Scientific Forecaster Discussion
fxus61 kgyx 120241
Area forecast discussion
National Weather Service Gray ME
941 PM EST Wed Dec 11 2019
Arctic air mass will drop south through the region tonight with
snow showers in the mountains and windy conditions. High
pressure will build in and then cross the region on Thursday.
Low pressure will track up the East Coast over western New
England Friday night through Saturday night bringing mainly
rain, possibly heavy rain to the area. Precipitation may briefly
start as a wintry mix before quickly changing to rain except in
the mountains where the highest elevations may see prolonged
wintry precipitation before changing over. Windy and colder
conditions follow Sunday into Monday. Another colder system will
approach New England Monday night into Tuesday that may bring
more wintry precipitation.
Near term /until 6 am Thursday morning/...
940 PM...the line of shsn with embedded squalls moving through
nrn New Hampshire and northwest corner of ME attm. Holding together fairly well,
but hrrr starts to weaken after 03z, so will go with this idea
as it moves away from best forcing and weakening lapse rates.
Have increased the pops in the grids further to the S and east
thru about 05z though.
645 PM...main issue this evening will be snow showers and
potential squalls over the far nrn zones, as second surge of
cold air moves in with wave aloft. Pretty good band coming
across nrn half of lk Champlain attm, with secondary bands in
the Adirondacks and Mohawk Vly of New York. These bands are currently
being enhanced by lk effect off Ontario, and will likely loose
some of their punch as they work way into the nrn half of New Hampshire.
Still the nrn part of the band may hold together better given
it's proximity to best forcing aloft, and so areas north of the
white mtns in New Hampshire and north and east of Rangeley and Jackman in ME are
where the best chc for a squall exists this evening. Otherwise
in and around the whites and into the mahoosucs some sct shsn
are expected. Temps should hold where they are until the front
GOES thru later this evening, and then drop quickly, with lows
from 5-10 above in the mtns and in the teens to the south.
as the cold air moves in overnight snow squalls are possible in
the mountains. Snow squall parameter continues to highlight the
Canadian border from 00-03z time frame. Further, forecast
soundings support this with a shallow saturated layer right in
the snow growth zone and steep low level lapse rates. Brief
periods of heavy snow with wind gusts to 35mph are possible as
this moves through. Have increased the pops along the Canadian
border as well as the snow amounts for this time period and will
issue an Special Weather Statement to highlight the potential.
As cold air moves in overnight expect windy conditions to keep
the lower levels well mixed and thus while temps aloft fall to
around -17c at 850mb, the mixed will keep the temperatures
above zero across the north. Have still leaned a bit on the
colder side of guidance as after the initial cold push this
evening some calming of the winds may occur in sheltered valleys
early tomorrow morning.
Short term /6 am Thursday morning through Friday night/...
high pressure will build in for Thursday with winds steadily
decreasing as the high crests over the region for Thursday
afternoon. Stuck with a consensus for the temperatures for what
should be a nice day. Thursday night had been looking like the
coldest night of the week as the high passes to our east but
some mid level clouds may prevent the radiational cooling from
taking hold in the north and so have not gone quite as bullish
on the cold as past forecasts. Still temperatures will remain in
the single digits overnight.
Long term /Saturday through Wednesday/...
high pressure will be well east of the area Friday morning with
return flow advecting warmer air into the region. Highs on
Friday will run 10 to 15 degrees warmer than Thursday with
mostly cloudy skies.
The next system of consequence will be an area of low pressure
that develops over the southeast US Friday. Deterministic and
ensemble solutions have come in better agreement with a westward
track of this system cutting up into the St. Lawrence Valley.
With milder air already moving into the region ahead of this
system and a westward track, this system is looking to be a
mostly rain event. Precipitation will break out from SW to NE
and may briefly start as a wintry mix before quickly changing
over to rain south of the mountains. In the mountains
precipitation will start as snow changing to a wintry mix before
changing to rain Saturday morning except for the highest
elevations where snow will last the longest. There are some
model differences with regards to quantitative precipitation forecast with the GFS trending
drier while the European model (ecmwf) and CMC suggest upwards of 2 inches are
possible. High precipitable waters and good orographic flow have led towards
the wetter solutions with 1 to 2 inches of quantitative precipitation forecast along and south
of the mountains. See the hydrology section for information
about river flooding.
The system moves northeast Sunday with upslope snow showers in
the mountains. High pressure builds into the region Monday
followed by low pressure tracking from the Ohio Valley towards
New England Tuesday. This system looks colder with a track
closer to the coast or just offshore.
Aviation /03z Thursday through Monday/...
short term... VFR will prevail through the next 36 hours.
Another push of cold air moves in tonight and as it does some
snow squalls are possible in the mountains with brief reductions
to visibility for hie through to Jackman. Nwly flow will
continue through evening with VFR and calm conditions for
Long term...low pressure will track over western New England
bringing widespread rain to the area Friday night into Saturday
night with MVFR likely. Conditions will improve to IFR Sunday
short term...a secondary cold front pushes through off shore
tonight with increasing nwly wind gusting across the waters.
Gales will remain in place and have actually increased
wind speeds above the median as the low level profiles of cold
air over the (relatively) warmer water should help support
mixing down of the higher wind speeds from aloft.
Long term...low pressure tracking up the East Coast over western
New England will bring possible gales and elevated seas Saturday
morning into Monday.
low pressure tracking up the East Coast will bring 1 to 2 inches of
rain to the region Friday night into Saturday night. Recent rain
and mild temperatures have lead to many rivers in New Hampshire to
be running high into the 90th percentile for this time of year.
While much of the snowpack south of the mountains has been decimated
from recent warmth, nohrsc estimates show that a ripened snowpack
remains from the New Hampshire lakes region southwestward towards
the border with Massachusetts and Vermont. This snow pack, although heavily reduced
will likely melt off with this system and along with rainfall
will lead to flooding concerns for rivers in central and
southern New Hampshire. Farther north, into the White Mountains
a rain on snow scenario will likely serve to moisten the
snowpack leading to less runoff and flooding concerns.
low pressure tracking to the west of the area Friday night
through Saturday night will bring strong onshore flow and
increasing near shore waves. Peak surge with this system is
forecast to occur a few hours after the mid-day high tide
Saturday and this with near shore waves around 5 to 7 feet may
pose some beach erosion and minor coastal flooding concerns.
Marine...Small Craft Advisory until 7 am EST Thursday for anz151-153.
Gale Warning until 7 am EST Thursday for anz150-152-154.