Heavy snow rates likely

The 12z and 18z GFS are extremely robust with the development of secondary low pressure just east of the region. By 00z Monday (7pm), H7 omega of greater than -20ub/s is indicated across SNH and CNH. Lapse rates are decent, so beyond boundary layer warmth, we still have H7 temperatures below -10C. This will provide for excellent snow growth. Frontogenic forcing will trigger snowfall rates of 1 to 3 inches per hour across interior CNH, and the possibility exists for some thunder. This is supported also by recent runs / trends in the ECMWF. A GFS solution delivers double digit snowfall to Cheshire County with the potential for more. Where the best banding sets up over NH (likely to our north and east), accumulations of up to 2 feet will be possible.

The NAM however continues to hold back on QPF. While the GFS spits out 1.25" to 1.5" across SNH, the NAM holds us to .5" to .75". Isn't it usually the other way around? For KeeneIn this case, the NAM is not consolidating the H5 vorticity, but keeps it in separate packets of energy. This is likely because of its higher resolution which sometimes plays tricks with the forecast. At the surface, this results in a slightly weaker secondary low, which consequently does not wrap moisture around into the region as efficiently as the GFS. It should be noted that SREF probabilities are still relatively low.

I am leaning toward the GFS with the rest of its model support, but still wary of the NAM. As for totals: Should be mainly rain inside of I95. East to west 1-4 inside of 495 and north of I90. 2-5 for SE NH. Interior RI and CT away from the coast should get 1-3. Northern higher terrain of CT could see 3-6. Expecting 3-6 for MA south of I90 and west of 495. Interior northern MA will see 4-8, possibly 5-10 for higher terrain of NW MA. SW NH (Cheshire and western Hillsborough) will see 5-10, possibly 12 over the higher terrain in northern Cheshire.

For Keene, I am holding with 6" - 9", but this has potential to be increased.