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000 
FXUS61 KGYX 130446
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1146 PM EST Thu Dec 12 2019

.SYNOPSIS...
High pressure moves east tonight with a warming southerly wind
beginning on Friday. Low pressure tracking up the East Coast
will spread rain across the region Friday night and Saturday,
although this could begin as some light icing especially in
interior areas. Low pressure moves off to the northeast Saturday
night with a cold front ushering colder air back into the area
from the west. Some showers could linger into early Sunday with
the temperature falling into Monday. The next low pressure
system will bring some snow on Tuesday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Update...
Temperatures have steadied off now after dropping quickly with
radiational cooling during the evening hours. Clouds will
continue to gradually thicken during the overnight hours as warm
air advection begins over the region. Sufficient warm air
advection to allow for a couple snow showers across our northern
border in Canada which the mesoscale models are depicting late
this evening.

Most of the remainder of the forecast will be unchanged.
However, 00Z guidance is upping the QPF for the tomorrow night 
into Saturday period. 

Prev Disc...
At 3pm a 1040 high was centered over New Jersey. Ahead of this 
subsidence was keeping skies clear over northern New England and
into the Maritimes. A few high clouds creeping into Vermont 
foreshadow the next day. Warm advection cloud shield stretches 
all the way up Lakes Erie and Ontario with southerly flow 
pushing temperatures into the 40s. As this begins to approach 
our area overnight look for cloud cover to increase as low 
pressure begins to develop over the Ohio River Valley. With 
increasing cloud cover expect overnight temperatures to be a bit
warmer, and yet with the falling temperatures aloft the overall
effect will be low similar to last night with single digits in 
the north. Because of this have strayed away from the colder MOS
guidance and instead gone with a consensus of the raw models. 
This will be largely dictated by the cloud cover and the eastern
portion of the forecast area, where clouds may be slower to 
arrive is more likely to have the coldest spots.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/...
Friday will see a warming trend and increasing clouds as the 
precursor to the next storm. Initially high pressure retreats 
to our east, allowing southerly flow to develop. Expect a steady
increase in temperatures as the high pressure remains on a 
similar latitude to us and will not provide as much help to hold
the cold air. Despite this, with the cold initial temperatures 
things will be slow to warm and many locations may stay below 
freezing tomorrow. 

With temperatures below freezing in the valleys through midday the 
concern becomes whether any precipitation will develop prior to the 
temperatures warming. While the upper levels remain dry, the lower 
levels moisten giving a chance for drizzle to develop on Friday 
afternoon. With surface temperatures remaining marginal expect 
pockets of freezing drizzle across southern New Hampshire. It will 
be a race between warming temperatures and the onset of
precipitation to determine whether it will be freezing drizzle 
or drizzle initially and with this uncertainty still there at 
24hrs out will leave it for the next shift to determine if a 
Winter Weather advisory is appropriate for a portion of the 
area. 

Friday night our focus shifts to the developing low. Consensus 
is now clear for a track to the west of us, allowing our area to
reach into the warm sector, at least aloft. Steady 
precipitation will develop after midnight on Friday night and 
continue through the day on Saturday. Expect precipitation to be
rain for all but the most northern zones where an initial 
period of snow my change over to sleet at elevations. 

Saturday the evolution of the temperatures may be a bit tricky.
Some colder air is likely to linger through the coastal plain, 
although this will still be above freezing, just not as warm as 
southern New England. Will likely see temps hold in the mid 30s 
across the coastal plain while would not be surprised to see 50s
on the water as a coastal front sets up. May even manage to get
KMWN as a warm point in the area for a while as the depth of 
the warm layer increases beyond 6kft. 

