311
FXUS61 KGYX 051728
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
128 PM EDT Wed Jun 5 2024

.SYNOPSIS...
Scattered thunderstorms develop early this afternoon and will
bring an isolated heavy rain threat along with an isolated
strong to severe threat. A trough approaches from the west
Thursday bringing periods of widespread rainfall which also
pose an isolated flood risk. Unsettled conditions persist
through the weekend with daily chances of showers and an
isolated afternoon thunderstorms.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
130pm Update...Quick update to get PoPs on track with current
convection. Showers and storms have blossomed well, but do hit a
limiter when getting too high. 12z NAMnest seemed to handle
initiation well, and current coverage aligns well with its
forecast. This depicts rounds of showers and storms through the
afternoon for interior ME and central/northern NH. Southern NH
may see much of the activity remain to the north due to dry air
in the low levels. That said, budding cu in the region could
bring a few showers and rumbles of thunder through the
afternoon. Elevated instability remains this evening so could
see activity linger, but widespread convection seems to taper
around or after sunset.

1030am Update...Forecast is on track with just some changes to
temp trends. Some elevated showers have tried to get going
across NH through mid morning, but cap is still in play and
blocking any further development. This should erode over the
next hour or so across the area and will likely see scattered
showers initiate and deepen through the late morning and early
afternoon. Coverage is still an uncertain aspect as overnight
guidance was fairly conservative. On the other hand, model
soundings have trended more robust with CAPE, so can expect
boundaries, convergence, and neighboring storms to initiate
additional showers/storms. 12z GYX radiosonde confirmed weak
shear through 6km, and this imbalance could lead to storms that
pulse unless they get more rooted. Sometimes this can result in
occasional microbursts as storms build, lack tilting, and
abruptly collapse.


640 AM Update...Subtle waves in NW flow at 500 mb have triggered
areas of showers with embedded thunder across western and
southern NH with additional areas of showers and thunder
upstream over VT. HI res guidance has struggled to capture this
activity and have increased PoPs and sky cover based on these
observed trends.

Previously...

No significant changes in forecast thinking for today with
scattered thunderstorms likely to form over the mountains around
mid day and tracking southeast through the afternoon. The 00Z
KGYX sounding measured a PWAT of 1.04 inches with PWATs forecast
to increase to 1.25 to 1.5 inches this afternoon. The 00Z HREF
mean brings MU CAPE into the 1000-1500 J/kg range by late
morning with most members initializing storms over the mountains
and points northward around noon. Storm motion winds will be
relatively weak upon initialization, although recent guidance
shows slight uptick in storm motion around 2 pm helping to
reduce residence time of storms over a particular location.
Current 1-hour Flash Flood Guidance across areas most likely to
see storms is generally greater than 2 inches and 3-hour Flash
Flood Guidance is 2.5 to 4 inches. Given the slight uptick in
storm motion, and CAMs suggesting storms will track over areas
with the highest Flash Flood guidance, the main concern will be
areas that experience multiple cells tracking overhead. There
are some CAMs showing isolated areas downstream of the mountains
picking up over 2 inches today. WPC maintains a Marginal Risk
for excessive rainfall, which continues be reasonable given the
dry antecedent conditions and the isolated nature of the
heaviest rainfall.

The threat for strong to severe storms has slightly increased
although deep layer shear continue to look modest at best around 25
kts. The latest HREF does show the potential for a couple robust
updrafts along and south of the foothills with some enhanced
convergence along the sea breeze boundary. There have been a few
runs of the HRRR that shows outflow winds around 40 mph, and
increased shear associated with the sea breeze boundary could lead
to storms producing small hail. SPC has placed areas downstream of
the mountains in a Marginal Risk for severe storms, although this
threat looks to be isolated. Otherwise, it will be a warm day with a
notable uptick in humidity as dewpoints climb into the low 60s south
of mountains.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Instability will wane going into tonight, while an axis of elevated
instability will remain over western Maine keeping chances for
showers going through the first part of tonight. Plenty of low level
moisture and weak winds will likely lead to fog developing tonight,
particularly along the coastal plain of Maine into SE NH. Lows will
range from the 50s to the mid 60s across far southern NH.

