845
FXUS61 KGYX 121329 AAA
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
929 AM EDT Fri Jul 12 2024

.SYNOPSIS...
Hot and humid conditions continue as a strong ridge remains
centered off the Eastern Seaboard. A stalled front lingers near
the coastline today. A weak area of low pressure south of New
England spreads more moisture into southern areas tonight and
tomorrow. Drier conditions can be expected Sunday with a weak
area of high pressure cresting over the region. Humidity
returns by early next week as the high moves offshore, and then
a stronger cold front has the potential to bring noticeably
drier air for late next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
9:30 AM Update: Going forecast in good shape this morning with
only very minor tweaks to latest temperatures/dewpoints. 12Z
GYX raob shows a substantial dry wedge in the H7-5 layer
which...with less surface-based instability today given slightly
lower surface-based moisture should keep any convection this
afternoon isolated and likely tied to the terrain. Heat indices
will reach towards 93-95F in our hottest locations of SE NH and
SW ME...and with this update do not see any changes warranting
the issuance of heat headlines.

6:35am Update... Refreshed temps through the morning as lows and
dew points managed to drop a few more degrees before sunrise.
Otherwise no notable changes with this update as the forecast
remains on track.

Previous...

Another hot and humid day is expected today as the ridge
continues to build off the Eastern Seaboard. The stalled front
lingering across the area has drifted to about the coastline,
and likely nudges just offshore this morning. This allows hotter
air to make it to the southern coasts on southwesterly flow,
with only the immediate coastline likely to see some moderation
off the ocean in the afternoon. The MidCoast remains cooler with
the southwesterly flow off the water. Away from the cooling
influence of the waters, heat indices rise to near 95 degrees
again today, but slightly lowering dew points into the upper 60s
should help heat indices to trend down slightly in the
afternoon.

Mainly dry conditions are expected for most of the day, but
some isolated pop up showers or a thunderstorm can`t be ruled
out, especially across the higher terrain. Then late in the day
and going into the evening a few showers may drift into far
southern New Hampshire as a weak area of low pressure moves
south of New England.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
A weak and disorganized area of low pressure down toward the
Carolinas spreads moisture up the East Coast tonight. This
brings an increasing chance of showers and some storms into New
Hampshire overnight, which continue moving into Maine tomorrow
morning. The bulk of the moisture is likely to pass to our
south, but enough could make it into southern New Hampshire and
coastal Maine to bring a period of heavier showers and storms
tomorrow morning.

With the lingering front serving as the main source for
forcing, a band of heavier rainfall is possible from this
system. It looks more likely to set up over Massachusetts, but
it could reach into the Seacoast and will need to watched
closely. With no strong or well defined forcing mechanisms or
features, it`s difficult to try to pin down where the heavier
rainfall will be at this point, but the best chance looks to be
across southern and coastal areas.

The bulk of this precip moves out by the early afternoon, and
then a line of showers and storms is likely to develop as a weak
cold front sinks through during the mid to late afternoon
hours, likely reaching the coast toward sunset. This round of
showers would be more brief and well defined, with a noticeable
dry spell between the two features during the afternoon hours.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
High Impact Weather Potential: Locally heavy rainfall potential
for southern NH/ME on Saturday. Beyond this...confidence is too
low to determine a particular day for a high impact weather
threat. However...a strong cold frontal passage is possible by
Wednesday/Thursday which would likely be the next potential for
more than isolated convection/heavy rainfall. Heat will continue
throughout the period with the greatest potential for advisory
level heat indices being Monday/Tuesday over southern NH and far
SW ME.

--Pattern and Summary--

Impressive 600 dam H5 ridge centered over the northwest
Atlantic which has been a driver for the extended period of heat
/some spots now reaching one week of days with highs at or
above 90F/. A shortwave moves across the region to open the
period Saturday... flattening the ridge somewhat. Next week...a
longwave trough will make it/s way across central
NOAM...eventually arriving in our area by the end of the week.
The flow ahead of this feature will allow a continuation of
hot/humid conditions as the flow turns WSW. The trough pushes
slowly towards the region by the end of the forecast
period...which should usher in drier/cooler conditions by the
end of next week. There are differences between the various
global deterministic/ensemble solutions at this range
particularly on the timing of this feature. In terms of
impactful weather...a coastal wave combined with the northern
stream shortwave mentioned above will bring precipitation
chances to open the period Saturday...with additional
precipitation likely by the middle/latter portions of next week
ahead of the arriving trough.

--Daily Details--

Saturday: A unique scenario to open the period as well
advertised oceanic upper low brushes by the area as shortwave in
the northern stream flow moves just north of the region. 2"
PWAT airmass will be available for these two waves to work with
and there are substantial probabilities for at least some
precipitation south of the mountains and will follow NBM
consensus blend which includes likely PoPs. Heavy rainfall
potential is there given the deep moisture as well as
unidirectional wind profiles with both shortwaves moving
generally parallel to the orientation of any bands of showers.
Certainly worth watching this period for excessive rainfall
potential.

Sunday - Tuesday: Back to the hot temperatures for Sunday
through Tuesday humidity first decreasing some on Sunday...then
returning to the area on Monday/Tuesday. Sunday should be storm-
free with weak shortwave ridging...but shower/storm chances
return for Monday and Tuesday as weak waves in the westerly flow
aloft move through the region. With temps aloft and boundary
layer moisture building... heat headlines look likely for Monday
and Tuesday...especially for southeast NH and far southwest ME.


Wednesday - Thursday: A more substantial cold front crosses the
region to end the long term forecast period with differences in
timing requiring chance PoPs for both days. Depending on this
timing...may need heat headlines again on Wednesday...with
robust flow aloft suggesting a severe threat if we align the
timing of the frontal passage with daytime heating. In all
likelihood... temperatures will cool by Thursday dropping close
to seasonal norms /70s north...80s south/.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
Short Term...Any lingering fog clears by mid morning, then VFR
conditions return to all terminals. Restrictions are likely
tonight as increasing moisture brings patchy fog and scattered
showers, with MVFR to IFR conditions likely. Showers linger
through the morning, then a period of VFR is likely tomorrow
before one last line of showers moves through in the late
afternoon. Patchy fog would be possible with IFR again Saturday
night.

Long Term...VFR conditions return on Sunday. Shower/storm
chances increase for Monday- Tuesday afternoons with will likely
bring scattered restrictions as well as overnight valley
haze/fog development.

&&

.MARINE...
Short Term...SCA conditions continue into this evening in
ongoing southwesterly flow across the waters. Locally dense fog
lingers through tomorrow at times. A stalled front near the
coast lifts north tonight, allowing winds to ease overnight. A
weak area of low pressure passes south of the waters tomorrow.

Long Term...Winds and waves are expected to remain below SCA
thresholds in the Saturday-Tuesday period. Low level moisture
may allow for the development of fog on Saturday...and again
Monday-Tuesday.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ150-152-
     154.

&&

$$


NEAR TERM UPDATE...Arnott