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000
FXUS61 KGYX 120351
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1151 PM EDT Thu Apr 11 2024

.SYNOPSIS...
Bouts of drizzle and fog will continue 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 /UNTIL 7 AM FRIDAY MORNING/...
Update...Mostly minor changes to reflect latest PoP trends based
on radar. I have added some fog visibilities of 1/2 mile...but
overall guidance forecasts a pretty fast lifting of visibility
as this next batch of rain sweeps thru so I will hold off on any
dense fog advisory at this time.

Previous discussion...The main line of showers is moving
through central and southern Maine at the time of this writing
with drizzle and fog continuing in its wake. RAP13 analysis
shows the center of low pressure over the Ohio Valley, with a
break in precipitation stretching back all the way to
Pennsylvania. Expect fog to redevelop, in places that rain may
have cleared it a bit, during this period of subsidence this
afternoon.

Another shortwave moves through this evening keeping showers
and drizzle chances in the forecast. Forcing than increases as
the upper trough begins to tilt negatively as it continues
moving eastward toward the region. In respect to timing of
heavier rain, would expect it to begin late tonight and
overspread the region Friday morning.

&&

.SHORT TERM /7 AM FRIDAY MORNING THROUGH SATURDAY/...
Update...Based on model forecasts of 70+ kt at 925 mb beginning
Fri morning I have issued wind advisory for the entire coast
into parts of interior western ME. Cold air dam should remain
fairly strong...but typically LLJs of this magnitude are able to
mix down a few gusts of 45 mph or more. Given the recent spate
of tree damage with winter weather...I am a little concerned
that more limbs than normal may fall from this kind of event.

Previous discussion...
Impacts:
*Periods of moderate to heavy rainfall will create river and
 small stream rises and some areal flood concerns in the
 mountains and foothills. Flooding will be more nuisance type in
 the coastal plain and southern New Hampshire.

Strong surface low pressure will be directed into the Great
Lakes Region by a potent upper level trough. At the same time a
well amplified ridge axis will be moving off to the east and the
resultant gradient flow will allow an atmospheric river,
originating straight from the Gulf Of Mexico, to advect moisture
into the region. While the juiciest values in this moisture
axis look to remain off shore, 12Z hires continues to suggest
PWATS will be upwards of 1.1- 1.4" across the area Friday
morning, which is well above normals for this time of year. With
the low level jet aligned along the moisture axis, this
ultimately amounts to widespread rainfall in the ballpark of
0.5-1.5". Locally higher amounts look possible in the higher
terrain, where orographic lift will help to enhance rainfall,
and maybe even the eastern Mid Coast as the moisture continues
to advect into that area throughout the day as the moisture axis
shifts east. Lapse rates steepen in the wake of the Low Level
Jet would could result in some isolated thunder in western New
Hampshire, but elsewhere lapse rates and CAPE look unimpressive.


We will be under a strong low level jet, but winds will be
secondary concern as we will have quite a temperature inversion
developing keeping higher winds from mixing down along the
coast. A cold air dam is also building which should help shelter
interior zones as well. The tight pressure gradient by itself
will allow for some stronger gusts however. Widespread south-
southeasterly gusts upwards of 25-35 mph should be expected with
a few gusts 40-50 mph in the eastern Mid Coast. The confidence
is not there at the moment to hoist a wind advisory based on
bufkit soundings continuing to show a large temperature
inversion and low level lapse somewhat lacking.

We should see some improvement Friday night as the low
continues northward and we see a lull with maybe just some
lingering showers in northern zones where forcing from the
trough becoming negatively tilted will continue. Otherwise skies
look to remain mostly cloudy with, clearing along the coast
toward daybreak, and low temperatures only bottoming out in the
low to mid 40s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Amplified 500 MB flow pattern across NOAM this weekend
gradually becomes less amplified through next week, although it
will be somewhat unsettled. Still see no major storms in sight.
Overall temps look near to a little above normal through the
period.

On Saturday will see 500 MB trough axis moving across the CWA,
however, the trough is weakening with the best forcing lifting
poleward, so expecting a mostly cloudy day, with a chance of
showers, especially in the mtns. It`s possible that as the
forcing pulls N the afternoon could be better than the morning.
Highs range from the mid to upper 40s in the mtns, to the mid
50s in the S. Some clearing expected overnight, with lows mid
30s to low 40s. Sunday looks like a fairly decent with mostly to
partly sunny skies as weak high pressure briefly moves across
the area. It’ll be warmer with highs ranging from the mid 50s in
the mtns to the low to mid 60s in the S.

A fast moving and weak system passes S of the CWA Sun night and
could produce a few showers. Highs pressure builds back in
again for Monday with highs in the upper 50s to mid 60s, and
partly to mostly sunny skies. Tuesday may be even warmer
depending on when cloud cover cover moves, but should stay
mainly dry, with Wednesday and Thursday looking showery, as
another round of WAA moves in aloft.

&&

.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
Short Term...Fog and drizzle developing across the area tonight
will keep conditions IFR/LIFR through this evening. Conditions
stay down through Friday morning as periods of moderate to heavy
rain move through. Conditions will begin to improve Friday
night from south to north as the low pressure departs. During
the day Friday many terminals will be experiencing south-
southeasterly wind gusts upwards of 30 kts, with coastal
terminals seeing gusts upwards of 40 kts. LLWS will also be
present through the morning Friday as a strong LLJ swings by.

Long Term...Some Saturday morning MVFR expected outside the
mountain, but all terminals but KHIE should improve to VFR in
the afternoon, while KHIE might stay MVFR into Sat evening.
Mainly VFR expected Sunday through Tue, although could see some
tempo MVFR in SHRA for a brief period Sun night.

&&

.MARINE...
Short Term...Winds and seas continue to build tonight above
conditions hazardous to small craft. By Friday morning
southeasterly wind gusts over the waters will be reaching gale
force and by the end of the day Friday seas will be 10-13 ft.
Conditions will slowly start trending down overnight Friday.

Long Term...SCAs will likely be needed Sat into Sat night , but
may be limited to the outside the bays. May need that SCA
through part of Sunday, but winds/seas should fall below SCA
levels Sunday night into Tuesday.

&&

.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 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...
A southeasterly flow off the Gulf of Maine will allow for a
modest storm surge tonight, and may once again allow Portland to
reach its 12 foot flood stage. Hampton is expected to reach its
11 foot flood stage as well. Therefore have gone ahead and
issued a coastal flood advisory to highlight these
possibilities.

High astronomical tides will continue through the end of this
week, albeit, lowering with time. Coastal flooding Friday or
Saturday will rely on whether or not significant surge lines up
with the higher of the high tide cycle which currently is the
overnight hours this week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch through Friday afternoon for MEZ007>009-012>014.
     Wind Advisory from 7 AM to 4 PM EDT Friday for MEZ019>028.
     Coastal Flood Advisory until 3 AM EDT Friday for MEZ023-024.
NH...Flood Watch through Friday afternoon for NHZ001>005.
     Wind Advisory from 7 AM to 4 PM EDT Friday for NHZ014.
     Coastal Flood Advisory until 3 AM EDT Friday for NHZ014.
MARINE...Gale Warning from 5 AM to 11 PM EDT Friday for ANZ150>154.

&&

$$

NEAR TERM...Legro