067
FXUS61 KGYX 091947
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
347 PM EDT Tue Jul 9 2024

.SYNOPSIS...
High pressure offshore will maintain very warm and humid
conditions for much of the week. A stationary front wavering
over the Northeast will provide a focus for showers and storms
into this evening. A trough will approach from the west
Wednesday transporting remnant moisture from Beryl into the
region Wednesday into early Thursday. Thunderstorms are again
possible Friday as a stalled remains over the region. A few more
scattered showers and storms are expected over the weekend.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
A short wave rotating through Quebec will continue to spread modest
forcing for ascent atop a buoyant airmass over the forecast area.
This will continue the threat for convection through sunset.
Currently, MU CAPE has built to 2000+ J/kg with deep layer shear
around 40 to 50 kts. This will continue to support strong to
severe storms with mainly multi cell clusters posing a damaging
wind threat while a transient supercell or two will bring an
isolated hail threat. After rounds of broken cloud cover across
southern NH, the latest satellite shows partly to mostly sunny
skies here into SW Maine. While scattered strong to severe
storms will remain possible across much of the area through
sunset... portions of south-central NH into SW Maine are worth
highlighting for severe storms into this evening as recent CAM
runs show MU CAPE building in excess of 3000 J/kg. CAMs and
recent runs of the HRRR suggest convection will be pushing off
the coast around 8 PM with little to no shower or thunderstorm
activity anticipated thereafter tonight.

It will remain warm and very humid tonight with temperatures and
dewpoints in the upper 60s to low 70s from north to south. This
humid airmass will also likely lead to patchy fog across much of the
area tonight.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Weak high pressure will be over New England to start the day
Wednesday while an upper trough and the remnants of Tropical System
Beryl approach from the west. This system will draw an anomalous
plume of deep moisture into the area Wednesday through Wednesday
night. The remnant surface low will lift a warm front into the
region Wednesday morning into the afternoon providing a focus for
showers and thunderstorms. The surface low will then track towards
the St Lawrence Valley through Wednesday night for additional rounds
of showers and thunderstorms. As this system moves through the
Northeast the warm front will bring the potential for severe
thunderstorms late Wednesday morning into the evening across
southern NH and SW Maine and the deep moisture in place will bring
the risk for flooding across much of the interior where a Flood
Watch has been issued. For more details regarding the flood threat
please see the Hydrology Section below.

The 12Z CAM suite is in decent agreement that filtered sunshine
will allow the atmosphere to destabilize across central and
southern NH into SW Maine by late Wednesday morning. All the
while, a warm front lifting through the region will lead to
curved and elongated hodographs. CAMs suggest that storms could
initiate near the warm front by early afternoon with the 12Z
HREF highlighting south central NH into SW Maine where storms
could sustain strong rotating updrafts. SPC has placed much of
this area into a Marginal Risk with a Slight Risk over portions
of SW NH. The concern with these storm will be damaging winds
early Wednesday afternoon into the evening and curved hodographs
will also bring the risk for a tornado.

Cloud cover will help keep air temperatures lower than today
while it will still be very warm with highs in the mid to upper
80s. Dewpoints will remain oppressive in the low 70s bringing
heat indices into the low 90s with the potential for a Heat
Advisory needed near the lower Merrimack Valley. Given the
cloud cover forecast have held off on a Heat Advisory for this
package.

The threat for strong to severe storms will diminish into
Wednesday night while the heavy rain threat will continue across
the northern half of the area into Thursday morning. It will
remain warm and muggy with patchy fog likely.


&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
The remnants of Beryl exits the region Thursday morning, not before
potentially leaving additional heavy rainfall over northeastern
portions of our forecast area. PWAT values will continue to be
extremely high with deep tropical moisture still in place. Areas
river will still be on the rise during this period.

Surface dew points will be in the 70s across much of the region. It
will be on the very warm to hot side once again as at
least partial sunshine develops during the day.

