Area Forecast Discussion
Issued by NWS Caribou, ME

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FXUS61 KCAR 200233
AFDCAR

Area Forecast Discussion
National Weather Service Caribou ME
1033 PM EDT Tue Mar 19 2019

.SYNOPSIS...
High pressure will slide south of the area tonight through
Wednesday then move east into the open Atlantic Wednesday night.
Low pressure will develop off the Mid-Atlantic coast on
Thursday and track north to our region on Friday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
10:30 pm update: main change this update was to lower lows
across normally colder spots, which generally were cooling off
faster than they did last night. Otherwise, only minor tweaks
were made to the forecast for tonight, with a clear sky and
light winds supporting strong radiational cooling. The
remainder of the forecast appears on track.

Previous discussion:
High pressure nearby to the south will bring a mostly clear and
moonlit night tonight with valley areas again significantly
colder than the ridges. Lows by late tonight will range from
near or just below zero in some northern valleys to the teens
and low 20s Downeast. Sunshine will give way to some increasing
high clouds on Wednesday, especially across the north. A return
flow around high pressure to our south will bring a light
southwesterly breeze. Wednesday afternoon will turn milder with
highs approaching 40 in most areas.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
On Wednesday night, high pressure will be offshore with a
tightening pressure gradient generating steady southwest winds
and warm advection. These factors and some cloud cover will
result in lows in the mid to upper 20s north while readings in
the lower 30s are forecast for Bangor and the coast. From these
elevated levels, Thursdays highs will jump into the low to
mid 40s under the continuing influence of the offshore high.
Meanwhile, an amplifying upper trough digging southward from the
Great Lakes region into the southeastern US will phase with a
rich supply of moisture with a disturbance along the Carolina
coast. This interaction is expected to result in explosive
cyclogenesis on Thursday. The question will be where. This is
important as the low will likely be driven nearly due northward
Thursday night into Friday towards Maine. If the low forms east
of Cape Hatteras, it may stay east of Maine with more snow. If
the low forms closer to the coast, it has a higher probability
of moving west of the forecast area with rain. SREF, many GFS
ensemble members and NAEFS support a more eastern track while
current operational models such as ECMWF and GFS support the
western track. Even at this point, significant uncertainty
remains in the forecast. With the eastern track, the antecedent
air mass is warm and boundary layer warmth will have to be
eliminated before any heavy wet snow could start. Even then,
areas closer to the coast may stay all rain. With the west
track, river ice break up and minor urban flooding will be the
concerns due to rainfall and snowmelt. Today`s 6Z and 12Z
guidance continues the westward shift...including the formerly
colder GFS- FV3. The new forecast uses the more westward track
with precip breaking out along the western border of the state
later Thursday, but most areas wont see precipitation until
late Thursday night. There will be some light accumulations of
snow in northern and western zones Thursday night before precip
goes to all rain. The rain is forecast continue most of Friday.
Rainfall could be heavy at times as PWATs move towards 1 inch
and elevated instability makes thunder possible. Rain will start
tapering off later Friday as the dry slot arrives. Colder air
will also arrive...changing rain to snow.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
On Friday night, rain will gradually change to all snow and
there could be some accumulation as the trowal of this major
storm crosses the area. There remains a lot of uncertainty on
the position of the upper low by this time...and the resultant
position of the trowal.  Strong winds start later Saturday as
the storm moves in the Canadian Maritimes. Most of the snow will
be over by later Saturday afternoon and its certainly
conceivable there will be enough for an advisory. The winds
continue Saturday night into Sunday. Gusts over 45 mph are
possible. Temperatures will warm up Sunday afternoon ahead of a
cold front that will cross Sunday night into Monday morning.
This front will bring a reinforcing shot of cold air for the
first half of next week. High pressure will build behind the
front and persist through the end of the forecast period.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
NEAR TERM: VFR conditions are expected to persist across the
area tonight and Wednesday.

SHORT TERM: Expect mostly VFR conditions Wednesday night into
Thursday. IFR to LIFR will be the prevailing condition Thursday
night into Saturday morning due to rain, snow and cigs. Embedded
thunderstorms are possible Friday towards BGR and BHB.

&&

.MARINE...
NEAR TERM: Winds and seas are expected to be light tonight and
Wednesday with a light offshore breeze overnight and then a
light return flow out of the southwest on Wednesday.

SHORT TERM: A Small Craft Advisory will likely be required
Thursday night into Sunday, but gale conditions are possible
Friday morning...and even more so on Saturday. Thunderstorms may
be possible over the waters on Friday.

&&

.HYDROLOGY...
The combined amount of rainfall and snowmelt may be enough to
lift ice and generate ice jam potential in the southern half of
the forecast area. River rises are progged at 2 to 4 feet which
should be sufficient to break up some ice.  Further north,
existing snowpack will likely absorb the rainfall without
issues. The combined T/Td thawing degree hour index is not
providing any caution signals as the period of warmer temps and
dew points is relatively brief.

Along the coast, high astronomical tides and storm surge at
Friday morning`s high tides seem likely to cause minor issues at
some of the usual trouble spots such as the Deer Isle Causeway,
Seawall Road, and Machias.

&&

.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...None.

&&

$$

Near Term...Bloomer/CB/Maloit
Short Term...MCW
Long Term...MCW
Aviation...Bloomer/CB/MCW
Marine...Bloomer/CB/Maloit/MCW
Hydrology...


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