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NWS Gray, Maine Forecast Discussion


000
FXUS61 KGYX 222035
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
335 PM EST Mon Jan 22 2018

.SYNOPSIS...
A frontal boundary will lift back north tonight and spread some
light snow across the area. This will gradually transition to
some drizzle overnight...which could get icy where temperatures
remain below freezing. By Tuesday morning steady precipitation
will be moving back in from the west. A period of sleet or
freezing rain will gradually transition to rain as the cold
front approaches the area. Once the front comes through we will
turn colder...but precipitation will come to an end.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Mid level warm front is moving steadily towards the forecast
area at this hour. Precipitation shield is fairly ragged
currently...but is expected to fill in as frontogenesis occurs
between the leading edge of WAA and cold dome in place. At the
moment however...precipitation has mostly come to an end across
the area. There may be some patchy drizzle or very light
snow...but I feel the most significant wx will move in around
the 22 to 23z window.

Most temps have fallen below freezing across the forecast
area...with parts of Srn NH and the CT River Valley hovering
around freezing. I expect this will be about the extent of the
coldest air. But that does leave room for accumulating snowfall
with this mid level warm front. Generally speaking 1 to 4
inches across the area...less in the S and more in the Wrn ME
mtns. Behind the mid level front we lose saturation and precip
may change to drizzle or freezing drizzle depending on surface
temps. The higher terrain may keep enough saturation to continue
light snow. Any ice amounts will be light from the overnight.

The main concern this evening will be watching to see if mid
level temps are warm enough to start as a mix right away across
Srn NH. In addition...the moist and mild air moving into the
colder air mass may lead to some areas of dense fog. No advisory
has been issued...but Srn NH into coastal Wrn ME would be the
most likely areas to see dense fog.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
The cold front and another area of steady precipitation will be
approaching from the W Tue morning. I expect significant parts
of the forecast area to remain below freezing at this time. This
round of precipitation will likely be freezing rain and sleet
for much of the area...before gradually transitioning to rain.
This will occur most rapidly along the coast and across Srn
NH...where strong Sly winds aloft help shove the surface front
Nwd. The interior will likely hang on to frozen or freezing
precip until around 18z...when ageostrophic flow becomes more
SEly. Given the precip rates and more marginal temps...ice
accumulation will mainly stay around a tenth to two tenths of an
inch. Enough to make some roads icy...but unlikely to cause
significant disruption to the power grid.

The rainfall amounts could be enough to contribute to some rises
on area rivers. This could be enough to cause ice movement and
additional ice jam flooding. See the flood watch for more
information.

As warm front moves into coastal area...especially Midcoast
ME...some of the stronger winds aloft may mix down. A small
window of near 50 mph wind gusts are possible if the warm front
can make it appreciably onshore around RKD. A wind advisory has
been issued.

Cold front sweeps thru the area late Tue...mixing out the dug in
low level cold. Precip will quickly end from W to E...with
upslope flow contributing to snow showers in the mtns.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
The deterministic model solutions are in decent agreement on the
long wave pattern through day 10. The pattern remains progressive
and begins to amplify with time. A steady progression of troughs
and ridges across the forecast area will result in several sharp
swings in temperature between well below and well above normal
readings. In the dailies...low pressure and associated shortwave
impulse exits into the maritimes on Wednesday with lingering
upslope clouds and snow showers for the higher terrain. A second
shortwave impulse and reinforcing shot of cold air arrives for
Wednesday Night and Thursday. The cold begins to ease on Friday
as ridging and rising heights arrive. A warm front lifts north
across the area Friday night with a southerly flow and well above
normal temperatures for the weekend. The more progressive GFS was
discarded as an outlier with the approaching frontal system in
favor of the ECMWF/CMC-Global solutions which brings the front
and steadier band of precipitation across the forecast area late
Saturday Night and Sunday. Colder air filters into the area by
Monday behind this system along with a return to below normal
temperatures to start the new work week.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
Short Term...Widespread MVFR and areas of IFR CIGs remain across
the forecast area in light NE to onshore flow. We are seeing a
break in precip at this time which will gradually fill in from
the W starting around 22-23z. CIGs will continue to lower as
warmer air aloft moves in. I expect widespread IFR or lower
conditions...with maybe HIE remaining MVFR to VFR in downsloping
this evening. Precip this evening is expected to be mainly
SN...transitioning to DZ or FZDZ behind the mid level warm front
between 03 and 06z depending on surface temp. Between 12 and 15z
Tue another area of precip will move in from the W. I expect
this will begin as a brief period of FZRA or PL before changing
to RA at all terminals...with CON and AUG most at risk of
hanging on to colder surface temps the longest. This is also
about the time strong winds aloft move overhead and lead to LLWS
conditions. Winds will be strong close to the surface so shear
will begin in the 1000 to 1500 ft range. Cold front sweeps thru
the region late Tue...and winds become Wly and conditions
improve to MVFR and VFR.

Long Term...

Wed...Sct MVFR in mtn -shsn. NW sfc wind gusting to 25 kt.

&&

.MARINE...
Short Term...NE flow over the waters will gradually become Sly
overnight as a warm front lift Nwd. Some patchy dense fog is
possible as that warmer air moves Nwd. Winds increase Tue...and
gales are likely over the outer waters and Penobscot Bay. Gale
warnings remain in effect. There is a chance gale force gusts
may occur over Casco Bay...but confidence was not high enough to
include in the gale warning. Winds become Wly behind the cold
front later Tue...and SCA conditions will continue overnight.

Long Term...

Wed - Sat...Small Craft conditions are likely...with gusts
approaching gale outside the bays.

&&

.HYDROLOGY...
A Flood Watch is in effect for the southern half of New
Hampshire as well as western Maine south of the mountains.
These areas are expected to get enough rainfall during the day
on Tuesday to cause ice movement and possible ice jams on area
rivers. This could lead to minor flooding especially near areas
already affected by ice jams...including the
Ashuelot...Piscataquog...Saco...and Kennebec.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch from Tuesday morning through late Tuesday night
     for MEZ012-018>028.
     Winter Weather Advisory until 6 PM EST Tuesday for MEZ007>009-
     012>014-018>022.
     Winter Weather Advisory until noon EST Tuesday for MEZ023>028.
     Wind Advisory from 11 AM to 9 PM EST Tuesday for MEZ027-028.
NH...Flood Watch from Tuesday morning through late Tuesday night
     for NHZ003>015.
     Winter Weather Advisory until 6 PM EST Tuesday for NHZ001-002-
     004-006.
     Winter Weather Advisory until noon EST Tuesday for NHZ003-005-
     007>015.
MARINE...Small Craft Advisory from noon to 11 PM EST Tuesday for ANZ153.
     Gale Warning from noon to 11 PM EST Tuesday for ANZ150>152-154.

&&

$$

NEAR TERM...Legro
SHORT TERM...Legro
LONG TERM...Schwibs
AVIATION...Legro/Schwibs
MARINE...Legro/Schwibs

NWS GYX Office Area Forecast Discussion

Courtesy of the National Weather Service forecast office Gray, Maine




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