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000
FXUS61 KGYX 110819
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
419 AM EDT Thu Apr 11 2024

.SYNOPSIS...
Rounds of rainfall punctuated by bouts of drizzle and fog will
continue today and tonight, before a cold front crosses Friday
bringing widespread soaking rainfall to the area. This rainfall
combined with significant snowpack loss and saturated grounds
will likely lead to minor or moderate flooding across the
mountains, with minor poor-drainage flooding possible elsewhere.
The front will also bring increasing south- southeasterly
winds, which may turn strong and gusty along the coast around
mid- day Friday. Winds remain gusty heading into the weekend
with scattered showers.

&&

.NEAR TERM /TODAY/...
Dreary weather on tap today as onshore flow off the Gulf of
Maine reinforces humid surface conditions and southwesterly flow
aloft reinforces the same through the remainder of the column.
The result is a rainy, drizzly day with temperatures remaining
in the 40s for the bulk of the area... except where flow is more
sheltered from that onshore component, likely in the Connecticut
River Valley and into the Merrimack where temperatures in the
50s and more likely.

The upper level configuration this morning features an upper
level ridge building up along the Eastern Seaboard, with low
pressure deepening over the Mississippi Valley. This see-saw
brings bands of warm frontal forcing SSW to NNE through New
England, keeping rain chances through the day today. Overall not
expecting this overrunning type of precipitation to be too
terribly efficient dynamically, however the deep warm cloud
depth and increasing PWATs to around 1" will still produce
decent rainfall rates even without a convective component.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
By this evening, low pressure over the Ohio Valley will be
intensifying, moving north into the Great Lakes as the southern
stream system comes into phase with a northern stream trough. At
the same time, an upper level ridge axis will be shifting east
offshore... allowing an atmospheric river associated with the
southern stream to pull north along the Eastern Seaboard and
into New England. This moisture axis and its associated LLJ are
the main feature as they cross tonight and Friday in terms of
weather impacts. With PWATs progged to reach 1.1-1.4" across the
area, the right timing of the moisture may set a PWAT record
for the Apr 12 12Z KGYX raob.

Overall, not a lot of change to the forecast thinking with this
round of model guidance. South-southeasterly flow with the LLJ,
with all of its warm cloud depth and moisture, will deliver a
widespread soaking rainfall of 0.5-1.5" to the area with any
amount of mesoscale forcing eking out higher totals. This is
most likely where orographic lift is maximized, placing a QPF
bullseye from the Whites across through the Western Maine
Mountains / Spine of Appalachia where HREF guidance suggests a
few 3+" amounts are likely. A secondary maximum appears to be
showing through the Camden Hills as well. How this translates
into impacts is detailed below in the dedicated Hydrology
section. For timing, am expecting heaviest rainfall to enter
from the southwest late this evening... spreading eastward
overnight and through Friday morning. The moisture axis exits
Downeast during the afternoon, however upper level troughing
will continue to support scattered showers through the remainder
of the day.

Aside from the heavy rainfall threat, there is some concern WRT
winds associated with the LLJ. Although it is a fairly strong
jet, there area a couple key factors that color me a bit
dubious for a strong/damaging wind threat. First, we are
building a classic CAD right now with cool, stable maritime air
socking into place across the interior as temperatures aloft
continue to warm...producing a strong LL temperature inversion
that would take very heavy rain to momentum-transfer down
through. Second, the 80 kt core of the jet is modeled to be
fairly elevated... at around 2500 kft, and with 40 kt winds only
getting down to around 1000 kft or so... still separated by the
inversion. The best chance for winds associated with the jet
will be along the Midcoast, where a few 40-50 mph gusts are
possible thanks to the PGF however I`m a bit skeptical across
the interior, especially west of I95. More widespread gusts are
likely with better mixing in the wake of the LLJ, up to around
25-35 mph in most places... developing first in the west and
spreading east into Maine through the day.

&&

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

An upper level low swings through on Saturday, with a cold
front passing through late in the day. Drier and warmer
conditions return late this weekend and early next week as a
ridge builds into the Northeast. A cool down it then possible by
midweek next week as a back door cold front approaches from the
Canadian Maritimes.

Details...

The upper level low associated with the ongoing system moves
through New England on Saturday. This brings increasing shower
activity by the afternoon hours on Saturday, especially across
the mountains. The most significant rainfall will have already
fallen by Friday, so any lingering showers would only serve to
slow the receding rivers progress. Chances for showers are lower
toward the coast, but a mainly cloudy and cool day is still
expected. The cold front associated with this system pushes
through late in the afternoon, finally bringing a return to
drier conditions.

Drier and warmer conditions are expected on Sunday as a ridge
builds into the Great Lakes and Northeast. Temps warm into the
60s in many spots with mainly sunny skies. Conditions warm
further into Monday and Tuesday, with some low 70s likely across
parts of southern New Hampshire.

