National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS61 KGYX 121451
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1051 AM EDT Fri Apr 12 2024

.SYNOPSIS...
Bouts of drizzle and fog evolve into a steady soaking rain this
morning as a cold front approaches from the west. Winds also
increase and become gusty, both before and after the front
crosses this afternoon and evening. 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. Showers linger into
tomorrow, with another front crossing. Drier and warmer
conditions return for Sunday. High pressure gradually builds in
early next week with a warming trend. Cooler conditions likely
then return late next week as a backdoor cold front enters New
England.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1050 AM Update...No wholesale changes to the going forecast
other than to load in latest observations and smooth trends
through this morning. These heavy bands of rain are quite
progressive, having already cleared southwestern New Hampshire,
however this band will be pivoting into the Maine coast and over
the Maine and New Hampshire mountains over the next couple of
hours and could locally put down another 2-3 inches of rainfall.
Flash flood warnings have been issued for the mountains where
snowmelt will exacerbate the runoff and continue river rises. A
couple reports of roadways being impacted due to flooding in
these areas have already been noted. An areal Flood Advisory had
been issued for the Maine coastal plain where excessive
rainfall will lead to pockets of urban flooding. Again, this
band is moving along and hires models continue to suggest it
clears are area early in the afternoon. Winds upwards of 40 kts
have been observed along the coast as the jet noses in, but they
have mainly been associated with heavy rain. Generally gusts
have been 25-30 kts.


Previous Discussion...
710 AM Update...Little to update, although I did lean more
heavily on warmer MOS guidance for temperature trends through
today... bringing temperatures further into the 60s over New
Hampshire.

A cold front and associated LLJ, moisture axis cross New
England today, directing a fire hose onto a ripened snowpack
across the foothills and mountains across our region. This will
lead to hydrological impacts, which are outlined in the
dedicated section below. The story remains the same in terms of
the synoptic set up... a deeply amplified pattern features a
southern stream low pulling an atmospheric river northward as it
comes into weak phase with a northern stream trough near the
Great Lakes. A surface warm front is lifting north this morning,
allowing temperatures to warm into the 50s to near 60 with rain
increasing in coverage and intensity. Onshore flow in southerly
gradient flow will keep temperatures closer to 50 over much of
Maine especially toward the Midcoast.

The system`s cold front crosses WSW to ENE this afternoon and
evening. Pre-frontal, an 80 kt LLJ will maximize moisture
transport resulting in widespread moderate to locally heavy
rainfall... maximized where orographic lift can act upon the
very humid airmass. Model guidance has been quite consistent
with the QPF footprint, with rainfall totals generally falling
between 0.75" and 1.5" for the lion`s share of the area. Given
SSE LL flow there will be terrain effects... with totals
dropping off to 0.5" or less north of the mountains, and with
2-3+ inch amounts across the Whites and western Maine Mountains.

The LLJ also brings some threat of wind, although there are a
couple factors working against this threat at the surface. Chief
among them is the presence of a beefy low level inversion
separating warm advection from the jet from cool onshore flow at
the surface. Pre- frontal, the inversion will be at its
steepest and the jet at its strongest. Still, increasing PGF
alone will help to bring winds up through the area, and should
improve mixing enough especially with heavier rain to bring a
few of the stronger gusts to the surface... in excess of 40 mph
along the coast where a wind advisory remains in place, in part
due recent tree damage from winter weather. Post-frontal, lapse
rates will improve however the core of the jet will have
passed... resulting in more widespread wind gusts in the 25-35
mph range.

The upper level trough driving the show will lag back and
provide support for additional showers behind the LLJ.
Aforementioned steepening lapse rates supporting better mixing
will also support weak instability, with a slight chance of
thunder occuring in this showers. This threat is generally
limited to western New Hampshire, as persistent onshore flow
will keep conditions too stable elsewhere.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Precipitation chances diminish this evening, except over the
mountains and western New Hampshire where cyclonic flow aloft
and low/mid- level moisture convergence keeps scattered rain
showers going overnight. Flow at the surface will still be
largely south- southeasterly however... so, there is some
question as to how much of the LL moisture will be scoured out
in lower elevations especially toward the Maine coast. Leaned on
cloudier and milder solutions with the assumption that
subsidence behind the cold front will help to lock moisture into
the boundary layer with lows in the 40s.

