and hot ahead

We may have gone over the "heat hump" this week, but it's going to remain plenty hot for a while, and the heat, coupled with rising humidities, will keep us in line for thunderstorms every day until Sunday, if the forecasters at Sterling are right.

The forecast has us facing 90 degrees or more almost every day from now into early next week. Worse, the system that brought tropical rains of the Gulf to soak parts of Texas this week is making its way into the Northeast, bringing more warm, wet air and increased chances of thunderstorms. A real summer steam bath into early next week.

So, go to the beach. The rain chances are somewhat lower out there, and the heat - upper 80s - will be a shade cooler than back here in Bawlmer. From where I'm sitting, it looks pretty darn nice out there right now.

Posted by Frank Roylance at 2:34 PM | | Comments (0)
Categories: Forecasts

July 26, 2006

Is dust keeping storms at bay?

It may be too early to say this hurricane season will fall short of prognosticators' expectations. But if it does, we may have African dust to thank for it. Weather observers have been noting the huge volumes of dust that have been blowing off the northwest coast of Africa this summer, into the eastern tropical Atlantic. That's normally the spawning ground for many of the Atlantic basin's big hurricanes. 

Some scientists believe that high volumes of aerosols - dust - in the atmosphere change the dynamics of hurricane formation. It could simply mark the infusion of dry air from the continent, which would interfere with hurricane formation. Or, it might act by reflecting sunlight and disrupting convection - rising currents of warm, moist air over the ocean needed for hurricane formation.

Here is a discussion of the issue. And here is a satellite image of the dust currently wafting off the African deserts and over the eastern Atlantic. Here is another from last week.

Scientists have tracked African dust clear to the United States. It is believed to play a role in providing micro-nutrients such as iron to the Caribbean Sea. And, it is suspected of transporting certain pathogens from the Old World to the New, some of which are thought by some to be affecting corals.

Posted by Frank Roylance at 11:31 AM | | Comments (0)
Categories: Hurricanes

July 25, 2006

Heat, outages coast to coast

Hot weather, combined with massive strains on the power infrastructure have caused outages and worse on both coasts and in the heartland this week. Here's a sampling from New York City, St. Louis and California. So say a little word of thanks when that AC clicks on today. It's not to be taken for granted these days.

It could also be raining way too much, as it has been in typhoon-weary South China, and Houston, where a tropical disturbance has sloshed ashore.

So we'll be seeing our temperatures break 90 in the next few days, with higher humidities. Hardly seems worth fussing about in light of the suffering elsewhere. Just unfurl the Slip 'n Slide and enjoy our good fortune.

Posted by Frank Roylance at 4:04 PM | | Comments (2)
Categories: Events

Storm Daniel heads for Hawaii

Our weather this week is so normal, and the Atlantic basin is so boring (so far) this hurricane season, that I am forced to look for today's trouble in Hawaii. And even that is looking less exciting than it did a few days back.

The island state appears to be in the bulls-eye of Daniel, a tropical system that looked pretty fearsome a few days ago, but has since faded. The storm is being watched by the Central Pacific Hurricane Center, in Honolulu. (I once visited the center during an 18-hour layover in Hawaii. It's on the campus of the University of Hawaii. Not a bad posting for those folks. Here's what you're missing by not living/working there.)

Anyway, here is what Hurricane Daniel looked like on July 21, when it was far at sea but flirting with Category 5 status. Here is what's happened to it since it ran into cooler waters, drier air and wind shear. And here is the forecast storm track. At this point, happily, it looks like vacationers on the islands may be in for some rain and crummy weather by Friday, but no calamity. Here's the forecast.

Posted by Frank Roylance at 11:25 AM | | Comments (0)
Categories: Hurricanes

July 24, 2006

California in the broiler

Now it's the Left Coast's turn to broil in the summer sun. Temperatures in the Pacific Coast states in recent days have soared toward the 100-degree mark in places that don't often get that hot. The power grid is struggling, and not always successfully, to keep up with demand for cooling energy. Better to hop in the surf. Here's a clip.

And here are the forecasts and conditions for San Diego, Sacramento, Portland, OR, and Spokane, WA.  You could go to Las Vegas, instead. But you'd better stay indoors. Here's the forecast.

Posted by Frank Roylance at 2:04 PM | | Comments (0)
Categories: Events

Complaints? Stifle them

The WeatherBlog's Complaints Dept. is closed for the week. Sorry. The forecast calls for sunshine most of the week, with daytime highs in the 86 to 89 degree range, which is almost exactly "normal" for this time of year. Ditto for the overnight lows - in the upper 60s to low 70s through the weekend.

On Wednesday, we go over the Heat Hump for the year, the date when the 30-year daily average temperatures begin their long, slooow cooling trend. That will continue through Jan. 30, when the average high of 41 degrees once again turns upward on the long climb toward summer.

There is a chance for some thundershowers later in the week, and through the weekend. But it's not a huge risk, and besides, it's gotta rain every once in a while to get the dirt off my car.

