Mesoscale Aspects of the 2007 St. Patrick's Day Storm

On 17 March 2007 a significant winter storm affected the Northeast United States. This storm produced an interesting mix of hazardous weather in Northern Maine. Snowfall totals across the northern tier of the state reached 14 in. (35.5 cm). Central and coastal areas in Maine received a prolonged period of sleet and some freezing rain followed by significant amounts of rainfall. Rainfall amounts ranged from 1.5 to 3.0 in. (~ 3.8 to 7.6 cm) leading to potential flooding issues due to melting snow. High winds speeds also were a factor with maximum wind gusts along the coastline topped 43 kts (22 m s^-1).

This storm provided an interesting forecast challenge. Computer model guidance provided reasonable solutions during the evolution of this event. However, the mesoscale forcing aspects of this storm were not well correlated with synoptic forcing as is typically the case with strong Nor'Easter storms. This made the quantitative precipitation forecasts output from the models suspect as the event unfolded.

We will provide a detailed overview of the meteorological evolution of this storm. Specifically, mesoscale forcing aspects will be compared with stability and moisture parameters to aid in the understanding of how this storm evolved. It will be shown that most of the forcing associated with the snowfall and rainfall occurred in an environment with strong mesoscale forcing, but weak synoptic forcing. We hypothesize that mesoscale forcing was the major contributor to upward vertical motion during a critical time period during this event when significant amounts of precipitation occurred.