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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KGYX 260401
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1101 PM EST Sat Jan 25 2020

.SYNOPSIS...
Low pressure will cross the region this evening bringing a mix
of snow north and rain in the south. Northwesterly flow will set
up with clouds and snow showers lingering in the mountains
through Tuesday. A few flurries remain possible through
Wednesday, but then a strong high will build in for the second
half of the week with clear skies and cold overnight
temperatures.

&&

.NEAR TERM /OVERNIGHT/...
11PM UPDATE...
Updated the forecast to remove the Flood Watch for New Hampshire
where the heavy rain has ended. Otherwise no current changes to
the forecast.

930PM UPDATE...
Back edge of the heavier rainfall has already arrived in
southern NH and will move east rather quickly this evening. Have
adjusted hourly precipitation timing to try to get a better
grasp on the ending time. An initial batch of showers has given
much of western Maine a pre- show with the precipitation, and
thus I have upped the precipitation amounts here just a bit. It
also seems likely that more of this precipitation will fall as
snow in the north with the freezing rain transition happening
around the time that precipitation is ending, so snowfall totals
have been bumped up a bit, though still covered by the Winter
Weather Advisory.

6PM UPDATE...
Made some slight adjustments to the forecast based on latest GYX
sounding data. Should see a preceding area of drizzle ahead of
the heavier precipitation. Once the heavier precipitation
arrives, it could begin as snow for a broader part of the
foothills or interior coastal plain as the lowest level
inversion tops out right around freezing and the one above it
should wet bulb below freezing. However, do expect continued
warming of this warm layer and a shift to all rain across the
area rather quickly. The fire hose will be pointed at our area
from offshore of southern New England, pivoting around through
the Gulf of Maine tonight. Expect a brief period of heavy rain
especially near the coast, while interior areas especially in
northwest Maine will see snow and areas of freezing rain. No
significant changes in previous forecast thinking regarding
precipitation amounts, though it`s possible that the low level
moisture stream squeezes out locally more rainfall right along
the coastal front. Primary flooding concerns center around urban
areas that might have poor drainage issues especially if snow
banks block efficient drainage.

ORIGINAL DISCUSSION...
***SHORT DURATION HEAVY RAINFALL EXPECTED TONIGHT***

A weaker atmospheric river of moisture ahead of an occluded
front will cross the region late this afternoon through late
this evening. 25.12z HREF is forecasting 1 to 2 inches of
rain...with the majority of that falling in a 3 hour window.
This is supported by upstream observations of 1 inch per hour in
parts of NY...PA...and NJ. Given the fresh snowpack I expect
that it will absorb much of that rainfall despite the heavy
rates. The bigger concern is that snowbanks are covering storm
drains in many areas and the faster runoff on streets in the
urban areas may lead to excessive ponding and minor flooding.
Flood watch remains in effect for this reason...more details in
hydrology section below.

Still seeing pockets of sub-freezing air across Nrn zones and
into the foothills. Increasing onshore flow and increasing winds
on top of that layer are leading to more widespread drizzle and
freezing drizzle. It looks like the winter wx advisory covers
the freezing drizzle areas well and no changes were made to
headlines. The Srn advisory areas will eventually change to
rain. The Nrn advisory areas will see some areas remain below
freezing and a slight longer period of sleet or freezing rain
after initial snow. Overall warming aloft and short duration are
expected to keep amounts on the light side. Will have to keep an
eye on freezing levels...as forecast soundings indicate the
highest summits may hang on to all snow. If that lowers a bit
that could bring the Wrn ME summits like Sugarloaf into play for
higher snow totals.

Finally SE LLJ will increase overnight and peak around midnight
give or take an hour based on location. NAM is probably the most
aggressive of any model...with 60 knots below 900 mb. Even in
that scenario the expectation would be for gusts in the 35 to 40
mph range. So I have kept wind gusts overnight generally below
30 kt outside the Midcoast.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
Forecast area remain in cyclonic flow and trapped low level
moisture should keep plenty of cloud cover in Wly upslope zones
into Mon morning. I expect snow showers as well...with at least
light accumulations in the higher terrain.

Temps will be mild Sun as colder air delays until upper trof
axis passes. Given that occurs overnight and CAA should keep
boundary layer somewhat mixed I blended in raw 2 m temps to
trend down to lows Mon morning.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Upslope flow continues through the first part of the week as an
upper level low slowly pulls northeastwards into the Maritimes.
Northwesterly flow will result in downsloping into the coastal
plain with clear skies across the south and mostly overcast with
snow flurries in the north.

