Synopsis
With mild air approaching, tonight will not be as much as a deep freeze as last night, but a freeze is in store for us overnight tonight. Tomorrow, things will get messy as rain showers will lead snow showers in their west to east progression. A cold front will begin to wreak havoc, producing single digit wind chills in parts across the state, and another potent lake-effect setup will occur Tuesday through Thursday across the northwestern counties. Beyond this, another system looks to bring some light rain into the southern border areas, yet it looks to far south to be impactful as the weekend fun begins!
Short Term (Monday Afternoon through Tuesday)
Looking at the surface, a dominant warm conveyor belt will be in action as day turns to night over PA. This will not prevent temps from dropping into the 20s, yet it will be warm enough to setup a warm surface layer ahead of the cold front looking to pass through starting Tuesday morning. Starting around 9 to 10z tonight (early Tue morning), mixed precip showers will progress around Pittsburgh, with a quick progression through the state, reaching State College by 15 to 16z, then hitting Philly by 19 to 20z, and completely exiting by about 4z Wednesday(for lingering showers in Scranton, out of Philly by 0z) The entrainment of warm air at the surface layer should allow for rain to fall for an hour or two before mixing with and turning to snow. Most places will see persistent precip for about 4 to 6 hours. The swift movement of the front is attributed to strong winds along the frontal boundary as well as the distance from its central low. All this was derived from the 12z NAM, but the 12z GFS and 15z SREF do not differ much from this solution. Strong winds within the system will work with the rapic cold advection to produce single-digit/near-zero wind chills statewide, yet it will be more bitter with the wind chills Wednesday, but Tuesday, the wind will indeed be noticed.
Long Term (Wednesday to Friday)
A west-northwest wind stacked throughout the 1000mb to 700mb layer will provide a juicy fetch across Lake Erie. This fetch will setup lake effect snow for the bulk of the Tuesday to Thursday period. The northwest counties will get hit the hardest, with 15z SREF means around 5 inches at the end of the week, yet snowfall rates will remain consistent at about 1" per 12 hours, at least at the Erie station. Areas further away will see at most 3" from this event, yet the strong winds in the layer will attempt to oscillate over the ridges to carry snow showers all the way to Centre and Huntingdon counties. Strong winds with this system overall will produce teen-regime wind chills, especially when the ridge for Thursday creeps in. Northwesterly flow will remain in control Thursday, keeping things cold with colder wind chills, but Friday starts a mild boost where light rain showers could fall along the southern counties, as implied by the 12z GFS. Keep an eye on this, forit appears that the shortwave aloft controlling the development of this cell will retract north, giving us potential for a little more than just showers going into the weekend.
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