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Posted at 01:10 PM ET, 02/28/2012

Toughest places to forecast weather: a match for Washington D.C.?

Washington, D.C.’s weather forecasting challenges were documented yesterday. From trying to nail down the rain-snow line in winter to predicting the timing and location of pop-up thunderstorms in summer, the fickle nature of D.C.’s weather presents problems for even the most seasoned forecasters.

What forecast challenges do other regions contend with? Are they as difficult as Washington, D.C.’s? Let’s take a look...

The Great Lakes


Dick Searing, left, helps pace a runner before the start of the Lake Effect Half Marathon, Saturday, Feb. 25, 2012 in Syracuse, N.Y. (David Lassman - AP)
If weather forecasting is challenging in the D.C. area, the lee (downwind) shores of the Great Lakes in winter would be a triple challenge. Those areas are what are known as the Great Lakes “snow belts,” where “lake-effect” squalls can indiscriminately and quickly pile up tremendous amounts of snow in some areas, while leaving nearby communities unscathed.

An old saying with great meaning for snow belt residents is (after a cold front moves through in the winter) “it clears up stormy.” What the locals mean is that, especially in early winter when the Lakes are still relatively warm and “open” and an arctic air mass sweeps through in the wake of a cold front, convectional cloud bands or “streets” develop. Strengthened by the temperature disparity between air and water, these bands can produce snow squalls, even thundersnows, of great intensity (3-5 inches per hour or more.) Later in the winter, as the water cools and even freezes, this process diminishes.

These fickle lake effect snow bands can sometimes reach as far south and east as the highlands of western Maryland and the eastern panhandle of West Virginia. And once in a great while, when an unusually frigid air mass crosses over the unfrozen Chesapeake, Maryland’s Eastern Shore has been known to experience Great Lakes-type snow squalls. But east of the mountains and west of the Bay, post-frontal winter weather in the D.C. area is typically clear to partly cloudy.

The Midwest and South


A tornado moves through Tuscaloosa, Ala. Wednesday, April 27, 2011. (Dusty Compton - AP)
More so than any other type of weather year, it seems like 2011 could’ve been classified “the year of the tornado,” with deadly severe weather outbreaks repeatedly occurring throughout the heartland, the Southeast, and even New England. Around the D.C. area, we’ve also had our share of tornadoes, or at least tornado threats. But it’s the heartland and the South, west of the Appalachians, where some of the most powerful twisters have formed historically.

In this geographically unique zone – free of obstructing mountain ranges – frigid, Arctic air from Canada clashes directly with steamy, moisture-laden air from the Gulf of Mexico and tropics.

The resulting temperature clash results in levels of instability unrivaled not only in the U.S. but also anywhere in the world. In addition to instability, spin in the atmosphere is a necessary condition for tornado formation, which requires wind shear, that is, winds blowing from different directions and at different speeds at different altitudes.

David Imy, a forecaster at the NWS Storm Prediction Center in Norman, OK, has the task of understanding and predicting when those same ingredients will come together.

From Imy’s point of view, the biggest forecast challenge in Oklahoma, and much of the Midwest and South for that matter, is to determine if, when, and where the “initiation of convection,” or rising air parcels, will occur. Akin to determining where a particular bubble will surface in a boiling pan, this is an incredibly difficult forecast problem. In the Midwest and the South, forecasters must confront this problem more than anywhere else. And given the region’s unparalleled potential for thunderstorms to fire up explosively and spawn violent, deadly twisters, the stakes could not be higher.

The Pacific Northwest

The city of Seattle is not normally known for bright blue skies and typical chamber of commerce weather. Instead, dismal, gray, overcast, and drizzly conditions are all too common, especially in winter. The marine climate, similar to that of London, allows for frequent repetition of the same forecast. Across the pond, they would say “a little bit of rain, here and there--now and then.”

Johnny Burg, a meteorologist with the Seattle office of the NWS, says that forecasting for the Puget Sound area is relatively straight-forward most of the time. With Seattle lying between two mountain ranges (the Olympic Range to the west and the Cascades to the east), the biggest challenge, however, is predicting the effect of easterly winds which can accelerate greatly as they blow over the Cascades and crash into the lowlands. Known as downslope windstorms, they periodically cause significant damage. Forecasting these events is also a major challenge in the lee of the Rocky Mountains. In Boulder, Colorado, these wind storms have produced damaging gusts over 100 mph.

By contrast, in Washington, D.C., downsloping winds from the more diminutive Appalachians are typically associated with mild weather and light to moderate winds.

The Southeast and Gulf Coast


Hurricane Irene off the Southeast coast on August 25, 2011
Aside from the forecasting dilemmas caused by severe thunderstorms and the occasional winter storm that affect the area from coastal North Carolina to south Texas, hurricanes present the biggest prediction challenges.

Although great strides have been made in predicting hurricane tracks*, unfortunately, this has not been the case with hurricane intensities. As a result, when one of these monster storms approaches, forecasters pay close attention for any signs of sudden strengthening (or weakening).

In August 2004, the National Hurricane Center (NHC) in Miami, Florida was indeed paying close attention to Hurricane Charley as it approached Florida’s west coast from the southwest. Nevertheless, experts failed to foresee the dramatic intensification that would occur just prior to landfall.

Initially expected to strike as a Category 2 storm (96-110 mph) during the morning of August 13th, Charley’s maximum winds, in the space of just a few hours, increased to Category 4 (131-155 mph). Ultimately, the storm caused about 30 deaths overall and 13 billion dollars in Florida damages alone.

NHC meteorologist Todd Kimberlain believes that although predictions of sudden intensity changes have improved slightly, there won’t be a real breakthrough for a while. This will depend upon current efforts to better understand and detect changes in the internal dynamics of these storms.

Due to its inland location, aside from the occasional exception such as Isabel in 2003 and Irene last August, D.C.’s primary hurricane threat is not from wind, but from the excessive rains from a storm’s remnants (e.g. tropical storm Lee), which local forecasters usually handle well. As a result, difficult hurricane prediction problems are not as common here.

Conclusion

So……in answer to the question, “Is D.C. weather more difficult to forecast than in other parts of the country?” It depends on which part you’re talking about during which season and what forecaster you ask.

(* According to Lixion Avila, senior hurricane specialist at the National Hurricane Center , “the error distance five days out is now the same as it was three days out 10 years ago.”)

By  |  01:10 PM ET, 02/28/2012

Categories:  Latest, Lipman, Local Climate, U.S. Weather

 
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