Scientific Forecaster Discussion
fxus61 kgyx 202229
Area forecast discussion
National Weather Service Gray ME
529 PM EST Wed Nov 20 2019
light scattered precipitation comes to an end tonight as a
system moves farther away. The next wave of precipitation may
produce a wintry mix Thursday morning, with snow showers and
gusty winds behind a cold frontal passage Friday. The active
weather pattern continues for the foreseeable future with
another wave arriving Sunday into Monday, and another by the
middle of next week.
Near term /until 6 am Thursday morning/...
update...have updated the forecast based on current surface
observations and latest radar imagery. Bands of precipitation
continue off the coastline with lighter precipitation over
southern Maine and southern New Hampshire. Snow showers will
continue in the mountains as well.
Latest mesoscale models suggest a mix of rain and snow showers
will continue until about 00z or 01z before exiting off the
Prev disc...upper level troughing south of the Gulf of Maine
had closed off today and was extending a trough back into New
England. This was producing light snow and rain showers as
moisture was advected into the region. We are seeing flurries as
far south and east as Gray ME where some lighter returns have
blossomed over southwestern Maine. Elsewhere large scale
cyclonic flow and northerly winds were ushering in drier air at
the surface and keeping precipitation mostly over New Hampshire.
Precipitation will diminish tonight as the forcing for ascent
moves east and ridging begins to build in. There will be light
rain possible along the coast and over the islands tonight as
well as some flakes over the mountains.
Skies become partly cloudy for most areas overnight with some
areas of stratus hanging on in upslope areas. Lows will be
dependent on cloud cover and how fast it decreases, but
locations will generally drop into the mid to upper 20s.
Short term /6 am Thursday morning through Thursday night/...
Thursday will be sunny with ridging passing over the region,
bringing a warmish day, although highs will still be a few
degrees below normal and in the mid 30s north to mid 40s south.
The ridge becomes positively tilted as it moves offshore. A
trough axis swinging into the eastern Continental U.S. Will begin to tilt
negatively and accelerate as it tries to develop a cutoff low.
Precipitation start times have been trending slower with start
times closer to daybreak Friday. This is because it will take
time for the atmospheric column to moisten with winds only
beginning to bring higher Theta-E air in after 00z Friday.
We will see early low temps Friday morning as the warm front
approaches and temperatures stay steady or begin to increase in
the early morning hours. We will likely see a wintry mix with
rain likely to the south and freezing rain or sleet more likely
north (and where precipitation starts sooner, such as the CT
river valley). Have used more of a blended approach with the
ensemble members during this time for temperatures aloft as
deterministic models seemed too cold to start. Again through
daybreak amounts will be light but we could accumulate a glaze
of ice which would be enough to make roads slippery.
Long term /Friday through Wednesday/...
the very active upper air pattern continues through the long
term forecast period with a wave train of systems lending to
overall low confidence in sensible weather with mixed
precipitation on The Table with each wave.
The first shortwave crosses Friday. H850 temperatures will
climb above freezing early Friday according to ensemble
consensus, which coupled with morning temperatures around or
below freezing across northern New Hampshire and western ME - and across
higher elevations - could lead to a period of light freezing
rain and/or sleet should precipitation arrive on the sooner end
of guidance. Otherwise, a switch to rain across the majority of
the area is expected as temperatures warm above freezing during
the day before a cold front crosses in the afternoon. Precipitation
coverage is a bit uncertain as the digging upper level trough
outpaces the surface front, splitting favorable forcing between
a prefrontal surface wave (presently progged to amplify over the
Gulf of Maine Friday morning) and the main cold front. Overall
kept consistent with model consensus, placing maximum pops over
the mountains and a secondary maxima over midcoast.
