402
FXUS61 KCAR 051756
AFDCAR

Area Forecast Discussion
National Weather Service Caribou ME
156 PM EDT Wed Jun 5 2024

.SYNOPSIS...
Weak high pressure drifts south of the waters through tonight, as
a trough of low pressure transits the area this afternoon and
evening. An storm system then slowly approaches from the west
Thursday through Friday night, then slowly crosses the region
Saturday and Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
130 pm update...Convective allowing models show a wider range
with respect to timing and less consistency in coverage for
convection this afternoon and evening. Shear is relatively
modest only, 20-30kt as well as CAPE generally 500-1000J/kg over
far western zones, with possibly some pockets of 1000-1500 j/kg.
This supports the idea of some strong to possibly severe storms
PWs around 1 1/3 inches support potential for locally heavy
rainfall. If it were not for wet bulb zero heights around 8-9kft
would think that would be the only threat, but cannot rule out
some small hail and with the strongest storms some gusts/hail
around severe limits over far western zones.

Over NE portions of the CWA, there is very limited CAPE and
being farther from the dynamical support of the shortwave
passing to the west, this should greatly limit if not make non-
existence the convective threat. Over Downeast Maine, the
seabreeze should preclude any significant convection over
coastal Downeast, and it likely should be towards evening, or
early evening by the time convection gets into interior
Downeast, so it should be weakening there.

Previous discussion...
A weak upper level shortwave will move southward from Quebec
this afternoon. This shortwave is rotating around the nearly
stationary vertically stacked upper low south of Newfoundland.
The shortwave will deliver cooler air aloft while warmer and
moister air arrives at lower levels. The resulting instability
is expected to produce 1000 to 2000 J/kg of SBCAPE this
afternoon, mostly in Piscataquis County, south/central Penobscot
and northern Hancock counties. By evening, the instability may
expand eastward towards interior Washington County. Stable
conditions are expected to prevail for most of Aroostook County
and have excluded mention of thunderstorms there. The sea breeze
will likely be a surface trigger for some stronger storms for
interior Downeast and north of Penobscot Bay. That means less
chance for thunderstorms towards the coast where the cooler
onshore flow will prevent convection.

In terms of thunderstorm threats, we have added mention of
locally heavy rain and small hail to the area with thunderstorms
forecast. PWs in the highest percentiles for this time of year,
slow storm motions, and thunderstorms reaching the trop should
produce heavy downpours. Hail rather than winds is the bigger
threat from stronger cells with a relatively low freezing level
and decent hail CAPE. Shear is not too impressive but may be
just enough to organize some weak/short-lived supercells with
hail. SPC has placed the area in a marginal risk for severe
thunderstorms today.

For tonight, thunderstorms will diminish and attention turns to
shallow fog formation towards the coast and where heavier rain
fell in the afternoon and evening. Lows will drop off into the
low to mid 50s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Thursday will provide a quick reprieve in the weather before an
occluded front approaches early Friday morning. Southeast flow
ahead of the occlusion will increase humidity and continue to
push the marine layer onshore, so areas of fog will continue
over Downeast. Otherwise, high temperatures will again reach the
upper 70s or low 80s. Warmest areas will be up north, where it
will take longer for clouds ahead of the front to move in.

The occluded front will make a very slow progression northward
Thursday night and Friday morning, with an accordingly slow
northward progression of increasing rain shower coverage as
well. By Friday afternoon, the most widespread coverage for
showers will be across the central Highlands, with some rain
also expected Downeast. QPF values will be heaviest Friday
afternoon over the central Highlands, with between 0.30 and 0.40
expected over a 6 hr period. Flooding is not expected to be an
impact, but smaller streams may rise quickly, especially with
the recent dry weather for antecedent conditions. Cooler
surface temperatures behind the front should limit instability,
so the chance of thunder for Friday afternoon will be limited.

The front will continue to progress northward as it deteriorates
Friday night. Lighter showers are expected across the north
through early Saturday morning. Low temperatures will remain
seasonable, in the mid-50s across the board.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Uncertainty continues through the weekend, with the upper level
low progressing eastward over Maine on Saturday. This will
increase the chances of showers through the weekend, but without
a specific forcing feature, the exact location of the showers
remains a little unfocused at this time. Therefore, PoPs were
lowered from categorical for the region, similar to the previous
forecast. Increased chances for thunderstorms are also expected
both Saturday and Sunday, with a slightly colder pool of air
aloft and the potential for afternoon heating increasing lapse
rates. Current forecast seems to indicate that the chance for
thunderstorms lies more to the south on Saturday as a shortwave
pushes northward on the east side of the cutoff low. Upper level
support will be slightly further north on Sunday and the higher
chance for thunderstorms will be across the Crown of Maine.

By early next week, it appears that the pattern will shift
eastward, and showers will slowly taper off as weak ridging
moves in. However, a fair amount of uncertainty remains, in
particular with timing of the pattern shift.

&&

.AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
NEAR TERM: VFR at northern terminals through the TAF period,
with possible exception of a very low chance of IFR ceilings
late tonight. With now the expectation that these terminals will
not see any convection this afternoon/evening, the fog/low cloud
threat overnight there is greatly reduced, and hence is no
longer reflected in the TAFs.

At southern terminals, VFR to get started, with scattered
showers and thunderstorms late this afternoon/early this
evening producing locally MVFR conditions possible - best chance
KBGR. Low level moisture from showers should allow for patchy
fog/low ceilings with IFR or lower probable late
tonight/Thursday.

Light and variable winds into Thursday morning, becoming SE-ESE
at under 10kt by mid Thursday morning.

SHORT TERM:

Thursday night-Friday night: VFR at Aroostook County airports.
MVFR or lower possible at southern airports extending into GNR at
night into the early morning.

Saturday-Sunday: Predominantly MVFR or lower probable.

Sunday night-Monday: MVFR or lower possible.

&&

.MARINE...
NEAR TERM: Seas will remain around 1 to 2 feet with a slight
increase later tonight. Southwest winds will shift towards
southerly tonight. The shift in winds will increase the
likelihood of fog for tonight as more humid air arrives over the
cold waters.


SHORT TERM: Winds will remain below advisory levels and
generally below 20 kts through the period. Seas will also remain
around 2 feet or less. Fog is expected at times, particularly
Wednesday night into Friday morning.

&&

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

&&

$$


Near Term...Maloit/MCW
Short Term...LF
Long Term...LF
Aviation...Maloit/MCW/LF
Marine...Maloit/MCW/LF