825
FXUS61 KGYX 311031
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
631 AM EDT Thu Jul 31 2025

.SYNOPSIS...
A slow moving cold front will stall across southern New England
today, continuing rain chances through Friday morning,
especially across southernmost New Hampshire. Dry weather with
comfortable temperatures and humidity levels will then follow
this weekend, lasting into early next week.

&&

.NEAR TERM /THROUGH TODAY/...
630 AM Update...Mainly updates to PoPs and QPF as showers are
beginning to stream into southwestern New Hampshire at this
hour. Rates are light so far, but are likely to pick up this
afternoon as temperatures warm a bit this morning and create
some instability. Generally the going forecast remains on track.

Impacts and Key Messages:
* The potential for heavy rain exists, mainly along the New
  Hampshire/Massachusetts border, as early as this afternoon.

We have quite an interesting setup today as low pressure rides
along a frontal boundary that will be to our south. This will
likely make for a tight gradient between the areas of rain,
mainly south of the mountains, and relatively clear weather to
the north. This is also making for quite a spread in modeled QPF
as there is some suggestion that some convective showers may be
embedded. The first opportunity for this may be with initial
onset of rain late morning early afternoon, across southern New
Hampshire near the Massachusetts border depending on how much
this area can warm before clouds and rain settle in. PWATs are
modeled to be around 1.5" during this time. Once that occurs,
the low levels will stabilize and transition any convective
showers to a steady rain. This area has been on the drier side,
so locations could stand to pick up a quick half an inch to an
inch with out much trouble. The precipitation shield will then
expand northward into the New Hampshire Lakes Region and far
southwestern Maine during the afternoon. I blended in some MOS
guidance to temperatures today to bring them down in southern
zones that will see clouds and rain set in early. This resulted
in high temperatures in the low to mid 70s across southern New
Hampshire and areas north of the mountains. Areas of Maine south
of the mountains are likely to see the warmest temperatures in
the mid to upper 70s as they stay on the northern edge of the
rain the longest.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
Impacts and Key Messages:
* The potential for heavy rain remains overnight, mainly along
  the New Hampshire/Massachusetts border. This could lead to
  some localized areal flooding, especially in poor drainage
  areas, and a low threat for localized flash flooding if an
  area sees repeated rounds of heavy rainfall.

Tonight: Rain continues to spread northward during the evening
and overnight. The latest HRRR has brought up an interesting
scenario that is low confidence based on timing and uncertainty
in high temperatures inland tomorrow, but something worth
noting. If inland areas warm enough during the afternoon, there
could be sufficient forcing for some convective showers to occur
on the northern edge of the line. This would spread some higher
QPF amounts into the New Hampshire Lakes Region and up through
the fishtail of Cumberland County. PWATs will be closer to
1-1.25" in this area so the HREF max suggests this might only be
on the order of 0.75-1". Otherwise, low levels will remain
stable and it will just be a lighter steady rain. Rain will then
begin to move southward after midnight with the bulk of it
clearing the coast around sunrise. Due to all the question
marks, the current QPF forecast stays closer to the HREF
probability match mean which has around an inch along the New
Hampshire and Massachusetts border, with 0.5-0.75" north of
Manchester up to Concord and southern York County. North of that
it quickly drops off with just around a tenth by the time you
reach the foothills. Again, the 00Z HREF max suggests that on
the high end some locations in southern New Hampshire could see
amounts upwards of 1.75" with 1" amounts extending into the New
Hampshire Lakes Region. This may lead to some minor areal
flooding, especially in poor drainage areas, and some localized
flash flooding could occur if heavier showers train over a
location. However, this is looking less likely based on model
trends and more like a beneficial rain event.

Friday: A 500 mb shortwave digs into the region Friday which
will push the frontal boundary south and out of our area. This
means showers taper off early, but wouldn`t be surprised if
clouds stick around for a good portion of the morning south of
the mountains, slowly clearing through the afternoon. High
pressure builds in with a cooler and drier airmass making for a
day with high temperatures only reaching the low 70s in many
locations, and maybe only topping out in the upper 60s in the
valleys.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Overnight Long Term Update...

Have incorporated the 01z NBM into the long term portion of the
forecast which yields little change. Fair weather is expected
through much of the period with a warming trend for Sunday and
Monday.

Previously...

Broad troughing aloft helps to drive surface cold front well
south of of our area Friday night. This will allow any lingering
precip across S NH to clear out, leaving cool Canadian high
pressure to dominate. With strong radiational cooling and a
crisp airmass, look for temperatures to bottom out with lows in
to 40s in the north, and 50s south both Friday and Saturday
nights. Can`t rule out some dense valley fog each morning given
the difference between water to air temps. The expansive area of
high pressure will serve to keep mostly sunny skies, with a few
cu in the mountains, and fairly light N winds under 10 mph for
Saturday. The high will start to move east by Saturday night,
allowing for some weak return flow and gradual warming into
early next week. Dry weather will continue well into next week
with the next chance for rain possible midweek. Models are
hinting at rain chances midweek associated with a mid-level
shortwave...but signals not strong enough to pin point timing or
extent of coverage. Overall, the trend will favor seasonable
temperatures and mostly dry conditions Sunday through Tuesday.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Short Term...Rain moves into the area today mainly effecting
MHT, CON, PSM, PWM and RKD. It may be heavy at times reducing
visibilities near IFR. Some lightning is possible as well, but
that is low confidence. Ceilings at these terminals will likely
drop to MVFR this afternoon and overnight, with VFR ceilings
prevailing at AUG, LEB, and HIE. Rain tapers off early Friday
morning with VFR ceilings returning. Low level wind shear is not
expected at this time.

Long Term...Mainly VFR with localized valley
fog/attendant reductions in visibility possible each late night
and early morning.

&&

.MARINE...
Short Term...Wind gusts and seas remain below SCA criteria
through Friday. Winds will be generally north easterly through
Friday, but a seabreeze may develop this afternoon. Rain that
may be heavy at times will move over the waters tonight into
early Friday morning.

Long Term...The period will start with northeast winds, but
despite ample mixing potential the strong high pressure centered
over the waters will keep winds 15kt or less. Winds will back
on Saturday, with return flow by Saturday night and Sunday. SW
winds will again remain under 15kt until Sunday night when a
brief surge could mix in some gusts around 20kt. Seas will
generally be 1-3ft seas at the start of the period will build to
2-4 ft by Sunday night with sw flow.

&&

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

&&

$$

NEAR/SHORT TERM...Baron
LONG TERM...Ekster/Jamison