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000
FXUS61 KGYX 110329 AAB
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1129 PM EDT Wed Apr 10 2024

.SYNOPSIS...
A series of waves will cross the region through the end of the
work week with increasing humidity, cloud cover, and showers
escalating to widespread rainfall. While some places will be
mild and humid, others toward the Gulf of Maine are likely to
remain cool and humid with onshore flow. In any case, a ripening
and melting snowpack combined with rain will lead to river and
stream rises, with a chance for minor flooding. A passing cold
front on Friday will introduce gusty winds, potentially strong
along the coast. Winds remain gusty heading into the weekend
with scattered showers.

&&

.NEAR TERM /UNTIL 7 AM THURSDAY MORNING/...
Update...Rain largely moving out of the area at this hour and I
have adjusted PoP accordingly. We will maintain WAA over the low
level cold dome...and this should result in drizzle breaking out
over time tonight. At this time this is mainly closer to the
mtns...or very near the coast...but I think expansion is likely
as the night goes on. I will continue to show a elevation
assisted pattern to the drizzle coverage.

Previous discussion...Little change expected in the near term
portion of the forecast. Latest radar imagery this afternoon
continues to indicate showers advancing into our forecast area
from southwest to northeast. The back edge as of 18Z was over
northeastern Pennsylvania. This coverage is more robust than the
latest HRRR solution.

In any case, showers will be predominantly confined to southern
portions of the forecast area overnight as the precipitation slides
south. There will be some patchy drizzle and fog overnight with a
raw southeast wind coming in off the Gulf of Maine. Overnight low
temperatures will be fairly uniform tonight, ranging from the upper
30s in the north to the lower 40s in the south.

&&

.SHORT TERM /7 AM THURSDAY MORNING THROUGH FRIDAY/...
On Thursday, a backdoor cold front will begin to turn northward
as a warm front. While the day will start out with relatively
low pops, the chance for showers will increase during the day as
a moist southerly gradient increases over the region as low
pressure tracks well to our west. Patchy drizzle and fog can be
expected once again with winds off the Gulf of Maine and plenty
of low level moisture in place. Afternoon high temperatures will
reach the 50s over southern New Hampshire and the Connecticut
River Valley with chilly 40s elsewhere.

A moist low level jet will enter the region Thursday night.
Scattered showers with patchy drizzle will switch to an all out
steady moderate rain over the region. Patchy fog will continue
during this period with temperatures bottoming out in the 40s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
High Impact Weather Potential:

* Minor river flooding likely on Friday with overland flooding
  possible as well.
* Strong southerly winds will near advisory levels along the coast
  Friday.  Gusty west winds continue into Saturday but not likely to
  necessitate headlines.

--Pattern and Summary--

+NAO will allow for a progressive pattern across North America
through the long term forecast period. A longwave trough across the
central portion of the CONUS today will deepen as it pushes east
into the eastern United States Friday/Saturday with heights slowly
building in its wake by Sunday into early next week as west-
northwest flow remains over the region.  Beyond this...troughing
over the southwestern United States will eject north and east with
building downstream heights and the potential arrival of shortwave
energy over the northeastern United States by the end of this
forecast period Wednesday.  The most impactful weather of the period
looks to be as the period opens on Friday as rainfall and snowmelt
combine for a flood threat.  A gradual moderating trend is expected
through the long term with high temperatures below normal for
Friday...warming to a bit above normal by the middle of next week.

--Daily Details--

Friday:  Deep southerly flow continues through the day ahead of low
pressure over the Great Lakes with a 1.5" PWAT plume overhead but
rapidly pushing east ahead of triple point & associated surface cold
front. Best forcing for ascent will be early in the day until
frontal passage...with afternoon precipitation becoming showery in
the moist...cyclonic post-frontal flow.  The high PWAT airmass and
good mid level forcing should allow for moderate rainfall rates
through the morning...which will bring our greatest potential for
overland flooding.  See hydro section below for more details on the
flood potential.

Winds:  Southerly winds at H9 reach 75-80kts with warm advection
scenario allowing for only pretty shallow mixing.  This suggests a
35-40kt gust potential along the coast which nears our wind advisory
criteria. The flow trajectory suggests some downslope potential
across far northern NH and western ME as well.  Mid morning-mid
afternoon appears to be the best potential for the strongest gusts.

