4/7/2007 Mid-Atlantic Snowstorm: Initial Estimates

[donsutherland1]

The NAM and GFS have moved into closer agreement in terms of a likely snowfall for a portion of the Middle Atlantic region tomorrow. At the same time, the trough that will be in place for the event rivals that of March 30-April 1, 1964 when a significant late-season event blanketed such cities as Baltimore, Richmond, Salisbury, and Washington, DC, though the placement differs somewhat.

NCEP Ensemble Mean 500 mb Anomalies at 48 hours:


March 30, 1964 500 mb Anomalies:


Taking into consideration the 1964 event and the computer guidance, I believe it is likely that some part of the Mid-Atlantic region could pick up 3"-6" of snow with locally higher amounts. Considering that much of the precipitation is likely to fall within a 6-hour period, dynamic cooling should ensure a mostly or wholly snow event for Washington, DC and northward. The appreciable or greater snows will probably fall across Baltimore, Salisbury, Washington, DC and Wilmington. Daily snowfall records should be challenged or broken in the Baltimore and Washington, DC areas.

Daily snowfall records for April 7:
Baltimore: 0.2", 1972
Washington, DC:
...DCA: 0.6", 1972
...IAD: 1.1", 1990

Lesser amounts could whiten the ground in Philadelphia and Atlantic City. Flurries or a burst of non-accumulating snow could occur even farther north.

At this time, my initial estimates are as follows:

Atlantic City: 0.5"-1.5"
Baltimore: 2"-5"
Philadelphia: 0.5"-1.5"
Richmond: 1" or less
Salisbury: 2"-5"
Washington, DC: DCA: 1"-3"; IAD: 1"-3"
Wilmington: 2"-5"

[donsutherland1]

Per the 0z GFS and NAM and latest radar trends, my final estimates are as follows:

Atlantic City: 1"-3"
Baltimore: 1"-3"
Philadelphia: 0.5"-1.5"
Richmond: 1" or less
Salisbury: 3"-6"
Washington, DC: DCA: 1"-3"; IAD: 1"-3"
Wilmington: 1"-3"

[Stephanie]

I saw a few flakes this morning. Fortunately, from the looks of the radar, the heavier snow was just off the coast of NJ. It's mostly cloudy right now.

[donsutherland1]

Verification:

How ugly can a forecast get? Few words can describe the following bust! Only Richmond was within the forecast range.

From 4/6/2007: 2:05 pm:
Atlantic City: 0.5"-1.5"; Actual: Trace; Error: 0.5"
Baltimore: 2"-5"; Actual: 0.2"; Error: 1.8"
Philadelphia: 0.5"-1.5"; Actual: Trace; Error: 0.5"
Richmond: 1" or less; Actual: 1.0"; Within range
Salisbury: 2"-5"; Actual: 1.0"; Error: 1.0"
Washington, DC:
...DCA: 1"-3"; Actual: 0.4"; Error: 0.6"
...IAD: 1"-3"; Actual: 0.2"; Error: 0.8"
Wilmington: 2"-5"; Actual: Trace; Error: 2.0"

From 4/6/2007 11:50 pm:
Atlantic City: 1"-3"; Actual: Trace; Error: 1.0"
Baltimore: 1"-3"; Actual: 0.2"; Error: 0.8"
Philadelphia: 0.5"-1.5"; Actual: Trace; Error: 0.5"
Richmond: 1" or less; Actual: 1.0"; Within range
Salisbury: 3"-6"; Actual: 1.0"; Error: 2.0"
Washington, DC:
...DCA: 1"-3"; Actual: 0.4"; Error: 0.6"
...IAD: 1"-3"; Actual: 0.2"; Error: 0.8"
Wilmington: 1"-3"; Actual: Trace; Error: 1.0"