Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 280807
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
407 AM EDT Thu Mar 28 2024

.SYNOPSIS...
A front stalls across New England today, bringing increasing
chances for rain. The steadiest and heaviest rains come
Thursday night as low pressure tracks northward offshore. This along
with significant snowpack ripening or, in the case of the
coastal plain and adjacent interior, significant snowpack melt
will increase the threat for flooding. Precipitation ends 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 /TODAY/...
Patchy fog continues this morning...mainly thanks to the colder
snowpack in place. This is tending to keep the fog coming in
waves as the warmer air pushes inland from the Gulf of ME. Fog
has been occasionally dense in the Kennebec River Valley...but
otherwise visibilities have been bouncing from around 1/2 mile
to 4 or 5 miles. At this time dense fog does not appear to be
widespread enough for an advisory.

Rainfall beginning to move into the forecast area at this hour.
A good soaking is expected...with HREF mean QPF around 2 inches
for coastal areas thru the event. Today rainfall rates will
generally be light to moderate...but consistent thru the
afternoon.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
This evening and overnight guidance suggests that rainfall rates
will pick up and may become briefly heavy at times. This will be
the most likely window for flooding impacts if they were to
occur. No change in the flood watch...which covers this time
period nicely. After priming much of the snowpack today an
additional inch or so of rain overnight combined with the snow
melt will start to push small stream water levels up. Hi-res
guidance is also coming around to the idea of more robust
forcing as low pressure moves into the Gulf of ME...throwing QPF
a littler farther west early Fri before coming to an end.

Rainfall is expected to quickly end from southwest to northeast
however...as the cold front slips thru the forecast area
finally. Gusty winds will develop late in the day as colder air
moves into the region. This will also cool the column on the
back edge of precip and some of that precip is expected to
change from rain to snow. This is especially true in the higher
elevations...though a period of freezing rain is possible there
as well as colder air undercuts the mild air mass currently in
place.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Overview: A negatively titled trough and deepening coastal low
will sustain snow into Saturday, mainly in our eastern most
zones. A weak wave then crosses Sunday with the bulk of the
forcing missing us to the south, but New Hampshire may still get
clipped with some light rain/snow showers. Some shortwave
ridging builds for Monday and most of Tuesday before a
potentially significant system approaches in the mid-week time
frame.

Impacts:
*Slick travel is possible Friday night as snow exits the area.

*Confidence is increasing, but still low, in a potentially
 significant system toward the middle of next week that may
 bring heavy rain or snow (or both).


Details: Snow will be coming to an end overnight/early Saturday
morning as low pressure continues its northward journey into
the Canadian Maritimes. It deepens as it does so, and with high
pressure nosing into the region this looks to create a very
tight pressure gradient. Widespread wind gusts overnight Friday
and Saturday may be in the 30-35 mph range with locally higher
gusts in the mountain terrain. Low temperatures Friday night
look to be in the 20s north of the mountains and low 30s to the
south, but with elevated winds expect it to feel about 10
degrees colder. Abundant sunshine likely helps temperatures warm
into the upper 30s and 40s Saturday. Winds will quickly
diminish overnight Saturday as the low exits the region and the
pressure gradient relaxes. Winds won`t exactly be going calm
overnight so would expect good mixing to continue and keep lows
only a few degrees cooler than the night before.

A shortwave trough passes overhead Sunday with a weak area of
low pressure exiting off the Mid-Atlantic coast. This should
keep the bulk of the forcing to our south, but some light snow
and/or rain showers can`t be ruled out during the day in New
Hampshire. Ridging builds in overnight Sunday setting Monday up
to be clear, dry and warm.

Tuesday remains mostly dry as well, but the evening begins our
window to watch for the possibility of another significant
spring storm. The global models tell a similar story with a deep
upper trough phasing with a strong coastal low, but
unsurprisingly they differ on timing, precip type, and track.
And it is not just each other they disagree with, significant
run to run waffling amongst themselves has made it difficult to
have confidence in anything more than "there looks like there
will be some sort of a system in the neighborhood next week". We
will continue to monitor trends as hopefully some details
become clearer over the next few days.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
Short Term...Widespread IFR or lower conditions this morning.
Much like yesterday some improvement in CIGs is possible during
the daylight hours...but moreso LIFR to IFR with plenty of
rainfall moving into the area. Likely not looking at significant
improvement in flight categories until cold front moves thru the
local area Fri. South of the mtns rapid improvement to VFR is
forecast once winds go northwest...while upslope clouds keep
MVFR CIGs to the northwest. Those northwest winds will
increase...with surface gusts at or above 25 kt at times.

Long Term...VFR should prevail for most areas by Friday night.
RKD to AUG and points eastward will likely still see some
MVFR/IFR overnight in lingering snow, but improve to VFR by
daybreak Saturday. Winds Friday night and Saturday will be
gusting from the northwest upwards of 30 kts for most areas. The
next chance for any restrictions will come with a weak system
passing through Sunday, but this should just be MVFR ceilings
and light rain/snow showers mainly confined to southern
terminals. Conditions improve back to VFR through Monday.

&&

.MARINE...
Short Term...Swell continues to diminish this
morning...remaining around 5 ft thru the day. With long period
nature I have cancelled the SCA...especially considering that
winds are forecast to increase and become gusty behind the cold
front Fri. A gale watch has been issued for the waters outside
the bays thru the first part of Sat.

Long Term...Northwesterly gales continue through the night
Friday behind departing low pressure. SCA conditions gradually
diminish through Saturday. By daybreak Sunday high pressure will
be settling over the waters keeping winds and waves below SCA
criteria through Monday.

&&

.HYDROLOGY...
A flood watch remains in effect 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 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 11 AM EDT this morning through Friday evening
     for MEZ014-019>022-024>028.
     Flood Watch from 11 AM EDT this morning through Friday
     afternoon for MEZ018-023.
NH...Flood Watch from 11 AM EDT this morning through Friday
     afternoon for NHZ008-010-012>015.
MARINE...Gale Watch from Friday morning through Saturday morning for
     ANZ150-152-154.

&&

$$

NEAR/SHORT TERM...Legro
LONG TERM...Baron


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