NWS Gray, Maine Area Forecast Discussion

FXUS61 KGYX 182020

Area Forecast Discussion
National Weather Service Gray ME
320 PM EST Sat Nov 18 2017

Low pressure moving through the Saint Lawrence Valley will push
a warm front northward through northern New England tonight.
Expect mostly rain as this moves through, but northern areas
could begin as light snow or freezing rain before the
temperature warms overnight. As the low moves east on Sunday it
will drag a cold front across the region from west to east,
causing temperatures to fall through the day and winds to become
gusty. Expect cold conditions continuing on Monday before a warm
up on Tuesday. Another cold front moves through on Wednesday
with cold air spilling in for the last half of the week.


As low pressure moves through the Saint Lawrence Valley tonight
a warm front will lift northward through New England. Already
seeing precipitation beginning across southern New England, and
this will spread northward into New Hampshire and Maine this
evening. The leading edges of this could begin as snow, but
expect this to be primarily a rain maker. The only exception
will be in interior parts of western Maine and northern New
Hampshire where low level temperatures may stay below freezing
for a while as the rain begins. Low level dry air is still
fairly impressive, and it is likely that as precipitation begins
it will cause temperatures to fall more through evaporational
cooling than radiational cooling. As the night goes on expect
temperatures to warm, and by morning it should be above freezing
just about everywhere. Have issued a Winter Weather Advisory
for areas that are most likely to see some light freezing rain
tonight. Do not expect much accumulation, but it will be just
enough to make roads slick.


A cold front will move from west to east across the forecast
area during the first part of the day on Sunday. This will shut
off the precipitation and shift winds to the west. Pretty good
cold advection signal behind this front suggests good low level
mixing and falling temperatures during the day. 850/925 MB winds
are forecast to be 40 to 50 KT, so expect with good cold
advection these will mix down with high efficiency especially to
the east of the mountains where downsloping conditions will aid
in the process. Have issued a Wind Advisory for this area,
though wind gusts will be primarily on the low end of Advisory
criteria. This could be just enough to down a few limbs and
cause a few isolated power outages. Winds stay up into the
evening hours, but will begin to lose their gust potential
overnight. With the low levels well mixed expect low
temperatures to be driven more by cold advection than
radiational cooling, and will generally be in the 20s.



High Impact Weather Potential:
* Gusty winds on Monday approach wind advisory criteria.

Pattern / Implications: The pattern across North America has been
rather progressive over the past week with shortwaves impacting our
region every two to three days.  Current and recent runs of the
deterministic and ensemble guidance suite continue this idea
through this long term forecast period...although with the NAO
beginning to shift negative and the AO following suit...its not
surprising to find both the GFS and EC /and their respective
ensemble means/ carving out a more long-lasting trough over the
eastern United States by the end of this forecast period into
next weekend. With the fact-paced flow in place...expect a bit
of a roller-coaster ride in terms of temperatures...with a few
shortwaves and associated precipitation chances.

Model Trends / Confidence: Deterministic and ensemble guidance is in
good agreement on the large scale pattern through Tuesday of next
week before diverging somewhat for the middle and latter
portions of the week. The primary differences concern the
handling of digging shortwave energy Tuesday night into
Wednesday. Recent GFS/GGEM solutions drop significant energy
along the western flank of advancing trough...closing off a mid
level low over the southeast on Wednesday while the 18.00Z
ECMWF favored more of this energy remaining with the northern
feature with a stronger H5 trough reaching the east coast on
Wednesday. 18.12Z ECMWF has trended closer to the GFS/GGEM
camp...and given much better ensemble support for this solution
will lean heavily in that direction with this forecast package.
Forecast agreement increases after this period with cool
northwesterly flow enveloping the northeastern United States.

The Details...

Monday: -1 to -2 sigma PWAT anomaly moves overhead under robust
northwesterly flow with high pressure arriving from the west
towards evening. Residual moisture and cyclonic flow will allow
ongoing mountain snow showers to continue through the morning
with decreasing clouds expected to rule the day. T9s generally
-5 to-10c indicate highs in the mid 20s north to mid 30s
 south...nearly 10 degrees below normal for the date.