Regardless of precipitation, gusty winds develop as the trough
aloft digs into New England, especially behind the main surface
front in deep cold advection. Have increased winds from the
inherited blend as a result, about 15-20 kts sustained Post
frontal passage. Temperatures tumble Post fropa with a transition to snow
where moisture remains, mainly in the upslope locations where
favorable northwest flow continues into Saturday morning. A few inches
are possible across upslope areas during that time. An early
look at higher resolution models shows favorable conditions for
for snow squalls Friday afternoon/evening as well in the
autoconvective Post-cold fropa environment
A dry airmass arrives early this weekend with a ridge axis
extending north into the area providing a quiet albeit cool day
on Saturday. Meanwhile further west over the plains, a cut off
trough is picked up by the active northern stream, tracking east-northeast
into New England. An associated surface low intensifies,
reaching the coast by Sunday afternoon before lifting and
occluding NE into the Maritimes. Although wind fields and
dynamic forcing don't look particularly strong at this time,
that may change, especially if the cut off low phases better
with a northern stream trough over eastern Canada.
Ensemble analysis highlights uncertainty centered around the
north/S depth of the trough aloft and thus the north/S position of the
surface low as it approaches the coast. It should be noted that
global deterministic model trends have begun to converge on a
surface track near to just inside the benchmark, but without
consistency to get too specific with this portion of the
forecast, especially with higher resolution models and the
latest 12z European model (ecmwf) keeping the system along the southern periphery
of New England. At any rate anticedent temperatures should be
cooler than Friday, so there are better chances for snow across
the board, but modeled h850 temps hovering near freezing
suggest another challenging precipitation type forecast with
rain, snow, and a mix all on The Table. Have stuck with
rain/snow/mix for now, following close to an operational blend
of guidance for temperatures and pops.
After this shortwave rotates NE into the Maritimes, long range
model suites agree on an overall amplification of the upper air
pattern over North America as a jet enters the West Coast and
digs a trough down through The Rockies early next week. This
gives US a brief period of ridging during the early/middle part
of next work week, thus a brief break in weather, but the
trough deepens and swings across the plains and into the eastern
Continental U.S. By Wednesday/Thursday.
Aviation /00z Thursday through Monday/...
short term...mostly IFR or MVFR ceilings out there this
afternoon and evening as a trough keeps some light -rasn in the
area. The trough will move farther away tonight as ridging
builds in, allowing ceilings to return to VFR in most cases.
Lingering MVFR at Whitefield will be possible with a few more
hours of -shsn in the morning.
VFR conditions everywhere for Thursday and Thursday night with
clouds increasing from the SW towards Friday morning, and
perhaps some light wintry precipitation arriving just before 12z
Friday at hie and/or leb.
Long term...VFR prevails throughout much of the long term period
however it is puncuated by waves Friday and again on Sunday
into Monday. On Friday, MVFR ceilings are likely with mixed
precipitation showers (rain south, possible freezing rain and
pellets north) likely leading to periods of IFR across the north
and interior portions of New Hampshire and ME. A cold front crosses during
the afternoon with gusty northwest winds to follow and a transition of
any remaining precipitation to snow showers with IFR vsby
possible in heavier snow showers and possible snow squalls.
Coastal areas are most likely to remain dry/VFR with this
system. Friday night into Saturday morning, MVFR ceilings are
expected to persist over hie and perhaps leb with periods of IFR
visibility in shsn. Sunday, another wave approaches from the
southwest, which will likely lead to lowered ceilings at least
across the south and along the coast with more mixed
precipitation restrictions likely.
short term...Small Craft Advisory conditions continue outside the bays through
Thursday early afternoon when winds and seas drop below Small Craft Advisory
Long term...a strong cold front will cross the waters during the
latter half of Friday. Cold advection will promote strong wind
gusts possibly to gale force outside of the bays Friday evening
continuing into Saturday morning. Winds and seas will gradually
diminish thru Saturday with a building ridge, but another system
approaches from the SW on Sunday which may again build seas into
the beginning of next week. Local wind fields don't look
particularly strong with this system, however larger swells
could pose an issue with easterly fetch and stronger winds out
have discontinued the coastal flood statement as we are past
Marine...Small Craft Advisory until 4 PM EST Thursday for anz150-152-