829
FXUS61 KGYX 151424
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1024 AM EDT Thu Aug 15 2024

.SYNOPSIS...
Strong thunderstorms are expected this afternoon. The greatest
threat will be across most of New Hampshire and adjacent western
Maine. Showers will be less widespread Friday, sticking mainly
in the mountains. This weekend the rain chances will become more
organized and possibly linger into early next week. Hurricane
Ernesto passes offshore late this weekend and Monday, bringing
an increasing swell and dangerous rip currents by Saturday
through midweek next week.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...
10:20 AM Update...Some upper-level jet divergence and steep
lapse rates coinciding with an upper-level low are continuing to
prolong thunderstorms in central Maine. Instability will
increase through the day as we continue to destabilize.

As for this afternoon, the Storm Prediction Center has placed NH and
a lot of western ME in a Marginal Risk for Severe Storms. Setup
looks to be similar to yesterday`s with an upper-level low
forming an east to west jet streak over the Canadian Maritimes.
This jet streak has shifted west over the past 12-24 hours,
shifting the right exit region of this jet streak farther to the
west. This means that storms this afternoon will also develop
farther to the west, most likely across central New Hampshire. Storms
will likely move southward through the evening, with a few
strong gusty winds and quarter-size hail possible.


Update...Convection continues to percolate this morning in
an area of jet divergence. I have updated PoP to continue this
slowly backing southwest thru the morning...though I could see
the need for additional updates...especially as we start to heat
up.

Previous discussion...Steep lapse rates persist along the
western periphery of an upper low pinwheeling over the Canadian
Maritimes. Thunderstorms have been percolating along that
gradient thru much of the night. Models have had a poor handle
on these storms...but as we head into the diurnal min for
convection we should see these continue to slowly diminish.

However with daytime heating and another S/WV trof moving thru
the flow...the afternoon with feature another increase in the
coverage of showers and storms. Much like yesterday steep lapse
rates around 7 C/km will support ample CAPE for storms. Shear
will remain light...but today looks to be a little higher than
yesterday. As a result the threat of severe weather is just a
little bit higher. I have included gusty winds and small
hail...roughly corresponding with SPC marginal risk area.
Storms should be pulse type...with collapsing cores and merging
cold pools leading to gusty winds later in the life cycles.

Finally near surface smoke looks similar to yesterday as well.
There is some suggestion from the HRRR that concentrations of
near surface smoke increase mainly across southern NH during the
afternoon. I have added haze to those areas using the latest
smoke model forecast.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH 6 PM FRIDAY/...
After showers and storms dissipate tonight areas of fog and
stratus will develop. It looks most likely around Penobscot
Bay...but will be a threat all along the western ME coast.

Fri will be another day with afternoon showers and storms...but
this time coverage looks to be more widely scattered to
isolated. In addition they look to remain confined mainly to the
higher terrain into the CT River Valley.

&&

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

A series of troughs affect New England this weekend and into
early next week. Generally cool and showery conditions are
expected, with some brighter periods in between. Hurricane
Ernesto passes offshore late this weekend and early next week,
bringing building surf and increasing rip currents.

Details...

By Saturday, the ridge passes and a trough begins to deepen
through the Great Lakes, with low pressure developing across the
Great Lakes as well. The low is very slow to make any eastward
progress over the following few days as the ridge stalls and
builds across Atlantic Canada through the weekend. With this
pattern, showers and scattered thunderstorms likely begin to
move into western areas late in the day Saturday, and make slow
progress eastward overnight Saturday. The progress mostly stalls
by Sunday, with western areas seeing a greater chance for
showers than eastern areas. There remains some question as to
just how far east it will progress, but at this point the coast
stands the best chance to see the driest conditions.

By Monday, a shortwave dives in and deepens the trough, while
also causing it to become more amplified and help the pattern
begin moving along again. With this, the greatest chance for
rain and showers in the forecast arrive late Monday as the low
progresses east. The trough continues to transit through on
Tuesday and possibly into Wednesday, keeping the chance for
scattered showers around.

While all this is going on, Hurricane Ernesto is expected to
pass near Bermuda on Saturday, and making it`s closest pass to
Nova Scotia on Monday. Ernesto helps to amplify the ridge
across Atlantic Canada, aiding in the slow down of the trough
progression, while also bringing it`s own effects. Building surf
and increasing rip currents remain the biggest concerns from
Ernesto, with a southeasterly swell building by Saturday. The
swell builds through Monday, and then will be slow to subside
through Wednesday. Rip currents become increasingly more
dangerous by Sunday, and continue through at least Tuesday. High
astronomical tides are also occuring early next week, so some
splashover is also possible. The track is favorable overall for
a long duration swell event, with the storm tracking mostly
northward for two days around Bermuda.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
Short Term...VFR conditions start day after fog lifts...and
then SHRA/TSRA develop. This will mainly occur over the western
half of the forecast area with local MVFR or lower conditions.
Some of those storms may be strong/severe and hail and gusty
winds are a threat. Fog/stratus is possible again
tonight...especially across western ME coastline.

Long Term...VFR conditions prevail more often than not Saturday
through early next week, but periods of MVFR ceilings and
showers are likely at times through early next week, especially
across interior terminals during the afternoon and evening.
Nighttime valley fog is also likely at LEB and HIE each night.

&&

.MARINE...
Short Term...Winds and seas will remain below SCA thresholds.
Sea breezes are expected each afternoon. Increasing humidity
will also introduce the threat of marine fog and stratus. This
morning convective outflow is disrupting the formation of that
fog...and this is possible again tonight.

Long Term...Weak pressure patterns prevail as broad high
pressure builds across Atlantic Canada into this weekend.
Hurricane Ernesto passes east of the Gulf of Maine late this
weekend and early next week, bringing an increasing
southeasterly swell starting on Saturday. The swell builds to
greater than 5ft by Sunday, and continues through midweek next
week.

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...Clair/Palmer
SHORT TERM...Legro
LONG TERM...
AVIATION...
MARINE...