Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 272320
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
720 PM EDT Wed Mar 27 2024

.SYNOPSIS...
A front stalls across New England through Thursday, bringing
increasing chances for rain before exiting on Friday. Low
pressure tracks offshore on Friday, bringing the steadiest and
heaviest rains Thursday night, along with significant snowpack
ripening or, in the case of the coastal plain and adjacent
interior, significant snowpack melt. Precipitation may end as
snow Friday, especially across the higher terrain, before things
become drier and gusty over the weekend. A weak system passes
through early Sunday, and then a more significant system is
possible toward the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
715 PM...Made a few minor changes, through this evening, just
to try time POPs based on current obs, and latest meso model
runs, but overall, the forecast doesn`t change much at all. I
don`t think anywhere will escape seeing a few showers before
midnight, but they may not come until late near Pen Bay.
Otherwise it should be showery through much of the night, with a
steadier rain developing in the pre-dawn hours. Temps fall off
some in areas that had some sun earlier today, but lows will
only drop to the upper 30 to low 40s.


Previously...Another humid night is expected, with widespread
fog as dew points continue to creep up atop snow pack. While
surface charts won`t show much if any sort of surface feature...
with light and variable or calm winds for the forecast area...
a developing frontal zone overhead will provide a focus for
rain, which will blossom from pockets of rain and rain showers
over the Connecticut River Valley today, into a more widespread
stratiform rain over the area as a whole late tonight.
Precipitation totals around 0.25-0.5" look likely, according to
ensemble percentiles. Low temperatures will closely mirror
expected dew points, remaining mild in the upper-30s and
low-40s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
The frontal zone remains overhead Thursday into Thursday night
with continued rounds of rain tracking SSW to NNE through the
area... generally picking up in intensity as time progresses.
This is mainly due to the phasing of a southern stream low
pressure system into the northern stream... which will bring
increasingly organized forcing along the frontal zone as the
southern wave rides north toward the Gulf of Maine. Hydrological
expectations are discussed in greater detail below in the
dedicated section.

In terms of sensible conditions... elevated dew points and
overcast or broken overcast skies, coupled with the widespread
rain, will keep conditions soggy and temperatures mild, topping
out in the 40s to near 50 on Thursday. A surface front will
begin to take better shape as it shifts offshore through the
day, which will allow north-northwest winds to develop. Although
light initially, winds will increase overnight as low pressure
deepens and approaches the Gulf of Maine... with gusts near 30
mph late Thursday night. What remains the bigger question in
the forecast is how quickly cooler, drier air enters from the
west Thursday night... and how quickly precipitation chances
start to diminish as a result. Am leaning on wetter solutions,
with continued area-wide precipitation chances continuing
through Thursday night, albeit with greatest confidence still
existing along the coast.

Finally... cold advection behind the front in northwest flow
will eventually bring temperature profiles down enough to
produce snow across the mountains, mainly in the north with
around an inch of potential by Friday morning.

&&

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

Low pressure passes through the Gulf of Maine on Friday,
bringing the last slug of precip to this week`s soggy stretch.
Breezy conditions follow on Saturday as the strengthening low
tracks through the Canadian Maritimes while high pressure builds
into New England for the weekend. A weak shortwave passes
through New England early Sunday morning as it passes around the
building ridge. Another system is likely toward the middle of
next week.

Details...

Models continue to wobble back and forth on how far west the
heavier precip associated with the strengthening low will reach,
but overall the consensus appears to be honing in on it keeping
it closer to the coastline. This puts most of the heavier
precip across the coastal plain where the snow pack is expected
to melt out. The high res guidance remains farther west with
the precip, but also shows a more significant change to snow by
Friday morning, which would help lessen the flood risk, but the
heavier rainfall before the change over could still lead to
problems. Given their recent performance, this forecast
continues to lean more heavily toward the global guidance. So at
this point areas south of the Foothills appear most likely to
have some minor flooding issues, which is where a flood watch
has been issued. Even outside of the flood watch, river rises
are still expected from the rainfall.

The low tracks offshore Friday and moves into Nova Scotia by
Friday night. Gusty winds develop behind the low as high
pressure builds in, so gusty conditions are expected on Saturday
as conditions dry out. Seasonable temps are expected behind the
system for the weekend.

