An early spring storm laid down 1 to 4 inches of snow across the metro region Tuesday. The 1.7 inches at Reagan National and 3.8 inches at Dulles were both records for the date.
The storm turned into yet another overachiever, with snowfall amounts exceeding our initial forecast in the immediate D.C. area and western suburbs. However, we correctly characterized the storm impacts and timing, even early on – stressing that most of the snow would melt on the roads, with the exception of some slush build-up in the morning hours. We also accurately predicted no school and government disruptions.
The lone problem with our initial forecast was low-balling the amount of snow that would accumulate on grassy areas. Our first call snow total forecast, issued Monday afternoon, for roughly 1 inch of snow across the region, was clearly too low.
But 10:40 p.m. Monday night, we increased our snow total west of the city to 1-3 inches, which wasn’t a bad forecast as most spots were in that range and only a few locations west and southwest of town reached 4 inches or more. On the other hand, that forecast still only called for 1 inch along the I-95 corridor – which was too low.
At 10:00 a.m. Tuesday morning, as it became clear based on radar, observations, and short-term modeling more than 1 inch would fall along the I-95 corridor (about 0.5″ had fallen by that time), we increased our forecast for this region as well as locations to the west (previously in the 1-3 inch zone) to 2-5 inches – which was a reasonable and appropriate adjustment – although made later than ideal.
Ultimately, you could argue we were too conservative with snow totals – which is a fair criticism. Leading up to the storm, models pretty quickly increased the amount of precipitation forecast and I would have liked to see us respond to this trend a bit faster and more decisively. The calendar and climatology probably made us overly cautious.
From a practical standpoint, however, the storm impacted the region exactly as we expected; it was not a hazardous event. I also think we did a reasonably good job nowcasting the storm and making the adjustments that were necessary.
I’d give us a grade of B- for this event as we passed the critical test of articulating how significantly the storm would affect the region even if our snowfall total projections fell a little short.
Your comments and feedback, as always, are appreciated.