Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

                            
000
FXUS61 KCAR 242141
AFDCAR

Area Forecast Discussion
National Weather Service Caribou ME
541 PM EDT Sat Aug 24 2019

.SYNOPSIS...
High pressure will remain overhead through Tuesday, then slides
offshore through Wednesday night. A cold front crosses the area
on Thursday.

&&

.NEAR TERM /THROUGH SUNDAY/...
535 PM Update: Not much in chgs to the going fcst. Sat imagery
conts to show SC/CU cldnss movg S of our FA via the Gulf of ME
as low to mid lvl subsidence conts to move into our FA from the
W. Otherwise, latest obsv sfc temps/dwpts were used to update
fcst hrly values of each into the ovrngt hrs and to construct an
approximate obsvd hi temp grid for this late aftn with no chgs 
to fcst ovrngt lows (posted at 6 am Sun) attm.

Prev Disc: Satellite as of 18z depicts a widespread area of 
stratocumulus with bases around 3-4kft AGL across the southern 
half of the CWA. High pressure currently centered over the Great
Lakes and Ontario will shift east towards Maine later this 
afternoon, resulting in decreasing gradient flow and winds 
despite daytime heating and mixing. High pressure overhead will 
favor subsidence, decreasing cloud cover quickly from north to 
south and aiding in efficient radiational cooling tonight. The 
cooler spots across Northern Maine such as Estcourt Station are 
likely to dip well into the 30s and may see patchy frost. 
Current thinking is the aerial extent of the frost is not 
sufficient for any headlines. River valleys will also see fog 
development later tonight.

High pressure will dominate on Sunday with very light winds and
mostly sunny skies aside from a few PM cumulus. BUFKIT forecast
profiles show very light winds of 0-5kts over the boundary 
layer at northern sites closer to the center of the surface high.
This should help temperatures warm efficiently, so a max 
temperature at the 75th percentile of guidance was preferred.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
A closed 700-500 hPa low passes to the S/SE Sunday night-Monday
as northern stream ridging remains anchored over northern parts
of the region. Likely will be too much subsidence under the
ridge for more than a few high clouds near the coast from the
passing upper low. As a result, with light winds, expect good
radiational cooling over the region Sunday night, with lows
around 5 degrees below normal, with larger departures in
normally cooler locations. Also expect some patchy fog,
especially in area river valleys. Highs on Monday should be 
near to slightly above normal.

Northern stream ridging builds back over the region Monday 
night and Tuesday as the closed low tracks farther into the 
Canadian Maritimes. Subsidence under the ridge should keep 
things dry, with minimal cloud cover. Good radiational cooling 
again Monday night, but air mass modification should yield lows 
a few degrees above the lows Sunday night. Should see some 
patchy fog Monday night as well. Highs on tuesday should be a 
few degrees above normal.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Northern stream ridging remains over the area Tuesday night,
then its axis slides to the east on Wednesday. It should remain
dry with minimal cloud cover, though could see an increase in
high clouds late in the day over far western portions of the
CWA. 

Full latitude 700-500 hPa trough approaches Wednesday night,
with a shortwave ahead of it bringing a slight chance to chance
of showers - mainly over western zones after midnight. This
trough axis crosses the area on Thursday. The models are now
suggesting the potential for a shortwave embedded in the trough
to trigger a weak surface low over the E gulf of Maine by late
Thursday - with this possibly enhancing any showers Downeast.
Still to early to buy into the specifics - but have increased
pops to high end chance Downeast Thursday afternoon noting
around 1/2 of the GEFS ensemble members support the GFS and
ECMWF.

The region remains under the base of a cutoff low over Hudson
Bay Thursday night-Saturday with SW flow aloft. It appears it
should be mainly dry during this time frame, though there is a
chance for a shortwave embedded in the flow to impact the region
during this time frame. So have mainly slight chance pops, given
historic poor model handling of this scenario. There is some
sense of consensus on a shortwave impacting mainly N zones on
Saturday - so do have low end chance pops then. 

Temperatures will run near to a few degrees above normal Tuesday
night-Saturday.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
NEAR TERM: CIGs have risen across the southern terminals such as
BHB and BGR where stratocumulus are still in place. Clearing is
expected this evening. The main concern later tonight will be 
patchy river valley fog, which is most likely to affect BGR and 
PQI. 12z NAM forecast soundings also show a chance of radiation 
fog formation at other sites. However, this is probably overdone
so fog mentions in TAFs were limited to climatologically 
favored sites. Fog will quickly dissipate around sunrise. Light 
winds and VFR conditions are expected Sunday.


SHORT TERM: 
Sunday night through Wednesday...VFR, except for MVFR or lower 
possibly in patchy fog, mainly near river valleys late at 
night/early in the morning each night.

Wednesday night-Thursday...MVFR or lower possible in isolated to
scattered showers.

&&

.MARINE...
NEAR TERM: Increasing east/northeast winds are expected tonight
with gusts up to 20kts. Temperature profiles become more stable
later Sunday afternoon, leading to decreasing wind speeds and 
gusts. Seas less than 3 feet expected.


SHORT TERM: A relaxed pressure gradient will limit winds to 10
kt or less and as a result seas to 3 ft or less Sunday night-
Wednesday. Swells could bring seas on Thursday to around 4 ft on
the coastal ocean waters.

&&

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

&&

$$

Near Term...VJN
Short Term...Maloit
Long Term...Maloit
Aviation...VJN/Maloit
Marine...VJN/Maloit