Area Forecast Discussion
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FXUS61 KGYX 210103 AAB
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
803 PM EST Fri Jan 20 2017
High pressure moves east tonight while a dissipating wave moves
into the region from the southwest. This will primarily just bring
some clouds to the area, though some light rain or freezing rain is
possible. Expect warm temperatures on Saturday as an upper level
ridge crosses the region. A cold front will drop south out of
Canada Saturday night into Sunday morning, bringing cooler weather
again. A storm system tracking up the coast will bring wintry
precipitation New England Monday and Tuesday.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Only minor changes to the forecast to account for current
640 PM Update...
Only a few changes to temperatures and winds for this update. Sky
cover remains entrenched with calm winds in place. Downsloping
winds on the north side of the Whites has kept clouds out of
portions of our northern counties but has since relaxed. May be
adjusted temperatures slightly upward here depending on if cloud
cover fills in shortly.
Cloud cover lingered much longer than initially expected today.
High pressure axis crossing the area saw a shift in the light wind
flow to a southeasterly return flow. This is allowing clouds to
dissipate to the northwest of the mountains (the downslope side),
while clouds pile up to the south and east of the terrain. This
cloud structure will play a role in temperatures overnight, as
areas in the clear will cool quite a bit more than areas stuck in
the clouds. Have decided to go above guidance values for southern
New Hampshire and most of the coastal plain of Maine where
temperatures may struggle to drop much below freezing. To the
north and northeast where clearing is expected, temperatures will
be colder, in the 20s to upper teens.
A sharp shortwave trough is moving northeast into New York state
this afternoon. This has been producing rain as it moved through
Pennsylvania, but as it arrives in New England the trough will get
lost in the ridge over New England. This area of rain has already
been breaking up a bit as the day has gone on and expect this to
continue this evening. By the time it arrives in New Hampshire
after midnight, it should be not much more than clouds. But some
light rain or freezing rain is possible, depending on surface
temperatures. Considering confidence in precipitation occurrence
is quite low, we do not plan to highlight the freezing rain threat
tonight unless/until it gets closer to arriving.
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.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
As the remnant wave moves east across the area expect a west to
northwest flow behind it with warmer air spilling in. Temperatures
should reach the 40s across the entire area. Downslope warming
could allow temperatures to reach the 50s in southern and coastal
areas. Models often under-forecast warm temperatures in January in
part due to the expectation that snow cover will have a greater
negative effect on high temperatures (an old snow pack often
negates this effect) and also due to extra mixing from the
downslope winds. Therefore went a little above guidance for high
temperatures in the south and the coastal plain on Saturday.
A trough dropping south through the Gulf of Saint Lawrence will
send a cold front south through Maine and New Hampshire Saturday
night into Sunday morning. This will bring colder temperatures
into the area, but may only reach the northeast part of the area
by Sunday morning. Temperatures generally expected to be in the
30s, dropping into the 20s behind the front.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Extended forecast focused mainly on the significant coastal storm
set to affect the region Mon thru Tue. Outside of that window I
stayed close to the multi-model consensus.
Some of the things we do know about the storm system
include...that it will be a slower mover. With a well develop
closed low...we should see precip occurring over parts of the
forecast area for at least 24 hours. I am also not particularly
concerned with lack of moisture or QPF in this event. Ensemble
guidance is showing significantly anomalous H8 u wind into the
region...in excess of -5 standard deviations. That is typically a
strong signal for higher QPF events...though such strong flow will
also likely have a terrain/upslope dependence to it as well.
Couple that Ely flow with a +3 standard deviation PWAT
anomaly...and the ingredients are there for a high QPF system.
This strong Ely flow will also develop in a well mixed boundary
layer initially. Winds...especially near the coast could become
quite gusty for a period Mon night. It is still a long way
out...but this type of Ely flow could produce advisory level gusts
or higher near the coast. Confidence is also fairly high that a
surface high pressure will be building SEwd into the Canadian
Maritimes ahead of the approaching system. This type of evolution
is very favorable for cold air damming and temps below guidance.
Given that we are still 5 or so days away from the
event...guidance is still struggling with handling that
damming...but the 20.12z ECMWF seemed to have the best handle on
it. The forecast leans heavily in this direction.
With all that said...there is plenty we are less confident in.
Both the GEFS and ECMWF EPS sensitivity argue that a key feature
in downstream evolution is the upper low pressure still sitting
off the Pacific Northwest coast. It still could take another 24 to
36 hours before this feature is onshore and can be well sampled by
the raob network. When this happens...models could shift more
strongly in favor of a warmer or colder scenario for our region.
At this time ensemble sensitivity points towards higher heights
across the Wrn CONUS and into Canada favoring a colder solution
for the Northeast. This is no real surprise...given that a
stronger high to our N would result in a colder temp profile
overall. However we will not know if models are handling those
heights well for another day or so.
Mid level temps will be critical in this forecast as they regard
to ptype. Given how mesoscale in nature that can be...confidence
is quite low in these temps. I leaned again towards the 20.12z
ECMWF mid level temps...which are cooler than the GFS...but still
do warm well above 0C from the foothills and S. This brings into
play all winter hazards...rain...snow...sleet...and freezing rain.
Overall I feel the high is in a strong position and deep...so
colder solutions are most likely. This could still mean a cold
rain however. But in general...snow at onset transitioning quickly
to rain near the coast. Interior will hold onto low level cold the
longest...with accumulating snow followed by sleet and freezing
rain. The best chance to remain all or mostly snow will be the Wrn
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
Short Term...Persistent MVFR cloud layer will remain in place for
much of the night to the south and east of the mountains. To the
north, it should be fairly clear. By morning a dissipating wave
will bring more clouds and an outside chance of some light
freezing rain to southern and western New Hampshire. Generally
expecting MVFR to possibly IFR conditions as this moves through
during the day Saturday, followed by VFR conditions again
Long Term...VFR generally expected thru Sun. A cold front dropping
Swd may bring widely scattered SHSN along it...but confidence is
low on coverage and timing. Ely onshore flow Mon may bring MVFR
CIGs into Srn and Wrn areas...especially MHT...PSM...CON...and
LEB. Conditions rapidly deteriorate Mon night into Tue. IFR and
LIFR will be widespread...except for maybe HIE where downsloping
winds keep CIGs higher. Interior terminals will see SN changing
to FZRA/PL...and maybe RA...while coastal terminals will see brief
SN changing to RA. Winds may also be gusty near the coast...with
sfc gusts in excess of 35 kts. IFR or lower conditions linger into
Short Term...Light winds expected over the waters as high pressure
moves by. A cold front will drop south into the Gulf of Maine
Long Term...A strong Ely flow will develop ahead of approaching
low pressure early next week. Winds will increase from SCA thru
gale force on Mon...with the best window for storm force wind
gusts on the outer waters looking to be Mon night. I have higher
confidence on wind gusts than the timing of them...so for that
reason no headlines have been issued. But gusts to 50 kts are in
the forecast...and the HWO will highlight the storm force gust
Despite being at the low part of our tide cycle...large building
waves may product some erosion and splash-over near the time of
high tide Monday night and Tuesday. Preliminary storm surge values
appear to be around 1.5 to 2 feet with a persistent...strong
easterly wind developing.