357
FXUS61 KGYX 292342
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
742 PM EDT Sat Jun 29 2024

.SYNOPSIS...
A warm front will bring a period of rain with a few embedded
thunderstorms to the region tonight before a potent cold front
arrives Sunday afternoon bringing the potential for strong to
severe thunderstorms. High pressure arrives early next week
with dry weather and seasonable temperatures expected for the
first half of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
730 PM Update...Little change to the going forecast for the
evening as as back edge to steadiest rainfall moving out.
However, convective showers and islolated thunderstormns
currently over Upstate NY will likely move ino western zones in
a few hours. Otherwise, cloudy and breezy.

High Impact Weather Potential: A few downpours are possible
overnight as well as an isolated thunderstorm though the threat
for widespread flooding and severe weather is low.

Pattern: Early afternoon water vapor imagery shows a potent
shortwave dropping through the western Great Lakes with a plume
of mid level moisture pushing into the northeastern United
States. Beneath this plume...a warm front is slowly advancing
through NY/PA with a broad region of light to moderate rain fueled
by increasing moisture and a 50kt southwesterly LLJ. Forecast
concerns for tonight center on rainfall potential as the surface
warm front lifts through the region.

Through this evening: Rain is overspreading the region from west to
east and this will continue through the evening hours with clouds
lowering.  SE NH may escape meaningful rainfall through 8pm...but
elsewhere conditions will turn wet. Temperatures won/t really move
much...largely sitting in the 60s across the area.

Tonight: Warm front lifts north and east through the region tonight
with 2" PWAT plume overhead this evening gradually shifting east of
the area by daybreak Sunday. While isentropic ascent up the frontal
surface in the presence of some weak elevated instability will be
sufficient to support rainfall...broader scale forcing appears
rather lackluster through the overnight with +DPVA mostly
brushing the international boarder with some weak height falls
overhead and some jet entrance support. Overall this suggests
occasional showers through the overnight...with the greatest
threat for a few downpours being over the mountains where the
synoptic scale forcing is best. From a hazard perspective...the
threat for flooding appears rather low...but nonzero given the
deep moisture/warm cloud depths. A mild night is in store given
continued warm air advection with lows falling into the mid 50s
in the mountains with 60s to the south.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
High Impact Weather Potential:
   *  Slight Risk of Severe Thunderstorms
   *  Primary threat: Damaging Wind
   *  Secondary threats: Localized flooding...hail and an
      isolated tornado
   *  Timing: 12pm-7pm

Pattern: Low pressure north of northern New England will move
north and east during the day with a cold front over western New
York as a positively-tilted shortwave and region of mid level
height falls pushes just north of the region through the day.
Our forecast focus will be on severe convective potential as the
surface cold front crosses the area Sunday afternoon. Also
watching heat indices across southern NH which may make a run at
advisory thresholds ahead of the front.

Sunday: Shortwave rotating through the positively-tilted longwave
trough races just north of the region through the day with 70kt H5
speed max moving overhead in tandem with right entrance region to
120kt upper level jet.  Should see some sun in the morning as we
move into the warm sector ahead of the cold front but
convection may already be ongoing across western New
York...strengthening as downstream instability strengthens. By
early afternoon convection will likely reach the mountains of NH
as well as the CT Valley with the mesoscale guidance favoring
the potential for one line of storms closer to the beset mid
level forcing moving from northern NH ESE through the Capitol
region of ME with another line moving across southern NH where
the best instability will be located and will be downstream of
the most likely location for morning convection.

Here/s a run through the convective parameters....

Instability: Sizable disparity in the guidance here with the
NAM nest and the HRRR in their typical wetter/drier
camps...respectively. Looking at upstream llevel moisture...a
compromise is likely best which favors 1500 J/kg of MLCAPE in
southeast of the mountains as surface dewpoints push just above
70.

Shear:  40kts in the 0-3km layer with 60kts in the 0-6km layer.
Hodographs are fairly straight and parallel to the approaching
frontal boundary. Expect initial cells to grow into lines with
bowing segments likely given ample 0-3km shear.  Within these bows
would be the best potential for a spin up.

Lapse rates: Decent in the H8-7 layer, but weaker /around 6C/ in the
H7-5 layer. Sufficient to support deep convection through the
afternoon.

Overall...this lines up well with the SPC outlook for damaging winds
posing our greatest severe weather risk with hail and an isolated
tornado lesser...but non-zero threats.

