429
FXUS61 KGYX 140151
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
951 PM EDT Mon May 13 2024

.SYNOPSIS...
A warm front will push towards the region tonight with a few
showers before much warmer air arrives across southern NH and
far southwestern ME for the day on Tuesday. A cold front will
drop towards the region bring the chance for showers and
thunderstorms Tuesday afternoon and evening. A stalled frontal
boundary will result in unsettled weather for the middle and
latter portions of the week with temperatures remaining
seasonable for mid May.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
950 PM...No changes for the overnight, just pushed near term
grids closer to current obs, but look for showers after midnight
in NH and closer to daybreak in ME.

655 PM...Updates mostly based on current obs, but did try to
better time POPs through the evening at least. Current radar
trends show that showers moving into drier air and dissipating,
although whatever is falling at cloud level is probably not
reaching the ground, given the dry low levels. Most of hi res
models suggest nothing but a few sprinkles in NH this evening
with better organized SHRA moving in after midnight.

Previously...
High Impact Weather Potential: Minimal.

Pattern: A brief period of shortwave ridging has moved overhead
today ahead of low pressure and associated mid level trough centered
over James Bay. This low will continue to press eastward through the
near term forecast period...flattening the mid level ridging
overhead with warm advection/isentropic ascent increasing
across the area. Thus...forecast challenges will be on cloud and
shower trends as the column moistens in the presence of modest
support for ascent.

Through this Evening: Expect diurnal Cu field to diminish from the
coast into the foothills...but clouds advancing from the west will
keep skies at least partly cloudy through the evening with 7pm
temperatures falling back into the upper 50s to lower 60s.

Tonight: Isentropic ascent at the leading edge of a modest 850 LLJ
will push across the region tonight with PWATs increasing to around
1".  All of the current run HREF members include some shower
activity in this region of ascent with the strongest signal for
rainfall towards the Canadian border which will be closer to the
best mid level forcing.  Will draw likely PoPs in this area with
lower values to the south.  There will be some diminishing mid level
instability...so a rumble of thunder can/t completely be ruled out
overnight. Lows will fall into the 40s for much of the area in line
with consensus guidance and consistent with southerly flow off the
cool Gulf of Maine waters.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/...
High Impact Weather Potential: An isolated strong to severe
thunderstorm is possible across New Hampshire Tuesday afternoon.

Pattern: Low pressure north of our region will continue to push east
through the short term forecast period with a warm front crossing
the forecast area Tuesday with the trailing cold front sagging into
the region from the north Tuesday night. Forecast challenges center
around convective potential ahead of the surface cold front and
locally heavy rain within this convection as mid level flow looks to
line parallel to the front.

Tuesday: Warm front...draped across the forecast area at 12Z will
push north and east with T8s building above 10C and PWATs moving
towards 1.25" through the day. Upstream cold front doesn`t make much
progress towards the region during the day with best llevel
convergence focused to the north...but modest instability across the
southern half of New Hampshire is likely as summer-like warmth moves
into the region. Short term ensembles based probabilities
suggest that the greatest threat for afternoon convection will
be in the foothills and mountains given both forcing location as
well as cool onshore flow developing towards the coast.

While forcing well south of the cold front looks rather weak...any
convection that does fire has the potential to be robust with 30-
35kts of deep shear and the potential for MLCAPEs to push 750-1000
J/kg.  Thus...there/s a chance for an isolated severe storm over
NH...with southerly flow trajectory greatly limiting convective
potential as you move east into Maine.


T8s pushing above 10C should allow temperatures across southern NH
and far SW ME /away from the immediate coast/ to rise into the upper
70s to around 80...with more cloud cover to the north and more
marine influence to the east holding highs back in the 60s.

Tuesday Night: Any instability wanes as surface cold front sags into
the region overnight.  Thus...weakening shower activity is likely
with a few rumbles of thunder through the evening.  Overnight lows
will be warmer given our location in the warm sector...with 50s
throughout the CWA.  Given elevated dewpoints and some shower
activity expect patchy fog as well.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Overview...

