-- Discussion containing changed information from previous version are highlighted. --
942
FXUS61 KGYX 041035
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
635 AM EDT Tue Jun 4 2024

.SYNOPSIS...
High pressure sinks south into the Gulf of Maine today
providing mostly fair weather outside of some afternoon showers.
Temperatures will run above normal today and Wednesday with
increasing humidity on Wednesday. Afternoon sea breezes are
likely, bringing cooler conditions to the coast. Chances for
showers and thunderstorms increase Wednesday as a trough
approaches from the west. This trough likely brings periods of
widespread rainfall late Thursday with unsettled conditions
persisting through the end of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
635 AM Update...Have increased cloud cover over the Lower
Merrimack Valley as low stratus has developed here. Satellite
trends do suggest this cloud deck is eroding with expectations
for clearing skies here over the next hour or so. Otherwise,
have refreshed T/Tds to capture latest observations.

Previously...

High pressure centered over Atlantic Canada will build into the
area this morning and becomes centered in the Gulf of Maine this
evening. This will provide another mostly fair weather day with
highs into the mid 70s to mid 80s across the interior. A sea
breeze likely develops by mid day keeping coastal areas several
degrees cooler. CAMs continue to suggest isolated showers will
develop over the mountains and across the Green Mountains that
drift into the CT Valley this afternoon.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
High pressure will continue to drift south away from the area
tonight with deep layer moisture gradually increasing towards
Wednesday morning. This increase in moisture will bring more in
the way of cloud cover along with potential for low
stratus/patchy fog along the coastal plain and slight chances
for showers across NH. Lows tonight will be in the 50s.

Things become more interesting Wednesday as an upper trough
swings into the Great Lakes while an upper low remains stubborn
in the Canadian Maritimes. This squeezes a ridge axis to the
west New England with little in the way for forcing over the
area, except for weak PVA from the north. The 00Z model suite is
in good agreement that PWATs will increase to around 1.5 inches
by Wednesday afternoon with MU CAPE building to 1000-2000 J/kg.
Deep layer shear is modest at best around 25 kts, so the threat
for severe storms is low, while as mentioned in the previous
AFD there are some ingredients coming together for the threat of
isolated flooding. CAMs are quite bullish in thunderstorms
developing over the mountains early Wednesday afternoon that
will initially be slow moving and capable of producing 1+ inch
per hour rainfall rates. Showers and thunderstorms will track
SE through the afternoon, maintaining themselves to the coast.
Another note on the heavy rainfall threat is the HRRR suggests
that there could be multiple rounds of convection in the
mountains up until sunset such that some areas could experience
multiple bouts of heavy rain. WPC has placed much western Maine
and the norther two thirds of NH in a Marginal Risk for
excessive rainfall, which seems reasonable given set up, while
dry antecedent conditions should help mitigate the overall
threat.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Overview: Rain chances improve during the long term. Expansive
low pressure will slowly slide east from the Great Lakes,
bringing periods of showers. The lows residence time will keep
unsettled conditions in the region at least through the weekend.


Details: Wednesday night, surface instability falls off with
some elevated instability remaining. This could prolong some
showers into the evening, but coverage should be on the
downtrend. Surface dewpoint depression closes across much of the
interior overnight. This could result in fog developing for
much of the interior. New developing low over the eastern Great
Lakes will hoist a warm front into southern New England Thursday
morning. This will lead to more synoptic forced rain moving
into the region slowly Thursday. While this surface low is
expected to pass off the coast, upper low and occluded front to
the west will prolong shower chances into the afternoon and
evening hours. This system will continue the unsettled pattern
for a greater portion of the extended forecast through the
weekend.

A chance of rain runs into early next week in the forecast, and
unfortunately due to the upper low, it will be difficult to
provide much more resolution in timing and coverage at range.
One hedge would be the chance for showers to increase during the
day and afternoon as daytime heating enhances avail instability.
The upper low will slowly move northeast through early next
week.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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Short Term...
1035Z Update...Low stratus and BR has developed over MHT with
satellite trends suggesting this deck will erode around 1130Z.

Previously...

VFR likely prevails through today. Increasing
moisture tonight will bring some threat of low cigs and fog,
while confidence is not high enough to put in the TAF. Wednesday
will likely start as VFR for all sites through the morning with
afternoon SHRA and TSRA developing over the mountains and
tracking towards the coast. TSRA cannot be ruled out anywhere,
while the highest probability for TSRA will be at KHIE and KAUG.

Long Term... Patchy fog may develop Wednesday night, with trend
to IFR ceilings is expected through Thursday. Thurs will also
feature invading SHRA/RA through the afternoon. With unsettled
weather expected through late week and the weekend, restrictions
will be likely at times amid fog, showers, and lowered
ceilings.
-- End Changed Discussion --

&&

.MARINE...
Short Term...Winds and seas remain below SCA thresholds as high
pressure builds in from the north today, settling into the Gulf
of Maine this evening. Patchy fog cannot be ruled out tonight
with a modest increase in southerly flow Wednesday as high
pressure drifts SE of the Gulf of Maine.

Long Term...Below SCA conditions expected, although with a humid
airmass arriving, fog development over the waters is expected
from mid week through the weekend. This could reduce visibility
at times for portions of the coastal waters. Broad, upper low
pressure will slowly track towards the region during this time,
lifting north early next week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$


NEAR TERM...Schroeter
SHORT TERM...Schroeter
LONG TERM...Cornwell