236
FXUS61 KCAR 042201
AFDCAR

Area Forecast Discussion
National Weather Service Caribou ME
601 PM EDT Thu Jul 4 2024

.SYNOPSIS...
A weak cold front will stall in the area tonight. The front
then slowly lifts back north Friday into Saturday as a warm
front. Another weak cold front will begin to cross the region
Sunday and move east of the region Monday. A surface trough is
expected to cross the area Tuesday.

&&

.NEAR TERM /THROUGH FRIDAY/...
6:01 PM Update: Seasonably warm and humid early evening across
the FA. Satellite pictures show cumulus fields across the north
and mainly cirrus across the Downeast Region. Area radars show a
few isolated showers in parts of the Saint Lawrence River
Valley, but nothing of note on our FA. The chance of any showers
this evening is very low with just the outside chance of an
isolated shower moving across the far northwest corner of the
FA. Low clouds and fog are expected to develop later this
evening and overnight Downeast with fairly high confidence.
Patchy lower clouds and fog will form across the north very late
tonight, but confidence is lower across the north than it is
Downeast.

Previous discussion:
A low pressure system to the north in Canada will swing a cold
front through the region tonight and Friday. For tonight, the
cold front will begin a slow transition from NW to SE. High-res
models show the blocking tropical high pressure over the waters,
which will keep the weak cold front from progressing much
further south of the Central Highlands. Thus, isolated to
scattered showers will stick to the far north through the early
part of the night and clear out by midnight. Afterwards, the
marine layer will progress north into interior Downeast bringing
areas of fog while patchy fog will develop in the north.

By Friday, a low pressure system intensifying over the Great
Lakes will start to lift a warm front across the region. During
the morning, the warm front will be over the Gulf of Maine, with
showers and patchy fog over coastal Downeast. By the afternoon,
CAMS models show the warm front moving into the Central
Highlands. Some guidance shows the warm front progressing
slightly faster with showers reaching into the North Woods by
the afternoon. Nevertheless, rain showers will cover the
majority of the center of the region. In addition, afternoon
heating and frontal lift will produce convection along the line
of instability. High res models show an unorganized area of
900-1200 J/kg of CAPE stretching from Greenville to Houlton,
which is to be expected along the higher terrain. Weaker, but
still high, CAPE north of this line will also produce
thunderstorms as well. Recent upper air model soundings show a
more impressive directional bulk shear, though the speed at the
surface and mixing layer are lower than previous events. Cannot
rule out possible strong pulse thunderstorms with the
instability. However, as the storms cross over the higher
terrain, they will be entering a more stable environment with
the S flow marine layer, weaken the storms.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
The warm front will continue to progress slowly northward
Friday night. Afternoon convection along the boundary will
gradually diminish in the evening. Otherwise, fog and low clouds
will spread northward under a frontal inversion. That will help
limit lows to the mid 60s for most of the area. The cool spot
will be the Downeast coast with an onshore flow producing lows
in the 50s.

The warm front continues to slowly push northward on Saturday
with rain likely. The low level frontal inversion is expected to
hold on much of the day, keeping highs in the low to mid
70s...even as 850mb temps surge towards 18C in the afternoon.
Surface-based instability is most likely to stay west of the
area due to the inversion. The exception might be the far
western portions of the North Woods. Given PWs around 2 inches
and strong deep layer shear, any surface-based convection could
be troublesome. In spite of the impressive precipitable water,
forcing looks weak and not expecting widespread QPF much above a
half inch. Locally higher amounts are possible with
thunderstorms. Did add mention of thunderstorms Saturday
afternoon and evening due to elevated CAPE and the chance that
the inversion breaks inland.

Weak low pressure slowly tracks across the area Saturday night.
Low level moisture advection along the low track increases the
risk of another round of fog and low clouds. Elevated
instability maintains a risk of thunderstorms through the
evening. Once again, lows will only drop to the mid 60s for much
of the CWA.

For Sunday, the low exits the area and ridging builds. In the
absence of any cold advection in the wake of the low,
temperatures will climb well into the 80s across much of
northern and eastern Maine. Humid conditions continue with dew
points in the mid to upper 60s. In terms of thunderstorms,
rising heights and warming aloft seem likely to overcome the
surface-based heating. Kept a slight chance of thunderstorms in
the forecast for the afternoon.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
The powerful subtropical ridge in the Atlantic will continue to
dominate early next week, keeping fronts from crossing the area
with cooler Canadian air masses. This mean temps and humidity
well above normal, but falling short of records. Both Monday and
Tuesday will bring highs in the mid to upper 80s. Onshore winds
will keep it a bit cooler along the coast.

The risk of afternoon thunderstorms increases Tuesday per the
04/12Z GFS while the 04/12Z ECMWF suggests a higher risk on
Wednesday. While operational models show strong dynamics for
Wednesday, the case for severe storms remains in doubt due both
to timing and potential for low level clouds limiting heating.
Did drop off Wednesday high temps back into the 70s based on
more cloud cover.

The cold front Wednesday night offers a good chance to bring
temporary relief to the heat and humidity for late next week.

&&

.AVIATION /22Z THURSDAY THROUGH TUESDAY/...
NEAR TERM: VFR conditions before midnight tonight. After
midnight, all terminals will drop to MVFR/IFR cigs. BGR/BHB,
IFR/LIFR cigs and vsby due to areas of fog. Light and variable
winds. For Friday, north terminals return to VFR conditions by
morning with -SHRA and possible TS by the afternoon. South
terminals remain MVFR/IFR due to cigs. Light and variable winds.


SHORT TERM:
Friday night...Thunderstorms are possible in the
evening...mostly north of GNR and HUL. Otherwise, fog is likely
to set in for all sites later in the night with IFR to LIFR vis.

Saturday...Fog and IFR cigs may be persistent into the
afternoon for coastal sites and as far north as Bangor. Other
sites will be VFR by afternoon. Afternoon thunderstorms are
possible for all sites.

Saturday night...Fog and IFR cigs will most likely move north
from the coast to affect all sites again. Thunderstorms are
possible in the evening.

Sunday...IFR cigs will gradually lift to MVFR in the morning and
all sites will gradually become VFR in the afternoon. There is a
slight chance of thunderstorms in the afternoon for inland
locations.

Sunday night...Expect generally VFR except possibly on the coast
to include BHB.

Monday into Tuesday...Mostly VFR except the threat of nighttime
fog and low clouds for coastal sites such as BHB.

&&

.MARINE...
NEAR TERM: Winds and seas will remain below SCA conditions
tonight and Friday. Reduced visibilities in areas of fog.


SHORT TERM: Stable conditions persist through the period with
little chance of any advisories. Adjusted winds downward this
weekend due to stability. Fog is a more likely threat in this
warm and humid regime. Everyday well into next week should
feature some degree of fog or haze.

&&

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

&&

$$


Near Term...CB/LaFlash
Short Term...MCW
Long Term...MCW
Aviation...CB/LaFlash/MCW
Marine...CB/LaFlash/MCW