While we're at it, I should take a paragraph here to thank Baltimore Magazine for citing's WeatherBlog as Baltimore's "Best Blog" for 2006. See the current edition. My 93-year-old mother agrees, of course, although she's not altogether sure what a "blog" is.

Posted by Frank Roylance at 12:10 PM | | Comments (4)
Categories: Forecasts

Hot, but compared to what?

Henry E. Temple, 80, of Baltimore, whose daughter describes him as "a big ol' weather geek from way back," believes there's a more accurate way to compare temperatures for two time periods than the one used by the National Weather Service. Here's his question:

"When comparing the same two calendar time periods from different years to determine which was the hotter time period, I believe that the area under the sawtooth of highs and lows starting from a baseline would yield a more accurate measurement than averaging high and low readings. I am curious as to your opinion on this assumption. Thank you.  - Henry E. Temple, Baltimore City

I'm no mathematician, Mr. Temple, but I agree with you. Simply averaging the daily high and low, or the month's high and low, ignores the dimension of time.

For example, imagine a day during a prolonged heat wave. When the new day begins at midnight, the temperature at BWI is still 83 degrees. It remains way too hot all through the wee hours. Fans and air conditioners are running all night. And when the sun comes up, it only gets hotter. The mercury climbs quickly to 90 degrees by 9:30 a.m., and by 2 p.m. it's 100 degrees. The heat persists into the evening. (We've had days just like this in Baltimore; you can look it up.)

Then around 11 p.m., a cold front pushes into the region. Thunderstorms break out, rain cools the pavement and a new air mass replaces the hot air. Temperatures at BWI drop from 80 degrees at 11 p.m. to 65 degrees by the time the day expires at midnight. Average temperature for the date: 82.5 degrees (100 degrees + 65 degrees divided by 2= 82.5 degrees).

Now consider another scenario. Same heat wave. Same high temperature of 100 degrees at 2 p.m. But this time the cold front moves in at 2:30 p.m. instead of 11 p.m. By 4 p.m., the temperature has dropped to 70 degrees, and by 11:59 p.m., it's 65 degrees at the airport. Average temperature for the day is 82.5 degrees (100 degrees + 65 degrees divided by 2= 82.5 degrees).

On the weather service record books, and for all eternity, the days will look identical. The high was 100 degrees, the low 65 degrees, and the daily average temperature was 82.5 degrees. But arguably, for anyone who had to be outdoors in it, the first scenario produced a much "hotter" more miserable day than the second. There were more hours with higher temperatures. Perhaps we need a new term - maybe "degree-minutes," or "heat-hours."

It's not an alien concept to the science. For example, hurricane researchers have a measurement for hurricanes that captures the element of time. In addition to a storm's maximum wind speed, and the maximum category it attains on the Saffir-Simpson Scale of Hurricane Intensity, scientists record "storm days" (the number of days a storm spins at tropical storm strength); "hurricane days" (the number of days a storm packs hurricane-strength winds); and "intense hurricane days" (days at Category 3 or higher).

That capacity to include time in the measurements allows a more precise comparison of storms and storm seasons. A storm that blows hard enough and long enough to be a Category 1 hurricane for 8 days, is clearly more of a menace than a tropical storm that reaches hurricane strength for only one day. Yet both are remembered and recorded as Category 1 storms.

And you're right, Mr. Temple, the way to capture that element of time in the temperature data would be to measure the area under the daily temperature curve, above a standard baseline. Makes sense, but it also involves a more involved and sophisticated calculation. The weather service folks and their computers are surely capable of it. But as far as I'm aware, nobody does it. And implementing it would mean a break from the way things have always been done, and a break from more than a century of continuous, comparable data - a valuable resource. So, while such a measure could be added to the database, I suspect it would never replace the old system of simple averaging.

Good question. Thanks. Comments always welcome.

Posted by Frank Roylance at 11:15 AM | | Comments (1)
Categories: Ask Mr. Weatherblogger

July 21, 2006

When the rains quit in Nebraska

Several years ago I talked The Sun into sending me out to Nebraska to do a story on people who travel far to see the stars. I flew out to Omaha and drove to Valentine, in the Sand Hills region of north-central Nebraska, to attend the Nebraska Star Party - a gathering of amateur astronomers under one of the darkest skies on the continent.

While there, I fell in love with the Sand Hills. It's place of rolling grasslands and vast cattle ranches, watered by springs and lakes that bubble up from the underlying sands and the Ogallala Aquifer beneath. The hills, it turns out, are actually sand dunes. Until about a thousand years ago the place was a Sahara-like desert, and the dunes were on the move. It was a barren wasteland, and could become one again if the rains quit.

The Sand Hills depend on spring and summer rainfall that pushes north and west from the Gulf of Mexico. It's not abundant rain, but it's enough to keep the grass growing and the cattle (and before them the buffalo) fed. Not surprisingly, scientists at the University of Nebraska have been studying the state's climate for many years, trying to understand why the rains stopped and turned their land into shifting sand, and whether it might happen again.

