There is nothing about tomorrow's forecast that is easy. I suppose I can say I have high confidence in a notable wintry event tomorrow. And between moderate amounts of snow and ice accumulation, I have confidence in numerous school closures across New England. But the specifics of the storm still are far from being ironed out. The 12z model guidance (Just 18 hours before the snow starts across SNE) is still in disagreement concerning the extent of mid level warming, as well as the strength of the storm itself. The 12z NAM fails to close off a 850mb, which limits the amounts of moisture thrown into the region. The problem is, without the closed low, the easterly low level jet is much weaker. The 12z NAM only prints out about .4" to .8" w.e. This compared to the GFS which has been consistently giving widespread 1.0+" amounts to SNE. The GFS has recently trended slightly drier (still 1+ amounts), however then we also have the NGM to take into consideration, which usually has a notable dry bias, and is more in league with the GFS at this point. Quite the forecasting challenge...

Models have also trended a little stronger with the mid level warming tomorrow, which could bring a longer period of freezing rain/drizzle in the afternoon and evening. The 12z ECMWF actually brings the zone of major icing further north, now covering much of the area that got hit last month.

Plus, there is still the question of snowfall amounts behind the storm Wednesday Night into Thursday morning.

Current timeline, as best as can be determined at this point:

Snow begins around 2am. Accumulations of 1.5" to 2.5" by 6am.

Snow could fall moderate to heavy between 8am and 11am, with 1"/hr rates possible. Totals through 11am 4" to 6".

Sleet should start mixing in by 11am, changing to all sleet by 1pm.

Freezing rain mixes in by 3pm, and lasts through 7pm. Ice accretion between .1" and .25"

Freezing rain and sleet should change to all snow before midnight, with light to moderate snow falling through 7am Thursday.

For what it's worth, here are a few snowfall forecasts for Keene (Through Thursday morning) from other sources:
NWS Point Forecast: 5" - 11"
NWS Zone Forecast: 6" - 11"
WMUR: 5" - 10"
Accuweather: 5" - 9"
Intellicast: 1" - 2"
TWC: 1" - 3"

So you can see the considerable range. However, we are also looking at what I would call the more reliable sources in the higher ranges.

And my current forecast: 5" - 8"

|posted by Sam Lillo @ 1/06/2009 02:33:00 PM