Synopsis
This week will mainly feature just a single threat for messy, wintry weather as a low pressure cell starts to trudge across the nation. Tuesday will be the wet day of the week with the bulk of the state seeing rain for the bulk of the afternoon with clearing starting to occur overnight. Afterwards, the will be a calmer scene Wednesday with just some hinting at snow for Thursday, but the main concentration of our forecast will be settled on rain for Tuesday, a cold yet pretty Wednesday, and a less worryful threat of snow for Thursday with a cold start to the weekend.
Short Term (Tonight through Wednesday night)
With showers already crossing through the western half of the state, there will be scattered showers across the central and eastern thirds of PA this evening and overnight tonight. The 12 and 18z NAM runs have precip falling within the areas where rain already exists, whereas the GFS has nothing anywhere. This gives me better confidence in the NAM's solution to the events occurring within the next 48 hours. With a low pressure cell beginning to strengthen and progress our way, it will bring some scattered rain showers for the morning and afternoon hours on Tuesday, and with warm advection occurring within the region with precipitation. Tomorrow will be a rain event, with the only chances of a wintry mix occurring along the ridges and plateaus. The rain event will be brief through this period however, for the low will quickly occlude and form a dryslot, which will help break the "comma" down into a northern sector, which will send the longer-lasting showers along the northern half of PA, and a southern portionwill dissipate into the southeastern U.S. This dryslot will quickly clear out the state overnight Tuesday, bringing with it post-frontal cold advection and frigid nighttime wind chills. With a tight pressure gradient prevalent throughout Tuesday and early Wednesday, there will be plenty of wind blowing accompanied by some bitter wind chills. The GFS also hints at lingering lake effect snow for overnight Tuesday, but anything that falls will be light and nothing to really worry about. The dryslot's main role will be opening up an area for high pressure to filter in, helping to calm the winds down and clear the sky for sunshine to dominate. This high will remain settled in the night, causing frigid overnight lows in the lower 20s statewide, with spots in the northeast and mountain valleys dipping into the teens.
Long Term (Thursday and Friday)
With the high beginning to make a quick exit, warm advection ahead of a weak cold front will make Thursday a cool, cloudy day. The NAM and GFS have pretty much the same idea of afternoon clouds billowing overhead, and both show a small section of flurries over the northwestern area of the state. This will generally be the result of weak convergence and thermal lift over the Great Lakes, and both models have the system too far north, leaving Erie and cities along the northern border too see any snow from this system. A weak cold front will also come into play overnight Thursday, leaving the state with another frigid night and a cold start to the weekend. Highs for these days will not depart too far from the freezing mark, with the warmest spots in the southern half seeing highs in the mid 30s for Thursday and Friday, and lows dipping into the teens.
Written by Steve Engblom
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