-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCAR 212231
AFDCAR

Area Forecast Discussion
National Weather Service Caribou ME
631 PM EDT Mon Aug 21 2017

.SYNOPSIS...
High pressure will build south of the area this evening. Low
pressure will approach from the west on Tuesday. The low will
track to our north Tuesday night into Wednesday as it brings a
cold front across the area.

&&

.NEAR TERM /THROUGH TUESDAY/...
-- Changed Discussion --
630 PM Update... Made adjustments to the sky forecast starting
out and then showed clouds filling in across the wnw as depicted
on the latest satl loop. Radar imagery showed some returns
showing up over the St. Lawrence River dropping se. Activity was
setting up on rich mid 60 dewpoint air but as they move to the
e, activity should weaken running into somewhat drier air(upper
50s). The latest run of the RAP has been consistent w/its
previous forecasts of showing some showers and perhaps a tstm
sliding across the Crown of Maine this evening. Daycrew appears
to have this handled ok. There is a weak frontal boundary as
stated by the daycrew that will slide across the region. This
boundary is coupled w/an upper disturbance as seen on the latest
WV satl imagery. The boundary is shown by the RAP to move
across northern areas. CAPE values are forecast to increase into
the evening w/0-6km shear hitting 30 kts. Decided to keep a
mention of tstms in for the far n and w through late evening.
RAP soundings show potential that if any storms fire, strong
wind gusts a possibility. The lacking ingredient is depth of the
moisture. Therefore, kept enhanced wording out attm. Will re-
assess things through the evening.

Previous Discussion...
A weak sfc front is located acrs cntrl Quebec and wl be
dropping south tonight bfr gradually weakening. Showers and an
isold tstm wl accompany the bndry into the St. John Vly tonight
as instability begins to wane with loss of diurnal htg.

Humid airmass rmns ovrngt with dwpts rebounding into the lwr 60s
and this wl lkly lead to patchy fog acrs the north as clds
dissipate.

Late tonight and Tue mrng wl be quiet, other than patchy fog as
brief ridging takes hold thru about 15z tomorrow. Wmfnt lifts
thru tomorrow aftn with showers and thunder dvlpng acrs the nw
aft about 18z. CAPES increase aft this time and 0-6km bulk shear
increase to 30-40kts in the aftn bfr increasing substantially
drg the evng hrs. PW values begin to rise in the aftn to nr 1.50
inches acrs srn areas, thus hv retained mention of hvy rain and
gusty winds to where convection is lkly.
-- End Changed Discussion --

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
For Tuesday night, a strong cold front will cross the area later
in the night. This front has the potential to produce locally
heavy rainfall and will maintain that threat in the forecast. PW
values will approach 2 inches with a deep warm cloud layer
around 13K ft. A strong LLJ will be in place and Corfidi vectors
show the possibility of some back-building cells. The LLJ also
heightens the threat of gusty winds mixing down with
thunderstorms and will maintain mention of that in Tuesday
night`s forecast. It`s still unclear how much of the action will
be with a pre-frontal trough or with the front itself later in
the night. Otherwise, it will be a warm and humid night ahead of
the front with lows in the mid to upper 60s for much of the
area. Humidity will be high with dew points also in the mid to
upper 60s. Fog is likely along the coast and in high terrain.
Elsewhere, marine layer moisture will be streaming northward in
the form of stratus and some patchy fog. On Wednesday, clouds
with the front will exit the Down East region with a few
residual showers...but no thunderstorms can reasonably be
expected. Fog and low clouds will linger along the coast during
the morning. It will be a rather breezy day with a deep mixing
layer and still warm with highs in the mid to upper 70s. The
cooler air behind the front arrives gradually during the day and
it will be cooler and less humid Wednesday night with lows
mostly in the low to mid 50s. The cool Canadian air mass will be
fully in place for Thursday with highs in the low to mid 70s and
dew points in the upper 40s to lower 50s. Some cu fields will be
possible north of Houlton with the NW flow.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
In the longer term starting Thursday night, a quiet and cool
pattern appears likely with persistent upper level troughing and
surface high pressure. The primary challenges will be
identifying cumulus and stratocu fields in the a north to
northwest flow...and when minor shortwaves may kick off some
light afternoon showers Friday, Saturday and Sunday. In general,
little precipitation is expected and will hold off on specifying
chance pops for these days.

&&

.AVIATION /22Z MONDAY THROUGH SATURDAY/...
NEAR TERM: VFR next 24 hours with potential MVFR vsbys btwn 07z
and 12z for northern terminals.

SHORT TERM: IFR conditions due to cigs, fog and thunderstorms
will affect all terminals Tuesday night. The low clouds will
linger into Wednesday morning for BHB and coastal sites, but all
of the area will be VFR by Wednesday afternoon and remain so
into Saturday.

&&

.MARINE...
NEAR TERM: Winds and seas will remain below SCA levels thru Tue
aftn bfr beginning to climb to near 5ft at the very end of the
period.

SHORT TERM: There is a credible threat of SCA conditions Tuesday
night into Wednesday in spite of the stable conditions and fog
that will be in place. Wind-driven waves could hit up to 6
feet. After Wednesday, no significant weather is forecast
through the end of the period.

&&

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

&&

$$

Near Term...Farrar/Hewitt
Short Term...MCW
Long Term...MCW
Aviation...Farrar/Hewitt/MCW
Marine...Farrar/Hewitt/MCW