Lewiston, Maine 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

833
FXUS61 KGYX 090922
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
522 AM EDT Wed Jul 9 2025

.SYNOPSIS...
A cooling trend starts today with a chance for afternoon showers
and thunderstorms. Chances for afternoon showers and storms
stay in the forecast through Thursday. High pressure will bring
a dry period Friday into the weekend with increasing
temperatures. Shower activity and possible heat returns the
beginning of next week.

&&

.NEAR TERM /THROUGH TODAY/...
520 AM Update...Mainly just freshened up PoPs as the area of
showers that moved through southern New Hampshire overnight will
be exiting off the coast over the next hour. Lack of
instability kept these as run of the mill showers with light
rates. Isolated light showers will continue in the mountains and
foothills through the morning before coverage increases this
afternoon.

Previous Discussion...
Impacts and Key Messages:
* Showers and thunderstorms today may contain brief downpours.
  With many locations saturated from recent rainfall, minor
  localized flooding is possible.

Backdoor cold front continues to march thru NH overnight. East
of the front cooler temps but a still moist air mass will
support low clouds and some patchy fog. The most dense fog
should remain over the waters however.

The front has also undercut the instability...with convection
expected to remain elevated thru morning. Showers continue to
percolate along the gradient between the remaining elevated
instability and stable air to the north. The 09.00z GYX sounding
showed around 600 J/kg MUCAPE locally...but the OKX sounding
was over 3000 J/kg. So as long as we keep southwest winds
aloft...some advection of this instability will continue
overnight. That should be good enough to warrant PoP remaining
in the forecast overnight...but slowly diminishing to
chance/slight chance by morning. We also still have PWAT values
near 2 inches...so any convection is going to be capable of
brief torrential rain. 1 to 2 inches per hour is possible with
any shower. If a flood threat were to evolve it would be because
the heaviest showers start to train in the same location.

The frontal boundary remains stalled south of the area which
will continue forcing for showers and thunderstorms this morning
and this afternoon. CAMs continue to suggest the possibility of
more robust convection reaching southern New Hampshire early
this morning currently being driven north by a cold pool. With
PWATs still around 2 inches, these could contain heavy rainfall
rates, but this is also an area that didn`t see much rain
yesterday so flooding issues may be limited especially if they
remain progressive. This will remain true as shower and
thunderstorm coverage increases again this afternoon. THe HREF
is still modeling PWATs around around 1.5", but as long as
showers/storms stay progressive we shouldn`t see many issues.
Corfidi vectors are more around 20kts tomorrow so there isn`t a
threat for training like there was yesterday and overnight.
Tomorrow will begin a cooling trend as high temperatures top out
in the 70s across much of the area with warmer temperatures in
the 80s holding on in the Connecticut River Valley.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
Impacts and Key Messages:
* Trends for Thursday will have to monitored as there is
  potential for strong thunderstorms to enter our CWA.

Tonight: A trough digging into the area will support scattered
showers overnight. With PWATs still modeled at 1-1.25" any more
robust showers could contain brief downpours, but the
progressive nature of them should preclude any flooding issues.
Otherwise, a cool night in the lower 60s is expected.

Thursday: The trough will swing through during the day Thursday
into the evening providing the forcing for showers and
afternoon thunderstorms. The latest runs of the CAMs suggest a
sharp CAPE gradient on the boarder of Vermont and New Hampshire
with maybe a couple hundred joules of CAPE making it into
western New Hampshire. Shear also looks modest, on the order of
30-40 kts, so some stronger storms look possible. SPC currently
has western New Hampshire in a Marginal risk which seems
appropriate as this set up looks marginal at best, but the
trends will be worth monitoring. With PWATs still around 1.5"
WPC also has western New Hampshire in a marginal risk, but storm
motion once again looks progressive, so while brief downpours
are likely in thunderstorms, flash flooding should not be an
issue. Thursday will be the coolest day this week with
temperatures in the low to mid 70s areawide (maybe a little
warmer again in the Connecticut River Valley).

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Evening update... No significant changes to the long term
forecast with the inclusion of the latest NBM. The first part of
the weekend continues to look dry with deep layer ridging
building over the region. After that we will see another trough
approach the region early next week bringing back afternoon
showers and thunderstorms through midweek. Temperatures will
also trend back above normal toward midweek.

Previous Discussion...
Impacts and Key Messages:
* Summer pattern with periods of showers and thunderstorms
* No strong signals for any significant severe or flash flooding
  thunderstorms at this time.

Front is expect clear the area by Friday morning with some
lingering daytime instability showers possible in the mountains, but
westerly flow is expected. Ridging is expected for most of the
weekend with building heat once again, but looking dry at this point
for Saturday. The second shortwave trough will approach the area by
late Sunday, with some timing difference is the ensemble guidance.
There is a chance for thunderstorms late Sunday, but timing of this
feature is plus or minus 18hrs at this point, so will see how things
trend.  Overall looks like a descent summer weekend, albeit a little
warm. Shower activity chances and heat likely to build the beginning
the next week as temperatures trend back above normal for the heart
of summer.

&&

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
Short Term...MVFR will be the prevailing condition today with
maybe some terminals able to break out into low VFR for a bit.
Showers and thunderstorms will be in the area in the area as
well, but will be widely scattered with low probabilities of any
one terminal seeing restrictions so there is no inclusion in
the TAFs at this time. Low MVFR ceilings or IFR fog is possible
tonight as abundant low level moisture remains in the area.
Thursday may be a similar situation with persistent MVFR
ceilings and a better chance for afternoon thunderstorms.

Long Term...Showers and thunderstorms expected on Thursday with
clearing for Friday through Saturday with VFR conditions
expected.

&&

.MARINE...
Short Term...Wind gusts and seas remain below SCA criteria
through Thursday as high pressure looks to nose in over the
waters. Fog development is likely tonight with onshore flow.
Thunderstorms may move over the waters Thursday afternoon.

Long Term...Conditions are expected to remain below SCA conditions
through this period. Thunderstorms are possible over the
coastal water Thursday evening.

&&

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

&&

$$

NEAR TERM...Baron/Legro
SHORT TERM...Baron/Legro
LONG TERM...Baron/Dumont