Area Forecast Discussion
Issued by NWS Portland, ME-- Highlight Changed Discussion --
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FXUS61 KGYX 171341
Area Forecast Discussion
National Weather Service Gray ME
941 AM EDT Mon Apr 17 2017
-- Changed Discussion --A cold front will cross the region today. High pressure will
build south from Canada tonight and Tuesday and will shift east
Tuesday night. Weak low pressure passes to our north on Wednesday
and bring some showers to the region. Weak high pressure moves
in Thursday with a steadier precipitation expected Thursday
night into Friday as low pressure passes to our south. The
precipitation could fall as some snow in the mountains.
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.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --935 AM...At 13z a cold front was draped across the Gulf of
Maine southward through the mid Atlantic region. A 1008 millibar
low was over the rooftop of Maine with a secondary cold front
extended through southeast Quebec and the upper Great Lakes.
Behind last night`s cold frontal passage low cloud on GOES
imagery was spreading gradually south and west on a northeast
flow into mid coast Maine. It`ll be a battle as to how far this
low cloud will spread as westerly flow strengthens today ahead
of the secondary cold front poised to drop south across the
forecast area. For this ESTF update...I made adjustments to near
term grids to reflect satellite trends as well as the 13z
Have updated the forecast mainly to adjust for early morning
temperatures. The front did manage to sneak into Augusta and
Rockland as noted by a wind shift to the northeast and the
arrival of some lower clouds, but it will be pushed back by a
west northwest wind as heating begins today. Once we lose the
heating this evening and the weak low moves east this front will
again make a push back to the west.
A trailing area of low pressure moves across central Maine today
with a west-northwesterly flow in place over northern New
England behind a cold front. Expect good mixing today on the
westerly flow, so coastal areas will warm up into the 60s to
near 70 again, with the warmest readings seen near the
coastline. This is well above normal, but still 15 to 20 degrees
cooler than yesterday. As the mixing begins we will see dewpoint
values drop into the 30s so it will be drier than yesterday was.
Clouds may linger for most of the day in the mountains where
temperatures will also be cooler, in the 50s.
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.SHORT TERM /TUESDAY/...
As low pressure moves east into the Atlantic a cold front will
drop southwest out of eastern Maine, back door style. This front
will be nearing the eastern part of our forecast area this
evening and will make it westward into eastern New Hampshire by
morning. The front may be accompanied by some clouds and maybe a
sprinkle or two as it tracks westward, but low level dewpoints
in the 20s suggest that widespread drizzle and fog is less
likely. The temperature will be falling into the 30s for most of
us but some northern locations will see the 20s.
For Tuesday the northeast to easterly flow will keep this cool
maritime air mass in place over Maine and eastern New Hampshire
with afternoon temperatures another 10 to 20 degrees cooler
than today... 40 degrees cooler than yesterday! The cool air
will not be felt as much to the west of the mountains where
easterly flow will be downsloping, so locations from Keene to
Whitefield will be about 10 degrees warmer than areas to the
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
The 500 mb pattern across the NOAM region remains very blocky
with large scale omega blocking over the continent bookended by
closed lows over the surrounding oceans and a deeper closed low
over the Arctic part of Canada. The Atlantic system looks to
weaken enough to allow a trough to deepen equatorward over New
England and the Maritimes for the latter part of the week, with
several waves moving through. This will make for an unsettled
period, and will keep us out of the warm air making for normal
to below normal temps. Another 500 mb low closes off to our SW,
and models in some agreement that it will slow down there and
allow some cooler ridging for the weekend.
Tue night should remain dry, although with onshore flow some
late DZ is not out of the question, but for now with dry low
levels to start the night, thinking it will probably be limited
to encroaching coastal stratus. Low will likely occur in the
evening and range from around 30 in the north to the upper 30s
closer to the coast.
Wed will see some showers, maybe a period of light rain as
surface low passes well to our north, along with best forcing,
although cold front will cross the region. Highs will stay cool
with mostly onshore flow ahead of the front, and range front the
mid 40s to low 50s. There is some agreement that the front will
pass far enough south for some weak ridging to develop Wed
night into Thu, and this may make for a dry, albeit mostly
cloudy and cool day, although may end up a few degrees warmer
than Wed with flow from the N-NE.
The best chance of steadier precip will be Thu night into Fri
as compact 500 wave moves through. It deepens the most to our
west, and then starts to fill a bit as it moves across the
region Fri, but should get some WAA going with precip likely.
This will mostly be rain but could be mixed with some wet snow
in the mountains and foothills, although any accums will likely
be limited to the higher terrain. Given a return to onshore flow
Friday look for highs limited to 45-50 in the south, and in the
mid-upper 30s in the mountains. The weekend is trending dry at
this point with temps moderating back to near normal as ridging
develops between closed low to our east and developing closed
low over the midwest CONUS.
.AVIATION /13Z MONDAY THROUGH FRIDAY/...
Short Term...Should see mostly VFR conditions today, though MVFR
ceilings may linger northwest of the mountains. A back door
front drops in from the northeast tonight and may be accompanied
by some MVFR stratus as it makes its way from Augusta to
Portsmouth by morning. This should scatter out and dissipate
during the day on Tuesday but could reform as a more robust
marine stratus layer Tuesday evening.
Long Term...An extended period of flight restrictions can be
expected late Tuesday night right through Friday as several
lows affect our region. IFR is expected Wed, with possible
improvement to MVFR Wed night, and maybe even a period of VFR
on Thu, especially away from the coast. IFR or lower should
return Thu night and Friday.
Short Term...Low pressure emerges off the coast near Penobscot
Bay today with a light northwest flow behind it. A back door
cold front will shift winds to the northeast overnight tonight,
gradually turning to the east Tuesday.
Long Term...Borderline SCA are possible in S flow ahead of cold
front Wed. Should stay below SCA Wed night into Thu night, and
may need SCA again Friday.
Expect low relative humidity this afternoon especially on the
coastal plain where humidity values below 35 percent are
expected with strong mixing. West northwest winds will gust to
around 25 MPH. A moist onshore flow on Tuesday will bring much
higher humidity levels, though it will be dry to the west of the
mountains with light winds expected. Moist air overspreads the
entire area Wednesday through the end of the week with periods
Significant melting of snow on Sunday caused rivers to rise and
some minor flooding is expected again on the Kennebec over the
next 24 hours. Colder air should allow snow melt to slow and
rivers should stay below flood over the next several days but
will remain high.