Through the middle part of the week split flow develops over the
central part of North America. While some weak waves pass both
north and south of us we remain largely average with just a
chance for precip on Wednesday when the northern stream wave
approaches. Have increased PoP for the mountains on Wednesday as
soundings show enough lift to eek out some flurries despite the
dry air mass.

Strong high pressure will build into the region for the end of the
week. With clear, dry, and calm conditions expect overnight
lows to drop quite well in the moutnains and have leaned towards
the colder statistical guidance for this.

Global ensembles would point towards a breakdown of this pattern for
the end of the week as the block in the Pacific breaks down and
we see a wave train propagate all the way to the east coast by
Saturday. With this type of scenario the most suspect part is
the timing. The split flow and blocks can`t last forever, and
it`s likely a trough will develop over the eastern CONUS
returning us to the storm track, but the time of return could be
as late as the end of the weekend or early next week. With low
confidence have kept PoPs to under 30 through the weekend time
frame.

&&

.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
Short Term...Widespread MVFR CIGs continue to gradually lower
with some areas of IFR now filling in. That trend will continue
into the early evening where widespread IFR or lower CIGs are
expected S of the mtns. Additionally VIS will lower in pockets
of DZ...especially where slightly upsloping SE flow occurs.
RA/+RA moves in from W to E tonight generally between 00z and
06z. LLWS is also expected beginning late this afternoon thru
late tonight. LLWS and +RA come to a quick end behind the
occlusion between 06z to 09z. VFR conditions expected S of the
mtns thru Sun night...upslope SHSN and MVFR CIGs expected N. HIE
may see local IFR in any SHSN.

Long Term... MVFR clouds and snow showers will linger in the
mountains through the first part of the week. Elsewhere VFR will
prevail in downslope northwesterly flow. By midweek a strong
high will being to build into the region and hold through the
end of the week keeping conditions VFR.

&&

.MARINE...
Short Term...Gales warnings remain in effect for all waters with
strong SEly LLJ expected tonight. Gales should be relatively
short duration...with a roughly 6 hour window of strongest wind
gusts. Winds and seas gradually diminish as offshore SCA gusts
Sun keep seas confused.

Long Term... Northwesterly flow will develop in the wake of the
departing low for the start of the week, with a few gusts to SCA
on the outer waters possible. High pressure will build in for
the end of the week with calm seas and winds.

&&

.HYDROLOGY...
Quick hitting heavy rainfall will move through the southern
portion of the region tonight with widespread 1-2 inches
expected in just over 6 hours. Water vapor imagery shows a deep
moisture plume extending well south into the Cape Hatteras
region ahead of a cold front. This moisture plume will meet both
the topography of the mountains, as well as the convergence
already seen in the surface observations along the coastal front
and the combination will focus precipitation just inland of the
coast. With frozen ground and drains blocked by snow the impact
will be more than normal for this rainfall amount and a flood
watch has been issued for the coastal areas.

For the rivers expect most points to stay below action as the
snowpack across the region remains at around 20-25% density and
will be able to absorb quite a bit of the rain. Points to watch
in southern NH include the Lamprey which may reach action and
Suncook at North Chichester where both the heavy rain and ice
affects may combine to reach action. Across southern Maine, the
Presumpscot at Westbrook is expected to peak around 10ft, but
with the focus of the mesoscale rainfall within the basin it has
the potential to reach action as well. A final note is that the
ice jam remains in place on the Kennebec at Augusta. Although
water levels have continued to drop and not a lot of runoff is
expected to reach the mainstem Kennebec the ice jams could move
at any time.

&&

.TIDES/COASTAL FLOODING...
East flow increasing today brought storm surge above a half foot
this morning. With increasing winds expected tonight I expected
at least a foot of surge on top of the tide. Given this is the
lower of the daily tides I do not anticipate any flooding...but
splashover is likely with building nearshore waves. The 10.0 ft
noon tide Sunday may also see additional splashover...but
offshore winds should again mitigate the flooding threat.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory until 7 AM EST Sunday for MEZ007>009-
     012>014.
     Flood Watch until 3 AM EST Sunday for MEZ018-019-023>026.
NH...Winter Weather Advisory until 7 AM EST Sunday for NHZ001>005.
MARINE...Gale Warning until 7 AM EST Sunday for ANZ150>154.

&&

$$

NEAR TERM UPDATE...Kimble
SHORT TERM...Legro
LONG TERM...Curtis