Less than 24 hours before onset of snow, the models should have a good lock
on what will happen.

First of all, no question that it will be all snow with critical thicknesses
(which reflect the mean temp of various layers of the atmosphere) are WELL
to our south. Cold high pressure is to our north. The column of atmosphere
will be very cold during the event, allowing a significantly fluff factor;
15:1 or perhaps 20:1 snow/melted ratio. The 1 AM GFS model solution
gives.025² melted for Boston which translates to 4 or perhaps 5 inches..
The 1 AM NAM model gives about .4² melted which puts Boston into the 6 to 8²
range. Thus, the various predictions of 3 to 8 ³ around here are confirmed.
However...

For a hefty snowfall, forecasters like to see the low pressure center pass
near/over the 40 degree latitude 70 longitude benchmark. You can place the
location of this point by imagining a horizontal line passing out over the
ocean from central NJ and a vertical line passing out over the ocean from
the eastern tip of Cape Cod. The intersection of these lines is the
benchmark. At 1 AM tomorrow, the NAM places the low about 100 miles south
of this benchmark. The GFS is about 150 miles south of benchmark. I find
it difficult to see us getting much precipitation at all, especially from
the GFS scenario, which has been the more consistent of these two models.
It is also important to mention that this storm is a relatively fast mover.
If we get about .10² melted we see 1 /12 to 2² of very easy to handle
snowfall here in Metrowest. (Inhale some black pepper, sneeze uponthe
drive, and its gone!) That's my ³guess².

As I mentioned above, the atmosphere will be very cold throughout the event,
giving a high fluff factor. However, the colder the air, the less water
vapor it is capable of ³holding². This translates to less rather than more
snow.

Each morning, Ric Werme posts Mt. Washington conditions. These observations
are very useful as they provide us with a realtime view of what's happening
at about 6,000 feet up. In particular, it is important to watch the wind
direction at the summit. At 8 AM, it is from the NW. Whereas, this
direction gives us a hint at steering currents., a continuation of this
direction through the day would confirm the notion that the low will stay
well south of us. On the other hand, if the wind at the summit backs to SW,
then all bets are off, and the low passes closer to us. (I recall that TV
mets of yore, such a Don Kent and Norm MacDonald often cited this
information. as a winter storm threatened).

Jot - Ashland, MA



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Jot Ross wrote:

Each morning, Ric Werme posts Mt. Washington conditions. These observations
are very useful as they provide us with a realtime view of what's happening
at about 6,000 feet up. In particular, it is important to watch the wind
direction at the summit. At 8 AM, it is from the NW. Whereas, this
direction gives us a hint at steering currents., a continuation of this
direction through the day would confirm the notion that the low will stay
well south of us. On the other hand, if the wind at the summit backs to SW,
then all bets are off, and the low passes closer to us. (I recall that TV
mets of yore, such a Don Kent and Norm MacDonald often cited this
information. as a winter storm threatened).

Jot - Ashland, MA




Jot...thanks...I have asked before what the Mt Washington rule of thumb
was for whether a nor'easter was going to occur, but I don't think I
ever got a good response (although I might have and then forgot it
again...). Thanks for the analysis. FYI the 3:47PM EST wind was:

Wind from the SSW (200 degrees) at 6 MPH (5 KT).
http://weather.noaa.gov/weather/current/KMWN.html

Thanks,
Janet