12/4 - 12/5 snow even

An upper level disturbance with an associated surface low will through the triangle region this evening and tonight. Light precip is expected to fall between 6:00 PM through the early morning hours. GFS and NAM are in disagreement on total qpf. HPC actually prefers the ECMWF model at this time. I don't see any reason to disagree as these types of upper level systems typically move through the region quickly. So will go with middle ground qpf amounts.

I expect the surface low to quickly and lightly strengthen as it spins over the App mountains. This occurred with a similar system last year and is supported by theories in centrifugal force in relation to atmospheric spinning parcels. Because of this effect expect slight warm air advection ahead of the surface low which should cause the majority of the light precip to fall as rain or a rain snow mix over the triangle. When the low pressure is to the east of the triangle the precip should transition to snow however, moisture levels will quickly fall as substinance moves over the region.

ECMWF trended sw with the system which would put it closer to the southernmost NAM solution... this could mean a bit more snow than mix.. as warm air advection would not be nearly as strong with a more southern solution.

The ground is warmish but the precip will be falling at night which should enhance potential ground accumulation. A band of moderate snow could fall around and especially north of the triangle as part of the associated weak deformation band. Expect the potential for up to an inch of accumulation especially in the grass areas over this more moderate band of precip.

A dusting to an inch of snow is possible tonight in the triangle.