Area Forecast Discussion
Issued by NWS Portland, ME-- Highlight Changed Discussion --
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FXUS61 KGYX 231622
Area Forecast Discussion
National Weather Service Gray ME
1122 AM EST Thu Feb 23 2017
Low pressure moving east through southern Canada will allow a
mild southwesterly flow to continue today. Highs will climb
into the 50s for most of the area with lower 60s across
southern New Hampshire. A weak cold front will try and push
south across the area this evening with a few rain showers
before returning north as a warm front by late Friday. A strong
cold front and more widespread showers will move across the
region Saturday night followed by a drier and colder air mass
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --1050am update: Some low stratus continues along the midcoast
but has generally burned off further inland. Visible satellite
imagery depcts well the area of low clouds over the midcoast and
areas extending further offshore. This should not be a problem
for the rest of the day as the southwest flow develops and
pushes that area further northeast and allows the area of clear
skies to move into that area this afternoon. Elsewhere partly
sunny skies expected with very mild temps. Guidance has been too
cold so some southern areas may reach well into the 50s and
southern NH possibly into the lower 60s this afternoon. Made
minor teaks to cloud and temps forecast based on above thinking.
Update...Tweaked forecast slightly to account for latest
observational trends. A band of moisture convergence along the
coast is allowing for some enhanced stratus/fog from PWM NEwd.
This is a narrow band...possibly tied to frictional convergence
at the land/sea boundary...because PWM has low ceilings while
here at the office skies are mostly clear even off to the E with
only patchy valley fog. Daytime heating will help to mix out
this low clouds near the coast.
Previous discussion...Biggest question today is just how warm
it will get across the forecast area. Currently the warm front
is more or less sharpening in place across the Northeast...and
is forecast to move more rapidly thru the area this morning as
we mix out. That last bit is the key...as we mix out. Recent
warm wx has led to significant model guidance struggles
regarding just how deep the boundary layer gets during the day
over snow pack. Many models failed to even produce a mixed layer
over the forecast area yesterday...yet we managed to climb well
into the 50s for much of the area. 23.00z KGYX raob showed a
residual mixed layer extending up to around H9. Given stronger
low level flow today and some partial sun possible I see no
reason why mixing to near H9 again is not possible. For max
temps I have blended the mixed down H9 temps with MOS guidance
and ignored the raw and hi-res model output. This gives me
fairly widespread 60s across Srn NH...with 50s elsewhere...which
looks on track for this afternoon. There is a little more bust
potential in areas that see more clouds than not...especially
the mtns...so temps could come under forecast values in those
areas if things break wrong.
A s/wv trof crossing Srn Canada will send a cold front into the
region early this evening. It is currently forcing a line of
thunderstorms across Lake Huron...impressive for Feb. That line
will be weaker by the time it arrives in our forecast area...but
convective nonetheless. The line is forecast to move thru the
mtns and central NH before decaying further as the best forcing
continues NE and away from our area.
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.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
The front washes out over the area tonight...and allows moisture
to pool S of it. I expect a little more widespread fog/stratus
as a result...and a very mild night overall.
Early Fri as the front tries to lift back N...there could be
some light precip along it. Given the large dry slot ahead of
the next s/wv trof I think models are over-forecasting QPF.
However Sly upslope flow could lead to more concentrated light
rain or drizzle in the mtns. S of the front will see another
mild Feb day...though not quite as warm as today.
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The models are in decent agreement on the longwave pattern through
late next week. While we`ll see some brief intrusions of colder
air into the region...ridging and above normal temperatures are
expected to dominate the extended period. In the dailies...we
begin the period with an impulse and associated surface low over
the upper Mississippi Valley. A warm front will extend eastward
into northern New England where light rain, drizzle and fog will
be ongoing. The warm front will gradually lift north across the
area on Saturday as the impulse pushes a surface low northward
across the Great Lakes. A glance at the forecast soundings for
Saturday makes me question how far north the surface warm front
will make it...and hence forecast high temperatures for the day.
The surface low will drive a strong cold/occluded front across
the area Saturday night with more seasonable air and upslope snow
showers to follow for Sunday. Another quick moving impulse will
race eastward along the U.S. Canadian border and drive a second
cold front across the area on Monday accompanied by a second round
of upslope snow showers. A weak ridge follows for Monday night
into Tuesday. By Tuesday night, warmer air returns in broad west-
southwest flow aloft. Both clouds and pops will increase in warm
air advection ahead of a disturbance expected to track to our
north and west down the Saint Lawrence mid week.
.AVIATION /16Z THURSDAY THROUGH MONDAY/...
Short Term...Main concern for the first part of today is
development of fog/stratus. A large area of marine fog/stratus
has developed off Srn New England coast this morning...but
forecast motion is generally E and not N. However weak onshore
flow along the coast may bring patchy stratus...like at
RKD...especially thru morning. Otherwise moisture lifting Nwd is
expected to remain mid to high level thru today. Tonight into
Fri...warm air and greater moisture will advect in and likely
lead to more widespread low clouds. IFR or lower is possible at
Srn NH and coastal Wrn ME terminals. There is also the
possibility for LLWS tonight as warm front lifts thru the area.
SW flow around 2000 ft is forecast in the 35 to 40 kt range and
light surface winds could lead to shear values around 30 kts.
Fri night - SAT...MVFR in -ra with areas of IFR in drizzle and
fog. SE sfc wnd Sat gusting to 25 kt at coastal terminals.
Sun...Sct MVFR in mtn -shsn. NW sfc wnd gusting to 25 kt.
Mon...Sct MVFR in mtn -shsn.
Short Term...SW flow will develop over the waters today as a
warm front lifts thru the area. With WAA over cold SSTs I expect
that winds will not be as strong as modeled. A few gusts near
SCA thresholds are possible along with seas building to near 5
ft. However at this time this looks to occur mainly after
00z...and will give the day shift another look at new data.
There should also be some developing fog/stratus over the waters
as warm/moist air moves Nwd into the region thru Fri.
Sat - Mon...SCA`s likely...wth gusts approaching gale outside the