A slow moving front stalls and washes out over the area on
Wednesday. At the same time, a slow moving cut off low pressure
system tracks through the Mid Atlantic and offshore from
Wednesday through Saturday before dissipating. Another slow
moving low pressure system will take a similar track south of
New England this weekend.

Details...

Overall the forecast over the last couple of days has trended
toward warmer and a longer duration of unsettled conditions. So
Wednesday and Thursday don`t look quite as wet as they had, but
Friday and Saturday now look to continue the chances for
showers.

Cut off low pressure systems are notoriously tricky for both
the models and forecasters to discern. With these being the
main drivers of our forecast this week, it`s worth noting that
further changes are likely as well in the coming days. The cold
front approaching from the north looks to be trending a little
slower, and not making as much southward progress. This allows
warmer temperatures for at least Wednesday and Thursday as the
marine air is delayed by at least a couple of days. At the same
time, the cut off low looks to be tracking more slowly. This
lessens the rainfall expected on Wednesday, but causes the
forecast to be quite similar for Wednesday through at least
Saturday with times of showers.

POPs are higher for Wednesday because it`s closer in time, but
at least scattered showers are expected Thursday through
Saturday as well. POPs on these days are likely to increase in
some spots as we get closer in time and certain areas become
more highlighted as seeing a better chance for rain. Overall,
the best chance for seeing the most frequent showers looks to be
across interior areas and the higher terrain. As for
temperatures, highs looks to generally warm into the 60s and 70s
each day, with the warmest readings found across western
locations, and generally cooler toward the coastline.

As we get into next weekend, the next system will be following
closely behind the first one. This likely increases chances for
showers further during the day on Saturday and Sunday. It also
looks to bring cooler temperatures, as easterly flow brings in
cooler and damp maritime air. As mentioned, this forecast has
been volatile over the last couple of days as the cut off low
regime continues. This weekend`s forecast is subject to change,
but that`s the way it looks to be trending at this point. Over
the last week or so, the trend has generally been toward warmer
and less wet conditions as we get closer in time, but it`s too
early to know at this point if that trend will continue this
weekend.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Short Term...

Summary: A warm front crossing the region tonight through early
Tuesday followed by a cold front Tuesday night will bring increased
chances for showers and possibly a thunderstorm with fog chances
increasing by Tuesday night.

Restrictions: Restrictions in showers...some fog and developing low
clouds are likely after midnight tonight outside of southern
NH...with MVFR/IFR possible before improving conditions for
Tuesday with AUG/RKD the slowest to improve during the
day...though showers and a few thunderstorms during the
afternoon may bring additional restrictions...again most likely
at LEB/HIE. Deteriorating conditions in low clouds and fog with
LIFR/IFR is likely Tuesday night.

Winds: Southeast winds 5-10kts /stronger along the shoreline/ are
will spread inland through the afternoon before diminishing
overnight.  Southerly winds will strengthen to 10-15kts for the day
on Tuesday before diminishing to 5kts or less Tuesday night.

LLWS: LLWS is not expected through Tuesday night.

Lightning: There is a very low potential for an isolated
thunderstorm overnight tonight with a greater chance for a
thunderstorm Tuesday afternoon and evening...particularly over New
Hampshire.

Long Term...Generally VFR conditions are expected more often
than not from Wednesday through Saturday, but periods of MVFR
conditions with showers are likely during this time period. By
next weekend, longer periods of MVFR to possibly IFR look likely
with more showers and some marine fog possible.

&&

.MARINE...
Short Term...Light winds are expected through early Tuesday
before strengthening southerly flow will bring building waves
with marginal SCA conditions possible by late Tuesday and
Tuesday night.

Long Term...A cold front stalls and dissipates across the
waters on Wednesday. A slow moving low pressure system tracks
south of the waters from Wednesday through Saturday. Seas begin
to build by Friday, with SCA conditions possible by late in the
week and this weekend.

&&

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

&&

$$

SYNOPSIS...Arnott
NEAR TERM...Arnott
SHORT TERM...Arnott/Cempa
LONG TERM...Clair
AVIATION...Arnott/Clair
MARINE...Arnott/Clair