Come Saturday morning a secondary cold front associated with the
northern stream longwave trough axis aloft sweeps across the
forecast area. This brings reinvigorated rain shower chances for the
day, along with more stratocu clouds, and also mixes out the
rest of the LL moisture and allows for a warmer day. Highs in
the 50s are in the forecast for most places.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Overview...

A ridge builds into the Great Lakes this week, while a trough
develops and deepens across the Canadian Maritimes. New England
finds itself on the edge of both a warm and cool airmass, with
both likely at times. A few disturbances also ride around the
ridge and bring the chance for showers a few times through the
week.

Details...

Overall the forecast for next week has trended cooler and a bit
wetter over the last couple of days. The ridge set to bring
warmth to much of the country looks to be setting up a bit
further west through the Great Lakes, allowing more of a cool
influence to reach New England as a trough develops across the
Canadian Maritimes. This placement on the edge of the ridge puts
New England in a position to see some weak systems transiting
around the ridge and into our area. The best chance for these
looks to be late Sunday, and then possibly again on Wednesday.

Despite the cooling trend to the forecast, there will still be
some warm days to be had. The highest confidence days for warmth
look to be Sunday, Monday, and Tuesday, with highs warming into
the 60s in most spots, and even a few low 70s in southern New
Hampshire. Any showers on Sunday look to be late in the day or
into the overnight hours.

By Wednesday, and to a greater extent on Thursday, the
deepening trough and cool surface high pressure center across
the Canadian Maritimes begins to be felt more as temps cool with
a backdoor cold front. The timing of this is still in question,
with the chance to sneak out one more warm day on Wednesday.
But by Thursday and Friday next week temps looks to be cooling
back into the 50s, and possibly 40s in a lot of spots. Showers
also become more likely during this timeframe as moisture from a
system in the Midwest begins to interact with the stalling back
door cold front. The details on these features remain unclear
at this point, but a return to cooler and damp conditions looks
likely by late next week.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
Short Term...Widespread IFR/LIFR CIGs continue this morning
with VSBY degrading further as bands of moderate rain cross the
region today. S LLWS is expected with these features, in excess
of 60 kts at its peak coincident with SE surface flow gusting
25-35 kts. A few gusts closer to 40 kts are possible along the
coast. RA shifts east this afternoon and evening with -SHRA and
S flow generally 15-25 kts in its wake. May see CIG improvement
to MVFR or VFR, most likely further west. Low CIGs are likely
to continue tonight into early Sat especially in the interior.
Improvement to VFR likely on Sat except for perhaps KHIE/KLEB
with increase W wind to near 25 kts.

Long Term...Mainly VFR conditions are expected Sunday through
Tuesday, with a few showers also possible late Sunday. During
the Wednesday to Thursday timeframe, some low ceilings or fog
are possible across coastal terminals, with showers and
nighttime fog possible at all other terminals.

&&

.MARINE...
Short Term...Increasing SE gradient flow eventually reaches a
gale this morning, lasting into the evening with building seas
of 9-14 ft. SSE winds continue around 25-30 kts thru tonight and
Sat, starting to turn more W by the end of the day and keeping
seas elevated at 5-10 ft.

Long Term...SCA conditions linger in westerly winds behind a
cold front into Sunday night. A weak disturbance crosses the
southern waters late Sunday, with high pressure then building in
for the early part of the workweek. A backdoor cold front may
bring SCA conditions in northeasterly winds, but timing on this
feature remains uncertain at this time.

&&

.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 have acted to compress, warm, and ripen
snowpack, but the heavier rain this 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 today 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, including
yesterday and today`s rainfall, with 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. Small streams draining in the
steep terrain could experience flash flooding, centered on this
morning and afternoon. Melt combined with saturated antecedent
conditions sets up ideal conditions for minor or moderate river
flooding in the Upper Merrimack (Pemi), Saco, Androscoggin, and
Kennebec basins. 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...
Astronomical tides are falling off from their peaks this week.
Some minor splashover can`t be ruled out during this afternoon`s
high tide with building seas, but otherwise the coastal flood
threat looks to be diminishing going into this weekend.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch until 4 PM EDT this afternoon for MEZ007>009-
     012>014.
     Wind Advisory until 4 PM EDT this afternoon for MEZ019>028.
NH...Flood Watch until 4 PM EDT this afternoon for NHZ001>005.
     Wind Advisory until 4 PM EDT this afternoon for NHZ014.
MARINE...Gale Warning until 11 PM EDT this evening for ANZ150>154.

&&

$$

UPDATE..Baron
NEAR/SHORT TERM...Casey
LONG TERM...Clair