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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

FXUS61 KCAR 170919

Area Forecast Discussion
National Weather Service Caribou ME
419 AM EST Sun Feb 17 2019

High pressure will build across the region Today and remain in
control through Wednesday night. Low pressure will pass well
south of the state on Monday. 


Temps will return to below normal readings for this term.

A NW flow coming off the open St. Lawrence will continue to
bring some scattered clouds across portions of northern and
western areas early this morning. The NW flow is forecast to
weaken later this morning which in turn will shut down the St.
Lawrence influence and allow for a good deal of sunshine.
Further s, high clouds streaming northward per the latest IR
satl imagery in response to an upper level disturbance. These
clouds will be pulling through the southern portion of the CWA
later this morning. 00Z UA showed decent caa at 925-850mbs on
the NW flow. Temps have dropped out substantially in the past 
24 hrs, w/some sites across closing in on OF such as Clayton 
Lake(K40B). Despite the sunshine today, daytime temps will be 
some 10 to 15 degrees colder than they were on Saturday.

For tonight, clear skies for the most part w/the exception
across the southern 1/2 of the CWA as clouds will be increasing
ahead of an apchg low pres system into PA. These clouds will put
a lid on temps keeping them in the single numbers and lower
teens. Further n, basically clear skies and light winds will
allow for good radiational cooling and for temps to drop off
sharply after sunset. Some areas across northern Aroostook
and Somerset County could be seeing temps dip below -10F by day
break Monday. This all hinges on whether skies can remain clear
as some of the model guidance is advertising some low clouds to
set up just after midnight. This would keep temps from bottoming
out. The GFS and GEM show this setup as does the latest run of
the SREF. The NAM and some of the Hi Res guidance such as HREF
are not as aggressive w/the cloud cover. Given the WNW flow
aloft and dry level from 850-600mbs, confidence is not high
enough to bring overcast conditions to the north. Therefore,
leaned toward colder temps. 


A massive area of high pressure will dominate through the
period. This high will ooze southward from western Canada on
Monday and reach the Great Lakes region by Tuesday morning. In
the interim, a very fast moving surface low will eject eastward
from the Mid-Atlantic region into the open Atlantic Ocean. The
upper trough associated with this low has minimal amplitude and
will be hard-pressed to push any moisture northward into the
forecast area. The only concern at all will be coastal Hancock
County where a few hundredths of an inch of QPF and favorable
snow ratios could generate up to an inch of snow Monday...most
likely with the upper trough passage towards midday. The air is
just too dry for precip further north.  On Monday night, cold 
air advection follows with H925 temps diving towards minus 25C 
in the Saint John Valley by Tuesday morning. This cold advection
and steady northwest winds could produce the need for a Wind 
Chill Advisory in northwestern zones late Monday night into 
Tuesday morning. With the cold air in place Tuesday will be some
5F colder than Monday and wind chills will remain below zero 
all day towards northern Aroostook County. The high shifts from 
the Great Lakes region towards Maine Tuesday night into 
Wednesday. Radiational cooling will be a forecast challenge 
later Tuesday night depending on the eastward progress of the 
high and subsiding NW winds. Will go with lows towards minus 15F
in the Allagash, but not as cold further east and south. &&

The big high will crest over the region Wednesday and move
offshore Wednesday night. Overrunning high clouds will increase
with an approaching frontal system on Wednesday night and have 
only gone with subzero lows in the northern zones and lows will 
likely occur not too long after midnight. Isentropic lift will
lead to snow developing over the area on Thursday. This system
will draw southern stream moisture, but guidance continues to
struggle with interaction with a northern stream upper trough.
The GFS has trended towards warmer and moister ECMWF and GEMS 
solutions in the past 24 hours and have continued to favor ECMWF
for the forecast. It is clear that most of the southern stream
moisture will remain south as cyclogenesis occurs with a triple
point over Delmarva and this low shoots towards Cape Cod and
south of the Gulf of Maine on Thursday. However, some moisture 
will be pulled north towards the decaying northern stream low in
Quebec. This moisture and high snow ratios in the convergence
zone could generate low-end advisories in northern zones while 
P-types could be an issue towards the coast. Do not foresee a 
NORLUN setup at this time. The system quickly exits the area by 
Thursday night. There's not too much cold air advection behind 
the system and expect temperatures just above normal Friday into
Saturday as an upper ridge builds with subsidence.


NEAR TERM: VFR for all terminals into tonight. The caveat to
this will be across the northern terminals n of KHUL, as some 
MVFR conditions could develop before 12Z. This will be monitored
today with the later guidance.

SHORT TERM: A brief period of IFR vis is possible at BHB Monday
due to snow. Otherwise, a few hours of MVFR cigs are possible
north of HUL on Monday. Otherwise, VFR conditions are forecast
Monday through Wednesday night. On Thursday, IFR to LIFR vis is
expected in snow and IFR cigs may impact BGR and BHB.


NEAR TERM: Conditions dropping below 25 kts w/seas subsiding.
The SCA has been dropped as conditions are expected to improve
through the day. The previous forecast had this set up nicely
and therefore, just tweaking was needed as WNW winds will drop
to speeds to around 10 kts by this afternoon. Seas will continue
to drop off to around 3 ft by evening. 

SHORT TERM: A Small Craft Advisory will likely be required
Monday night into Wednesday morning. Light freezing spray is
forecast for Monday.





Near Term...Hewitt
Short Term...MCW
Long Term...MCW