Well, that was quite a night. Rain, wind, snow, ice, even thunder and lightning. And this morning, slippery roads and school delays. And almost none of it was in yesterday's forecasts.
But my editor, Mike Himowitz, knew it was coming. Yesterday, as senior editors were calling for a Wednesday story on all the mild weather in January, he warned them that such a story would upset the gods and bring snow and ice and other wintry woes. We write about a weather trend, and it comes to a crashing end.
Sure enough, the brass woke up this morning with a warm-weather story on the front page, and ice and a dusting of snow on the ground, and realized Mike was right.
The wild night was enough to stir some comments and queries from normally quiet WeatherBlog readers. Here are two:
From Robert Loskot - "Snow on green leaves, as my sainted mother always used to say. Here in Upper Crossroads in Harford County, we not only had about a half dozen displays of staccato-like, vicious lightning with thunder that shook the dishes in the cabinets, but we received a burst of snow that turned the yard a dusty white with the grass tufts showing through. It was an impressive 20 minutes, reminding me of that bygone commercial: It's not nice to fool Mother Nature."
And this from David Gerstman - "Last night about 10 PM two of our sons came upstairs excitedly telling us that there was a "thunder snow" going on. We were of course aware of the thunder as it had been quite loud. And it was unusual to hear at this time of the year. But the idea of there being a thunder storm in which it was snowing is not something I ever remember.
"How (in)frequent are such occurrences? Since I suspect that the Weather service doesn't actually track "thundersnows" let me ask what unique conditions (if any) must occur for there to be a "thundersnow."
Obviously, thundersnow is very rare. Meteorologist David Schultz has studied the phenomenon and estimates that only seven in 10,000 recorded thunderstorms produce snow. But there are a lot of thunderstorms, and a lot of snowstorms. So there are plenty of opportunities for thunderstorms to produce snow, or snowstorms to produce thunder. I can recall several severe winter storms in Baltimore since I moved here 25 years ago that have been spiked by claps of snow-muffled thunder.
But the question this morning is why the cold front that ripped through the region last night produced lightning (which makes the thunder we heard) and why it wasn't forecast more than a few minutes before it occurred. So, I called the NWS forecast office in Sterling, Va. and asked meteorologist Brian Guyer what happened last night.
He said lightning (and therefore thunder) requires strong vertical motion in the clouds. That motion strips electrons from water and ice particles and creates an electrical difference between the ground (positive) and the base of the clouds (negative). When that difference is strong enough, a spark - a lightning bolt - jumps the gap.
In a severe winter storm, that electrical gap is created by the strong vertical motion of falling snow and ice. That's true "thundersnow."
But last night's event, despite the date, was not a typical winter storm, Guyer said. "It was just associated with a cold front."
A cold air mass was driving south and east out of Canada, barging into the warmer air ahead of it that's made January here so mild. And because cold air is more dense, and therefore heavier than warm air, it drove under the warmer air like a shovel, and forced it to rise.
That vertical motion along the fast-moving moving front produced the electrical charge that gave us our lightning, and thunder. It's different from the kind of thunderstorms we see in mid-summer. In those, the sun heats air at the surface and starts it rising by convection, forming towering thunderclouds that produce the familiar lightning and thunder.
"But in the spring and fall you do see storms that form along cold fronts," Guyer said. But "much of this month has been like March" in Maryland, he said. So last night's storm was really a springtime, cold-front thunderstorm in late January. Any snow that came with it was no more than flurries triggered by the cold air and moisture behind the front.
No such storms were predicted in yesterday's forecasts, so I asked Guyer whether they took forecasters as much by surprise as the rest of us.
"I wouldn't say it was a surprise," he said. "It was more that there were not strong indications in the models or in any (balloon) soundings that showed we would have as much instability as we saw at the surface ... The amount of instability that did come to the surface was more than we anticipated. And it was very brief. It moved through very quickly."
Sounds like a surprise to me.