A ridge gradually builds into the Great Lakes and Northeast
through early next week. A weak shortwave rides along the
northern edge of the building ridge and passes through New
England on Sunday morning, bringing a chance for some light rain
and snow showers. The ridge continues to build in through
Monday with a gradual warming trend, with temps running a few
degrees above average.

By next Tuesday or Wednesday another storm system looks
increasingly likely to affect the area. With what, how much, and
for how long remain very broad and unanswered questions at this
point however. There is also still the chance the system mostly
misses to the south. It will be several days before better
details emerge on this on this system, the next in an
ongoing active pattern.

&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
Short Term...Although we have some improvement this afternoon,
with some southern terminals experiencing brief bouts of VFR,
widespread IFR/LIFR CIGs return this evening through tonight
with low to no flow and IFR, potentially local LIFR VSBY
developing in BR, SHRA and eventually RA. RA and low CIGs
continue through Thu, with some improvement to VSBY. Significant
IFR/LIFR persists or returns Thu night, with increasing
northwest winds... gusting to around 25 kts late.

Long Term...MVFR to IFR conditions prevail into Friday at most
terminals, with western terminals seeing better conditions
overall. Eastern terminals see restrictions linger into Saturday
as western terminals improve to VFR Friday night. Gusty
conditions with northwesterly gusts to 30kts are likely on
Friday into Saturday. VFR conditions return by late Saturday and
persist into Saturday night. A period MVFR ceilings are
possible early Sunday, especially across southern terminals,
with VFR returning by late in the day and continuing into
Monday. Restrictions are likely again next Tuesday or Wednesday
with rain or snow likely impacting the area from another storm
system.

&&

.MARINE...
Short Term...Winds remain light while swells gradually diminish
to around 5 ft tonight into Thu. Winds gradually return out of
the north, the north-northwest late Thu and overnight, becoming
gusty to 25-30 kts by early Friday morning.

Long Term...Low pressure tracks across the eastern waters
Friday and moves into Nova Scotia on Friday night.
Northwesterly gales are possible Friday night and Saturday as
the system moves away and high pressure builds into the
Northeast. Conditions gradually fall below SCA levels by late in
the weekend. Another storm system is likely toward midweek next
week.

&&

.HYDROLOGY...
A flood watch has been issued for portions of
southern NH and SW Maine. The primary impact will be small
stream and river rises, and flooding along low water crossing
and urban areas due to rain and snowmelt. A slow moving frontal
boundary will sync up with a southern stream low pressure system
to bring an extended period of rain to the area tonight through
Friday. Moderate rainfall will combine with warmer temperatures
and high dewpoints for snowmelt, with losses of 1.25 to 1.75"
from the existing snowpack, less in the headwaters. The snow
condition will be a player in this event as snow in the
mountains has a low density and is expected to hold, while the
snowpack in the coastal watersheds are more ice than snow and
will release fairly easily. There is a zone between the
mountains and the coast where there is a mixed bag of snow
conditions that will likely hold in some areas and melt out in
others. This complicates the calculations on the cumulative
runoff, adding uncertainty to the river forecasts particularly
in the Lower Kennebec River. The latest forecasts show river
rises across all watersheds, with isolated minor flood levels
reached.

The strength of the storm as it moves northward will determine
the western extent of the heavier rainfall Thursday into Friday.
The latest forecast track will keep the heaviest rainfall
across central and eastern Maine, with the regional flood risk
highest along the MidCoast and lower Kennebec River Valley with
1.5-2.5" of rain and 1.5" of snowmelt. Though there will be
less rainfall, the cumulative rain/snow runoff could be
sufficient for small stream and urban issues into southern NH
and SW ME. A slight wobble in the track or longer duration of
rain could easily result in more widespread impacts. Moderate
river flooding is not expected at the time of this issuance,
with probabilities less than 10%. Note: Many climate sites are
in the top 5 wettest on record, with this late month event
expected to approach all time records for Augusta and Portland.
Portland`s record 11.24" in 2010, Augusta`s is 9.71" in 1953.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch from Thursday morning through Friday evening for
     MEZ014-019>022-024>028.
     Flood Watch from Thursday morning through Friday afternoon for
     MEZ018-023.
NH...Flood Watch from Thursday morning through Friday afternoon for
     NHZ008-010-012>015.
MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ150-
     152>154.

&&

$$

SYNOPSIS...
NEAR TERM...Casey/Cempa
SHORT TERM...Casey
LONG TERM...Clair
AVIATION...
MARINE...
HYDROLOGY...


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