NWS: Moderate El Nino winters can be Md.'s snowiest
For those readers hoping for a snowy winter this year after a series of disappointments, there is hopeful news Monday morning out of the National Weather Service's Sterling forecast office. (Likewise, for those who loathe the ice and slush, dangers and inconvenience of wintery weather, these will be discouraging words.)
Forecaster Jared Klein has done a statistical analysis of winters since 1950 and has found 17 winters that were influenced by the El Nino phenomenon in the tropical Pacific, like this one is expected to be. The long and short of it, says Chris Strong, also at Sterling:
"With moderate strength El Nino's [like this one] we have statistically the greatest chance of above-normal snowfall."
What they're saying is that not all El Nino winters are alike for the mid-Atlantic states. Some will be snowy; some not. Here's how they tend to break down, according to Klein:
* On average, weak El Nino winters bring below-average temperatures and below-average precipitation. Not generally conducive to lots of snow.
* Strong El Ninos, on average, bring us above-normal temperatures and precipitation. The cold air tends to remain well to our north, so most of the precipitation falls as rain rather than snow.
Moderate El Ninos, on the other hand, seem to offer the greatest statistical chance that moisture and storms passing across the southern U.S. will "seed" the Atlantic coastal storms that tend to bring us our deepest snowfalls. We've already seen plenty of coastal storms this fall, including the big one last week that battered OC's dune line, and another one today.
Nothing is guaranteed, of course. There are other shorter- and longer-term climate patterns - including the North Atlantic Oscillation - that can determine whether there will be, for example, enough cold air in place to make snow-makers out of the coastal storms.
That helps to explain why, of the 17 El Nino winters since 1950, eight produced above-normal snowfalls, while nine were below-normal. (Weak La Nina winters can produce big snow, too, as it did in January 1996, right, although that's less common.)
Still, there is plenty to look forward to this time, Klein said. "The above-average El Nino winters have been associated with some of our snowiest winters, especially during moderate El Nino episodes. With the ongoing El Nino episode expected to continue, even strengthen to moderate levels this winter, El Nino will likely play an important role with the winter climate here in the greater Baltimore and Washington, D.C. area."
Among the most memorable snowstorms in El Nino winters was the Feb. 11, 1983 storm that dropped 22.8 inches on Baltimore. Then there were three storms in 1987: Jan. 22 (12.3 inches), Jan. 25 (9.6 inches), and Feb. 22, (10.1 inches).
Here is another summary of the El Nino effect on Baltimore snowfall, also from the NWS at Sterling:
"El Niño winters in the Baltimore Region mean a milder than normal December. They also tend to be all or nothing when it comes to snowfall. Either there are no significant snow storms and season snow totals average less than 5 inches or there is a tendency toward multiple snow storms with seasonal totals above 30 inches. These storms usually occur in January and February. November, December, and March often see little or no snow."
Here are the snow totals for the past 10 years at BWI. The long-term average (1971-2000) is 18.2 inches:
2008-2009: 9.1 inches
2007-2008: 8.5 inches
2006-2007: 11.0 inches
2005-2006: 19.6 inches
2004-2005: 18.0 inches
2003-2004: 18.3 inches
2002-2003: 58.1 inches
2001-2002: 2.3 inches
2000-2001: 8.7 inches
1999-2000: 26.1 inches