A short wave trough over central Montana is visible on the current water vapor imagery. This wave will traverse the northern tier of the nation tomorrow in fast zonal flow, reaching the Great Lakes region Monday night. At the surface, strong cold high pressure will be entrenched over New England. An inverted trough will move over the Ohio Valley Monday evening, with low pressure forming near Long Island Tuesday morning. Vorticity advection and warm and moist air advection from the south will encourage lift and the intensification of an area of moderate precipitation mainly north of the Mass pike early Tuesday morning. Model guidance has been fairly robust with QPF, showing a large region of >.5".
Forecast soundings are nearly isothermal up through 750mb near 0C. The main concern is boundary layer temperatures. At this point 1000-850mb thicknesses are marginal for snow around 12z (8am) Tuesday. Considering possibly a weak elevated warm layer, we could deal with a brief period of sleet or freezing rain too.
Model guidance has been trending south overall with this system in the last few day. At this time no wintry accumulations are expected in Cheshire County. Further north and in higher elevations, some first light accumulations of the season can be expected.
A significant coastal storm remains possible for Friday-Saturday. The potential exists for first accumulations of the season in southern NH and heavier snowfalls further north. More details will be posted tomorrow. Stay tuned!
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