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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

FXUS61 KCAR 211442

Area Forecast Discussion
National Weather Service Caribou ME
1042 AM EDT Wed Aug 21 2019

High pressure will slide east of the area today. A warm front
will approach this afternoon and lift across the region this
evening. A cold front will cross the area Thursday. The cold
will move out across the Gulf of Maine Thursday night into 
Friday. High pres will gradually build toward the region from
the west Saturday into Sunday.


1040 am update...
Line of showers and tstms mvg in fm Quebec ahd of s/wv. Latest
MRMS data shows gradual weakening this mrng as they appch the
state with vry stable airmass present per 12z KCAR raob. As
airmass destabilizes in the next hr or two with temps currently
in the lwr 70s, may see storms reinvigorate this aftn. 

Another complex of storms is beginning to enter SW Maine ahead 
of warm front. Hv adjusted pops to account for latest radar
trends for this update. Severe parameters not as impressive as
yesterday with ongoing convection resulting in slow destabilization
of airmass this mrng. Expect that cluster mvg in fm the
southwest wl fizzle as it heads into fairly stable airmass this
aftn. Line of convection mvg into the Hudson Vly as of 14z
represents the most likely chc for svr wx acrs CWA late this
aftn and evng. Main threat looks to be strong winds but bigger 
threat appears to be locally hvy rainfall with PW values 
increasing to nr 2 inches.

Prev discussion blo...
High pressure moving off to the east today combined with a
trough of low pressure approaching from the west will bring an
increasing southerly wind, increasing clouds and increasing
humidity today. Surface heating will allow capes to build to
between 500 and 1200 J/KG across the area setting the stage for
some thunderstorms as the warm front lifts into the area late
today into this evening. The instability, although marginal in 
strength, is very deep, up to as high as 35K feet. Moisture is 
expected to increase with precipitable waters nearing 1.8" by 
the end of the day. A strong trough digging from Ontario into 
southern Quebec will also provide divergent support aloft to 
help spawn and carry convection into the area. A complicating 
factor is a shortwave currently rounding the bottom of the 
trough and lifting through the upper Ohio valley early this 
morning. Models differ on where the focus of this shortwave 
energy tracks with the NAM and SREF carrying a thunderstorm 
complex from this shortwave up and into the northern part of our 
area while the GFS and ECMWF carry the body of this shortwave 
and its convection across Downeast. SPC has all but the 
northern portion of the area in a slight risk today. The deep 
cape and deep moisture suggest heavy rain and perhaps flash 
flooding may be the greatest concern. Otherwise, west central 
areas late today and central locations early this evening seem 
to have the greatest chance for any severe weather including 
strong winds and hail given the timing and potential track of 
the embedded shortwave. Will keep enhanced wording for gusty 
winds and small hail in the forecast with categorical pops 
across south central areas late today into this evening and high
likely pops further north. The convection will move away late 
tonight. A cold frontal boundary following strong low pressure 
to our north will push across the area Thursday possibly 
spawning more thunderstorms, mainly during the afternoon across 
eastern areas.


The cold front is forecast to slide off the coast Thursday 
evening and stall in the Gulf of Maine as the upper flow 
parallels the front. Cooler and drier air will begin filtering 
into the region overnight as winds shift to the WNW. 

A disturbance is forecast by the NAM/GFS and ECMWF to move up
along the stalled front in the Gulf of Maine to set off some
showers on Friday. The bulk of this will remain off the coast 
and decided to carry 20-30% for shower over the coastal waters. 
Further n, an upper trof will start sliding toward the region
and w/cold air aloft and heating at the sfc, this will be enough
for clouds to form. There appears to be enough forcing in the
mid levels and llvl moisture convergence to allow for some
showers across the north and west. Stayed close to the 
daycrew's thinking of 20-30% for showers. It will be cool 
w/daytime temps in the upper 60s to lower 70s. Clearing Friday 
night and colder w/temps dropping back to a range of 45-50 
across the northern 1/2 of Maine. Some low lying sites, such as 
the valleys could see lower 40s. WNW winds are expected to stay 
up around 10 mph. The upper trof is shown by the ECMWF and GFS 
to push off to the east by Saturday afternoon w/high pres at the
sfc moving in from Canada. The stalled front across the Gulf of
Maine will slide further out to sea. Clouds will form during 
day across the northern and western areas. Still a cool day 
w/temps below normal for last week of August.


There is some discrepancies in the long range guidance on what
shapes up for Sunday into Monday. The 00Z GFS and its ensemble
mean show high pres at the sfc and aloft building across the
region into Tuesday w/dry and gradually warmer conditions. The
ECMWF on the other hand shows a closed upper low developing
over the NJ/NY region w/low pres at the sfc lifting to the ne.
This low is then expected to pass well e of Nova Scotia on 
Monday bringing some light rain to eastern Washington County.
The Canadian Global shows a solution similar to the GFS.
Therefore, decided to lean away from the ECMWF solution and go
w/a blend showing high pres ridge hanging on into into early 
next week. This will lead to dry conditions and near normal


NEAR TERM: VFR conditions this morning will likely lower to MVFR
then IFR late today in lowering clouds, and then be MVFR to IFR
in low clouds, rain and scattered thunderstorms tonight.
Conditions may improve to MVFR and, in some areas, VFR on
Thursday, but locally drop to IFR in any thunderstorms Thursday
mainly during the afternoon. Winds will be light to moderate 
southerly with some light SSW wind shear possible Downeast late 
today into this evening. 

SHORT TERM: VFR Thursday night w/WNW winds 5-10 kts. 

VFR Friday into Saturday w/the exception of the northern 
terminals and some MVFR cigs could set up briefly in the 
afternoon both days w/some shower activity. WNW winds 10 to 15k

VFR continues right into Sunday w/the winds dropping off to
around 10 mph from the W.


NEAR TERM: Wind and seas are expected to remain below SCA
through Thursday. Humid air over the waters may result in fog
across the waters tonight into early Thursday. 

SHORT TERM: No headlines expected. SW winds 10-15 kt Thursday
night will shift W on Friday. Seas will build to 3-4 ft. There
will be the risk of some showers w/front nearby. Winds will 
drop off Friday night right into Saturday keeping a W direction.
Seas will be dropping back to 3 ft due to the offshore wind. 
Shower activity will end as the front slides further out to sea.
Looking into Sunday, light winds 5 to 10 kt and seas 2-3 ft.





Near Term...Bloomer/Farrar
Short Term...Hewitt
Long Term...Hewitt