Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS61 KGYX 151143 AAA
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
643 AM EST Sun Dec 15 2019

.SYNOPSIS...
A complex frontal system crosses the area tonight with strong
winds over much of the area Sunday. High pressure builds into 
the area Monday. Low pressure tracking from the Ohio Valley 
towards southern New England will bring mainly light to moderate
snow to the area late Monday night into Tuesday afternoon. Snow
showers are possible Wednesday followed by much colder air for 
the end of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
645 AM Update...
Forecast is on track this morning with a few light showers
moving in over the mountains. Windy conditions have have already
started and will become gustier as the day goes on.
Temperatures, dew points, and sky cover was adjusted for this
update. 


Previous discussion...
Surface analysis shows that a cold front is crossing the region
this morning, with the parent low pressure already located well
north in the St. Lawrence River Valley. This boundary is mainly
a wind shift and the demarcation line of stronger winds. Later
today a secondary cold front will sweep across ushering in the 
colder and drier airmass. Strong CAA as well as deep mixing and
a tight pressure gradient over the area will allow winds to 
gust to near 50 mph at times. KGYX VAD wind profiles are
currently showing about 40 kts at 2kft, and a substantial 
portion of this is already mixing to the ground in the wake of 
the first front. Have extended the wind advisory to include the
entire forecast area, and started it at 7 AM given that we are 
already seeing gusts near 35 kts. 

Otherwise there is some stratus that remains in upslope areas,
and there will be some isolated to scattered snow showers today
over the highest peaks, which could see some moderate snowfall
accumulations through tonight. Skies will gradually clear out
in downslope flow later this afternoon. Highs today will occur
at daybreak with temperatures falling throughout the day.
Needless to say it will feel very cold with the wind chill.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
Cold high pressure builds in tonight into Monday with single
digits likely tonight across the north and teens across the
south in strong CAA. Highs warm into the teens to the lower to
mid 30s just along the coast. A system to our south may
introduce some cloud cover towards the evening from the SW.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Model guidance has slowed the next system slight...with precip
likely holding off until Tue now. Not much has changed from
previous forecasts. 15.00z raobs got a sampling of the S/WV trof
over Nrn CA last evening...and my expectation is for less wild
swings in model guidance from here on out as a result. Some of
the same concerns...as stated in previous discussions...
remain. Saturation of the snow growth zone and mid level warming
are consistent signals showing up on guidance. This would point
towards a less efficient snowfall than average. That being said
there is strong isentropic ascent in the WAA ahead of the
wave...so if we can trend towards greater saturation a period of
enhanced snowfall is possible Tue. For now I have gone with
lower than average snowfall ratios and QPF generally less than a
half inch. That does still give a fairly widespread 2 to 4
inches for much of the Srn half of the forecast area. Given that
this is the higher confidence area...that is also where I keep
the high likely and low categorical PoP in the forecast. The
15.00z GFS is still a fairly robust wave...so there is room for
this system to trend in either direction.

There is good model agreement on an Arctic S/WV trof diving out
of the NNW and across the region Wed. Despite the continental
origin the trof passage will likely come with scattered snow
showers...and I cannot rule out some snow squalls in the mtns
especially. The real story will be the H8 temps of -20C pouring
into the area behind the trof. With the 2 SD below normal air
mass settling over the region...a couple days of highs in the
20s and lows in the single digits looks likely.

Lots of uncertainty beyond that however...as a PV streamer
across the central CONUS drifts Ewd. How the Nrn stream
interacts with this feature will drive the forecast thru the
weekend. It could be another trof passage...or it could be a
more phased system and widespread precip locally. For now the
multi-model consensus will be the starting point with a chance
of snow showers.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
Short Term...Some MVFR ceilings still out there this morning in
stratus banked along the higher terrain. VFR will prevail today
everywhere as a cold front ushers in drier air...with the 
exception of KHIE which could see -SHSN today resulting in MVFR
conditions. Winds will be the main concern today with about 30+
kts already being reported in strong cold air advection.
Vigorous mixing will keep this scenario going all day and expect
the odd gust to 30-40 kts. Winds begin to diminish overnight.
There is some LLWS out there this morning as winds in the
1.5-2k ft AGL are around 45 kts. 

Long Term...After a VFR start to the day...lowering clouds and
SN breaking out Tue will bring widespread IFR or lower to the
area. The bulk of the SN will fall during the day and into the
evening...before gradual clearing and return to VFR from W to E.
A strong trof and much colder air arrives Wed...with a period of
gusty winds possible Wed night. SHSN chances with the trof are
low confidence...except for upslope regions of the mtns. HIE
will likely see MVFR CIGs and local IFR or lower in SHSN in the
vicinity.

&&

.MARINE...
Short Term...Gale warnings continue through tomorrow morning 
with gusty westerly gales starting this morning. Seas remain in
the 8-13 ft range from the bays to the outer waters.

Long Term...A wave will pass S of the waters Tue and Tue
night...with snowfall reducing visibility over the waters. Winds
may stay below SCA thresholds...but seas are expected to build
above 5 ft outside of the bays. A secondary trof axis crosses 
the waters Wed...with strong CAA expected. Gale force wind gusts
are possible outside of the bays...continuing into Thu. Winds 
and seas gradually diminish as cold high pressure builds into 
the area.

&&

.HYDROLOGY...
The Suncook River at North Chichester has finally crested...and
along with the Presumpscot at Westbrook...continues to fall.
There continue to be a couple rivers rising...but they are
expected to remain below flood stage. Overall the trend will be
down with water levels today. Next update to FLS is expected
when Westbrook falls below flood stage in the next few hours.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Wind Advisory until 1 AM EST Monday for MEZ007>009-012>014-
     018>028.
NH...Wind Advisory until 1 AM EST Monday for NHZ001>015.
MARINE...Gale Warning until 6 AM EST Monday for ANZ150>154.

&&

$$

National Weather Service Glossary of Abbreviations