The Uncertainty of Forecasting Snowfall

A "High" Impact Winter Storm is on Tap  (Source: NWS)

Millions of people from the Nation’s Capital northward are poised to see the largest winter storm since “Snowmageddon” in February 2010.  Although the last two winters have had above average snowfall in the Mid-Atlantic Region, this prospective winter storm has the increasing potential of being not only high impact but could also be a historic storm.

The computer forecasting models that meteorologists use, such as the American model, “GFS” and the European model or “ECMWF” among others have shown remarkable consistency in suggesting that a coastal storm would develop on Friday.  Given the cold air that’s already in place, that would create an ideal scenario for snowfall in the Mid-Atlantic Region.  However, it’s unusual for the models to show such general agreement so far in advance, so meteorologists take notice when they do. 

These forecast models use a series of mathematical equations that rely on surface data to provide a forecast or solution.  Since surface data is limited over the ocean, it’s important to wait until a storm comes ashore so the models can incorporate more data and improve their reliability.  Since the approaching storm (that will serve as the catalyst for the anticipated coastal storm) only came ashore from the Pacific Ocean yesterday, the models should do a better job today and tomorrow of predicting how much snow is likely to occur in the Mid-Atlantic Region.

Two other key variables to monitor are the exact location of the expected coastal storm and where it tracks.  A shift in storm track of only 50 miles could make the difference between rain, mixed precipitation and snow.  If the storm tracks farther south or east, that would mean less mixed precipitation and a lower snow total for the Washington, D.C – Baltimore corridor.  A storm track farther north but offshore would result in more snow as it draws in both cold air and Atlantic and Gulf moisture – similar to the record snowstorms of December 2009 and February 2010. 

It’s important to remember that while the weather forecast models are more accurate than they used to be, they still aren’t perfect.  There is an inherent amount of uncertainty involved in forecasting winter weather.  That’s why social media is both a good and bad thing.  It helps meteorologists communicate the latest forecasts to the public and also serves as a conduit for viewers to interact with their favorite meteorologists.  The downside is that weather rumors often spread online and it’s hard for casual observers to separate legitimate information posted by scientists as opposed to sensationalized posts designed to get headlines – such as those calling for significant snow or ice accumulations a week or more in advance. 

It isn’t possible to accurately forecast snowfall amounts more than 48 to 72 hours in advance.  That’s why it’s important for people to rely upon meteorologists – such as those on the WUSA9 weather team, as well as the Capital Weather Gang.  I’ll be working with my colleagues on the WUSA9 weather team to provide the latest updates.

Washington, D.C.’s Top Ten Snowstorms (Measured at National Airport – Source: NWS)

1.  28.0” (January 27-29, 1922)

2.  20.0” (February 12-14, 1899)

3.  18.7” (February 18-19, 1979)

4.  17.8” (February 5-6, 2010)

5.  17.3” (January 7-9, 1996)

6.  16.6” (February 10-11, 1983)

7.  16.4” (December 18-19, 2009)

8.  16.4” (February 16-18, 2003)

9.  14.4” (February 15-16, 1958)

10.  14.4” (February 7, 1936)