Sunday Afternoon Tech Discussion
Synopsis
The first of a series of cold fronts is currently driving through the state. In addition to another shot of arctic air, the next system will bring snow showers or even snow squalls to much of the state on Monday. The overall pattern looks very active going into next weekend as another potential storm system develops over the Midwest and Ohio Valley.
Short Term (Now through Tuesday)
A strong cold front and an associated 984hPa low over Quebec will continue to move away from the region tonight, easing the pressure gradient which has driven the strong winds today. Attention then turns to the next shot of cold air which will begin to enter the state Monday afternoon as a low pressure develops near lakes Huron and Champlain and moves eastward. While the global models such as the GFS & ECMWF show only a few hundredths of an inch of QPF, the NAM and 4km NAM show widespread bands of snow with at least a dusting over much of the state. 18z 4km NAM guidance shows 850mb temperatures of less than -20 Celsius over nearly all of the state by 15z Tuesday. The lake effect fetch will be mainly westerly through Tuesday, which will limit the lake effect snow showers over the Laurels and central mountains. Due to potential MOS biases with advection and abnormally low temperatures, raw GFS/NAM data was favored for temperature forecasts during the period.
Long Term (Wednesday through this weekend)
Wednesday and Thursday will be very cold as 850mb temperatures remain at or below -20C. Lake effect snow will continue to pile up in the snow belts of northwest Pennsylvania through Wednesday night. Flow will shift from westerly to southerly ahead of the next area of low pressure which will develop over the Midwest and move through the Ohio Valley on Thursday. The 12z global models seem to have formed somewhat of a consensus, with the ECMWF tracking the low over northern/central PA and the GFS tracking it over southern PA. This subtle difference could be significant with respect to precipitation type, however. Warmer air will advect northward along the eastern side of the low pressure area. Cold air damming will limit the advection process near the surface, however 850mb temperatures may rise above freezing and change precipitation over to sleet or even freezing rain over southern parts of the state Thursday night.
Synopsis
The first of a series of cold fronts is currently driving through the state. In addition to another shot of arctic air, the next system will bring snow showers or even snow squalls to much of the state on Monday. The overall pattern looks very active going into next weekend as another potential storm system develops over the Midwest and Ohio Valley.
Short Term (Now through Tuesday)
A strong cold front and an associated 984hPa low over Quebec will continue to move away from the region tonight, easing the pressure gradient which has driven the strong winds today. Attention then turns to the next shot of cold air which will begin to enter the state Monday afternoon as a low pressure develops near lakes Huron and Champlain and moves eastward. While the global models such as the GFS & ECMWF show only a few hundredths of an inch of QPF, the NAM and 4km NAM show widespread bands of snow with at least a dusting over much of the state. 18z 4km NAM guidance shows 850mb temperatures of less than -20 Celsius over nearly all of the state by 15z Tuesday. The lake effect fetch will be mainly westerly through Tuesday, which will limit the lake effect snow showers over the Laurels and central mountains. Due to potential MOS biases with advection and abnormally low temperatures, raw GFS/NAM data was favored for temperature forecasts during the period.
Long Term (Wednesday through this weekend)
Wednesday and Thursday will be very cold as 850mb temperatures remain at or below -20C. Lake effect snow will continue to pile up in the snow belts of northwest Pennsylvania through Wednesday night. Flow will shift from westerly to southerly ahead of the next area of low pressure which will develop over the Midwest and move through the Ohio Valley on Thursday. The 12z global models seem to have formed somewhat of a consensus, with the ECMWF tracking the low over northern/central PA and the GFS tracking it over southern PA. This subtle difference could be significant with respect to precipitation type, however. Warmer air will advect northward along the eastern side of the low pressure area. Cold air damming will limit the advection process near the surface, however 850mb temperatures may rise above freezing and change precipitation over to sleet or even freezing rain over southern parts of the state Thursday night.
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