With a direct connection from the warm ocean to our south 
expect precipitation amounts to be impressive for this time of 
year and 1-2 inches is expected. A focus for that will likely be
along the coastal front. This highest risk for flash or areal 
flooding would be along this precip axis along the coast. 
However without any snow on the ground in this area there will 
be nothing to block drains or contribute to runoff, which limits
the flooding. On the other hand, frozen ground may make what 
falls runoff that much more. This will be something to monitor 
over the next day or two but right now do not feel there are 
enough red flags to warrant a flood watch on the basis of 
rainfall.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Low pressure moves NNE through New England and into the Saint
Lawrence Valley Saturday night with a cold front moving west to
east behind it. This front will be mostly through our area by
Saturday evening, bringing an end to the steady rainfall.
However, behind the system some showers could linger especially
in the mountains. The temperature will be falling as cold air
pours in from the west. Expect precipitation to shift to a rain
or snow pattern depending on the surface layer temperature. The
cold continues to pour in on Sunday. Although high temperatures
may reach the 40s on the coastal plain due to good downsloping,
this could actually occur in the morning with temperatures
falling during the afternoon. In this sort of flow we have to
start thinking about wind speeds as a cold advection wind would
be especially favorable for mixing down stronger winds from
aloft. 850MB winds of 50KT suggest there is a good deal of
stronger gusts to mix down, so have adjusted the forecast a bit
higher on wind speeds than what the multi-model blend suggests.
At this point widespread gusts to 35 MPH or so are expected,
though it is possible that we eventually need a wind advisory
here.

High pressure nudges its way eastward on Monday with
temperatures likely topping out near freezing in the south and
near 20 in the north with winds decreasing through the day.
Monday night would typically be the coldest night behind the
front, and we will get in on some decent radiational cooling in
northern and eastern areas. However, expect increasing clouds as
the night goes on as our next low pressure system begins
affecting the area. This will likely limit cooling for most of
the area with lows in the teens and 20s.

The next low tracks to our south on Tuesday and at this point it
looks like this will be a mostly snow event for our area.
Although it's too far out for official snowfall amount
forecasts, it looks like a light to moderate snowfall event
centering on southern New Hampshire and coastal Maine. Even
colder air pours in behind this low as it departs on Wednesday.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Short Term...VFR conditions will hold through the next 24 hours
as high pressure moves to the east. Increasing clouds will
remain above 10kt initially before lowering steadily tomorrow
afternoon approaching MVFR by 00Z Saturday when light precip
will develop across the western portion of the area. 

Long Term...Should see conditions improving for most areas
Saturday night as the steadier rain moves to the east. However,
lingering MVFR conditions are likely in the mountains through
the day Sunday. It will also be rather windy on Sunday as west
winds gust to 30 or 35 KT at times. These winds gradually
diminish into Monday with conditions becoming VFR even for the
mountains.

&&

.MARINE...
Short Term...Gale watches or warnings may be needed per current
forecast model solutions for next upcoming event in some areas.

High pressure will cross the waters tonight into tomorrow. 
Another low will move up the St Lawrence valley on Friday night 
into Saturday. Increasing southerly flow may bring winds to near
Gale force, but with some uncertainty in the low track will 
hold off on a Gale watch for the moment. 

Long Term...West winds behind the departing low will likely gust
to gale force over the Gulf of Maine on Sunday with these winds
diminishing on Monday. The next low pressure passes to our south
on Tuesday with winds likely remaining below advisory levels
with this one.

&&

.HYDROLOGY...
Most rivers have long since peaked after our recent rainfall
event, although river levels remain high. Most of the snow south
of the mountains has been eradicated except for some areas of
southern New Hampshire. We expect another round of rain
beginning Friday night and lasting through Saturday. A general 1
to 2 inches of rain is expected, however 00Z guidance continues
to suggest there could be locally higher amounts.

Areas most likely to see rises closer to flood stage would be 
in southern and possibly central New Hampshire where some 
continued snow melt.

&&

.TIDES/COASTAL FLOODING...
We are entering a period of higher astronomical tides, and this
will coincide with the next storm system moving through the area
on Saturday. The highest tides are on Saturday and Sunday 
afternoons, each at 10.6 FT at Portland. The tide on Saturday
will have the greatest potential for an added storm surge as
onshore flow may increase water levels by about a foot. Waves on
top of this could cause splash over and beach erosion in
vulnerable areas. By Sunday winds will be offshore and expect
the surge to no longer be a factor.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

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