Technical Discussion

Synopsis...

After the large low pressure system that brought copious amounts of rainfall to the region (upwards of 3-4") over the last 2 days, a northwesterly flow will set up from now through the weekend resulting in lake effect snow for areas such as Erie, Bradford, Johnstown, and Somerset into the weekend.  On Saturday evening/Sunday morning, a clipper swings south from the upper midwest bringing a chance of some snow showers to southern/western portions of the state during that time period.  This clipper will then ride up the east coast well offshore, strengthening as it progresses northward...this will result in a reinforced northwesterly flow and an even better shot at some lake effect snow for the usual suspects later in the weekend and early next week.  Temperatures for the entire period will range from the upper 20's - low 30's in the northwest to upper 30's to low 40's in the southeast.

Short Term (through Saturday afternoon)...

Not much to talk about in this time period other than the lake effect snow that will persist over the northwest zones and Laurel Highlands.  Portions of Erie and Crawford County will likely see total snow accumulations by 12z Saturday of around 2-4" close to the shore and in valleys and upwards of 5-10" in the snowbelt region if the snow bands can progress that far inland.  Otherwise, the rest of the state will be in the mid 30's to low 40's with a mix of sun and clouds during this period.

Long Term (Saturday evening - Monday night)...

Both the WRF and GFS are now in pretty good agreement on the evolution and progression of the clipper moving down from the upper Midwest dropping down into the lower Ohio Valley between 18z Sat - 0z Sun.  WRF yesterday had the low a little stronger and farther north but has trended toward the GFS solution of a weaker system farther to the south.  Thus, my thinking is to trend lower on any sort of probability of precip over the southwestern zones during this time period based on the model solutions.  9z SREF's still have around a 75% prob. of precip. over Washington, Fayette, and Somerset counties on Saturday night/Sunday morning.  After the clipper swings through, it will move well offshore and progress northward, strengthening under the negatively tilted trough over the eastern CONUS.  Thus, this will provide a strong northwesterly flow to the region, kicking up the lake effect yet again in the Sunday - Monday time frame, with some significant accumulations possible depending on where the bands form.  Interesting to note that the models are showing the low making a loop over the northeast in the Tuesday - Wednesday time frame.

Forecaster: Kyle Imhoff