Scientific Forecaster Discussion
fxus61 kgyx 160840
Area forecast discussion
National Weather Service Gray ME
340 am EST Mon Dec 16 2019
high pressure builds into the area today. Low pressure tracking
from the Ohio Valley towards southern New England will bring
mainly light snow to the area Tuesday. Snow showers are
possible Wednesday followed by gusty winds and much colder air
for the end of the week.
Near term /until 6 PM this evening/...
narrow surface ridge of high pressure building across the
forecast area today will allow any remaining gusty winds to
diminish. It may take a little longer for ern portions of the
forecast area...but the overall trend will be lighter winds thru
the afternoon hours. Otherwise sunny but cool temps during the
Short term /6 PM this evening through 6 PM Tuesday/...
I do not have high confidence in the low temp forecast for the
overnight period. We start with surface ridging which will start
to retreat thru the night. So we may see quick drop in temps and
a leveling off for the rest of the night. The question is how
long temps drop for before that occurs. So there is some bust
potential on the cold side of the current forecast. We may also
see some clouds encroach on srn zones with the right entrance
region of the upper jet drifting newd towards the area
The real concern of the forecast starts most likely after
sunrise Tue morning with snow breaking out over the forecast
area. A shortwave trof near The Four Corners region will induce a
wave along the baroclinic zone draped over the Tennessee Valley
that will move newd thru Tue evening. The shortwave trof will more or
less shear out over the northeast...but the initial forcing will
be in the form of fairly strong warm air advection. Model guidance supports
strong sloped ascent over much of the region...and likely a
fairly broad shield of precip rather than a concentrated band.
Even the most mild of forecasts aloft keeps the mixing confined
to extreme srn New Hampshire...so the event is most likely all snow for the
forecast area. There are lingering questions though as to how
efficient snow growth with be. Model guidance continues to show
a relatively dry snow growth zone that at the very least would
keep snow ratios on the low side. Snow ratio grids attempt to
get at that across the srn third or so of the forecast area.
More consistent saturation is shown thru the middle of the the
forecast area...so higher ratios and higher storm total snowfall
is possible in a band from leb thru izg. The 16.00z eps is still
showing plenty of members that struggle to get quantitative precipitation forecast very far north
into the forecast area...and some high-res guidance is showing
a fairly dry forecast locally as well. I have forecast a broad
swatch of 1 to 3 inches across the srn two thirds of the
forecast area...but that may even be too high for some areas.
Given the aforementioned concerns I have not issued a winter wx
advisory for Tue. The other consideration was the morning
commute and timing of snow...but guidance has been continually
slowing the onset down...and I am not confident that snow starts
before the commute is winding down. I will let the day shift
get one more look today with a wider range of high-res guidance
Long term /Tuesday night through Sunday/...
the ensemble and deterministic model solutions are in decent
agreement on the long wave pattern through late this week. We
begin the period with broad west-southwest flow aloft in advance of
an upper trough over the central Continental U.S.. the trough will translate
east with an upper low dropping into New England on Thursday
before heights begin to rise with an approaching upstream ridge.
By next weekend...considerable uncertainty in sensible weather as
models have a tough time with amount of interaction between
northern and southern stream impulses. In the dailies...southern
stream impulse and associated ocean low vicinity of the 40n/70w
benchmark slide well offshore by Wednesday morning. The County Warning Area is on
the northwest periphery of the precipitation shield with any
measurable quantitative precipitation forecast likely confined to southern and coastal sections. A
northern stream impulse and closed low follow quickly on the
heels of the departing ocean low late Wednesday and Wednesday
night. Associated Arctic cold front is likely to produce a few
mountain snow squalls with its passage Wednesday night. Models
all suggest an east-west trough briefly forms from the Gulf of
Maine into mid coast Maine and produces at least some light
accumulating snow. However...the exact location remains
uncertain at this time. A fresh Arctic airmass will bring well
below normal temperatures Thursday and Thursday night with a
gusty northwest wind making for a bitterly cold day Thursday.
Winds drop off by early Friday as a ridge of high pressure
builds across the area for Friday into Saturday. Unsettled
weather returns by the second half of the weekend.
Aviation /08z Monday through Friday/...
short term /through Tuesday/...VFR expected thru at least Tue
morning. An approaching wave of low pressure will spread snow
across the area generally after 12z Tue. Expect conditions to
rapidly deteriorate LIFR as snow begins in the morning. There is
some lower confidence in how long lower visibility lasts as snow
intensity may let up towards midday. That being said much of the
day should feature IFR or lower conditions at all
terminals...except for possibly hie and Aug on the nrn edge of
Tue night...areas of IFR psb in -sn at coastal taf sites. North surface
wind gusting up to 35 kt.
Wed PM - Thu am...MVFR in mtn shsn with brief LCL IFR in snow
squalls. Areas of MVFR psb vcnty of Penobscot Bay in -sn Thu am.
Thu...northwest surface wind gusting to 30 kt.
short term /through Tuesday/...winds continue to diminish on the
waters this morning. Bays have been converted to scas...and gale
warnings will likely be able to expire and convert to scas on
time at 6 am. Small Craft Advisory conditions continue into midday for the
bays...and outside the bays into the evening. Snow overspreads the
waters Tue morning...and by late afternoon NE winds and seas
may be approaching Small Craft Advisory thresholds.
Fri...sca's likely outside the bays.
Marine...Small Craft Advisory until noon EST today for anz151-153.
Gale Warning until 6 am EST early this morning for anz150-152-