335
FXUS61 KGYX 161821
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
221 PM EDT Wed Jul 16 2025

.SYNOPSIS...
Relief from today`s hot and humid weather will be on the way in
the form of a cold front Thursday. However one more day of
sticky weather is expected ahead of that boundary with mid to
upper 90 heat indices possible in southeastern New Hampshire
once again. Showers and thunderstorms will be possible Thursday,
and depending on timing some of those could be strong to
severe. And while rainfall will not be widespread, if it does
rain it will likely be torrential. Cooler and drier weather will
arrive Friday and continue into the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Impacts and Key Messages:
* Warm apparent temperatures overnight will add to accumulated
  heat stress from today.

The ridge breaks down tonight as a shortwave trough begins to
make its approach toward the region. This will shift flow more
southwesterly leading to an increase in moisture, so expect
increasing cloud cover with most areas at least partly cloudy
early Thursday morning. This increase in moisture will lead to a
rather warm and humid night area wide with low temperatures
only bottoming out in the mid 60s in northern zones and upper
60s elsewhere. Areas in the Heat Advisory today maybe even only
bottom out in the low 70s. There is a low chance for a few
showers to make it into western New Hampshire in the early
Thursday morning hours, but the bulk of showers/storms
associated with the shortwave should hold off until later.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
Impacts and Key Messages:
* Thursday may feature strong thunderstorms capable of
  producing gusty winds and heavy rain. Training/backbuilding
  and/or repeated rounds over a location would pose a localized
  flooding threat.
* Heat indices climb into the mid to upper 90s in southeastern
  NH for a third day, so the Heat Advisory has been extended.

An approaching shortwave trough will provide forcing for an
initial round of showers and thunderstorms late Thursday morning
into the the early afternoon. This likely ends up being focused
in the mountains and foothills where some clearing will be
realized before the best forcing arrives. Farther south and near
the coast usually holds on to the marine layer influence a bit
longer and has a lower chance of seeing much from this initial
round. MLCAPE values around 1000-1500 J/kg and modest shear
(around 20-25 kts) suggest organized convection, but mid-level
lapse rates around 5 C/km may limit storms from getting too
strong. The thing to watch will once again be the rain rates
associated with these storms. Another moisture plume enters the
area early on Thursday driving PWATs up into the 1.75 to 2"
range once again. As we have been seeing lately, this easily
allows any robust showers or storms to produce rates 1 to 2" an
hour. Fortunately storms do look progressive with mid level flow
on the order of 25-35 kts, but with flow nearly parallel to the
forcing localized flooding may occur with training of storms
over a location.

Low pressure then moves eastward over Quebec late
afternoon/early evening dragging an attendant cold front through
the northeast. There is much more uncertainty in what might
transpire with the forcing from this front. With pretty much all
of the hi-res ensemble members having the initial round in the
morning, there is quite a bit of variation between them in how
robust a potential second round of convection may be. Not all
that long ago we saw cloud debris from a morning round of
showers/storms inhibit instability development ahead of a
frontal passage, leading to minimal coverage and sub- severe
nature. This is a possibility again, but if areas can clear out
in between rounds a marginally severe threat does exist. CAPE
values are modeled more in the range of 1500-2000 J/kg south of
the mountains and this is an area that isn`t expected to get
worked over during the morning, so the frontal passage may be an
opportunity for those areas to see a stronger storm, but lapse
rates remain a hindering factor. Lapse rates do ever so slightly
steepen across northern areas which will be closer to the
parent low, so if convection is able to re-initiate, stronger
storms will be capable of gusty winds and have maintained that
in the forecast as a result. For reason listed above heavy rain
is the more concerning threat, especially if convection is going
to go over areas that see heavy rain during the morning round.
In total the HREF localized probability match mean has bullseyes
around an inch in the western Maine mountains, with ensemble
maxes suggesting 2-3" locally are in the realm of possibility.

Cooler and drier air makes some progress into the area behind
the front. Timing is always tricky, but it is a good bet that it
will at least make it into northern zones with low temperatures
able to fall into the upper 50s. South of the mountains holds
on to some elevated dewpoints and therefore limits cooling to
the upper 60s. Patchy fog development is possible Thursday
night, especially in areas that see rain.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...

Overview:
*High Pressure moves in for the weekend

*Cold front moves in Saturday night into Sunday

*High Pressure returns for the start of next week.

Details:
A zonal 500mb pattern should allow for near-average temperatures for
the end of the week. Temperatures generally look to be in the upper
70s and lower 80s on Friday and Saturday. The zonal pattern does
align with the wildfire smoke in Oregon, so a little haze can`t be
ruled out Friday. High pressure should keep things mostly dry Friday
and Saturday.

Saturday night, a cold front arrives from the west.  The front
should move through the area during the day Sunday, and should being
some showers and storms to the area. Uncertainty is still high on
the exact placement of the front and its parent low, but conditions
should generally improve through the day Sunday.

Early next week, high pressure moves in with a mostly zonal pattern
remaining. Highs will be pretty similar to what they should be
Friday and Saturday, with upper 70s and lower 80s forecast Sunday
through the first half of the week.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Short Term...VFR through the evening with patchy fog possible
at terminals again tonight which may bring about brief IFR/LIFR
restrictions toward sunrise. Confidence is high at RKD that
Marine fog will bring about restrictions most of the night.
Tomorrow will feature scattered showers and thunderstorms which
will create a mix of VFR and MVFR ceilings. Thunderstorms will
be scattered and probability is low for individual sites being
affected so they are not included in the TAFs at this time. Low
level wind shear is not expected at this time.

Long Term...VFR expected through the day on Friday and Saturday.
Saturday evening through the first half of Sunday, restrictions
may lower as a cold front moves through the region, bringing
showers and storms. Conditions gradually improve Sunday and VFR
returns by Monday. &&

.MARINE...
Short Term...Wind gusts and seas remain below SCA criteria
through Thursday night. Southerly flow will continue allowing
for areas of fog to develop again tonight and Thursday night.
Showers and Thunderstorms may move over the waters Thursday
afternoon or evening.

Long Term...Northwest winds at 8-14kts expected on Friday.
Winds slacken through Friday evening, and shift to southerlies
at 8-12kts by the end of the day Saturday. Winds lighten up by
the second half of Sunday, with a wind shift back to
Northwesterlies expected by Monday morning. 2-4 ft seas are
expected through the whole period and SCA issuance is not likely
at this time.&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Heat Advisory until 8 PM EDT this evening for MEZ018-019.
NH...Heat Advisory until 8 PM EDT this evening for NHZ008-010-011-
     015.
     Heat Advisory until 8 PM EDT Thursday for NHZ012-013.
MARINE...None.

&&

$$

NEAR/SHORT TERM...Baron
LONG TERM...Palmer