Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Gray ME
728 PM EDT Tue Oct 22 2019
onshore flow will strengthen this evening ahead of an approaching
frontal system. Rain will overspread much of the area this evening
and become heavy at times overnight as an area of developing low
pressure tracks along the frontal boundary. Along the coast,
winds will become gusty. The storm system will quickly exit
into the Maritimes by Wednesday afternoon with drier weather
behind it. A ridge of high pressure follows for Wednesday night
and Thursday. A cold front will cross the area Friday with a
few clouds and scattered showers. High pressure and drier air
follows for the upcoming weekend.
Near term /until 6 am Wednesday morning/...
update...deep onshore flow is pulling low clouds and drizzle
inland across parts of srn New Hampshire at this hour...and that will
continue to expand and lift nwd into wrn ME this evening. Steady
rain is still a couple hours away from wrn zones...and will
generally last about 6 hours before rapidly clearing from the west
thru Wed morning. Rain may briefly be heavy at times...but
overall it will be a moderate rain event. Main question will be
winds overnight as low level jet lifts up the coast. Strong inversion is
leading to negative lapse rates in the lower
atmosphere...coupled with low level jet winds generally at or below 50 kt
at h9 mean that gusts have the potential to underperform. Will
maintain the Wind Advisory at this point as it will get gusty
for parts of the midcoast...but overall strong gusts should be
relatively scattered. Will also bump winds in the near term up
in downslope zones of the mtns...as stable conditions near the
summits are supportive.
Previous discussion...at 18z a ridge of high pressure was
draped across the Maritimes and northern and eastern Maine. A
986 millibar low was over the Great Lakes with a trailing
frontal system through the lower lakes and Appalachians. The
remnants of Nestor were centered well southeast of the 40n/70w
benchmark. Clouds were gradually thickening and lowering across
the area in onshore flow ahead of the advancing frontal system.
For tonight...a coastal low develops along the the front
vicinity of Delaware-Maryland-Virginia then tracks northeast as impulse GOES
negative tilt. Rain overspreads the area this evening then
becomes heavy at times after midnight with approach of the
surface low and 60 kt low level jet. The frontal system will
also tap into some of the offshore moisture from the remnants of
Nestor...leading to higher quantitative precipitation forecast totals mainly over our northern
and eastern Maine zones. Quantitative precipitation forecast will range from near one-half inch
vicinity of the Connecticut valley to near two inches over our
northern and eastern Maine zones. We'll see some gusty winds as
well along the immediate coast...mainly from Casco Bay through
the midcoast with stronger winds confined to the area near
Penobscot Bay. Lows will range from the mid 40s to lower 50s.
Short term /Wednesday through Wednesday night/...
on Wednesday...rain tapers and clearing commences from
southwest to northeast by afternoon following passage of the
frontal boundary and coastal low. The exception should be
mountain sections where we'll hold on to clouds for the balance
of the day. Highs will range from the 50s across northern and
eastern sections...with the remainder of the area reaching the
lower 60s. Mostly clear and cooler Wednesday night as a ridge of
high pressure builds by to our south. Lows will range from the
mid 30s to around 40.
Long term /Thursday through Tuesday/...
unsettled weather conditions for the upcoming week, compared to
the dry weather of September.
A ridge will crest over the mid Atlantic region Wednesday night,
allowing for mainly clear skies and breezy conditions. The
breeze will keep overnight lows in the upper 30s to lower 40s
across the region from north to south.
A weak surface cold front and cyclonic flow aloft will allow for
scattered showers Thursday into Friday. By Friday night, a fast
moving upper level trough will enter the region from the west.
This may bring a brief period of steady rain to southern areas.
A large area of high pressure will allow for dry weather over
the weekend. This will be followed by an upper level low
rounding the top of the ridge early next week with showers
spreading across the region once again. The 12z model suite
suggests there is quite a bit of uncertainty as to the track of
Aviation /23z Tuesday through Sunday/...
conditions lowering to MVFR then IFR from SW to NE this evening
in rain and fog. Surface winds may gust up to 25 kt at coastal
terminals overnight. Conditions improving to VFR from SW to NE
Wednesday as low pressure and a frontal system slide offshore.
Long term...VFR conditions through Thursday night. MVFR
conditions possible Friday night into early Saturday as an upper
level trough crosses the region.
short term /through Wednesday night/... scas in increasing onshore
flow ahead of an approaching frontal system. Tonight, 10-15 ft
seas develop along with gale force gusts across mid coast waters
before subsiding by mid day Wednesday. Scas then persist area
wide the remainder of Wednesday. Lingering Small Craft Advisory seas are likely
outside the bays Wednesday night.
Long term...scas will linger into Thursday morning because of
gusty winds and seas.
a fast moving frontal system crosses overnight and early tomorrow
with models continuing to send a wave of moderate to heavy
rainfall S to NE across eastern New Hampshire into central Maine. In
general models have consistently yielded 1-2" of rainfall over
these areas with a sharp cutoff north of the mountains owing to
favorable southeasterly downslope flow. Much of this could fall
over a 6 hr period however 3 hr ffg of 2-3" suggests water
impacts ought to be minimal except locally where fallen leaves
may block drains. Expect modest rises on local Brooks and rivers
as a result at any rate, particularly across the headwaters of
the Androscoggin, Saco, and Kennebec basins.
Marine...Small Craft Advisory until 6 PM EDT Wednesday for anz153-154.
Gale Warning from 2 am to 11 am EDT Wednesday for anz150>152.