Attention then turns to better forcing for ascent arriving
Thursday as a trough swings through the Great Lakes. This trough
with advect deep moisture into the region with PWATs climbing to
1.5-2 inches. A surface low will be tracking through the eastern
Great Lakes with a warm front will lifting into SW New England.
The placement and how far north this front gets Thursday
remains in question and will be important for both a focus of
moderate to heavy rain along the front Thursday morning and
whether it lifts far enough north for instability to build
Thursday afternoon. The 00Z CAM suite suggests this front will
struggle to lift north of NH/MA border leaving the best
instability south of the area. However, with the front near the
NH/MA there be a heavy rainfall threat in the vicinity. The
approaching trough will spread the best forcing for ascent into
the area late Thursday with a second round of rain and
thunderstorms across the area. WPC has placed the entire are in
a Marginal Risk for excessive rainfall given the high PWATs, and
multiple bouts of rain crossing the same areas.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Overview: We return to wetter weather as the 500 mb pattern
shows a ridge over the Atlantic blocking an upper low over the
Great Lakes through the extended period. This will result in
daily chances for rain showers as multiple waves rotate around
this low and over our region. Right off the bat we could see
some particularly heavy rain that may cause some localized
flooding.


Details:
Vertically stacked low pressure will continue to send fronts
through the region along with shortwaves rotating around the
upper low Friday into early next week. This will necessitate
shower chances through the remainder of the week and into early
next week, however not everyday will be a wash and some will be
drier than others. Temperatures look to remain pretty steady
with highs in the 70s and lows in the 50s each day. Can`t speak
much on exact details about the rain day to day at this time
range, but it is worth mentioning that return flow from the high
pressure offshore will keep an onshore component to the wind
for a majority of this period so PWAT values are looking to stay
up around an inch. It is also worth mentioning that the low
level pattern continues to show flow rarely exceeding 20 kts and
as we get into the weekend and early next week shower activity
will become more convective in nature as we see clearer skies
and warmer daytime temperatures. Isolated flooding will have to
remain in the backs of our minds as we continue through this
upcoming stretch of wetter weather.

&&

.AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
Short Term...SHRA and TSRA are possible late this morning into
afternoon. These will be focused over the mountains into the
coastal plain of Maine with KHIE and KAUG seeing the highest
likely hood of a TSRA, followed by KPWM, KRKD, and KPSM. For
the remaining TAF sites a SHRA or TSRA cannot be ruled out while
most recent guidance suggest this activity will stay to the
east. Patchy fog will be possible across much of the area
tonight along with low cigs near the coast bringing the
potential for IFR/LIFR. More widespread rain and isolated TSRA
are forecast for Thursday with flight restrictions likely
through the day.

Long Term...VFR looks to prevail through the rest of the week,
but isolated to scattered showers and thunderstorms will be
possible each afternoon. Winds remain 5-10 kts with gusts 10-15
kts through Sunday.

&&

.MARINE...
Short Term...Winds and seas remain below SCA thresholds today
through Thursday. Thunderstorms that form over the land have the
potential to track into the waters and could contain gusty
winds. Increased moisture will also bring patchy fog over the
waters tonight into Thursday morning. Low pressure approaching
from the west will bring steady onshore flow Thursday along with
periods of rain and patchy fog.

Long Term...Conditions hazardous to small craft are not expected
through Sunday. Showers and thunderstorms are possible each
afternoon this week. Winds are primarily onshore at 10-15 kts
through Sunday as high pressure remains over the atlantic and
low pressure remains inland.

&&

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

&&

$$


NEAR TERM...Cornwell/Schroeter
SHORT TERM...Schroeter
LONG TERM...Baron