Scientific Forecaster Discussion
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Area forecast discussion...updated
National Weather Service Gray ME
454 am EDT sun Sep 22 2019
high pressure sliding offshore will bring deep southwest flow
over the region through Monday. That will mean a continuation of
very warm temperatures for late September. Gradually a cold
front will approach Monday, bringing showers to the area into
Tuesday. Cooler, but still seasonable temperatures will follow
the front Tuesday.
Near term /until 6 PM this evening/...
update...have expanded valley fog further and included more
dense fog wording than previous update. Increasing low level
moisture along with favorable radiational cooling is allowing
valley fog to really expand in coverage.
Previous discussion...fairly widespread valley fog...with
locally dense fog in the CT River Valley...will linger thru
sunrise. A very warm air mass and SW flow will help that fog
lift quickly as daytime heating commences however.
Attention then turns to just how warm we get today. Given
widespread readings in the 80s yesterday...I see no reason why
we do not at least repeat that today. 22.00z gyx soundings
showed mixing thru 800 mb...and doing that again today would mean
fairly widespread readings in the mid to upper 80s. I have
increased forecast highs above guidance for the favored SW
downslope areas in srn New Hampshire and adjacent swrn ME.
Short term /6 PM this evening through 6 am Monday/...
SW return flow continues ahead of an approaching cold front. I
still expect the bulk of the showers to remain along that
boundary and farther north near the warm front. I cannot rule out a
stray shower...but overall I have slight chance pop at best.
Increasing cloud cover and gradient flow keeping advection
going will keep min temps much warmer than past nights. Srn New Hampshire
will likely see some readings struggle to fall below 65. Will
have to watch for any breaks in cloud cover that could
facilitate radiational cooling...as increasing low level
moisture would favor fog formation.
Long term /Monday through Saturday/...
a cold front will stall to the north of New England on Monday as
a new area of low pressure forms to our west. With the front
lingering to the north, expect rain chances to be lower in our
area especially during the morning. However, as the day GOES on
the new surface low tracks east along the former cold front and
drags a new front in from the west Monday evening. This will
provide the best chance of shower activity Monday evening into
Monday night. With our area staying in the warm sector on
Monday, expect highs to once again reach the low to mid 80s
across the region. Some cloud cover could hold temperatures a
few degrees cooler than they are today, but it will still be a
warm and humid day. With the warm, humid air mass in place ahead
of a cold front we can't rule out the possibility of a stray
thunderstorm, however overall instability remains quite low so
the threat will be fairly minimal. The front clears the coast
overnight Monday night bringing any shower activity to an end.
Upper level low pressure slowly moves across the region on
Tuesday. As it does so expect afternoon showers to develop
especially in northern areas. Temperatures will be 10 to 15
degrees cooler beneath the cool upper low, with warmest
temperatures in the south and coast with an offshore flow. The
upper low moves east Tuesday night with showers coming to an end
in the evening and high pressure nudging in from the west. With
less humidity in place, we should see lows falling off into the
40s and 50s again. High pressure crosses the area on Wednesday
with temperatures at their coolest... highs in the upper 60s to
low 70s which is still a few degrees above normal for this time
The next trough swings toward the area on Thursday, with much of
the energy passing to our north. It will drag a cold front
toward New England, though, along with our next chance of
showers. Slightly cooler on Friday behind the front, but this
cooler air won't last long as the upper ridge begins building to
our west again with warm temperatures returning for the end of
the week and the weekend.
Aviation /09z Sunday through Thursday/...
short term...local LIFR conditions in valley fog will continue
thru sunrise this morning. Remaining fog will lift and widespread
VFR conditions prevail into tonight. Increasing clouds and
gradient keeping a light breeze up I think fog will be less
likely than the past couple of nights.
Long term...a cold front moves in from the west Monday evening
which will bring a chance of showers as it crosses the area.
Could see some MVFR conditions in these showers but otherwise
expecting mostly VFR conditions. VFR conditions likely continue
through Thursday with the possibility of valley fog in the early
short term...SW flow today into tonight over the waters. Went on
the lower end of guidance given the warm advection over
relatively colder waters. Late tonight some seas well outside
the bays may build to near 5 ft.
Long term...southwest flow continues on Monday, though went a
bit below guidance on wind speeds due to relatively poor mixing
expected. Wave heights will be highest in the central to eastern
Gulf of Maine where the fetch will be greatest. A few waves of 5
feet are possible there. Cold front moves through Monday night
with an offshore flow expected Tuesday. High pressure builds in
behind the front through Wednesday.