Winds:  With the core of the H5 trough overhead...model soundings
suggest a great llevel mixing setup...with mixing height reaching
above 6 kft.  This should take full advantage of winds at this
height around 40kts. Thus...expect winds 15 to 25 mph
sustained...with gusts of 30 to 40 mph likely.  Can/t rule out a few
gusts around wind advisory levels.  Future shifts will certainly
need to watch for the potential for additional wind advisory

A combination of coupled llevel wind flow /1000 mb geostrophic winds
around 20kts/ and a period of SCT/BKN mid level cloudiness
should help lows from getting too out of hand...but a few
isolated locations may be able to radiate. However...teens and
20s look most likely for lows...close to model consensus.

Tuesday: Return flow with rapid warm advection moving T8s back above
freezing.  Given the setup...a return to warmer than normal
temperatures is expected.  It again looks breezy...but now from the
southwest as backing flow aloft strengthens to +1-2 sigma at the H8
level. T9s reach back towards 5C which indicate that given good
mechanical mixing...southeastern NH will likely reach into the
lower 50s...but it won/t feel quite this warm given the breeze.

Wednesday-Thursday:  As described above...forecast confidence
decreases somewhat for the important Thanksgiving travel
period...although the 18.12Z guidance suite is trending towards a
consensus.  This would favor a moisture-starved northern stream
shortwave and associated frontal passage on Wednesday followed by
high pressure briefly building into the region for Thanksgiving.
Temperatures near climatology on Wednesday ahead of the front
Wednesday moving back below normal for the Thanksgiving holiday.

Friday-Saturday: Have to keep an eye on the cutoff energy over the
southeastern states as next northern stream shortwave arrives from
the west.  There have been varying signals for some semblance of low
pressure along the east coast Friday...but with the most likely
solution keeping precipitation offshore.  Thus...would await the
surface low associated with the northern stream shortwave for any
sensible weather impacts. No signal for significant departure of
temperatures from seasonal norms...with chance PoPs for


Short Term...VFR conditions give way to IFR ceilings and rain
this evening and overnight. Winds shift to the west behind a
cold front tomorrow morning. By tomorrow afternoon strong cold
advection will allow these winds to gust up to 35 or 40 KT
before diminishing a bit overnight.

Long Term...Improving to VFR Monday with continued strong
northwesterly wind gusts to 35kts. Expect VFR conditions to
largely dominate the week...with a cold frontal passage
Wednesday bringing the potential for some restrictions in
shra/sn on Wednesday.


Short Term...Expect gale conditions as a cold front moves
through early on Sunday. There is a chance that southerly winds
reach gale force ahead of the front, but the big show will be
behind the front when winds shift to the west and gust up to 45
KT in a cold west wind. Gusts should diminish below gale force
by around midnight Sunday night. Wave heights will be highest
further from shore.

Long Term...Another period of gale force gusts over the outer
waters is likely on Monday with SCAs elsewhere...with winds
diminishing...but waves remaining elevated Monday night. Winds
shift southwesterly and strengthen on Tuesday with SCAs likely
to continue into Wednesday before diminishing winds and waves
are expected for the end of the week into the weekend.


ME...Wind Advisory from noon Sunday to midnight EST Sunday night
     for MEZ012-018>028.
     Winter Weather Advisory from 8 PM this evening to 6 AM EST
     Sunday for MEZ007>009-012>014.
NH...Wind Advisory from noon Sunday to midnight EST Sunday night
     for NHZ004-006-008>010-012>015.
     Winter Weather Advisory from 8 PM this evening to 6 AM EST
     Sunday for NHZ001-002-004.
MARINE...Gale Warning from 6 AM Sunday to midnight EST Sunday night for



NEAR TERM...Kimble
LONG TERM...Arnott

NWS GYX Office Area Forecast Discussion