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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

                            
000
FXUS61 KCAR 202209
AFDCAR

Area Forecast Discussion
National Weather Service Caribou ME
609 PM EDT Tue Aug 20 2019

.SYNOPSIS...
High pressure will cross the region tonight. A warm front will 
cross the region Wednesday. A cold front will cross the region 
Thursday. Another cold front will cross the region Friday. High 
pressure will build across the region later Saturday through 
Sunday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
6:09 PM Update: Satellite pictures show that other than a few 
cumulus clouds in northeast Aroostook County it is clear across 
the entire FA early this evening. Tonight will be a clear night 
with seasonable temperatures as high pressure centered across 
southwest Maine slowly moves off the Down East coast overnight. 
Added a bit of patchy late night river valley fog across the 
Aroostook and Saint John River Valleys toward day break and 
lowered the lows a few degrees in the broad northwest valleys, 
but otherwise no changes at this time. 

Previous discussion:
High pressure will cross the region tonight through early 
Wednesday with mostly clear skies. Low pressure will begin to
intensify across Quebec province Wednesday, drawing a warm 
front toward the region late. Shower/thunderstorm chances will
increase, from west to east, Wednesday afternoon. Based on
forecast soundings, helicity and shear values indicate the 
potential for rotating storms later in the afternoon and 
evening. A low level jet also begins to strengthen in advance 
of the warm front. Have included enhanced wording for gusty 
winds and hail across western portions of the forecast area from
late Wednesday afternoon into the evening where severe 
thunderstorms are possible. Low temperatures tonight will range 
from around 50 to the mid 50s north, to the mid to upper 50s 
Downeast. High temperatures Wednesday will range from around 80 
to the lower 80s across much of the region, with mid to upper 
70s along the Downeast coast with onshore winds.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
Shortwave or area of remnant convection will track across New 
England Wednesday evening and overnight. This will bring chance
of thunderstorms with small hail or gusty winds early, and 
heavy rain throughout.

Anticipate a swath of rain and showers to accompany this as exit 
region of upper level jet approaching from the west adds 
support to plenty of moisture in lower levels. Thunderstorms 
will potentially be embedded, and in the highly sheared 
environment, would pose a gusty wind threat. At the evening 
timing, these storms will mostly rely on mixed layer instability
with close to nil surface based CAPE. Some of the convective 
composites or parameters (such as STP or SCP) may be giving 
erroneously high numbers due to large amounts of helicity or 
shear vs. comparatively low instability within the complex. 

How guidance handles the system as it tracks east on Wednesday 
will vary the region of best forcing and thus wind/hail threat. 
This expands to heavy rain threat as well, but more confidence 
here with lifting warm front. Know much of the FA will be in 
warm sector with moisture values like PWAT surging into 1.5-2
range during evening and overnight hours. Precipitation 
Potential Placement highlights Downeast as greatest chance for 
heavy rain as well as converging and nearly balanced Corfidi/sfc
wind vectors. These vectors become more uniform in direction as
cold front begins to slide through the north early Thursday 
morning. Downeast would be under threat of more thunderstorms 
Thursday afternoon if cold front is slow enough, allowing 
surface instability to gain strength once again during day. 
Potent 40-50kts of 0-6km shear will also be in place for chance 
of a isolated stronger storm over interior Washington/Hancock Co
if some clearing occurs. Front will track to clear Downeast 
Thursday night with dry conditions expected for much of the area
Friday. Some remaining moisture could bring a isolated shower 
or two in the Crown of Maine during afternoon. High temperatures
will be cooler on the way into the weekend.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Upr lvl trof wl be exiting into the Canadian Maritimes at the start 
of the long term with just an isold shower possible Fri evng. Med 
range guidance differs on upr air pattern beginning 00z Sun with 12Z 
GFS indicating the base of a H5 trof ovr Long Island vs CMC/EC H5 
low in vicinity of New England. Latest GFS appears to be more 
realistic for the extndd portion of the fcst with ridging at the sfc 
and aloft vs the latest EC. GEFS ensemble indicates high pressure 
both at the sfc and aloft with EC also hinting at high pressure at 
the sfc along with wk low aloft. Hv sided twd GFS for the long term 
with temps blo normal throughout the weekend. Temps begin to 
moderate on Mon as return flow commences with high nosing ewrd into 
Canada ahd of next system mvg in fm the Great Lks by the middle of 
next week.

&&

.AVIATION /22Z TUESDAY THROUGH SUNDAY/...
NEAR TERM: VFR conditions are expected tonight through early 
Wednesday. Variable conditions are possible later Wednesday with
a chance of showers/thunderstorms. Some of the thunderstorms 
could produce gusty winds and hail later Wednesday afternoon 
and evening, particularly across western areas.

SHORT TERM: 
Wednesday Night-Thursday Morning...MVFR to IFR still likely 
with periods of heavy rain and a chance of thunderstorms. Fog 
could hinder operations as well lowering visibilities. 

Thursday...IFR in morning with fog, improving to VFR across the
north. MVFR is possible Downeast with remaining clouds and 
chance of thunder in afternoon. S winds 10 kts veering to SW.

Thursday Night through Sunday...VFR with some MVFR possible 
Friday and Sat afternoon. Winds WNW 10-15 kts with some higher 
gusts.

&&

.MARINE...
NEAR TERM: Winds/seas will remain below small craft advisory
levels tonight through Wednesday. Shower/thunderstorm chances 
will increase later Wednesday afternoon and evening. 

SHORT TERM: Below SCA conditions expected. A few gusts of wind 
may approach 25 kts Wednesday night/Thurs morning with patchy 
fog, but expected to remain around 20 kts through Thurs night 
again with patchy fog moving in. Waves of 2-4 ft through 
Thursday night will increase Fri afternoon, but remain below 
5ft. Waves decrease 2-3 ft Sat and Sun.

&&

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

&&

$$

Near Term...CB/Norcross
Short Term...Cornwell
Long Term...Farrar
Aviation...CB/Norcross/Cornwell
Marine...CB/Norcross/Cornwell