Here's a release from the university describing the latest findings by their researchers, who say it was a shift in the prevailing winds a thousand years ago - perhaps linked to climate change in Medieval Europe - that turned on the rains from the Gulf and began watering - and stabilizing - the Sand Hills. What they don't know yet is what it would take to turn the rains off again, an event that would choke the economic life from the region.

Posted by Frank Roylance at 5:53 PM | | Comments (0)
Categories: Drought

Cool "ice halo" in torrid AZ

As Arizonans broiled in 100-degree-plus heat, ice crystals hovered just five miles over their heads. Sunlight refracted through the crystals created an eerie, rainbow-like halo, which was captured by photographer Peter Strasser, in Tucson. Here's the link.

Here's an explanation for the phenomenon, and here's another shot, by Alan Tasky. 

Posted by Frank Roylance at 12:16 PM | | Comments (0)
Categories: Cool pictures

Beryl blows by Nantucket

Tropical Storm Beryl passed over the island of Nantucket, off the southeast coast of Massachusetts, overnight. It's now scooting toward the northeast at more than 23 mph, and it is expected in Nova Scotia later today. Here's the latest (and last) advisory as this storm continues to weaken and merge with surrounding weather systems. Here's the satellite loop. And here's the forecast track.

Here's an AP story on the storm's minor impact on Nantucket, via the website of my alma mater, the New Bedford Standard-Times.

This is the kind of storm that tends to lull people into a state of mind that says they have little to fear from tropical storm systems. Our memories are short, and most storms miss us, or pass by without much impact. Our experience begins to tell us that tropical storm systems are no big deal. Then we fail to prepare, or act appropriately when real danger finally looms. It's always that last storm that bites us. "We should have gotten out," they said, as they floated away.

Posted by Frank Roylance at 11:56 AM | | Comments (0)
Categories: Hurricanes

July 20, 2006

Wet weekend ahead

Another cool front approaching from the upper Midwest will bring even cooler temperatures this weekend, but the cooler (80s) air will have to collide first with the moist, warm air from the Gulf that accompanied now-departing Tropical Storm Beryl. And that will likely trigger showers and thunderstorms. The forecast shows a 50 to 60 percent chance of thunderstorms through the weekend.

Some of those storms could be severe. The National Weather Service has posted a hazardous weather outlook for late tonight and tomorrow. But the threat could persist through the weekend.

For the beaches, here's the forecast. Looks like a risk of storms all weekend, but there should be some good stretches of beach time, with temps in the 80s. Any Beryl-related high surf and rip tides should be abating as the storm moves east. The greater hazard lies on the New England coast.

Posted by Frank Roylance at 4:19 PM | | Comments (0)
Categories: Forecasts

Thar she blows!

Tropical Storm Beryl appears headed for southeastern Massachusetts, with Cape Cod, Martha's Vineyard and the old whaling center of Nantucket already under tropical storm warnings. The forecast there doesn't look all that bad. Some gale winds and high waves. But it's nothing the islanders haven't seen before.  Tourists may get a kick out of it, and Dramamine will be in order aboard the ferries.

Here's the latest advisory. Here's the view from space. And here's the latest storm track forecast.

In the meantime, the storm is tracking off the coast of Maryland. That should be kicking up some waves at the beaches, but so far it looks pretty tame.

Posted by Frank Roylance at 9:27 AM | | Comments (0)
Categories: Hurricanes

July 18, 2006

Tropical depression forms off Carolinas

Hurricane forecasters in Miami have reported the development of the season's second tropical depression, a couple of hundred miless southeast of the Outer Banks. It's not a tropical storm yet. But it's the first disturbance to get the Hurricane Center's interest since Tropical Storm Alberto formed in the Gulf early last month. Tropical storm watches have been issued for eastern North Carolina.

Here's the latest advisory. Here's the view from space. There's a great deal of uncertainty in the discussion about where this weather system will go. It could move onto the North Carolina and Virginia coasts or out to sea. Here's the official forecast track, for now. If it does go ashore, it will likely threaten no more than lots of rain. You can watch for new developments and advisories at the National Hurricane Center website.

Posted by Frank Roylance at 11:03 AM | | Comments (2)
Categories: Hurricanes

Hoo doggies, it's hot

OK, so it was 90 degrees on the car's thermometer at 9:30 this morning. That's danged hot. And the forecast warns of highs near 100 degrees this afternoon - AT THE AIRPORT. Downtown, on the streets, on the rooftops, it's sure to be hotter. Heat advisories are up again today for the afternoon and evening. Once again, it's going to be hot nearly everywhere across the lower 48.

Humidities, too, will be high - even worse than the relatively mild dew points in the 60s yesterday. And air quality is sure to be nasty, as well. So heed the advice coming from public health officials and stay indoors as much as possible, find a cool place to hunker down and wait it out.

Relief, of a sort, is en route in the form of a weak "cold" front from Canada. It should drop the highs for the rest of the week into the normal range for this time of year in Baltimore - upper 80s to low 90s. The front's approach could bring a few thunderstorms, some of which could become severe. In the meantime, the heat and humidity afford us a small chance of storms throughout the week.

