Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 140859
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
359 AM EST Sat Dec 14 2019

.SYNOPSIS...
Low pressure developing along the East Coast will move north
through New England today. Expect warmer conditions and moderate
to heavy rain across the area. Once the low moves away, a cold
front will push through and usher in colder weather on very
gusty westerly wind Sunday. The next low pressure system tracks
near southern New England on Tuesday with a chance of wintry
weather for New Hampshire and Maine.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Early this morning MSAS pressure analysis showed a front along
the coast while farther south a warm front approached and is
currently south of the Gulf of Maine. Aloft, vorticity was
streaming into northern New England ahead of a strong wave
moving out of the Deep South. At the surface low pressure was
riding up the eastern seaboard. Warm air advection will continue
ahead of the storm today as another low forms off the Jersey
coast in response to strong pressure falls aloft.

Observation sites reported freezing drizzle and freezing rain
overnight across portions of the interior and mountain valleys.
Winter weather advisories were not extended as temperatures have
been gradually coming up this morning in steady WAA. Some
stronger bands of rain are currently rotating into southern NH.
Models have increased storm total rainfall from 1-2" to more
like 1.5-3" with most of this falling in southern NH and in a
swath over the coastal plain...shadowing the coastal front which
is where the Flood Watch remains in place through this evening.
Expecting several rounds of moderate to heavy precipitation
today into tonight. Likewise ensemble river forecasts have
increased the number and magnitude of possible river flood
points. To put it in perspective, GEFS QPF M-climate values are
peaking near the all time max for this time frame, relative to
their 30 year reforecasts...over southern NH and SW Maine
especially.

Visibility will be reduced today in heavy rain and fog.
Temperatures do however continue to creep up, with upper
30s/lower 40s across the mountains and some locations near the
coast reaching 50 degrees as the coastal front moves inland.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Anomalous deep low pressure moves up the St. Lawrence River
Valley tonight, with a triple point moving across NH as the
attendant cold front surges northeast. Along the cold front
expecting another batch of light to moderate rainfall through
Sunday morning. Behind the cold front extremely cold air will
arrive, changing any remaining precipitation over the higher
terrain to snow showers. Expecting a few inches over the highest
peaks.

The main concern Sunday will be the extremely gusty winds.
Forecast soundings are indicating about 50 kts just off the
deck, most of which will be able to mix to the ground in strong
CAA. MOS guidance has 20 kts at several sites throughout the
day, so have bumped up gusts a bit more, just shy of wind
advisory criteria. Think the majority of of gusts will be around
35-40 mph. Along the coast and over the higher terrain it will
be the windiest, and it is likely we will get scattered power
outages.

Highs will only peak a couple degrees higher in the mountains
compared to their lows...putting them just above freezing during
the day Sunday. Over the coastal plain lower to mid 40s are
expected with sunny to partly cloudy skies.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Overall with a busy short term and moderate to heavy rainfall
expected the extended forecast is very close to the multi-model
consensus blend.

There was a bit more focus on the Mon night/Tue period...as that
looks like the next shot at wintry precip. Still looking at
likely precip...but low confidence in evolution. There continue
to be some red flags...both with mid level warming possibly
leading to mixed precip...and mid level drying leading to poor
snow growth or drizzle/freezing drizzle. Given the RH fields on
the 14.00z model suite...models may be overdoing QPF
slightly...as it typically in dry slots. Still thinking a fairly
uniform snowfall...around or just below advisory criteria. I
suspect model guidance will begin to converge towards a solution
over the course of the day...as S/WV trof moves onshore in the
Pacific Northwest. Given that it is forecast to be ongoing
around the Tue morning commute...this will be one to watch.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
Short Term...Moderate to heavy rain is falling at all the TAF
sites this morning, and this will continue throughout the day
and into the night as low pressure passes through the area.
Conditions range from MVFR to IFR, and will vary throughout the
day depending on if a rain band is overhead or not. In general
though expect poor visibility and low ceilings due to
precipitation and fog through tomorrow afternoon. Once a cold
front comes through in mid morning, conditions will gradually
improve, but winds gusting to 25-30 kts are likely at all sites.
LLWS remains in the TAFs this morning before stronger winds can
mix to the surface.

Long Term...VFR conditions prevail Sun night into Mon. Next
system approaches from the SW Mon night. Conditions will quickly
deteriorate to IFR or lower in SN as a band lifts SW to NE thru
the forecast area overnight. Srn zones may see a brief mix at
times Mon night...but confidence is low. Conditions quickly
improve Tue to VFR again...except for the vicinity of HIE where
upslope flow will keep some MVFR CIGs locally.

&&

.MARINE...
Short Term... Gales begin later this morning and continue
through the weekend. There will be a brief lull this afternoon
before winds once again return to stronger gales on tonight.

Long Term...Gales Sun night will gradually diminish...with SCA
conditions likely lingering into Mon afternoon. A weaker system
will pass to the S of the waters Tue with more CAA in its wake
for Wed. Another period of SCA conditions is expected then with
offshore flow...with a chance at some gale force gusts outside
the bays.

&&

.HYDROLOGY...
QPF/Flash flooding: QPF amounts have increased through the
coastal plain with up to 3" possible. With the frozen ground
and small creeks and streams already running high from the last
event, expect this will result in some minor flooding. With the
heaviest rainfall in the 12-18Z time frame this would be the
time for any flash flooding if the heavy precipitation is able
to remain in one spot or pass over the same area in several
batches.

Rivers: Greatest threat for river flooding is across southern
New Hampshire. Here around 2" of QPF is expected in addition to
the melting of the remaining 1-2" of SWE still on the ground
from the prior big snow event. The combination will lead to
minor flooding on several rivers including the Suncook,
Contoocook, Warner, and Piscataquog. This area remains in a
Flood Watch.

Across the White mountains the rainfall totals will be lower -
0.75 to 1.5 inches, which will be able to be at least partially
absorbed by the snowpack. Thus while there will be rises on the
rivers significant flooding is not expected.

&&

.TIDES/COASTAL FLOODING...
The combination of increasing onshore winds and building wave
action will coincide with relatively high astronomical tides
this afternoon. The astronomical tide this afternoon in
Portland is 10.6 ft. At this point, the addition of storm surge
is expected to push water levels right to or just over the
minor flooding threshold, with building wave action likely to
cause minor splash-over and beach erosion in vulnerable areas.

Another aspect of this tide cycle will be that most of the rain will
have already fallen by the time of high tide around noon. The timing
of the high tide will cause runoff to drain more slowly from the
marshes and tidal waterways, which could be enough to cause some
minor flooding issues on roads and drainage areas within the tidal
zone around the time of high tide.

Winds will turn offshore and waves will be subsiding in time for the
Sunday high tide cycle, and coastal flooding issues are not expected
at this time.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch through this evening for MEZ018>028.
     Coastal Flood Advisory from 11 AM this morning to 3 PM EST
     this afternoon for MEZ023-024.
NH...Flood Watch through this evening for NHZ008>010-012>015.
     Coastal Flood Advisory from 11 AM this morning to 3 PM EST
     this afternoon for NHZ014.
MARINE...Gale Warning from 7 AM this morning to 6 AM EST Monday for
     ANZ150>154.

&&

$$

NEAR TERM...Hanes
SHORT TERM...Hanes
LONG TERM...Legro


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