C&P from NWS Scientific forecaster

NWS Scientific Forecaster

Synopsis...

high pressure will dominate the region with warm temperature

through Wednesday. On Thursday, a clipper system will bring light

snow to the area followed by high pressure through Saturday. A

cold front Saturday night will pass threw the region, but near

normal temperatures and dry weather is expected for Christmas.

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Near term /through tonight/...

shallow shortwave passing by to the north will drive a weak

frontal boundary through the region overnight. High clouds ahead

of this system currently pushing in from the west and will be

around through the evening hours before pushing east after

midnight. Return flow around high pressure east of Cape Cod also

throwing some low level moisture into coastal zones. As boundary

layer winds turn more westerly overnight expect this moisture to

affect mainly midcoast areas this evening before pushing east.

Expect clouds to move into northern zones after midnight and a few

snow showers may enter the picture toward Wednesday morning. Lows

overnight will range through the single numbers north and through

the teens south.

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Short term /Wednesday through Wednesday night/...

high pressure will build south of the region on Wednesday.

Increasing upslope flow and lingering low level moisture will keep

clouds and low chance pops for snow showers in the forecast

through the morning hours in the north. Expect diminishing clouds

in the afternoon. Elsewhere partly to mostly sunny skies will

prevail. Highs on Wednesday will top out slightly above normal

with readings in the upper 20s to mid 30s north and mid 30s to

lower 40s south.

High pressure will push offshore Wednesday evening as weak low

pressure approaches from the west. Expect increasing clouds during

the evening and light snow will over-spread the region from west

to east through daybreak. Expect any accumulations in the south to

be light and spotty. Mountains and foothills may pick up an inch

or two by morning. Overnight lows will generally bottom out in the

lower to mid 20s.

&&

Long term /Thursday through Tuesday/...

an Alberta clipper system will move through the region from the west

on Thursday and will produce light snowfall across most of the area,

which will affect the morning commute and last through the day.

The Alberta clipper that moves through the area on Thursday will

live up to its reputation in being fast moving with light

precipitation amounts. Although it is a sharp shortwave trough that

will drive this system, there will not be a strong moisture

connection available with it. Generally expect 1 to 3 inches of snow

for most of the area. The coastal and Island Area will see snow

mixed with rain at times, which will limit their snowfall totals to

around 1 inch or less.

High pressure will build in from the south and bring westerly flow

behind the system on Friday. We will see an influx of warmer

temperatures through Saturday. A cold front will pass through the

region Saturday night with colder air moving into the region.

Christmas day will be dominated by high pressure and temperatures

from the upper 20s in the mountains to the upper 30s to low 40s

along the coast and islands.

High pressure to our south over the mid Atlantic will bring a

westerly flow behind the system on Friday, with temperatures near

normal for this time of year. Should see a little warmer air in the

area on Saturday as warmer air from the middle of the continent

vents off to the northeast ahead of a northern stream trough which

drives a cold front into the area Saturday night.

High pressure crossing the area Christmas night will bring a chance

for good radiational cooling. Both the GFS and European model (ecmwf) are in pretty

good agreement on this, though the raw model forecasts which go into

our blends do not do well on these nights, especially as

temperatures begin to warm aloft by morning. Because of this, the

best approach seemed to be to blend the superblend of models with

the much colder mex which would be expected to perform better in

radiational cooling due to its use of statistical adjustments. Some

high level cirrus clouds may move in from the west by morning, but

this may not be enough to keep temperatures from dropping into the

teens and single digits.

GFS and European model (ecmwf) are in broad agreement on a large trough which is

forecast to move into the western United States later this week and

tack through the northeast early next week. But there is still

differences in how fast and how much precipitation we will see from

this system. The GFS is the fastest solution that has

precipitation starting on Monday afternoon to evening and exiting

our region by Tuesday morning. The European model (ecmwf) has precipitation

starting Monday evening as shower and then steady precipitation

would not start to Tuesday morning and exit the area until

overnight Tuesday. Precipitation type may be a bit of a question

with this system, but there is too much uncertainty in the various

possible tracks to put too much detail into the forecast at this

time. For now will go with mostly snow, changing to rain in

southern areas.