Temperatures:  Temps at H8 will be at or above 10C to start the
day...settling back to +3-5C by late afternoon in the post frontal
airmass. Highs will be determined mostly by mixing and any breaks in
the clouds which appear most likely across southern NH.
Here...expect highs to push into the middle 60s...with 50s to the
north and east of this...and coastal communities likely stuck no
higher than about 50 given the onshore flow.

Saturday/Sunday: Cold advection continues Friday night into
Saturday with the longwave trough axis overhead.  Moist...cyclonic
flow and decent lapse rates below H7 suggest showery conditions to
continue on Saturday with precipitation increasingly taking the form
of snow in the mountains. The airmass dries significantly pushing
into Sunday which will allow for a drier...and somewhat warmer
day...particularly south of the mountains where highs may near 60F
as T9s rebound above +7C. We/ll have to watch a northern stream wave
that the model consensus pushes just south of our area Sunday
evening/Sunday night which may prolong the unsettled weather.

Monday/Tuesday: A weak high pressure ridge axis arrives for the
beginning of the week...which combined with a dry airmass /PWATS
around 0.25"/ should allow for a quiet start to the week with some
questions on how much temperatures moderate as the GFS/GEFS
advertises a bit more of a northerly component to the low and mid
level flow the the ECMWF/EC-EPS more northwesterly.  Will follow
temperatures above seasonal norms...with 50s in the mountains and
60s elsewhere.

Wednesday: By the middle of next week...there is strong agreement on
low pressure in the western Great Lakes with warm advection ongoing
over our area with moisture also increasing.  There is some spread
among the various guidance members as to the arrival of a warm front
and associated precipitation chances.  At this range...mentioning
the chance for showers is prudent though at this range...ensemble
signals suggest a relatively light rainfall event which would not be
a significant flood concern.  This increase in clouds and associated
shower chances will mean somewhat lower high temperatures to end the
forecast period...but likely remaining above normal.

&&

.AVIATION /04Z THURSDAY THROUGH MONDAY/...
Short Term...MVFR conditions will continue through the evening hours
with ceilings occasionally falling to IFR in showers and patchy fog.
Overnight, more widespread IFR conditions can be expected with a few
pockets of LIFR in low clouds.

Similar conditions will continue on Thursday with widespread IFR
conditions in low ceiling with drizzle and fog at times in addition
to the showers. Thursday night will continue to have IFR conditions
in moderate rain with patchy fog and localized LIFR conditions.

Long Term...LIFR CIGS/VSBYS with rain and fog along with gusty
/20G30kt/ south-southeasterly winds for the morning Friday with
improving conditions arriving from southwest to northeast
through the day. Showery conditions with occasional MVFR
restrictions will persist under moderate winds from the west for
Saturday. VFR conditions are expected to dominate Sunday-Monday
with westerly winds continuing.

&&

.MARINE...
Short Term...Moist southeast winds will continue tonight and Thursday
over the coastal waters. Areas of drizzle and fog will reduce
visibilities in addition to scattered showers. The gradient
increases Thursday night over the region as low pressure tracks well
to our west. Seas will continue to build as well.

Long Term...Southerly gales likely Friday/Friday evening as strong low pressure
moves through the Great Lakes region and north of New England. Gusty
west winds continue through Saturday with SCA conditions continuing.
Winds/waves will subside for Sunday and Monday as weak high pressure
builds towards the region.

&&

.HYDROLOGY...
A flood watch is in effect for the snow covered portions of the
Western Maine Mountains and Northern New Hampshire.

The rain through Thursday will act to compress, warm, and ripen the
snowpack, but the heavier rain Friday morning will be the catalyst
for flooding. The combination of strong winds and high dew points
(50s) over an 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 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 3 inches in the mountains, less on the north
facing slopes. However, the PWATs are 2-3SD above normal, and with a
moisture feed to the Gulf we should be prepared for locally higher
amounts. 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 Thursday night through Friday afternoon
     for MEZ007>009-012>014.
     Coastal Flood Advisory until 3 AM EDT Thursday for MEZ023-024.
NH...Flood Watch from late Thursday night through Friday afternoon
     for NHZ001>005.
     Coastal Flood Advisory until 3 AM EDT Thursday for NHZ014.
MARINE...Gale Warning from 5 AM to 11 PM EDT Friday for ANZ150>154.

&&

$$

NEAR TERM...Legro