Tuesday Night Technical Discussion

Synopsis:

High pressure will continue to dominate over the Mid-Atlantic Region for the first half of the week. A low-pressure system to our west will track over the great lakes and eventually to the north of us, and it's associated cold front will bring scattered rain showers across PA Wednesday night into early Thursday morning. Behind the front a northwest flow will provide cold air advection and a chance for scattered lake effect showers for northwestern counties Thursday night through Friday. High pressure will return to the area and provide mostly clear skies and slightly warmer conditions for the weekend.

Short Term: (Tuesday night through Wednesday night)

Cloud cover tonight should moderate temperatures, with the 18Z 12km NAM indicating mid to upper 30's for the western half of the state and low to mid 40's for the eastern half of the state due to low-level clouds associated with the southeasterly flow off the ocean. The mean southerly flow will persist during the day Wednesday providing warmer temps ahead of the cold front associated with the low-pressure system to our west. This low pressure will slowly make its way toward the great lakes and begin to push the high pressure currently over the region off the coast. The system will pass north of the region and its associated cold front will cross the state. The 18Z GFS and NAM, as well as the 21Z SREFMEAN, agree with the timing of the cold front to reach western counties by Thursday around 06Z and the pre-frontal precipitation to reach northwestern counties by Thursday at 03Z.

Long Term: (Thursday into the weekend)

As the cold front crosses the region it will bring widespread scattered rain showers for the entire state. A northwesterly flow will follow behind the front and initiate cold air advection as the 540dm line dips just south of the state Thursday night into early Friday, indicated by the 18Z NAM and GFS. The northwesterly flow will also provide a chance for scattered lake effect rain/snow showers Thursday night through Friday morning, mainly for the higher elevations in the northwestern portion of the state. High pressure will return to the region Friday night, but quickly move off the coast by Saturday evening. Another low pressure will move well north of PA and an associated shortwave will traverse New England on Sunday. Precipitation is not likely anywhere in the state and high pressure will follow in the wake of the shortwave passage for the beginning of the workweek.

~ A.J. Herbert