Here, while we're at it, are some other stories about summer weather gone amok in China, South Korea, and the United Kingdom.

Posted by Frank Roylance at 10:24 AM | | Comments (0)
Categories: Forecasts

July 17, 2006

How "brutal" is Maryland weather?

Damon Costantini writes to ask whether Maryland has more extreme weather than "nice" weather. Here's his note:

"Do we have more days over the course of a year in Maryland when it is considered 'very nice out' as opposed to extremes of heat or coldness?

"What I mean is, it seems like there are less times in Maryland when we say 'wow it is really nice out ' (ie, about 70-75 with a cool breeze) than there are times when we say 'ugh, it's brutal out' (ie, 100 degrees and humid or 25 degrees and freezing).

"Using an assumed general consensus on what 'nice out' is as compared to 'brutal out', do we have more brutal extremes than we have 'nice' days in Maryland? Or does it just seem that way because we possibly notice the extremes moreso than we may notice when it is nice out? "

Damon, I'd say without any hesitation whatsoever that we notice and remember the extremes more than the "nice" days. I suspect your question was prompted by the current heat wave. And reader traffic on this blog invariably peaks when we're facing a snowstorm, as we were in mid-February, or when we're enduring some other misery such as last month's rains. When the weather is benign, only the poets among us take notice.

I'm going to climb way out on a limb here, Damon and guess that you're a Maryland native. Anybody who has grown up or lived nearly anywhere else will agree with me that Maryland has the longest, nicest spring and fall of nearly anyplace in the country.  Winters here are generally short and mild. I've lived and worked in New Hampshire and upstate New York, and I know what "mud season" and "lake effect snows" are. We have neither here. I've had to take my car battery inside for the night to ensure the car started in the morning; I've watched the snow piles melting in May, and witnessed the leaves turning in late August as a fragile New England summer rushes away.

Sure, we can have bouts of cold weather and ice in Maryland. Some of us can remember the bay freezing over, or record snows collapsing the roof of the railroad museum. And we know what summer heat and humidity mean.

But this is neither Plattsburgh nor New Orleans. Extreme events, while memorable, are brief and few. Mostly Maryland enjoys long seasons of gorgeous weather in spring and fall, and short, mild winters. Summers are sultry, but we adjust and learn to stay out of the mid-day sun. Sometime late in August, we almost always get a break in the heat and look forward to months of fine weather. We don't turn the AC on in earnest until June, and resist the furnace switch until  November.

Weather records show we routinely see some highs in the 60s - sometimes 70s - in every winter month. Summer days in the upper 90s and 100s are pretty uncommon. Using your criteria for "brutal" - that is, 100 and above or 25 and below - here is the tally for last year:

2005 Summer days of 100 degrees or more:  None

2005-2006 Winter days that never rose above 25 degrees: One.

On the other hand:

2005-2006 Winter days that reached 60 or more: 11

That's my response. Readers? Any comments?

Posted by Frank Roylance at 5:25 PM | | Comments (3)
Categories: Ask Mr. Weatherblogger

Nineties. Get used to it.

Today and tomorrow look like the worst days in what promises to be a long, hot and miserable week in the Land of Pleasant Living. The forecast shows highs in the 90s every day, all week, with plenty of humidity in the air. Relief in the form of a cool front from Canada may stall to our north.

A heat advisory has been posted for today, extending into the evening. And it's likely to be posted again tomorrow. With high humidity, the heat index - really the "misery" index - is expected to climb to 105 degrees. That's what it "feels" like, because high humidity slows our body's ability to cool itself by sweating. That sweat has to evaporate to have its cooling effect, and that's more difficult when the atmosphere is already loaded with moisture.

After tomorrow, things will "cool" a bit. But the humidity will remain high, so it will continue to feel very uncomfortable. And as the heat wave continues, even though daily highs are a bit lower, homes and workplaces that were bearable in the early days of the Big Heat will become less so. Vulnerable populations will begin to be seriously distressed and ill.

The demand for power to run fans and air conditioners will also go up as this heat wave lengthens. Public utilities will come under more stress, especially in light of the the fact that this heat wave is not limited to one region of the country. Twenty-one states yesterday reported at least one station with highs of 100 degrees or more. Forty-seven states hit 90 or more. This heat is cooking almost everybody from L.A. to GA. So power-sharing will be difficult. I would not be surprised to see brownouts somewhere in the East by week's end.

And, we can expect the air quality to deteriorate in the high heat. You can monitor just how bad it's getting by clicking here, and then on the map point closest to the city you're interested in. For Baltimore, click here.

None of this should come as a complete surprise. This is, after all, the hottest week of the year in Baltimore, on average. See Friday's post.

Posted by Frank Roylance at 11:54 AM | | Comments (1)

July 14, 2006

Hot times in the old town

It's that time of year - moving into what has been the hottest week of the year, on average. The Baltimore forecast calls for highs in the 90s beginning on Sunday and stretching into all of next week. Monday's forecast calls for an AIRPORT high of 99 degrees. That could threaten the 101-degree record set for the date in 1988.

