NWS Gray, Maine Area Forecast Discussion



000
FXUS61 KGYX 191051
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
651 AM EDT Tue Mar 19 2024

.SYNOPSIS...
Mountain snow showers gradually diminish today as cyclonic flow
weakens ahead of an approaching clipper. The clipper brings more
widespread snow showers Wednesday and Wednesday night, with a
period of accumulating snow likely across northwestern areas
Wednesday night into Thursday. Strong gusty winds follow the
system on Thursday as cool high pressure builds into New
England through Friday. Low pressure likely brings a more
widespread round of accumulating snowfall on Saturday, with
another storm possible late in the weekend. Unsettled conditions
may linger into early next week as the pattern becomes much
more uncertain.

&&

.NEAR TERM /THROUGH TONIGHT/...
651 AM Update...Little change at this time, except to expand
flurry/sprinkle mention through the couple of hours before
ceilings start to lift and scatter a bit more.

Previously...A shortwave trough axis driving snow showers
through the mountains this morning exits east today, leaving a
cooler, more seasonable airmass in its wake along with a brief
dry trend. Deep cold advection in cyclonic flow keeps lapse
rates steep and mixing strong... allowing flow to become
unblocked once again, which will have clouds track toward the
coast. Precipitation diminishes by this afternoon as weakly
diffluence flow and a shortwave ridge axis move in from the
west. For sensible conditions, there is still a fair amount of
mid-level moisture evident in modeled fields and satellite
imagery this morning, so I think another day of stratocu is a
fair forecast for the region, along with highs in the 30s and
40s. Well- mixed gradient flow ensures a steady WNW breeze
gusting near 20 mph.

The shortwave ridge crossing this evening will allow winds
quickly diminish, although hot on its heels will be falling
heights associated with the next approaching system. Light snow
showers are forecast to enter the Connecticut River Valley
around or after sunset, and will continue to overspread the
mountains overnight... perhaps spilling into the foothills and
toward the coast toward dawn. Temperatures will be mostly in the
20s... except teens in the northern ME Lakes region, and 30s
toward the Lower Merrimack.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
A clipper tracking through a negatively tilted trough rolls
through New England Wednesday into Thursday, bringing a bout of
showers and accumulating snow. Snow shower activity mostly
across the mountains through the morning will expand in coverage
with the diurnal trend, and as a pre-frontal trough axis shifts
SW to NE through New England... mixing with rain toward the
coast, and becoming more rain than snow over the interior as
temperatures warm. Temperatures are forecast to reach into the
40s for most places, as mixing and breaks in the clouds will
allow sun to help in some places... although wet-bulbing and
shower intensity ought to keep wet flakes around in the
foothills.

One of the bigger questions with the system is the degree to which
precipitation with this system will be stratiform vs showery. Broad
warm frontal forcing may support more stratiform precip in the
morning. During the daytime, CAMs entering the forecast range
suggest steep lapse rates from deep CAA combined with strong mixing
aided by surface heating favors more showery precipitation and also
contributes to elevated snow squall parameters during the day
Wednesday across the mountains. While snow accumulation would be
more hit or miss, showers could be briefly intense and lay down a
quick dusting up to an inch or so.

Better stratiform potential exists during the evening and overnight,
when a vorticity maximum barrels in from the west to quickly deepen
the surface low as it reaches coastal Maine. The negatively tilted
trough extending to the coastal low may place the Maine mountains in
a favorable position for banded snowfall, with the added benefit of
westerly to northwesterly upslope flow. Being the NW quadrant of the
low... the conceptual model favors higher snow ratios too, with cold
advection behind the low bringing thermal profiles into the snow
growth zone, overlapping with mid-level ascent. Meanwhile further
south and west, dry slotting would diminish precip potential, except
in the upslopes... with a gusty west wind eventually mixing in as
the low exits east. It is important to note that a shift northward
of the upper level wave may dry slot up to the international
border... leading to little additional accumulation other than from
showers.

All in all snowfall totals may necessitate a winter weather
advisory, especially when considering the spirit of it as a
travel- oriented product. While showery activity during the day
time would hardly amount to and inch or two across the
mountains, there is certainly some good upward potential for
heavier snowfall totals later in the evening and overnight
toward the north if they get under a ban d. While ensemble
means point to QPF of around 0.3-0.5" between Bangor and the
Maine mountains, medians are higher, suggesting a skew toward
higher- end snowfall potential... especially across the peaks
and ridges. Current forecast calls for accumulations up up to
7-10 inches near the international border, and across the
summits elsewhere... with valley totals more in the 3-5 inch
zone. But, this could be a feast or famine situation depending
on mesoscale influence.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Overview...