Thereafter, 12Z operational models and ensemble solutions
suggest persistent warmth and humidity will continue throughout
the long range portion of the forecast. Short waves crossing through
the region will allow for scattered showers and thunderstorms most
days, especially during the afternoon hours and away from the
immediate shoreline. The exception may be on Sunday when some
ridging will occur aloft over the region.

Overnight fog may be problematic, especially over the coastal
waters with such high dew points over the Gulf of Maine. Have
included patchy fog most overnight and early morning periods.

A pattern change may occur next week as a trough enters southeastern
Canada. Cooler and drier air may reach New England during that
period.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Short Term...Scattered TS will continue to be a threat through
00Z this evening. Storms diminish after 00Z with VFR likely
prevailing for much of the night, although patchy fog cannot be
ruled out. KRKD and KAUG will have the greatest chance for
flight restrictions tonight in fog. VFR likely prevails for all
TAF sites Wednesday morning. Showers and thunderstorms develop
late morning into the afternoon and will bring the threat of
flight restrictions mainly along a line from KLEB to KCON to
KPWM and points northward into Wednesday night. Patchy fog will
bring the threat for flight restrictions across much of the
area.

Long Term...Mainly VFR during the daytime hours through much of
the extended. However, there will be some scattered shower and
thunderstorm activity especially during the afternoon and
evening hours leading to brief periods of IFR conditions. LIFR
and IFR conditions may occur during the nighttime periods.

&&

.MARINE...
Short Term...Steady southerly flow will prevail over the waters
through Wednesday while gusts remain at or below 20 kts. Seas
will also stay below SCA thresholds. Storms forming over the
land will have the potential to track into the waters this
evening before diminishing after sunset. Humid air over the
waters will continue the threat for marine fog tonight through
Wednesday night.

Long Term...A persistent southerly flow will continue over the
coastal waters through the period. However, for the most part
this will be below SCA levels. Patchy fog may be problematic
with the high levels of moisture over the region leading to low
visibilities at times.

&&

.HYDROLOGY...
Tropical-like downpours possible Wed-Wed night, Flood Watch in
effect. WPC has issued a rare Moderate Risk for the White
Mountains region of NH, with a slight risk for the remainder of
the CWA. Have left S ME and NH out of the watch based on dry
antecedent conditions and lesser risk of heavier rains.

The remnants of TD Beryl will interact with an incoming upper level
trough over the Great Lakes tonight. The low will track eastward
into New England, where it will pull tropical-like moisture into the
region on Wednesday. PWATs are likely to reach 2-2.25, which is 2-3
standard deviations above normal, and warm cloud depths 14.5-15k ft.
This will support the warm rain collision-coalescence process and
highly efficient rainfall rates. Discrete cells in the early
afternoon should be progressive enough to limit flooding, but there
is the possibility that training and backbuilding will occur. A
northward progressing warm front will stall/occlude by Wednesday
night, becoming the focus for backbuilding/training and the primary
flood risk area. The CAMs and mesoscale models favor a more
southern track with this boundary than the synoptic scale runs,
with the consensus being around the
Lakes/Mountains/international boundary regions. Current
antecedent conditions do not favor widespread flooding as soils
have the capacity to absorb the initial forecasted rainfall and
streamflows are low which is near normal for this time of year.
That being said, the rainfall rates are expected to be extreme
which will overwhelm ground infiltration initially, so rapid
runoff is a concern for all areas particularly in steep terrain.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch from Wednesday afternoon through late Wednesday
     night for MEZ007>009-012>014-020>022-033.
NH...Flood Watch from Wednesday afternoon through late Wednesday
     night for NHZ001>009.
     Heat Advisory until 8 PM EDT this evening for NHZ010-012-013.
MARINE...None.

&&

$$
NEAR/SHORT TERM...Schroeter
LONG TERM...Cannon
HYDROLOGY...Jamison