First, Friday

The ECMWF and GFS have amazingly had a rather steady forecast for a major winter storm on Friday. This helps to add confidence in the forecast of heavy snow across much of New Enland into NY, and PA.

A large and strong piece of energy currently sitting off of the California coast, will rotate south and then east into the southwest states by Thursday morning. As the -EPO jet intensifies out west, high pressure will be pulled southward into central Manitoba, and then into Ontario by Thursday night.

Strong high pressure to our north is the key, and will in fact keep temperatures 5 to 10 degrees below the normal through the duration of the event. This will guarentee precipitation type as snow at least north of the Mass Pike. Here in Keene, with surface temperatures of 23 to 28 during the day Friday, and 10 to 15 Friday Night, I do not foresee mixing being an issue at all (which is definitely a unique senario considering this past winter, and this month so far). South of the Mass Pike, sleet could be an issue, and getting down toward NYC, precipitation may change to rain towards the end of the storm. This would still be after a decent sized front end dump of snow.

Surface low pressure will develop Thursday and intensify as it heads into the southern Lakes region by Friday morning. With the strong high pressure to the north, boundary layer cold air will be kept in tact. There will be a tight 850mb temperature gradient, with temperatures near 0C across northern NJ, -10C close to Keene, and -20C temperatures entering northern Maine. Overrunning warm air will cause precipitation to develop over the region Friday morning. With high Q-vector convergence suggesting areas of strong ascent with omega as much as -15 to -20ub/s, precipitation intensity will increase rapidly. Combined with high PWAT values, snowfall rates of 1 to 3 inches per hour will be possible during the day Friday. This will however be a fast mover however, and should be done within 12 hours of its arrival.

Model guidence is uniform in showing widespread .75+" QPF, with areas up to 1.5" with thermal profiles still favorable for snow. Even the GFS ensemble mean show a 99mb low with QPF maximum of 1.25 to 1.5" across CT. QPF looks like the main forecasting issue. Not that there is considerable disagreement among model guidence, just that the placement of maximum water equivalent will dictate whether we get 4 inches of snow or 18 inches of snow. At this point, I am comfortable using 4 inches as a bare minimum.

The GFS, GGEM, and ECMWF have been suggesting a wide stripe of 6 to 12 inches with upwards of 18 inches.

At this time, I think 6" to 12" is an appropriate forecast for Friday morning through Friday Night.

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Doesn't stop there. Another major storm is possible on Monday. I probably will not have time to post on this tonight though.