573
FXUS61 KCAR 050103
AFDCAR

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

.SYNOPSIS...
A weak cold front will stall in the area overnight. 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/...
9:03 PM Update: A mild and fairly humid evening across the FA.
Inland temperatures north of Bangor remain mostly in the low 70s
while it is much cooler along the coast. Area radars show a
line of showers in the Saint Lawrence Valley that extends across
portions of the Gaspe Bay Peninsula. The only lightning strikes
in the past 2 hours have been across central portions of the
Gaspe Bay Peninsula. A few of the showers may drift into the
North Woods and parts of the Saint John Valley over the next
couple of hours. The humid air mass will likely lead to the
formation of low clouds and fog along the coast later tonight,
and by daybreak some of the low clouds and fog might work north
into portions of eastern Aroostook County.

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 /01Z FRIDAY THROUGH TUESDAY/...
NEAR TERM: VFR this evening. Moderate to high forecast confidence
on IFR conditions developing after midnight at KBHB and KBGR in
low clouds and fog. Low to moderate confidence on a period of
IFR ceilings and visibility at the Aroostook terminals late
tonight. Conditions at the Aroostook terminals are expected to
improve to VFR Friday morning (if lower conditions develop late
tonight), but only slowly lift to MVFR at KBGR and KBHB. A
return to VFR likely at KBGR during the afternoon. S/SW wind 5
to 10 knots becoming light and variable later this evening.
Light wind on Friday, mainly W at the northern terminals and
S/SW at KBGR and KBHB.

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: The wind and seas will remain below SCA conditions
overnight 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