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-- Discussion containing changed information from previous version are highlighted. --
453
FXUS61 KGYX 211519
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1019 AM EST Thu Feb 21 2019

.SYNOPSIS...
Snow winds down this morning as a warm front lifts northeast
across the region. It will warm up into the 30s and 40s today
before a cold front drops in from the north tonight. High
pressure slides in from the west through Saturday. The next
storm system will develop in the southern plains and track into
the Great Lakes spreading more precipitation into the New
England on Sunday. Snow may transition to freezing rain before
coming to an end Sunday evening.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1000 AM Update...
Quick update to drop expired winter weather headlines in New
Hampshire. Areas of light snow continue in western Maine but
expect this activity to end over the next couple of hours. Have
also adjusted pops and weather based on latest radar trends. No
other changes planned attm.


Prev Disc...
800 AM Update....
Quick update to adjust pops and wx across the region. Fairly
large area of freezing drizzle left in the wake of last nights
precipitation. Should see this light freezing precip through mid
morning before mixing gets going and starts drying out the low
levels. Aside from a few temp/td tweaks...no other changes
planned attm.

Prev Disc...
Precip is winding down early this AM, and have adjusted POPs
for a speedier end to precip this morning with it ending across
most of the CWA between 12Z and 14Z. Going to hold the
advisories as they are because there is some FZDZ in spots where
there are no radar echoes, and it is the morning commute.
Overall total snow amounts will likely fall closer to 2-4"
across much of the area.

Previously...Our weak but double barrelled low pressure system
will track east this morning, and precip will end quickly from
W-E during the early to mid morning. In fact, back edge of
precip is into SW NH at 0830Z, as there is very little dynamic
forcing, and the precip is being driven by WAA, which will shut
off once the sfc low to our S passes by. There could be a short
period of FZRA/FZDZ in srn zones as it ends, but it should all
be done with by 12-14Z in most places. After that once the wind
shifts to W around midday, skies will begin to clear and temps
will warm into the upper 30s to low 40s S of the mtns. In the
mtns, upslope flow will allow clouds to linger with snow showers
and some additional accumulations.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
A secondary cold front will push thru early this evening and
this will shift winds a bit more NW, and allow some colder air
to filter in, but all in all should mainly be clear with lows
around 20 in the mtns, where clouds/SHSN will linger, to the mid
20s in the south.

Friday looks mostly sunny and on the mild side, as sfc high
builds over the CWA, with highs 30-35 in the N to around 40 in
the south.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
High pressure moves directly across the area Friday night
allowing for good radiational cooling conditions. Low level
dewpoints suggest the floor for low temperatures will be in the
low teens, with only the coldest valleys dropping into the
single digits. As the high moves east on Saturday we will warm
back up into the 30s to low 40s.

The next precipitation maker is currently dropping south along
the California coast rotating around the broad upper low over
the inter-mountain West. It will emerge over the southern
plains Saturday morning with low pressure forming over the Texas
Panhandle and tracking northeast into the Great Lakes. With yet
another storm tracking to our west, this means another messy
precipitation type forecast for our area. However, unlike most
of the previous warm frontal precipitation makers this season,
this time the warm front lifts in from the south bringing a
better easterly pressure gradient to the north of it. Such a
flow is a more pronounced cold air damming signal than has been
seen yet this season. Thus we expect that precipitation likely
starts as snow around midnight Saturday night but transitions to
freezing rain on Sunday where warmer air is able to advance
northward aloft.

There remain a few areas of uncertainty regarding the Sunday
forecast. The first involves the formation of secondary low
pressure as the trough axis nears the coast. The ECMWF closes
off the new surface low to our south which aids in keeping
deeper cold air over our area and limiting the advance of warm
air aloft. This means more snow than freezing rain. Meanwhile
other models still allow for a further northward advance of warm
air aloft bringing a more widespread threat of freezing rain on
Sunday. In addition, temperatures do not start off all that cold
Saturday night so the strength of the low level inversion is a
bit unclear. If this inversion does not set up properly, then
the cap to the cold air dam won`t form and the easterly flow
will pull in warmer air and change precipitation to rain for the
southern half of the area. But if it does set up, this wind flow
regime would suggest that the cold air dam would hold in place
across most of the area even including southern New Hampshire.
Current forecast represents a bit of a blend of all these
possibilities, allowing for a moderate advance of warm air aloft
while holding the cold air dam at the surface for interior
western Maine and central New Hampshire but bringing warmer air
in for southern New Hampshire and coastal Maine.

Precipitation will be increasing in intensity as it moves
across the area on Sunday, aided in part by the development of
that secondary low pressure over the Gulf of Maine. Current
forecast calls for moderate to heavy snow accumulation over
interior western Maine while lighter snow amounts are expected
for western and southern New Hampshire where a precipitation
type transition to freezing rain is more likely. Total icing is
expected to be light and the preceding coating of snowfall will
likely limit the impacts of it a bit.

As the broader trough axis crosses the area Sunday evening winds
will shift to the west allowing better mixing of the low levels.
This means areas that were in the cold air dam will see a brief
warm up before cold advection takes over. Pressure gradient is
pretty tight and the low level jet is strong enough to suggest
that with the mixing Sunday night and Monday we will see some
stronger wind gusts. Gusts to 35 to 45 mph are possible.

High pressure builds in from the west Monday and Tuesday. Good
low level mixing on Monday means temperatures will make it into
the 30s, but it will be almost 10 degrees colder on Tuesday. The
next wave to move through our region is most likely to arrive on
Wednesday, however there is still considerable disagreement
among the models on where this will track and how it will
evolve. The GFS tracks this wave to our north while the ECMWF
tracks it to the south and much colder.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
Short Term...Look for improvement to VFR around midday, except
KHIE which will see lingering MVFR cigs and SHSN into this
evening. VFR will persist thru Friday.

Long Term... VFR through Saturday, but then ceilings lower
Saturday night as the next frontal system approaches. Expect IFR
or worse conditions as snow spreads across the area early Sunday
morning with a transition to freezing rain likely in southern
New Hampshire and possible into southwest Maine. Winds shift to
the west Sunday evening behind a cold front with conditions
improving to VFR but with strong west winds.

&&

.MARINE...
Short Term...Not sure we`ll see SCA winds until late this
afternoon when cold front pushes through and winds shift to
west. These west winds will continue thru tonight, but should
subside on Friday.

Long Term...High pressure moves across the area Saturday morning
with light winds shifting to the south and then to the east
Saturday night. Low pressure forms along a frontal boundary as
it moves into the Gulf of Maine Sunday evening. Expect an east
to southeast wind gusting to 30 KT or so ahead of the low Sunday
morning but shifting to the west behind it Sunday evening. The
west winds will have better low level mixing and will allow for
wind gusts of 35 to 45 KT on Monday and diminishing a bit into
Tuesday.

&&

.TIDES/COASTAL FLOODING...
Storm surge of around a half foot will combine with high
astronomical tides today to produce minor coastal flooding and
splash over at high tide which occurs around noon. A Coastal
Flood Advisory is in effect from 10 AM to 2 PM Thursday for
coastal New Hampshire and southwest Maine.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory until noon EST today for MEZ007>009-
     012>014-018>028.
     Coastal Flood Advisory until 2 PM EST this afternoon for
     MEZ023-024.
NH...Coastal Flood Advisory until 2 PM EST this afternoon for
     NHZ014.
MARINE...Small Craft Advisory until 7 AM EST Friday for ANZ150-152-154.

&&

$$