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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

FXUS61 KCAR 240331

Area Forecast Discussion
National Weather Service Caribou ME
1131 PM EDT Fri Aug 23 2019

High pressure will build across the region through Sunday, then
slowly move east Monday and Tuesday. Low pressure from the west
will begin to approach on Wednesday into Thursday.

1130pm Update...Perhaps a few remaining sprinkles or isolated 
showers in far Northern Maine. Otherwise a dry night. Moved up 
ending of isolated showers in far Northern Maine by two hours. 
Also decreased sky cover a bit over entire area for next few 
hours based on current obs.

Previous Discussion... Latest Sat imagery conts to show a slow 
SE spread of SC/CU from an initial s/wv rotating SE across Nrn 
ME arnd a semi-closed upper low ovr the Gulf of St Lawrence. 
Current radar only shows very lgt rn shwr returns attm, but both
clds and isold-sct sprinkles and shwrs will cont to make a swrd
push as a second s/wv moves SE acoss the FA from Cntrl QB erly 
this eve. Llvl 925-850mb moisture progs indicates that enhanced 
SC cld cvr could reach as far S as interior Downeast areas by 
erly Sun morn, but likely not any shwrs. Winds will diminish 
somewhat this eve with the loss of diurnal htg resulting in 
decoupling with stronger winds alf. Otherwise, cld cvr and 
breezy NW to N winds will keep temps from falling below 50 deg F
for erly morn Sat lows xcpt ovr the NW where mid to upper 40s 
are likely. 

Sat will begin ptly to msly cldy across the FA, but skies will
gradually clr out by aftn as the upper low moves E ovr the open
N Atlc and subsidence from ridging both at the sfc and alf 
works ewrd ovr our FA from Cntrl QB. Winds will be breezy from 
the N, spcly late morn, but not xpctd to be as strong as this 
current aftn.

With clr skies, dry air, and winds becmg lgt and vrbl Sat ngt,
ideal radiational cooling conditions are xpcted with many lctns
across the N and Cntrl vly lctns reaching lows in the 40s and 
coldest Nrn vly lctns in the mid to upper 30s by erly Sun morn, 
resulting in a mention of patchy valley frost at these coldest 
sites. Lastly, as is typical with successively colder fall like 
airmasses spcly on radiational cooling ngts, patchy rvr 
evaporational fog will form late Sat ngt into erly Sun morn due 
to the difference between still warm rvrs and much cooler air 

The period will be dominated by an anomalously strong upper
level ridge over Quebec and a resulting blocking pattern over
the Northeastern U.S. favoring dry conditions. With the core of
the upper level ridge well to the north, temperature anomalies
will remain modest. The most notable differences will be at
night due to mostly clear skies and ample radiational cooling,
which will lead to below normal lows. River valley fog is also
possible again Sunday night.

A weak upper level low will also become trapped underneath the 
ridge over Coastal New England. The low will progress 
northeastward towards Nova Scotia Monday afternoon as it becomes
influenced by a building upper trough over the Northern Plains.
Current guidance maintains an offshore or parallel shore flow, 
which along with limited surface support and meager moisture 
should reinforce dry weather.

Upper level ridging will persist over Northeastern Canada and
into Maine for the start of the week, maintaining dry
conditions. The ridge axis will gradually move east through the
period, moving over Newfoundland by Wednesday. This will allow
the 500h trough over the Northern Plains to slowly build
eastward over the Great Lakes. Southerly flow ahead of the
trough will gradually become more amplified, which will advect
warmer air aloft and higher surface dew points into the area by
the middle of the week. A transition to above normal
temperatures, particularly at night, is expected Wednesday night
through the rest of the week. While there are differences with
how exactly the upper level pattern develops, an increase in
precipitation chances can also be expected later Wednesday
through Thursday night.

Invest 98L currently off the eastern coast of Florida will move
north-northeastward around the building subtropical ridge near 
Bermuda and ahead of the aforementioned upper trough over the 
Great Lakes. Currently, the ridge appears weak enough to allow 
the system to curve near or just east of Nova Scotia by 
Wednesday or Thursday, remaining well away from our forecast 
area. However, some uncertainty remains; A couple outlier EPS 
members bring the system along the western edge of the guidance 
envelope and into or close to New England. Progress of the 
system should be monitored, particularly for those with marine 
interests due to increasing wave potential by the middle of next
week. See the National Hurricane Center for the latest 

NEAR TERM: Generally VFR clg/vsbys xcpt MVFR clgs likely late 
tngt/erly Sat morn at KFVE and possibly at KCAR and KPQI. 
Patchy MVFR/IFR vsbys in fog are possible at low lying TAF sites
near rivers late Sat ngt and erly Sun morn. 

SHORT TERM: Mostly favorable/VFR flight weather is expected with
mainly light winds and favorable VIS/CIGs through Tuesday.
Patchy river valley fog is possible Sunday night. Southerly 
return flow is expected Tuesday night into Wednesday. Increasing
dew points and onshore flow may cause lower CIGs/VIS near the 
coast, including BHB.

NEAR TERM: No marine hdlns xpctd for this ptn of the fcst with
fcst wv hts ovr our waters about 80 to 90 percent of blended
WW3/NWPS guidance wv hts, with NWPS emphasized for near shore 
waters. Wv spectral groups will be at arnd 6 sec for short 
fetch wind directions spcly in the vcnty of our immediate 
coast and 10 to 12 sec for residual long pd swell from low pres
systems well out into the open Atlc.

SHORT TERM: No issues expected through early next week. The
progress of a tropical system moving north-northeastward from
Florida will need to be monitored for Tuesday night through
Thursday. The primary impact will be higher waves/swell. The
magnitude will depend on the strength and track of the system,
which is still uncertain and could significantly alter the
current wave height forecast. A track taking the system well to
the southeast is most likely. See the long term and National
Hurricane Center products for additional details.


Near Term...Foisy/VJN
Short Term...Strauser
Long Term...Strauser