Be on alert for surprise snow
A preface here: there is a lot going on in the atmosphere over the region Friday. Snow shower activity this morning is being caused by a warm front nosing in from the southwest. There will be a pause in precipitation before a cold front approaches in the afternoon. There is also an upper level trough working into the region. The axis thereof will influence snowfall amounts for Saturday. While all of this is going on, an ocean storm forms well to the southeast, but sets up an inverted trough scenario as the axis of the upper level trough passes through, which could enhance snowfall along the coast.
The bottom line here is the potential for surprise snowfall with quick accumulations through Saturday.
The HRRR here looks at the convective side of the situation. While the term "convection" is associated more for thunderstorms, it is also apart of winter weather, and in this case the risk of snow squalls. Cold air advection steepens the temperature lapse rates and with moisture combines to set up strong gusty winds, spurts of heavy snowfall, which leads to whiteout conditions and slick roads.
The main threat for these squalls appear to be in the afternoon into mid-evening for southern areas. An inverted trough sets up and passes through the region overnight into Saturday, which could bring areas of squalls and shots of heavy snow through early afternoon. The HRRR shown here shows the potential for all of this well.
Not shown with this model is the upslope snow showers for the mountains which could bring several inches of accumulation there through Saturday as well.
Where the squalls pass is where the accumulation comes south and east of the high country. The idea of an inverted trough has me thinking there could be a surprise couple of inches or more of snow from Portland to Eastport through Saturday afternoon.
While all of this is going on, the wind comes in.
It will feel like January Saturday night into Sunday
With the upper level trough and associated surface high working in behind a rapidly intensifying storm tracking to Newfoundland, arctic air pours into the region Saturday night into Sunday. Folks in the mountains could see a wind chill advisory posted. Sunday appears to be bitterly cold with the wind. As the high moves in and the storm moves well northeast, the icy breeze settles down Sunday night.
Potential storm early next week
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Penn State '21
AMS / NWA