While the ridge will continue to build and bring warm
conditions to much of the Northeast, high pressure builds into
the Canadian Maritimes and likely serves as a spoiler to the
warmth in New England by midweek with a backdoor cold front
moving into the region. Models had been back and forth on this
feature, but over the last few runs more and more ensembles
members continue to trend toward the cooler solution.

The high likely pushes the backdoor front in either Wednesday
or Thursday. Temperatures have started to be trended downward
with this forecast, but remain between the cool and warm
solutions. So while 50s are currently forecast, the reality is
likely to be that highs will either be in the 40s or 60s. So
while still avoiding too much of a jump in one direction with
this forecast, the trend looks to be toward the cooler side at
this point by midweek next week.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
Short Term...Widespread IFR/LIFR in low CIGs south of the
mountains this morning continues through today and tonight with
periodic drops in VSBY due to RA and BR. Steadier RA develops
tonight into tomorrow, with increasing SE flow especially along
the coast. Strongest winds of 30-40 kts along the coast are
expected during the day Friday, coinciding with the passing of a
LLJ which will also likely produce SSE LLWS across at least
southern terminals and possibly all terminals. CIGs see some
improvement from west to east later Friday, with 20-30 kt winds
out of the south behind the heaviest rain.

Long Term...Lingering MVFR to at times IFR is likely in showers
on Saturday, especially at LEB and HIE. VFR then returns
Saturday night, and persists through early next week. Gusty west
winds to 30kts are possible at all terminals Saturday night and
into Sunday. Some low clouds are then possible along the coast
by midweek next week, with ceiling restrictions possible.

&&

.MARINE...
Short Term...Steadily strengthening gradient flow today through
tonight culminates in the passing of a front on Friday with
southeasterly gales expected. Seas follow a similar trend, with
10-15 ft seas gradually developing by Friday. This humid flow
over the waters is likely to produce fog and drizzle, embedded
amongst rounds of rain.

Long Term...Southwesterly winds shift to near gale westerly
winds behind a passing cold front late Saturday. SCA conditions
linger through the weekend as high pressure builds across the
waters. Fair conditions are then expected for early next week.

&&

.HYDROLOGY...
A Flood Watch remains in effect for the snow covered portions of
Western Maine and Northern New Hampshire with no changes this
morning.

Repeated rounds of rain today into tonight will act to
compress, warm, and ripen snowpack, but the heavier rain Friday
morning and afternoon will be the catalyst for flooding. The
combination of rain, strengthening winds, and high dew points
in excess of 50F over the isothermal snowpack will lead to rapid
melt with expectations up to 4” SWE loss. Complete melt-out
below 2,000 ft is likely, particularly on S/SE facing slopes.

The greatest flood risk will be focused Friday morning as
moderate to heavy rainfall pushes through ahead of a cold front.
The current QPF forecast is for 1 to 2 inches in the mountains
through today and Friday, less on the north facing slopes.
However, the PWATs are 2-3 SD above normal, and with a moisture
feed from the Gulf we should be prepared for locally higher
amounts around 3 inches. Melt combined with saturated antecedent
conditions sets up ideal conditions for potential flash
flooding and moderate river flooding in the Upper Merrimack
(Pemi), Saco, Androscoggin, and Kennebec basins. Small streams
draining in the steep terrain could experience flash flooding.
This melt will route downstream, causing potential flooding
impacts on low elevation rivers as well. Outside of the snow
covered areas, locally heavy rainfall may elicit poor drainage
and nuisance flooding in urban areas, especially if heavier
rainfall totals materialize.

&&

.TIDES/COASTAL FLOODING...
Very high astronomical tides will continue tonight with the
tide in Portland at 11.4` (MLLW). A southeasterly flow off the
Gulf of Maine will allow for a modest storm surge tonight, will
allow Portland to reach its 12 foot flood stage. Hampton should
come in around its 11 foot flood stage as well.

High astronomical tides will continue through the end of this
week, albeit, lowering with time. Future coastal flooding this
week will rely on whether or not significant storm systems will
line up with the higher of the high tide cycle which currently
is the overnight hours this week.

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch from late Thursday night through Friday
afternoon for MEZ007>009-012>014.
Coastal Flood Advisory from midnight tonight to 3 AM EDT
Thursday for MEZ023-024.
NH...Flood Watch from late Thursday night through Friday
afternoon for NHZ001>005.
Coastal Flood Advisory from midnight tonight to 3 AM EDT
Thursday for NHZ014.
MARINE...Gale Warning from 5 AM to 11 PM EDT Friday for
ANZ150>154.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch from late tonight through Friday afternoon for
     MEZ007>009-012>014.
NH...Flood Watch from late tonight through Friday afternoon for
     NHZ001>005.
MARINE...Gale Warning from 5 AM to 11 PM EDT Friday for ANZ150>154.

&&

$$

NEAR TERM...Casey
SHORT TERM...Casey
LONG TERM...Clair