824
FXUS61 KGYX 151226
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
826 AM EDT Tue Jul 15 2025

.SYNOPSIS...
Drier weather returns today with heat and humidity building in
through late week. Chances for afternoon showers and
thunderstorms return late week.

&&

.NEAR TERM /THROUGH TODAY/...
825 AM Update...Just a quick update to cancel the Dense Fog
advisory as visibilities are rapidly improving across the area.
The upper cloud deck has cleared the area, so once the remainder
of the fog and low stratus burns off we will have clear skies
with a warm and humid day expected.

645 AM Update... Issued a dense fog advisory for portions of
western ME based on latest sfc observations. Otherwise, no
changes were made at this time.

Previously...

Key Messages:

-Increasing heat is expected today with afternoon heat indices
 into the lower 90s in many interior locations with middle 90s
 in extreme southern NH.

Discussion:

Nighttime microphysics satellite imagery early this Tuesday
morning shows a sharp clearing line quickly moving eastward in
the wake of the cold front. As the skies clear through dawn this
morning the lingering low-level moisture will likely result in
the formation of radiational fog in locations that are not
already currently foggy. The last of the rain is now over the
Gulf of ME and islands and therefore a dry remainder of the
overnight can be expected. Current temperatures are primarily
into the upper 60s/lower 70s and little in the way of additional
cooling is expected given the small dew point depressions.

Surface high pressure will build to our southwest today with
southwesterly flow prevailing across the region. This combined
with partly to mostly sunny skies will allow high temperatures
to warm into the upper 80s to near 90 degrees across most of the
region away from the immediate coast along with the mountains.
Dew points will begin the day into the lower 70s but some
increased afternoon mixing should lower them a bit into the
upper 60s. Therefore, heat indices will be within a few degrees
of actual air temperatures.

Latest guidance indicates that Canadian Wildfire smoke will
arrive from north to south today with ASOS/AWOS observations
over southern Quebec already reporting haze. The ME and NH DEP
is forecasting moderate particle pollution and based on this and
ground truth to the north I added haze to the grids.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
Mainly clear skies will prevail tonight along with light winds.
Some weak radiational cooling is possible but it will be another
warm night given that dew points will remain elevated, limiting
the cooling potential. Radiational fog may develop late along
with some marine fog along the coast. Overnight lows will fall
into the 60s across most locations.

Stout Bermuda High will continue to maintain a humid airmass along
the eastern Sea Board Wednesday. Dewpoints in the upper 60s to low
70s combined with highs in the low 90s will bring heat indices into
the mid 90s across interior western Maine and much of New Hampshire
south of the Whites. Embedded short waves within SW flow aloft will
bring slight chances for a shower or thunderstorm across western NH
Wednesday afternoon and evening.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Long Term Update...Embedded short waves within a weak trough that
migrates east through the end of the week will bring chances for
showers and thunderstorms. The latest NBM brings the highest chances
for showers and storms Thursday while a lagging cold front will
continue chances through Friday. Global models and the 00Z NAM
suggest there will moderate instability Thursday with modest deep
layer shear and high PWATs so this will be the next day to watch for
any strong to severe storms and torrential rainfall. High pressure
will build in over the weekend bringing a cooler and drier air
mass.

Previously...
Pattern Overview: A shortwave trough crosses Thursday bringing
a chance for showers and thunderstorms, but the better day looks
like Friday as additional forcing comes in the form of a
surface front. Zonal flow through the weekend will keep
afternoon showers in the forecast with some suggestion that a
sharper trough may approach early next week.

Impacts and Key Messages:
* Heat and humidity peak midweek with heat indices reaching the
  mid to upper 90s in southeastern New Hampshire and
  southwestern Maine.

Details:

Thursday and Friday: Thursday sees increasing clouds and
shower/thunderstorm chances as a shortwave trough crosses the
area. CSU machine learning continues to show low probabilities
that a few storms could be on the stronger side. Long range
ensembles are showing another surge in moisture during this time
frame with the continued southwesterly flow driving PWATs up
across the area, so these probabilities are likely stemming from
precip loaded storms. With that being said any storms would be
capable of producing heavy rain which could lead to localized
flooding. Dewpoints peak in the low to mid 70s on Thursday, but
surface temperatures will be a degree or two cooler than the day
before. Despite the cooler temperatures, higher dewpoints
likely will necessitate Heat Advisories for Thursday as well.
Thursday remains a warm night with temperatures similar to
Wednesday night. Friday looks very similar with the addition of
a surface front that would provide further forcing potentially
leading to more widespread showers/storms. Trends will have to
be watched during this time period as timing of fronts is always
tricky, but nonetheless CSU continues to show low probabilities
of stronger storms and WPC has targeted these days with
Marginal Risks for the heavy rain potential. Depending on the
timing of the front there is likely going to be an interesting
temperature gradient with locations behind the front dropping
into the 70s with lower humidity and locations ahead of the
front during peak heating in the mid to upper 80s with humidity
holding strong. If the front does clear the area by nightfall,
it would make for a cooler night as well.

Saturday-Monday: A drier airmass is ushered in behind the front
for the weekend with temperatures feeling much more pleasant.
Zonal flow aloft, with some suggestion of brief shortwaves
rotating through, keeps low chances of pop-up afternoon showers
and storms in the forecast. Global models than suggest a sharper
trough and surface low pressure develop early next week which
may be the next best chance for widespread showers and storms,
but this is still out in time and unsurprisingly models greatly
vary in representation of this feature, so its only worth a
mention for now.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Short Term...Low ceilings combined with FG will continue to
result in locally IFR-LIFR restrictions through an hour or so
either side of 12Z this morning. Mainly VFR conditions are then
expected later today with SW winds of 5-15 kts. Ground FG may
develop again tonight, especially across coastal and valley TAF
sites. Otherwise, VFR conditions and light S-SW winds will
persist on Wednesday. No LLWS is anticipated.

Long Term...Low stratus and fog will be present Wednesday night
and Thursday morning bringing about IFR/LIFR restrictions.
Ceilings during the day Wednesday should be VFR with more in the
way of MVFR ceilings looking likely with widespread shower
activity and a few afternoon thunderstorms Thursday and Friday.

&&

.MARINE...
Short Term...Winds and seas to remain below SCA thresholds
through the period. Marine fog will persist through this morning
before dissipating some later today and then returning again
tonight.

Long Term...Wind gusts and seas remain below SCA criteria
through Friday. Increasing southwesterly flow will continue
areas of fog development through at least Friday morning.
Afternoon showers and thunderstorms may also move over the
waters on Thursday and Friday.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...Heat Advisory until 8 PM EDT this evening for NHZ012-013.
MARINE...None.

&&

$$

NEAR TERM...Baron/Tubbs
SHORT TERM...Schroeter/Tubbs
LONG TERM...Baron/Schroeter