T8s pushing to +18C should allow highs to reach near the 90F mark
given sufficient sun.  This...in addition to dewpoints moving above
70 will allow a few spots in southern NH/SW ME to approach heat
advisory levels...but not high enough or long enough to warrant any
headline issuance today.

Sunday Night: With the surface cold front near the coast to begin
the period...expect any convection to quickly be exiting the region
with mesoscale guidance suggesting a few showers along a secondary
trough/cold front that crosses the region overnight.  Best potential
for these overnight will be in the mountains with at least partial
clearing elsewhere. Cold air advection will push T8s back into the
upper single digits by daybreak Monday with lows to fall into the
50s in the mountains and lower 60s elsewhere.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
At 500 MB across NOAM and environs we still a pattern that
gradually favors warmer and more humid conditions, although
nothing that I would call hot through next week. We will near
the boundary of the sub-tropical over the Atlantic and the jest
stream to our N, so we can expect some rounds of SHRA/TSRA, but
no significant widespread events.

However, on Monday we will start off less warm, but still not
out of ordinary summer temp ranges. There is a little
convergence in central and S NH as NE flow runs into a bot of
dead flow over S New England, so will see more clouds here, and
maybe a couple showers Monday afternoon, but I think this area
Is still partly sunny, with mostly sunny skies to the N and E.
Highs will mostly be in the 70s.

Monday night will be the coolest of the stretch with clearing
skies and light winds. Expect lows in the upper 40s in some mtns
pots and generally low to mid 50s elsewhere. Tuesday looks
mainly sunny and dry with low humidity, as high pressure crosses
the region, and highs 80-85, but cooler along the mid-coast.
Flow shifts SW as the sfc high shifts offshore, and the
resultant return flow will bring in more humid conditions.
Wednesday looks mainly dry though, but with partly sunny skies
and highs 80-85 once again.

A weakening cold front moves in from the NW Wed night, and
loses its steam over the CWA, so some SHRA and maybe some TSRA
are possible Tue night into early Thursday, but expect clearing
skies and warm and humid conditions on Thursday.

Weak high pressure moves in for Friday, so its be dry, but
still warm and humid. Next weekend remains uncertain as we sit
beneath weakly anticyclonic flow and troughing to our W, which
the means the potential waves and rounds of convection, but it
should stay on the warm and humid side.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Short Term...

Summary: Deteriorating conditions expected through tonight as a warm
front crosses the region with showers and a few embedded
thunderstorms.  Showers end Sunday morning...with another round of
showers and strong to severe thunderstorms in the afternoon before
partial clearing Sunday night.

Restrictions: MVFR CIGS are building across the terminals this
afternoon as showers arrive from the west.  Expect deterioration to
IFR or low MVFR this evening and overnight with low CIGS and
some fog development. Improvement to VFR is expected on Sunday
morning with showers/thunderstorms bringing additional
restrictions in the afternoon. Some fog development is possible
HIE/LEB Sunday night with restrictions possible here.

Winds: Southerly winds 10kts will continue through tonight before
shifting southwest and increasing to 12g18kts for the day Sunday.
Winds turn northwest less than 10kts behind the cold front Sunday
night.

LLWS: Southwesterly winds in the 1.5-2kft layer strengthen to 40-
50kts with LLWS expected overnight tonight.  This will end Sunday
morning with no additional LLWS through Sunday night.

Lightning: Very isolated thunderstorms are possible for the
overnight.  On Sunday...chances for thunderstorms increase for the
afternoon with the potential for thunder throughout the terminals in
the 18Z-00Z timeframe. Some of these storms could be strong to
severe with damaging winds. No lightning is expected Sunday
night.

Long Term...VFR expected Monday through Wed, with possible
valley fog Monday night. Then more widespread flight
restrictions possible Wed night into early Thu in SHRA/TSRA and
some fog.

&&

.MARINE...
Short Term...SCA conditions due to both winds and waves are
expected to continue through Sunday ahead of an approaching cold
front. Winds shift slowly shift northwesterly and diminish
Sunday night...though residual SCA waves will likely persist
through the first half of the night.

Long Term...Generally light flow is expected through the middle
of the week with winds and seas staying below SCA levels, but it
could pick up some Wed night or Thu.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 11 PM EDT Sunday for ANZ150>154.

&&

$$

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