Here's AccuWeather's take on the heat as it pushes in from the Southwest.

The rain chances for Baltimore drop to zero after Saturday, so there will be plenty of clear sky and time for the sun to bore in and drive the mercury higher.

The average daily highs at BWI-Marshall over the 30-year period from 1970 to 2000 are 88 degrees between July 16 and 25 - the highest of the year. The overnight lows for that period average 66 degrees. They finally start to retreat on Aug. 5.

Suddenly, a nice February snowstorm begins to sound appealing. Or a sprint to the beach. Here is the showery OC forecast.

Speaking of heat, the first six months of this year in the continental U.S. turn out to have been the hottest on record - since 1895 - according to the National Oceanic and Atmospheric Administration. Last month was also the second-warmest June on record. Here's the release.

Sunday update: Here's Weather Channel weather blogger Stu Ostro's take on all this heat and how it relates, or doesn't, to global warming.

Posted by Frank Roylance at 6:08 PM | | Comments (0)
Categories: Forecasts

July 13, 2006

Why no rainbow?

David Gerstman writes to Ask Mr. WeatherBlogger about rainbows:

"On Sunday we were headed back from the Catskills; south on 81 through Pennsylvania. Shortly after we passed Hazelton a storm passed us - traveling eastward. After we passed through the storm we could see the setting sun in the west and the overcast sky to the east.

"In similar circumstances at home those would be conditions to create a rainbow. But on Sunday we didn't see one. Why not? Other than sun shining on a passing rainstorm, what other conditions are necessary for a rainbow? - David."

Sunshine and rainfall are both necessary to produce a rainbow, David, but they aren’t, by themselves, sufficient. It’s all about angles, and French mathematician Rene Descartes figured it all out in 1637. Here's what I learned after poking into your question for a while:

Rainbows occur when sunlight strikes the spherical drops of rain as they fall from clouds. The light enters each drop and sort of ricochets around inside the droplet. It gets refracted, or bent, as it passes from air to water, reflected off the rear inside surface of the drop, then refracted again as it passes from water back into the air and back toward the observer. It emerges at an angle 42 degrees from the original path of the sunlight.

In addition, the refraction splits the white light into its various constituent frequencies, or colors, each of which bends at a slightly different angle – between 42 and 40 degrees. That’s what produces the concentric bands of color. We see just one color from each droplet, depending on our angle of view.

The size of the droplets, too, affects the colors we see. The smallest drops produce very white bows, including "fog bows." (Airline passengers can sometimes see such fully circular fog bows or "cloud bows" when they look out the window toward a cloud that’s in the opposite direction from the sun.) The largest droplets yield very red and yellow rainbows, weak in greens and blues.

Sometimes, some of the sunlight knocks around inside the droplet a second time, emerging at a slightly different angle, and we see a double rainbow.

What we actually perceive is the combined effect of light refracted and reflected from every droplet in the shower, and of the angles at which it returns to our eyes.

But to see any rainbow, the observer has to be exactly between the sun and the rain – facing what scientists call the "anti-solar point," or the spot in the sky directly opposite the sun.

The ‘bow" is actually the top portion of a circle with an angular radius from the observer of 42 degrees around that point. The Earth blocks the lower portion of the circle. At sunset, with the sun at the horizon, the top of the arc would be 42 degrees above the horizon.

I’m not sure why you didn’t see a rainbow on your trip south on I-81. There are a couple of possible answers.

If you’re not standing (or driving) directly between the sun and the rain shower, you will see nothing, or perhaps only a partial bow. Or, I would guess that if high clouds float between the sun and the shower, observers on the ground might be able to see both, but the direct sunlight may not reach the falling droplets. So, no rainbow.

That’s why rainbows (and consequently pots of gold) are so rare. And delightful.

You can read more about rainbows here. And here's a link to rainbow photos.

Posted by Frank Roylance at 10:30 AM | | Comments (1)
Categories: Ask Mr. Weatherblogger

Amazing NASA footage

Ever wonder what it would be like to parachute from the edge of space to the ocean? Me neither. But NASA strapped a camera to the side of one of the solid rocket boosters that helped launch the shuttle Discovery into space last week, and has posted the results for all to see. Just click on the link, and then on the "cool movies" link in the text.

The video begins at launch. We're looking down the booster as the launch pad and the ground drop away. We're on the starboard booster - one of the two reusable rockets on each flight - as it separates from the shuttle, and falls away while the orbiter continues on toward orbit. Then we ride with the booster as it falls back toward the Atlantic Ocean, tumbling at first before it pops its parachute. And we're there when it splashes into the water and bobs around in a tangle of parachute lines waiting for the recovery ship. So cool.

Posted by Frank Roylance at 10:03 AM | | Comments (1)
Categories: Cool pictures

July 12, 2006

New Yorkers await celestial event

If skies are clear, New Yorkers who find themselves on the streets of Manhattan at around 8:27 this evening will be treated to an annual celestial event that evokes thoughts of Stonehenge - the great stone markers in England that served the ancients as a celestial calendar.

