Scientific Forecaster Discussion
fxus61 kgyx 131227 aac
Area forecast discussion...updated
National Weather Service Gray ME
727 am EST Wed Dec 13 2017
behind the departing low pressure a strong cold front will cross
the region this afternoon. Along and ahead of the front
scattered snow showers are possible south of the
mountains...with heavier snow and some accumulation likely in
the higher terrain. Temperatures today will likely fall through
the day...ending up the teens by the evening. Wind gusts in
excess of 35 mph will make that air feel bitterly cold. The
coldest air of the season will move into the region behind this
system for the remainder of the week...with a few chances for
additional snow showers.
Near term /until 6 PM this evening/...
update...bulk of the precip outside of the mtns has moved east of
the forecast area at this hour. Minor adjustments to temps and
dew points. Otherwise no significant change to the forecast.
Previous discussion...upper low pressure is beginning to
approach nrn New England this morning. At the moment lift ahead
of it...along the 800 mb cold front...is leading to a band of precip
across the midcoast. I have increased pop to likely...and have
a mixed bag of ptypes. There may be some rain along the
immediate coast where warmer air still lingers...but inland
temps at or below freezing are probably leading to a little bit
of everything with mid level temps still just above freezing.
This will be short lived precip however...as the surface low
moving into downeast ME will drag precip with it.
The upper low itself will likely provide for fairly widespread
precip early in the day. The cooling column will support snow
showers vs mixed precip by then though. The real cold air will
move into the region behind the trof axis...which will also help
mix down stronger winds aloft in cold air advection. There does appear to be a
window of possible 40 kt gusts from about 21z to 00z. Given the
recent snow and ice...tree limbs may be more susceptible to
breaking and leading to power outages...so I have issued a Wind
Advisory for srn New Hampshire and adjacent swrn ME. Elsewhere gusts of 25
to 30 kts are likely in the afternoon.
The developing strong wly winds will also help to focus snow
showers in the higher terrain. Very low snow growth
zones...lingering low level moisture...and orographic lift will
likely result in numerous snow showers...and efficient snow
accumulation despite low quantitative precipitation forecast. Several inches additional
accumulation are possible today...and given that there is no
discernible break in snow for the mtns...I have extending the
winter storm warnings thru the evening for those areas. Given
the well mixed boundary layer...snow showers may be able to top
the mtns and move downstream...but significant accumulations
are not expected there.
Short term /6 PM this evening through 6 PM Thursday/...
chilly night on tap...especially considering the gusty wly flow
that will be continuing. Temps will fall into the teens S of
the mtns...where downsloping and a well mixed boundary layer
will keep readings relatively mild considering the air mass
moving in. In the mtns and north readings will bottom out in the
single digits. With winds staying gusty overnight...wind chills
will fall to as cold as -10 in the nrn zones...and to near zero
S of the mtns. Cross barrier flow...cold temps...and lingering
low level moisture will keep snow showers going along and upwind
of the mtns as well...though coverage should be less widespread
than the afternoon.
On Thu a trailing shortwave trof will pass S of the forecast
area. Though at this time it looks far enough S to avoid
significant impacts...it will likely spread some cloud cover
into srn zones...and may even bring a period of very light snow
to srn New Hampshire. The main story however will be the cold temps...with
afternoon highs staying in the 20s S of the mtns...and teens and
even single digits in the higher terrain.
Long term /Thursday night through Tuesday/...
the mean long wave trof position remains anchored across the
eastern US while the high amplitude ridge across the West Coast
remains in place. The coldest air of the season will move into
the region with this long wave trof as a series of clipper
systems move through this long wave trof over the outlook
period. These clipper systems will each have very limited
moisture due to their source region, but enough to allow
scattered snow showers and reinforcing shots of Arctic air in
their wake. The first of these systems will arrive Fri night and
exit by late Sat. Then another similar clipper Sun night into
Mon. Generally stayed very close to superblend models for the
One item to note, min/Max temps may not be cold enough for Thu
night through Fri night due to the fresh snow cover.
Aviation /13z Wednesday through Sunday/...
short term...areas of MVFR cigs will be slow to scatter out as
upper low moves overhead. Near Penobscot Bay and at rkd warmer
air being transported from just offshore into the colder air
inland will continue LIFR cigs for a couple of hours before
lifting with the approach of the cold front. That cold front
will also help to scatter out MVFR cigs elsewhere. Shsn will be
likely in the mtns...with leb and hie possibly seeing local IFR
or lower conditions thru the day. Scattered shsn are less likely
downwind of the mtns...but it cannot be ruled out. In addition
after 18z thru about 00-01z surface wind gusts at or above 30
kts are possible at all terminals...especially across srn New Hampshire and
mht/psm/con. Gusty wly winds will linger into Thu.
Long term...VFR conditions except MVFR/IFR in any snow showers
with the next clipper system to move through the area Fri night
short term...a strong cold front is expected to cross the waters
today. Strong wly winds will develop in the cold air advection behind the
front...with gale force gusts expected for all waters. A strong
gale is possible outside of the bays. Winds will diminish in the
bays this evening...but gale force gusts will linger outside the
bays thru the overnight. Winds and seas will remain above Small Craft Advisory
thresholds thru Thu.
Long term...strong gusty west winds continue into Thu night due
to the combination of strong cold air advection over the warm waters and the
pressure gradient. High pres beings to settle south of the
waters Fri allowing winds to diminish.
A strong northwest flow develops with possible gale force winds once
again in the wake of the next clipper system which exits off
the coast Sat night.
ME...Wind Advisory from 1 PM this afternoon to 9 PM EST this
evening for mez018-023.
Winter Storm Warning until 7 PM EST this evening for
New Hampshire...Wind Advisory from 1 PM this afternoon to 9 PM EST this
evening for nhz008>015.
Winter Storm Warning until 7 PM EST this evening for
Marine...Gale Warning until 11 am EST Thursday for anz150>154.