Technical Forecast Discussion
Synopsis:
A ridge of high pressure will build in Monday morning and keep the weather relatively calm and seasonally cool across the Commonwealth until Wednesday. The high pressure will be sliding offshore Wednesday night, allowing some clouds associated with an approaching cold front from Canada to move into our region. Some moisture will be tapped in by this cold front on Thursday from the southeast, so expect some showers on Thursday. Another low pressure will develop along this cold front once the front reaches the East Coast. The placement of this new low and how much cold air will be in place will ultimately determine how much and what type of precipitation we will get on Friday and Saturday.
Short-term (Monday - Wednesday)
A ridge of high pressure will build in to our north on Monday and the northeasterly winds will usher in seasonally cool air from Eastern Canada. The skies will be mostly sunny with a few clouds on Monday in response to this building ridge. The weather will remain calm on Tuesday and Wednesday as lots of sinking air associate with this ridge of high pressure will keep clouds from developing. The temperatures will also be seasonably cool with highs near 50s and lows in the lower 30s.
Mid-term (Wednesday night - Thursday night)
Some clouds will be moving in from the west later Wednesday night associated with an approaching cold front. The cold front itself is relatively moisture starved according to model guidance. However, a cut off low near the Gulf Coast is going to swing some moisture to the north and allow the cold front to tap in some of this moisture. Showers will commence on Thursday and should remain scattered in nature. Showers may taper off into isolated drizzles Thursday night. However if there is enough cold air in place, some of the higher elevations may see a few snowflakes mixed in.
Long-term (Friday - The Weekend)
Currently there are a lot of disagreements among the guidance models regarding the placement and the strength of this Canadian cold front. The GFS, WRF, and ETA are teamed up suggesting a flatter, shallower trough to move in from the west. If this solution is true, then there will be less chance of precipitation on Friday because any low pressure that develops along this cold front will be well offshore. Only expect a few isolated showers on Friday and possibly some snow flurries in higher elevations of northwestern PA. However if the trough is sharper as what the European and the Canadian models are predicting, it will have a chance to absorb in the cut-off low situated in Deep South; making it more negatively tilted. With a more negatively tilted trough along the East Coast, there is a greater chance for coastal lows to form. If this solution verifies, mainly rain will be expected on Friday across the entire Commonwealth due to warm air advection. However as the low strengthens offshore and usher in cooler air from the west, there is a chance for the rain to change to snow in the higher elevations on Saturday as the 850-mb temps will be well below the freezing mark. Things get really complicated if the moisture from Tropical Storm Tomas comes into play, which will bring copious amount of rain to the Northeast during the upcoming weekend. As of now, only the Canadian model has a slightest hint of this solution and it has been regarded as an outlier.
by David Wang
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