New Yorkers will have to make-do with their skyscrapers and east-west street grid, but the effect could be almost as dramatic as the setting sun throws its light directly down all the island's cross-town streets. It only occurs twice each year at sunset, today and May 28. Read more here.

In the meantime, we have an extremely hazy day today in Maryland. Not much of a sunset visible this evening, I'd guess. Here's how it looked yesterday from space.

Posted by Frank Roylance at 3:07 PM | | Comments (0)
Categories: Events

Tropics calm, for how long?

The tropics remain calm as July approaches its mid-point. Thus far we have seen only one tropical storm, Alberto, which drew much attention from a Katrina-spooked media corps as it came ashore on the northern gulf coast of Florida on June 13. One person died in the storm, but elsewhere its winds and flooding and tornadoes did relatively little damage.

By this time last year, the Atlantic basin had already produced five tropical storms - three of which grew to hurricane force. These included:

TS Arlene:  June 8-13. Landfall on the Florida panhandle

TS Bret:  June 28-30. Landfall in Mexico.

Hurricane Cindy: July 3-7. Category 1. Landfall in southeast Louisiana.

Hurricane Dennis:  July 4-13. Category 4 storm that left 42 dead from Cuba to Florida.

Hurricane Emily:  July 11-21. The only Category 5 hurricane ever recorded in July. Struck Grenada, and Mexico. Six were killed, and 90,000 were driven from their homes in Mexico.

The rest of the 2005 season was similarly hyperactive, with 28 named storms, the last of which faded away in early January 2006.

While the quiet early weeks of the 2006 season have been welcome, they are no guarantee that we will escape this year unscathed. Atlantic hurricane seasons typically peak between mid-August and early October. And it only takes one bad storm in a heavily developed area to make a terrible season.

Forecasters have predicted above-average activity this year, but falling somewhere short of last year's record count. Sea-surface temperatures are warm and, with few hurricanes thus far to sap that energy, the seas remain well-primed for storms. Anything above 80 degrees Fahrenheit (26.6 Celsius) will support tropical storm formation when other conditions fall into place.

Posted by Frank Roylance at 9:05 AM | | Comments (0)
Categories: Hurricanes

July 11, 2006

Why no barometer?

Jim Anthony, of Mt. Airy, asks: "Why is the barometer reading for the Baltimore area NOT listed in the papers, and very seldom shown on TV ???"

I know, Jim. I like a good barometer, too. I inherited a handsome brass one from my grandparents. And I have an electronic one as part of the wireless weather station on the WeatherDeck in Cockeysville. It's a fascinating instrument. It measures changes in atmospheric pressure that can signal a frontal passage, or the end of the worst part of a storm, or the approach of better, or worse weather.

I can't answer for the TV stations. We do still include it on the main page. As near as we can tell, The Sun dropped its barometer readings from the printed weather page sometime in the late 1990s or early 2000s. You're the first reader we can recall who's raised a question about it. That suggests something about how many people relied on it.

It was probably dropped to make more room for other data. Our weather page - actually a half-page on the back of the Maryland section - is crammed with information compiled by a commercial service. It includes national and international temperatures and forecasts for 89 cities, national and Maryland weather maps, daily, monthly and annual weather data, lunar phases, sun and moon rise and set times, ultraviolet, air quality and pollen readings, marine forecasts and tide tables and wave heights and water temperatures on the bay and at the beaches. Oh, and there's a five-day forecast and some guy chewing on his spectacles.

That's a lot to pile onto half a page. I'm looking at a copy of The Sun from July 9, 1952, and if you subscribed then you got a daily half-column containing yesterday's temperatures for 32 U.S. cities, a one-paragraph, two-day forecast for Baltimore, hourly temperatures for the day before, tide, sunset and sunrise times, a pollen count from Hopkins, cumulative precipitation data for the day, month and year, and - yes - barometer readings taken at 8:30 a.m., 2:30 p.m. and 8:30 p.m.

There was also a hand-drawn national weather map on another page, showing isobars, or lines of equal barometric readings. (It ran adjacent to the passenger, mail and freight stats for the day at Friendship Airport; they indicated 362 people flew out that day on 54 flights, and a ton - 2,067 pounds - of freight arrived. Boy, have those numbers changed! But I digress.)

Even with all the information on today's weather page, we could probably shoehorn in a barometer reading. The more important question seems to be "why bother?"

Barometer readings and isobars are indirect indicators, and arguably less accessible and useful to the vast majority of readers, on the vast majority of days, than explicit local reports and forecasts. I would argue that relatively few readers fully understand what atmospheric pressure is, or what changes suggest about the weather to come.

So, they're gone, along with the daily passenger counts at BWI.

But we aim to serve our readers, so we're investigating whether and how we could restore barometric readings to the Weather Page - maybe the previous day's high and low, like the temperature. If anyone else out there, besides Jim, would like to see them return, leave a comment here and I will be sure our "deciders" see it.

