Synopsis:
The storm system that brought a brief period of heavy thunderstorm Monday morning will continue to make its way offshore. A cold front will sweep through Pennsylvania late Monday night and bring cooler temperatures to the region for Tuesday. More clouds will move in Tuesday night as a Midwest storm system approaches. Expect mostly rain Wednesday and Wednesday night as the Midwest storm system passes, some of the higher elevations may see periods of wintry mix. The bulk of precipitation should be gone by late Thursday morning, but the clouds will linger. The temperatures will also be below average for the rest of the week after the storm.
Short-term (Tuesday – Tuesday night):
The low pressure system that brought the Northeast showers and thunderstorm in the dawn hours of Monday will continue to slide offshore. The cold front associate with this departing system will sweep through the region Monday. Behind the cold front, we will no longer see temperatures in the upper 60s to low 70s, but only in the low 50s. A ridge of high pressure over northern Ontario will usher in some drier air from Canada. Expect partly cloudy skies Tuesday morning, but clouds will build once again in the afternoon as another storm system approaches from the Midwest. The clouds will start out as some high cirrus clouds as surface warm air associated with a warm front overruns the pre-existing cold air over the region. The clouds shall gradually thicken throughout the night and some showers may break out toward daybreak starting from west to east.
Mid-term (Wednesday – Thursday night):
The trickiest part regarding this forecasting period has to be the precipitation type. Most of the models had colder solutions earlier today with Central and Northern Pennsylvania seeing mostly periods of wintry mix and freezing rain. However, as the day progressed, these models have adjusted to considerably warmer solutions. The precipitation should start early Wednesday morning as warm low level moisture overruns the colder air supplied by the high pressure over eastern Canada. The precipitation type will vary across the State, depending on how much colder air will remain in place. The early WRF model has the coldest solution with the sub-freezing cold air column stretching from 850-mb all the way down to the surface for much of Pennsylvania. This solution would put the central and northern parts of the state under an area of snow, sleet, and freezing rain. The GFS on the other hand had a warmer solution with the 850-mb freezing line along the PA-NY border. However, the latest short-range model runs have removed their cold bias. It looks like most of the central Pennsylvania will see mainly rain, though some sleet may still mix in over the valleys and ridges where cold air damming is favored. The rain/snow will continue into Wednesday night but should gradually taper off as the low transfer its energy to an offshore low on Thursday. The precipitation should end as snow showers for just about everywhere in the State, except for the southeastern portion. Clouds will linger for much of the day on Thursday as a prevailing cyclonic flow swings some moisture over our region.
Long-term (Friday-Saturday)
There will be some breaks in the clouds on Friday as the midweek storm system departs. A high pressure bringing some much colder air for the end of the week will keep majority of the clouds to the southern half of the state. However, as we go into Friday night, a 500-mb shortwave racing across the upper Midwest will trigger the development of another low pressure system along a stationary front stretching across the Tennessee Valley. The low pressure will gradually strengthen the 500-mb trough amplifies. We might see another snowstorm bearing down on us over the weekend depending on the degree of amplification. So stay tuned.
David Wang
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