Area Forecast Discussion
Issued by NWS Caribou, ME

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FXUS61 KCAR 202245

Area Forecast Discussion
National Weather Service Caribou ME
645 PM EDT Mon May 20 2024

High pressure will ridge across the region through Tuesday,
then build south of the area through the middle of the week. A
strong cold front will cross the area Thursday, followed by high
pressure Friday into next weekend.


630 PM Update:
An axis of around 1000 j/kg of MLCAPE currently extends across
the far NW portion of Maine this evening, with two areas of
active showers and thunderstorms. The first just north of Van
Buren will move into a less favorable environment and weaken,
staying primarily NE of the Canadian border. The second area
near Quebec City is also expected to weaken as it approaches the
border with loss of daytime heating over the next few hours. No
significant changes were needed to the previous forecast.

Previous Discussion:
The axis of the upper level ridge will begin to sag to the
south tonight. For this evening, a vort max will move across the
north bringing isolated showers to the Crown of Maine and
slightly further south into Aroostook depending on the amount of
convection this afternoon. Upper air model sounding, especially
high-res, show less instability than previously forecast.
However, the CAPE values are greater than 1000 J/kg in the North
Woods and lapse rates are fairly steep in the same area, thus
decided to leave isolated thunderstorms in the forecast for this
evening. The instability decreases drastically after the
passage of the shortwave and loss of daytime heating. Expect
another night of gradually increasing stratus desk with the
onshore flow with patchy fog across the region. Temps will be in
the upper 50s in the north and upper 40s in the south.

For Tuesday, the upper level ridge will continue to influence
the region with a vort max, currently of the Great Plains, will
move NE towards the area. For Tuesday morning, patchy fog will
dissipate early, then could should start to break with the
increasing heat of the day. By the afternoon, rain showers will
begin, but the high-res and CAMs models are inconsistent with
the timing of the convection across the region. Instability
values across the north are concerning for thunderstorms,
including some becoming severe. With the steep lapse rates, the
skinny CAPE withing a very moisture column, high mid and low
level RH, and PWATS above normal, heavy rain is expected with
the storms. In addition, an invert V sounding and elevated DCAPE
indicate that some storms will contain gusty winds. Depending on
the high temps and breaks in the clouds, these storms have the
potential to last into late evening. Temps will reach into the
lows 80s across the region, expect Downeast where temps range
from mid 70s inland to mid 60s on the coast.


In general, a powerful upper ridge will continue to dominate
area weather through the period with subsidence and warming.
The warmest temperatures of the year can be expected during the
period with highs reaching the 80s and lows over 60F for large
portions of the forecast area by Tuesday and Wednesday nights.

A series of weak fronts riding the northern periphery of the
ridge through the period represents the forecast challenge in
terms of thunderstorms and exact hi/low temperatures Tuesday
night into Wednesday.

On Tuesday night, expect a convective disturbance currently in
the western Great Lakes region to ride over the upper ridge and
into northern zones with thunderstorms. Guidance continues to
offer a wide variety of timing and intensity solutions for the
compact shortwave embedded in the flow. It is still unclear if
an MCS will develop and track across southern Quebec Tuesday
afternoon. The majority of guidance has the disturbance
arriving Tuesday evening and affecting the forecast area well
into the night. Thunderstorms are definitely a threat with
locally heavy downpours, but timing well past peak heating
reduces interest in any enhanced wording for Tuesday

Lows in the northern half of the forecast area will
be near 60F while an onshore flow of cool marine air will drop
coastal lows towards 50F with the threat of fog.

The frontal boundary location remains the nexus between
temperature and PoP forecasts into Wednesday. At this point,
have played for nominally cooler highs in northern zones due to
the lingering boundary, but mid to upper 80s or higher seems
likely for the Bangor area. If the frontal boundary moves
northward more rapidly, these mid 80s may extend northward
across the entire forecast area. In terms of convection, expect
the upper level ridge to build on Wednesday and cap convection.
Did mention a slight chance of afternoon thunderstorms in case
the cap breaks or there is a large timing error regarding the
disturbance expected Wednesday night. SBCAPE numbers could be
rather impressive by later Wednesday afternoon.

This instability continues into Wednesday night. Thunderstorms
are again a threat for Wednesday night as a weakening warm
occlusion moves through the area. Clouds, precip and warm
advection will keep lows in the 60s and humidity will reach its
zenith so far this year with dew points in the lower to mid 60s.

These dew points will continue ahead of a strong cold front on
Thursday. The cold front will act a potent trigger for
widespread convection. All of the ingredients for an active day
seem to be in place: CAPE, strong shear and anomalously high
PWs. About the only issues to lessen severe potential will be
unfavorable early timing for the frontal passage and persistent
early morning clouds behind the occlusion. It has been quite a
few years since we have seen a favorable setup for severe
weather in late May. The hydro aspect will also have to be
watched given the deep moisture.


The front will exit quite quickly Thursday night and bring very
welcome relief in terms of temperatures and dew points for
Friday and throughout next weekend. There will still be the
chance of showers with a secondary cold front and upper trough
on Friday. The 20/12Z GFS is now suggesting the threat of
another round of thunderstorms Friday afternoon with the
secondary front, but it is not well supported by other guidance
at this point.  Highs return to the 60s to around 70F for the
holiday weekend with lows in the 40s.


NEAR TERM: Aroostook Terminals...Mainly VFR for early tonight,
then possible MVFR cigs for HUL and PQI depending on if the low
clouds and patchy fog reach this far north. For Tuesday, VFR
conditions with possible isolate showers and thunderstorms in
the afternoon.

Downeast Terminals...Mainly VFR this evening, then IFR/LIFR
cigs tonight with patchy fog. By Tuesday morning, cig and patchy
fog should lift making for VFR conditions the rest of the day.

SSW winds 5-10 kts.

Tuesday night...VFR except a slight chance of fog at BHB. Light
south winds.

Wednesday...VFR with a slight chance of afternoon thunderstorms.
Light south winds.

Wednesday night...Predominately VFR with a chance of
thunderstorms. A slight chance of fog at BHB. A chance of MVFR
tempo IFR cigs later in the night north of HUL. Light south

Thursday...VFR tempo IFR in strong thunderstorms along a cold
front. Light south winds outside of thunderstorms.

Thursday night into Saturday...VFR with tempo MVFR cigs possible
north of HUL early Friday. Scattered showers possible north of


NEAR TERM: Winds and seas will remain below SCA conditions
tonight and Tuesday.

SHORT TERM: Warm and relatively humid air moving over the cold
waters is likely to cause fog at times Tuesday night into
Thursday night. The stability will reduce winds and seas through
next week. In general, southwest winds around 10 to 15 kt can
be expected until Friday night when winds will become more
westerly. By Saturday night, winds will become more northerly. Seas
will mostly run 2 to 4 feet, but become 1 to 2 feet this weekend
as high pressure builds over the waters.





Near Term...LaFlash/MStrauser
Short Term...MCW
Long Term...MCW