Posted by Frank Roylance at 6:00 PM | | Comments (5)
Categories: Ask Mr. Weatherblogger

It's haaaawt ...

This, my friends, is July in Bawlmer. Temps poking into the 90s, humidities of the tropical rain forest variety, and little prospect for relief. And it's not even close to record misery hot. Just ordinary, garden variety, it's-midsummer-in-Baltimore-so-quit-your-whining hot.

The forecast calls for highs this week in the high 80s and low 90s. That's about normal for this time of year - the hottest of the season on average. Humidities will be high thanks to a flow of air from the Gulf of Mexico. There's a small chance for thundershower-type relief every day through Thursday. But don't look for a big break on the temperature or humidity. There's a weak cold front dawdling off to our north and west, but it's not expected to push through here until the weekend.

But cheer up. It could be lots worse. The northern Plains are in for even hotter weather. And the weekend, at least, looks sunny. Here's the early beach forecast.

Posted by Frank Roylance at 11:40 AM | | Comments (0)
Categories: Forecasts

June ended warm and very wet

This will come as news to absolutely no one. And on top of that, it's coming 11 days late thanks to a vacation on the high seas. But in the interests of consistency and a complete record, here are the stats from the month of June.

June was extraordinarily wet. BWI-Marshall recorded 7.32 inches of rain in all, nearly 3.9 inches above the 30-year average for the month. That's essentially two months of rain in one. The overage can be blamed on a solid week of rainfall between the 23rd and 29th, when a gusher of moist, tropical Atlantic air took aim on a stalled cold front draped across the Northeast. The wet air rain up over the cold air, and dropped its moisture. The result was some extensive flooding, especially across the Susquehanna River watershed.

The wettest day was Sunday, June 25, when 2.75 inches fell at BWI - a new record for the date, shattering the 1.95 inch mark set on June 25, 1872. But it rained for seven straight days, leaving 5.14 inches in all. Without that week, June would have ended drier than average. In fact, even with all that rain, BWI through June 30 remained 2.72 inches short of average precipitation for the calendar year.

The average temperature was 73.1 degrees, or 1.2 degrees warmer than the 30-year norm. The hottest day was June 18, when the thermometer at BWI hit 95 degrees - no record. There were six days in the 90s, and 15 that topped out in the 80s. The coolest days were June 10 and June 14, when the daytime high rested at 73 degrees. Nice.

Not surprisingly, with all that rain, most of the month was cloudy or partly so - 28 days in all. Only 2 were rated clear- June 18 and 30.

For those of you who write the checks, June ended with 252 cooling degree days, or 6.7 percent more than average. That means that the warm weather boosted demand for air conditioning by 6.7 percent above the average for June. And that means, all else being equal, we shelled out that much more dough to keep cool. That, of course, will be quickly forgotten once our July bills from BGE come in, reflecting the 15 percent rate hike that began July 1. An ice bag on the forehead will help.

Posted by Frank Roylance at 10:57 AM | | Comments (0)
Categories: By the numbers

July 10, 2006

Vacationing in Delaware?

Here's a little geography lesson on the nation's second-smallest state, with a neat view from orbit. Now, go back to the beach and amaze your family with your knowledge. And be a mensch; take them a cool one.

Posted by Frank Roylance at 11:53 AM | | Comments (1)
Categories: Cool pictures

July heats up

Vacation's over ... sigh ... and it's way past time to plug in the numbers for July. This is, of course, our hottest month. The average high temperatures peak at 88 degrees during the third week of the month. Then, mercifully, the shortening days and decreasing sun angles begin to work their magic and temperatures start to slip.

But not by much. The average high only drops a degree during July, to 87. And average nighttime lows stick at 66 degrees.

Record high temperatures for Baltimore-Washington International Thurgood Marshall Airport remain in the upper 90s and low 100s all month.

The all-time hottest day on record for Baltimore was on this date - the 10th - in 1936, when air conditioning was rare and Baltimoreans sometimes slept out in the parks to beat the heat in those airless little rowhouses. Don't try that today. It was 107 degrees that day. The most recent new record high set for July was 100 degrees, reached on the 4th in 2002. The coolest record daily high temperature is 97 degrees, set on July 12, 1908, and matched on July 24, 1987.

The coldest July day on record at BWI was just five years ago. On July 3, 2001 the overnight low touched 50 degrees, a day after reaching 51 degrees, a record for a July 2 in Baltimore.

July also still hosts a record set during the first year of official record-keeping for the city. On July 28, 1871 the instruments recorded 2.28 inches of rain, which still stands as the wettest July 28 on the books.

The wettest July was in 1889, when more than 11 inches fell downtown. The driest was in 1955, with just 0.30 inch of rain. Normal July precipitation is 3.85 inches, based on the 30-year record from 1970-2000.

