Area Forecast Discussion
Issued by NWS Caribou, ME

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FXUS61 KCAR 242000

Area Forecast Discussion
National Weather Service Caribou ME
400 PM EDT Mon Jul 24 2017

Low pressure tracks south of the state late tonight. High
pressure then builds in Tue through Wednesday night. A cold
front enters the state Thursday and is expected to stall.


Not surprisingly, given the very dry 12z KCAR sounding and dry
model forecast soundings for KBGR and KBHB, precip has been
rather sluggish advancing into our CWA. Precip finally started
reaching the ground at BHB in the past hour, but from a high
9000 ft deck. That said, better returns are moving into the
SW`rn CWA in earnest now, so am comfortable with an increase to
likely pops for Bangor by 21z. The GFS and ECMWF did shift a
bit north on the precip shield and surface low position with the
12z runs, so QPF was tweaked up (not by much). Also did
increase POPs over the previous forecast, especially for Bangor
and Downeast, since Bar Harbor is already reporting rain and
Bangor seems likely to get at least an extended period of light
rain. QPF ranges from nothing in the Saint John Valley to around
a quarter inch or so along the coast.

Precip chances drop off after 06z tonight as the Low shifts
south of Nova Scotia. It`s likely that the last of any
lingering showers will clear out by late morning as the base of
the upper trough swings through the CWA and clears away to the
east. Expect gradual clearing from the northwest later Tuesday.
As for temps, clouds and increased dewpoints will keep tonight
warmer than the past few nights, with lows in the low to mid
50s. Highs tomorrow will generally be similar to today, ranging
from the upper 60s to low 70s.


Tuesday night will be the last of the cooler nights that started
this past weekend. Lows will drop to the mid to upper 40s north
and upper 40s to lower 50s in the southern half of the forecast
area. A rather steep radiation inversion will generate shallow
patchy fog later in the night, but the inversion and fog will
quickly be eradicated by dry southwest winds on Wednesday
morning. These winds and sunshine under high pressure will
propel temperatures back to the lower 80s Wednesday afternoon,
but humidity will still be reasonable. Clouds will gradually
increase Wednesday night. These clouds and the warm southwest
flow means lows will be around 60F...except cooler along the
Down East coast due to onshore winds. The increasing clouds will
be associated with a weakening cold front that will enter the
northwest corner of the area late Wednesday night and slowly
creep southward by later Thursday. The expected cloud cover
over most of the area led to a decrease in highs to the lower
70s while dew points creep back to the 60s. The lower temps,
clouds and weakening front led to a decision to go with just a
slight chance of afternoon convection.

A complex situation develops Thursday night into Friday night in
which the front stalls and either a wave develops...or in the
case of the GEMS and ECMWF...a full-blown coastal low develops
that affects the area into Friday night or even Saturday. The
24/12Z operational GFS scenario was not given much credence in
this forecast, but the actual forecast currently mirrors the
GEFS mean. There`s a lot of uncertainty before fully jumping to
GEMS and ECMWF solutions too. These solutions hinge on a more
defined shortwave trough in the Great Lakes region on Thursday
night and a strong jet on the backside that will eventually
generate a cut-off upper low. The ensemble approach taken in
this forecast maintains chance pops over large portions of the
area through Friday night due to the uncertainty and goes with
highs in the 70s on Friday and Saturday...rather than the 60s
dictated by GEMS/ECMWF. Higher confidence in dry conditions and
seasonable temperatures is warranted Sunday into Monday.

NEAR TERM: While it is currently raining out of a high VFR deck
for KBHB and KBGR, expect gradual lowering of CIGs through the
evening and overnight. KBHB is likely to be the first to MVFR
conditions in some rain this evening, and may have some IFR vis
or CIGs for a time, as well. KBGR is less certain to see MVFR
CIGs, but did include a period in the TAFs for Tue AM. Quite
possible that northern sites will remain VFR through the period
as low pressure remains well to the south.

SHORT TERM: Patchy shallow fog may reduce vis near sunrise
Wednesday morning. Otherwise, expect VFR conditions from Tuesday
evening into late Wednesday night. At that point, some coastal
stratus/fog may affect BHB and Machias while MVFR cigs are
possible north of HUL and GNR. The fog will burn off, but the
lower cigs in the north may persist through Thursday morning due
to a slow moving cold front. Isolated thunderstorms will be
possible along the cold front on Thursday afternoon. The front
will tend to stall Thursday night into Friday with the threat
of IFR cigs and vis. Confidence in VFR conditions returns Friday
night into Saturday.

NEAR TERM: Winds should remain below SCA criteria through Tue
evening. Seas may flirt with SCA criteria late tonight into Tue
AM, but for now have opted to not go with an advisory.

SHORT TERM: Fog becomes more likely Thursday into Friday. There
is a chance of a coastal storm Friday into Friday night which
could necessitate a Small Craft Advisory. Mariners should
closely monitor forecasts for this period.


Near Term...Kredensor
Short Term...MCW
Long Term...MCW
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