March Lion

Some thoughts on the possible 3/5-7/2013 storm...

1. The strong blocking that has been in place since the start of the month has strenghtened further overnight. The AO is now -3.470. The current blocking regime has now lasted 27 consecutive days.

2. The computer guidance is in strong agreement that interior portions of the Mid-Atlantic region will likely pick up a significant snowfall. Baltimore and Washington, DC could also pick up 4" or more. Some of the guidance is more aggressive with snowfall amounts for Washington, DC and Baltimore. The heaviest snows, where one-foot or larger amounts could occur will likely cover western/central Virginia and western Maryland. Such cities as Charlottesville, Sterling, and Frederick could be in the area where some of the heaviest snow falls.

The NAM brings a foot of snow to Washington, DC (DCA). Since 1840, there have been four storms that brought 10" or more snow to Washington, DC in March:

March 16-17, 1843: 12.0"

March 27-28, 1891: 12.0"

March 7-8, 1941: 10.7"

March 29, 1942: 11.5"

3. There is major disagreement on the computer guidance as to whether appreciable or even significant snows could extend from the northern Mid-Atlantic region into New England. The ECMWF has consistently argued against such an outcome. The GFS has argued for such an outcome in its last three runs in a dramatic switch that is almost reminscent of its taking the lead on what turned out to the be the Boxing Day Blizzard of December 2010. The pattern is sufficiently complex and the pieces sufficiently close that either the ECMWF or GFS could score a dramatic coup or a dramatic bust.

Climatology would argue for a more northward extent of the precipitation. Not all of the precipitation would fall as snow, along coastal regions.

At the same time, historic experience with storms that dumped 4" or more snow in Washington, DC (DCA) in March with an AO-/PNA+ setup would support the ECMWF. Since 1950, there have been 5 such cases:

March 5-7, 1962: DCA: 4.0" (much heavier amounts farther west); NYC: 0.2"; BOS: 0.4"

March 30-31, 1964: DCA: 5.8"; NYC: None; BOS: None

March 3, 1978: DCA: 4.1"; NYC: 5.0"; BOS: 9.2"

March 1-2, 1980: DCA: 4.9"; NYC: None; BOS: None

March 9, 1999: DCA: 8.4"; NYC: None; BOS: None

In terms of the blockbuster Washington, DC storms cited earlier, only the March 1843 and March 1941 storms brought significant snow to New York City and Boston.

Hence, at least at this point in time, I lean toward a scenario somewhat closer to the ECMWF when it comes to the northern Mid-Atlantic and New England, but with not quite as sharp a cutoff and 6" or greater snows extending into metro Washington, DC. The possibility of at least some accumulation of snow in the northern Mid-Atlantic and southern New England areas exists. There remains a smaller chance (probably about 1-in-3) that a 6z GFS-type solution works out.