Posted by Frank Roylance at 11:37 AM | | Comments (0)
Categories: Almanac

July 2, 2006

Gone fishin'

Your intrepid WeatherBlogger is taking a break. I'll be back here in the Blog Control Blockhouse on July 10. In the meantime ... break a buck and buy a newspaper, will ya? Our families have to eat, too. Through the magic of planning ahead, I have left enough fascinating and informative "Weather Page" (last  page, Maryland Section) items to keep the dead-tree version of The Sun fully stocked until I return. Until then, clear skies, calm seas.

Posted by Frank Roylance at 7:50 AM | | Comments (0) | TrackBacks (3)
Categories: Notes to readers

Jimmycane defined

My Weather Page entry in Saturday's Sun included a long list of variants on the term "hurricane," compiled by Chris Landsea, a hurricane researcher at the National Oceanic and Atmospheric Administration. The last word I included was "jimmycane."  The word prompted the following response from Heather Dewar, an environmental writer, former Sun reporter and Florida native. Many thanks, Heather. Chime in anytime.

"I can't explain the origin of the word 'jimmycane' but I can tell you that is is NOT a synonym for hurricane.

"A jimmycane is a lesser storm. The term was used in Florida when I was growing up to describe a violent storm that blows in with little or no warning, does a bit of damage, and quickly moves on. My dad used it whenever we got caught in a squall on the boat: 'Aw, it's just a jimmycane.'  This was meant to be reassuring.

"The word was never used widely and is very rare today. You hear it mostly from people who grew up in the rural parts of the state. I suspect my dad picked it up when he was a college student in Gainesville in the 1950s. I don't know if it is used elsewhere in the hurricane belt.

"As for the origins, it's fun to guess. Many old-time Floridians pronounced the word hurricane as 'harrycane.' Maybe some old-timer was claiming he'd been hit by a hurricane, and his friends didn't think so, and made fun of him by moving on down the alphabet from Harry to Jim."

"I have a cat named Jimmycane. She is gray with underlying streaks of yellow, like the eerie sky you sometimes see before a summer squall, and she tends to blow into a room, quickly wreak havoc, and move on.  - Heather"

Posted by Frank Roylance at 6:20 AM | | Comments (2)
Categories: Hurricanes

July 1, 2006

July 4th sky spectacular!

It would be hard to imagine a more entertaining spectacle in the night sky than the one Marylanders can witness on the evening of July 4, if they're  paying attention - and if skies are clear.

On this one night, when lots of us are outdoors after dark anyway, we'll have the moon, the solar system's largest planet, and the biggest spacecraft anyone has ever seen - all making an appearance at the same time, and all visible with the naked eye.

Oh, and there may be fireworks, too.

Here's the deal: By about 9:30 p.m. - just about the time the fireworks are ending - the moon and Jupiter will be side-by side, low in the southwest. The moon will be at its first-quarter phase. Its right side will be illuminated by the sun, which will have set below the western horizon almost exactly an hour earlier.

Just to the moon's right (west) is the bright star Spica, in the constellation Virgo. The other (brighter) "star" to the moon's left (east) is the planet Jupiter.

But the climax of the evening will come at about 9:37 p.m., when the International Space Station will rise above the northwest horizon. It will look like a bright, steady, fast-moving star, headed toward the eastern horizon. When it first becomes visible to Marylanders, it will actually be more than 200 miles above Lake Michigan, speeding toward the southeast, passing over Lakes Huron and Erie, across New York, Pennsylvania and New Jersey, and then out over the Atlantic.

If the shuttle Discovery launches this weekend, there may actually be two spacecraft in view, including two station crewmen and seven shuttle astronauts. If they've already docked, you'll see just one point of light. But if they launch late, you may actually see two, flying one behind the other, as the shuttle chases down the station for docking. What a sight on the 4th of July! But it will all depend on the timing.

From the Baltimore area, the station will apear to fly through the bowl of the Little Dipper - just east of the Big Dipper's bowl. At about 9:40 p.m. it will reach its highest point - about 60 degrees, or two-thirds of the way up from the northeast horizon to the zenith (straight up). The station will fly on, passing close to bright Vega, a star at the apex of the Summer Triangle, before disappearing into the Earth's shadow at 9:42 p.m.

Take the kids and have a Happy Fourth! To read more, click here.

Posted by Frank Roylance at 10:57 AM | | Comments (2) | TrackBacks (1)
Categories: Sky Watching
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About Frank Roylance
This site is the Maryland Weather archive. The current Maryland Weather blog can be found here.
Frank Roylance is a reporter for The Baltimore Sun. He came to Baltimore from New Bedford, Mass. in 1980 to join the old Evening Sun. He moved to the morning Sun when the papers merged in 1992, and has spent most of his time since covering science, including astronomy and the weather. One of The Baltimore Sun's first online Web logs, the Weather Blog debuted in October 2004. In June 2006 Frank also began writing comments on local weather and stargazing for The Baltimore Sun's print Weather Page. Frank also answers readers’ weather queries for the newspaper and the blog. Frank Roylance retired in October 2011. Maryland Weather is now being updated by members of The Baltimore Sun staff

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