Low pressure pulls away on Thursday, with windy conditions
behind the system. High pressure crosses through on Friday, and
then one or two systems likely affect New England from Saturday
through early next week.

Details...

The strengthening low pressure system moves through eastern
Maine and into New Brunswick Thursday morning. Snow transitions
to more snow showers across northern areas Thursday morning,
while most other areas dry out by midday. Westerly winds quickly
become gusty and strong, with gusts over 50 mph possible during
the daytime on Thursday as the strong low pulls away, and high
pressure builds in. Outside of the mountain peaks, winds look to
be strongest across southern New Hampshire. Wind headlines may
be needed for this set up.

Winds ease Thursday night, but breezy conditions likely
continue into Friday morning. Temperatures will also be cooler
than we`ve experienced most of this month, so it will feel cold
overnight Thursday as lows dip into the teens, and wind chills
dip into the low single digits to below zero. By late Friday,
high pressure will have progressed far enough eastward to bring
calmer conditions. The high will be progressive, with the ridge
axis crossing through Friday night and moves toward Newfoundland
through Saturday night. A stronger high builds to the north
across Quebec and Labrador through weekend, reaching near 1050mb
by early next week.

The forecast for the weekend has shifted significantly since 24
hours ago as the Euro and it`s ensembles have tracked
northwestward by several hundred miles with the weekend system,
a solution the GFS alone was showing yesterday. This appears to
be in part from a shortwave in the northern branch being more
amplified on Saturday, and the high being located further north,
rather than across New England. Now, the northern system alone
looks to have the potential to bring accumulating snow to much
of the area on Saturday, while another stronger storm develops
off the Carolina coast.

The break in the ridge provided by the northern branch
shortwave allows the southern storm with its rich moisture to be
drawn further north. The GFS is now showing a solution where
the northern branch phases more with the southern system, and
the Euro is very close to making this solution happen as well.
Several Euro ensemble members are showing this now, and we will
need to monitor if this trend continues over the next few runs.
With such a large shift in the Euro from last night, it`s not
unreasonable to think it will shift further to more of the
phasing solution, rather than the cut off low off the Carolina
coast solution. If this happens, there is then much more
moisture in play with the system for New England, and a
rain/snow line this would be highly dependent on the track. With
multiple shortwaves, a potential cut off low, and a strong high
present, there are many moving parts that will need to be
sorted out over the next day or two before a clearer picture
arises.

Beyond this weekend the forecast for early next week becomes
highly uncertain, with options ranging the chance for a cut off
low meandering offshore bringing precipitation, to a cold dry
airmass behind a departing low pressure system. These details
will become more clear once the weekend system becomes better
sorted.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Short Term...VFR prevails today into tonight with WNW winds
gusting to near 20 kts. MVFR CIGs and IFR VSBY in SHSN become
more likely overnight in the mountains, and become possible
area-wide on Wed with locally intense SHSN in the north and
SHSN/SHRA further south. Steadier snow and IFR/LIFR develops
over W ME into N NH Wed night, while VFR returns or continues in
S NH and SW ME with increasing westerly winds, gusting to
20-25+ kts late.

Long Term...Gusty westerly winds of 40kt are possible on
Thursday as snow ends and VFR return to most terminals. MVFR
ceilings likely linger at HIE through midday Friday as upslope
flow continues. Winds ease somewhat Thursday night, but 30kt
gusts remain possible overnight before easing by midday Friday.
VFR conditions then give way to IFR with snow likely on
Saturday. MVFR to IFR conditions remain possible through Sunday
as well, depending on the track of a second storm on Sunday.

&&

.MARINE...
Short Term...Breezy west flow AOB 25 kts today diminishes below
15 kts tonight, coinciding with 3-5 ft seas diminishing below 3
ft. Flow returns out of the SSW on Wednesday approaching SCA
thresholds, then turns W overnight with a crossing front. Wind
gusts will increase from there, to around 30-35 kts by dawn
Thursday.

Long Term...Westerly gales are possible Thursday and Thursday
night as a strengthening low pressure center moves into New
Brunswick Thursday morning. High pressure builds in behind the
low and crosses the waters late Friday. Low pressure tracks
eastward across the waters on Saturday. A stronger low develops
off the Carolina coast this weekend, and may track northward
into the Gulf of Maine by Sunday.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$

NEAR TERM...Casey
SHORT TERM...Casey
LONG TERM...Clair

NWS GYX Office Area Forecast Discussion