Scientific Forecaster Discussion
fxus61 kgyx 082129
Area forecast discussion
National Weather Service Gray ME
429 PM EST Thu Dec 8 2016
a strong cold front will cross the area this evening...with
occasional snow showers. This will be followed by a stronger cold
front late tonight. Mountain snow showers will continue through
Friday...with several inches of snow possible north of The
Notches. The coldest air of the season will move in behind the
front...with highs struggling to break freezing even at the
coast. High pressure will build in for the weekend continuing
cold temperatures. A low will approach the region on Monday with
snow spreading across the region and rain mixing in along the
coast through Tuesday.
Near term /tonight/...
the first cold front is crossing the mtns at this time...forcing a
broken band of snow showers thru the forecast area. Based on area
webcams and a small handful of automated observations...visibility
has dropped to 1/4 mile at times in these squalls. Temps are also
falling below freezing behind the front...especially in the mtns
and foothills. So some refreezing of minor snow accumulations will
likely occur on roadways. I have issued a couple spss to handle
this threat into the early evening. After the passage of the
front...temps will gradually decrease overnight in a well mixed
environment. Upslope snow showers will tend to stick closer to the
high terrain...as Froude numbers go back towards critical after
the initial surge of cold air advection. Then the secondary Arctic front
approaches the forecast area around midnight. Once again deeper
mixing will allow some snow showers to cross the ridge line and
track towards the coast. Snow squall parameters do appear
favorable for some of these to also be heavy at times. The focus
of the heaviest precip however will remain closer to the highest
Short term /Friday through Friday night/...
cold northwest flow will continue on Fri. Closed mid and upper level lows
will remain over the Canadian Maritimes...with strongly cyclonic
flow directed over the high terrain. With a lingering pool of low
level moisture upstream in Canada...upslope snow showers should be
favorable for moderate accumulations over parts of nrn New Hampshire and
adjacent wrn ME. It is not out of the question that a winter wx
advisory may be needed for a few zones.
Farther S...high temps will struggle towards freezing with strong
cold air advection thru the day. Wind gusts will top out around 25 to 30 kts at
times...making it feel even colder. Cold air advection continues into the
overnight...so mixing will limit the overall cooling off of temps.
Long term /Saturday through Thursday/...
A relatively zonal flow will persist through the start of next
week...with a series of weak waves moving through. By Tuesday a
long wave trough develops over Hudson Bay and cold air shifts
southward into the central Continental U.S.. this will allow for a storm
system to move up the Ohio Valley and into northern New England.
The weekend begins with cold high pressure building into the
region. Mountain snow showers will come to an end of Saturday with
clearing skies. Winds will decrease through the region as the
pressure gradient decreases. Overnight temperatures will drop to
near zero through the mountains... with isolated valleys below
zero. A few clouds remaining in upslope regions would be enough to
prevent widespread below zero temperatures.
On Sunday clouds will start to move in from the west in advance
of a developing system moving up the Ohio River valley for Monday.
The trend over the past few days has been to push back the timing
of the storm... with precipitation not moving into our
southwestern areas until very early Monday morning. Expect
precipitation to begin as snow region wide and spread across the
region through the day on Monday. By Monday night the
possibilities expand with the changing storm track. GFS tracks
further inland which has the effect of allowing warm air aloft to
infiltrate through southern Maine. With the high pressure for
Saturday and Sunday the cold temperatures are likely to remain
dammed at the surface, so warm air aloft would put a period of
mixed precipitation into southern Maine coastal plain. While a
mixed scenario is one possibility, it is not the only one.
Increasing strength of cold air aloft could also drive the storm
track slightly further south keeping any above freezing
temperatures off shore in teh Gulf of Maine. At this point have
leaned towards a colder solution, in part because of the strength
of existing cold air mass.
The track of the storm will also have an impact on the winds,
with a south track resulting in a more classic Nor'easter type set
up with gusts too around 30along the coast. A inland and warmer
scenario keeps the center of the storm over US and results in
lower wind speeds. Have hedged to the stronger winds in keeping
with the colder solution.
The active pattern continues through next week with another
chance for precipitation on Wednesday.
Aviation /21z Thursday through Tuesday/...
short term...first cold front is crossing the mtns at this hour
with a band of snow showers along it. Very brief IFR or lower
conditions are possible with this front...mostly likely to hold
together thru Aug...possibly rkd. Northwest flow develops behind the
front...keeping areas downwind of the mtns VFR tonight. Hie will
remain MVFR in upslope clouds...and occasional MVFR cigs may work
into leb overnight. Hie may also see rounds of shsn that drop
vsbys to IFR or lower at times...especially with Arctic frontal
passage around midnight tonight. Strong northwest flow continues
Fri...with surface gusts around 25 kts. Upslope shsn continue at
hie thru the day.
Sunday night MVFR clouds moving in west to east. Expect IFR snow
to develop late Monday. Tuesday may see a period of mixed precip
along the coast.
short term...I have upgraded the outer waters to Gale Warning for
Fri...and made the bays scas beginning this afternoon. First cold
front will cross the waters this evening...with winds increasing
to Small Craft Advisory thresholds. The secondary Arctic front crosses the area
tonight. Gale force wind gusts will begin behind this front.
Strongest wind gusts will linger into Fri evening before gradually
storm developing Monday into Tuesday will result in wind and waves
increasing to near gale.
Marine...Small Craft Advisory until 11 PM EST Friday for anz151-153.
Gale Warning from 10 am to 11 PM EST Friday for anz150-152-154.