Area Forecast Discussion
Issued by NWS Portland, ME

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233
FXUS61 KGYX 231152
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
652 AM EST Thu Jan 23 2020

.SYNOPSIS...
High pressure provides fair weather and above average
temperatures today. A cold front will sink gradually south into
the area late Thursday through Friday accompanied by a few
clouds. A coastal system passes this weekend with accumulating
snow possible over higher terrain, rain along the coast, and a
mix between over the foothills. The system exits early next week
with quiet weather to follow.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Update...
Have updated the forecast based on current observations and
trends this morning. Temperatures have bottomed out below zero
in a few areas this morning as radiational cooling dominated the
region under clear skies and light winds.

Thin, Cirrus clouds will be crossing the region today as
moisture crosses over the top the ridge. There should be a
rebound in temperatures with afternoon highs above freezining in
most locations.

Prev Disc...
Very quiet conditions will continue in the near term portion of
the forecast. A large ridge of high pressure along the Eastern
Seaboard will allow for winds to continue from the southwest
both at the surface and aloft. Despite a chilly start to the
morning with radiational cooling in some areas, temperatures
will rebound and top out above freezing in all areas today as
some melting of the snowpack occurs. Temperatures will be
highest over southernmost New Hampshire where readings to reach
the lower 40s under mostly sunny skies.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
A few clouds will pass through the region tonight as a moisture
starved and weak cold front slips through the region. Winds will
shift to the north, but remain light through the period.

A light northerly flow will continue on Friday, however
temperatures will be above freezing once again with readings in
the lower 40s over southernmost New Hampshire. High pressure
will shift from north of Maine to the Canadian Maritimes as what
little Arctic air we have exits the region.

All 00Z models then indicate low pressure will enter the
Northern Ohio Valley, allowing a secondary area of low pressure
to begin to develop over the Mid Atlantic region. This brings us
to the long term portion of the forecast.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
     Mountain snow and coastal rain Saturday night into Sunday...

By Friday night, a closed (nearly cut-off) 500 mb trough will be
positioned over the lower Ohio Valley. Through its connection
with the southern stream, and its disconnect with the northern
stream retreating back into Canada, a healthy warm sector
develops ahead of the system over our area with 850 mb
temperatures above freezing and PWAT increasing to 0.75-1" by
Saturday afternoon. At the surface, low pressure occludes into
the upper Ohio Valley and Great Lakes region while southern
stream energy advecting up the front of the trough spurs
cyclogenesis over the Mid-Atlantic coast. As the former low
decays Saturday, it approaches the strengthening coastal low,
combining over New England by Sunday with accumulating snow,
moderate rainfall, and gusty coastal winds. Model consensus
suggests the low pressure center crosses the Maine coastal plain
Sunday into Sunday night. Impacts associated with this system,
with some model-to-model and run-to-run consistency by this
time, are centered Saturday evening through Sunday morning with
showers persisting under the upper level low into Monday
especially over the mountains with favorable upslope flow behind
the departing low.

High confidence exists in: mostly rain along the coast/southern
NH and mostly snow over higher terrain including the Whites and
western Maine mountains; and a period of gusty winds in excess
of 30 mph along the immediate coast Sunday morning.

Medium confidence exists in: QPF of at least 1.25" over the
coastal plain with a sharp cut-off near the international
border; and snow ratios on the low side of average with poor
overlap between favorable dendrite growth and strong ascent.

Low confidence exists in: strong coastal frontogenetic forcing
leading to periods of moderate to heavy rainfall along the
coast; and minor splash- over during high tide Sunday (current
timing suggests peak winds/waves occur around low tide however).
Although long- range models have consistently painted 1-1.5"
QPF through Sunday morning, the CMC (interestingly) and some
higher-res CAMs coming into view hint at strong forcing along
the coastal front leading to over 2" of rain there, which may
cause some issues depending on rain rates should this occur.
Snowfall over higher terrain looks to stay in the 4-7" range,
however should stronger slantwise forcing be realized due in
part to stronger coastal frontogenesis, this could be higher.

Ensembles continue to show more uncertainty than deterministic
agreement leads on with substantial spread in crucial 850 mb
temperatures as well as the degree of frontogenetical forcing
that can be realized. The keys to forecast uncertainty lie
mainly in the low- to mid-levels as a result. Although the 500
mb pattern has good consensus, the evolution and interaction of
the 2 surface lows and their attendant low/mid-level
circulations as the upper level trough axis sharpens and rotates
into New England will dictate system track and strength of
forcing. How warm antecedent conditions are will have bearing on
how much mixed precipitation we end up with, and if sleet cuts
into snowfall totals.

Dry air starts to intrude aloft by mid-Sunday which decreases
likelihood of impacts after that point, although the low
overhead keeps shower chances through the day. The upper level
low crosses by the end of Monday, helped along by the northern
stream over Canada, with upslope snow showers ending. Beyond
this point long range models generally agree that the overall
synoptic pattern becomes trough dominant into the middle of the
next week with gradually cooling mid- level temperatures, likely
bringing a return to near-normal temperatures.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Short Term...VFR conditions expected in all areas with just some
high, cirrus clouds from time to time today through Friday.

Long Term... VFR prevails through much of Saturday under light
easterly flow. Ceilings gradually lower as rain and snow
approaches from the southwest Saturday evening with associated
MVFR (in rain) and IFR or worse (in rain or snow) visibilities
expected. Gusty NE winds develop along the coast overnight into
Sunday morning with coastal and southern rain, northern/mountain
snow persisting. Expect winds to go variable as low pressure
crosses Sunday. Showers with periodic restrictions persist
through Sunday, Monday in the mountains, with northwest flow
settling in.

&&

.MARINE...
Short Term...The surface gradient will remain weak today.
However, southwesterly winds from aloft may allow gusts up to 20
kt along the outer waters today. A weak cold front will then
cross the waters from the north overnight. This will allow winds
to veer to the west, northwest. As low pressure heads towards
the Mid Atlantic region, winds will switch to the northeast on
Friday.

Long Term... A low pressure system crosses New England and
perhaps the northern Gulf of Maine Saturday night through Monday
with building winds and seas. SCAs develop by Saturday evening
with period of easterly to southeasterly gale force winds
possible that night into Sunday morning. The system slow exits
by Monday evening with decreasing northwesterly winds.

&&

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

&&

$$
NEAR/SHORT TERM...Cannon
LONG TERM...Casey



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