Area Forecast Discussion
Issued by NWS Caribou, ME

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FXUS61 KCAR 201945

Area Forecast Discussion
National Weather Service Caribou ME
245 PM EST Tue Feb 20 2018

A strong ridge of high pressure will remain anchored off the
Southeast coast through Friday. A cold front will drop south
into northern Maine early tonight then lift back north as a warm
front late tonight. A cold front will cross the state Wednesday

A strong, warm ridge of high pressure will remain to our south
tonight as high pressure over eastern Canada pushes some cooler
air into the far north. A frontal boundary will be across the
area between the two air masses. Moisture running along this
front will bring occasional light rain to the region tonight.
Some freezing rain is likely over the far north as subfreezing
air from Canada seeps into the low levels. The frontal boundary
will lift north as a warm front late tonight. Warm advection
over the cold ground surface will likely produce fog across much
of the region late tonight and some locally dense fog is
possible. A winter weather advisory remains up across northern
Aroostook County where a bit of freezing rain is likely.
Wednesday will be very warm as the strong ridge to our south
combined with low pressure tracking north of the area pulls
some very warm air up across the area. Highs will approach 60
Downeast and 50 over the north. Northern areas will likely
remain mostly cloudy while Downeast areas have partial sunshine.

On Wednesday night, cold air will filter into the area with a
fairly rapid freeze in northern zones that could produce some
slick roadways. Further south, temperatures will remain above
freezing until later in the night. The relatively short duration
of the record warmth and lack of significant rainfall mitigates
hydro concerns at this time and no Flood Watch will be issued
now, but rivers will continue to rise into Friday. The biggest
concern will be ice break ups and subsequent jams, but
projected river rises are less worrisome than yesterday. On
Thursday, high pressure builds with temperatures still above
normal, but substantially cooler than Wednesday. Most guidance
is trending colder and have lowered Thursday`s highs. The big
H500 ridge will remain off the Carolina coast and a weak
disturbance will shoot northeastward on Thursday north of this
high...and south of the big surface high building over the
state. This means a good deal of high clouds in the southern
half of the forecast area on Thursday and maybe a brief sprinkle
for the outer islands of Hancock County. On Thursday night, the
1040mb high pressure crests over the area. Lows were adjusted
downward due to good potential for strong radiational cooling.
On Friday, another weak disturbance in the southern stream will
rapidly approach from the southwest. Clouds increase later in
the day with a weak overrunning event that will produce mostly snow
Friday night.

For Friday night, sub-advisory snowfall of no more than 2-3
inches is expected with precipitation ending as rain in southern
zones. Temperatures will be warmer behind this system on
Saturday with highs in the upper 30s to lower 40s. Somewhat
cooler air arrives Saturday afternoon behind a cold front. High
pressure building Saturday night presents another good
opportunity for radiational cooling...especially in northern
zones. Clouds will increase quickly on Sunday ahead of yet
another shortwave moving in the southern stream out of the lower
Mississippi Valley. This system will have better upper level
support and is expected to phase with a northern stream
shortwave. A secondary low will develop along the coast and cut
off warm air advection. As a result, this system should be all
snow except along the coast. Most areas should receive around 4
to 6 inches as it stands now. The exception would be the coastal
zones where P-type issues will cause a significant decrease in
accumulations. High pressure gradually builds Monday into
Wednesday with seasonal temperatures.

NEAR TERM: IFR conditions in low clouds are expected tonight
and some freezing rain is likely in some far northern spots.
Conditions should improve to VFR Downeast around mid morning and
improve to MVFR across the north around midday Wednesday. Some
wind shear is likely Wednesday, especially over the north, for
SW winds at 2K feet around 35kt.

SHORT TERM: Expect VFR conditions Wednesday night until later
Friday afternoon. IFR conditions due to snow and cigs will occur
Friday night into early Saturday morning. Cigs will lift to VFR
by Saturday afternoon and all sites will remain VFR until later
Sunday afternoon when IFR vis in snow returns.

NEAR TERM: A SCA will be up for Wednesday for southwest winds
gusting up to 25 kt. Warmer air moving over the colder waters
will likely produce some areas of dense fog over the waters
tonight through Wednesday.

SHORT TERM: An SCA will be needed Wednesday night into early
Thursday morning for the outer waters. The outer waters will
likely need another SCA Friday night. A brief gale is
anticipated later Sunday.

Will be watching the rivers closely on Wednesday night into
Thursday for some possible ice movement. Decided not do issue
any flood watch headlines, due to a few reasons. First, QPF
still looks light for this event with generally .50" or less
expected. Second, is the longevity of the thaw expected. Even
though temps are above freezing for parts of the Penobscot river
watershed today, they won`t be that warm with most areas staying
in the mid 30s. The real warmth will come on Wednesday and we
are expecting rapid snowmelt with dewpoints surging to 50
degrees and temps will also reach into the upper 50s for the
lower Penobscot watershed and low 50s for the upper part of the
watershed. Fortunately, the cold front will quickly push
through Wednesday evening and night dropping temps quickly back
below freezing. The longevity of the warm spell will be too
quick for areas that still hold a significant snowpack. We do
expect river rises due to run-off, but current forecasts are
only showing a few feet of a rise, not enough to really break up
the ice. There will be weakening of the ice pack though,
especially on the edges, so some ice will be moving around, but
no significant ice jams are expected. Overall threat is there,
but current thinking is the threat is low. Users with interests
on area rivers across the lower Penobscot watershed should keep
a river watch Wednesday through Wednesday night.

ME...Winter Weather Advisory until 4 AM EST Wednesday for MEZ001-
MARINE...Small Craft Advisory from 7 AM Wednesday to 7 AM EST Thursday
     for ANZ050>052.

Near Term...Bloomer
Short Term...MCW
Long Term...MCW
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