Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 090326

Area Forecast Discussion
National Weather Service Gray ME
1026 PM EST Mon Mar 8 2021

High pressure over the region will move south of the area
tonight and through the middle of the week allowing
significantly warmer air to flow into the region with the
warmest temperatures of the year thus far likely in the
Wednesday through Friday period. A cold front will cross the
region on Friday with a few rain showers followed by much colder
temperatures for the weekend.


Have updated the forecast based on latest mesoscale models and
observational data. Clouds will continue to increase and thicken
late this evening across the region. Snow showers over northern
New York State will enter our forecast area with a chance for
snow showers mainly over the mountains tonight through Tuesday
however a stray flurry or snow shower is possible elsewhere.
Light accumulations of snow will be possible through Tuesday.
Have raised pops slight across the region for later tonight into
Tuesday, however 00Z sounding still indicated plenty of dry air
in our forecast area. Dew point depressions remain
significantly high as well.

Only minor changes to the wind and temperature forecasts. Mainly
lowered temperatures by 2-3 degrees especially over eastern
areas which remained clear for the longest this evening.

Prev Disc...
Impacts...Minimal. Isolated to scattered snow showers possible
in the mountains with very light accumulations possible.

It is difficult to get much quieter than today was with high
pressure poking into New England. However, a look at regional
satellite and radar imagery shows that things are about to
change, even as the overall sensible weather remains quiet. A
shortwave is passing through southern Ontario and Quebec,
producing snow showers that are poised to enter upstate NY this
evening. While clouds will increase throughout the region as we
head into the evening and overnight ahead of the approaching
shortwave, any snow showers should be limited to the mountains
where very light accumulations of snow are possible. The cloudy
skies should put a floor on low temperatures tonight, but lows
will still range from the mid teens in the mountains to the mid
to upper 20s south.


Impacts...Minimal. Isolated rain/snow showers possible in the
mountains Tuesday morning.

We are already seeing building mid-upper level ridging in New
England this afternoon, and while the shortwave moving through the
region may briefly slow the process, the ridging will continue to
build on Tuesday. At the same time, broad surface high pressure
builds over the eastern U.S. The overall result is a dry short term,
with lingering isolated rain/snow showers in the mountains Tuesday
morning the only chance at precipitation through the period.

Tuesday will also be the first day of the mid-week warmup that we
have been talking about for a few days now. Temperatures will climb
rather quickly Tuesday morning as clouds move out of the area in the
wake of the shortwave, though they will linger in the mountains
through the day. Some southern NH locations should hit 50 degrees
while the rest of the region south and east of the mountains will
rise into the mid to upper 40s. High pressure crests overhead
Tuesday night and should lead to rather ideal radiational cooling
conditions. While I did blend in some cooler guidance, clouds may
hinder cooling for parts of NH, and otherwise came up with lows
similar to tonight (mid teens to upper 20s).


High Impact Weather Potential: Minimal.

--Pattern and Implications--

Ensemble guidance this afternoon is in good agreement on a shift of
the North Atlantic Oscillation into the strong positive
territory...while the EPO shifts positive for a shorter time.
Overall this spells a loss of blocking across the northern latitudes
with a large push of Pacific air into North America.  This is a warm
source region for our area and this is borne out in what will be the
largest weather story for at least the first half of the long term
forecast...warm temperatures.  Beyond this...pattern across the
Pacific becomes more amplified...with the downstream wave train
driving a trough in to the northeastern United States this weekend
with a return to more seasonable temperatures...with potentially a
day or two of below normal temperatures. High pressure over the
Gulf Coast largely keeps this moisture source region from being
available...with the only expected weather-maker being during
the shift back to the colder regime on Friday...though much of
the shortwave energy will north of our area by that point. This
weekend...with the source region for our air turning
poleward...and thus drier...outside of mountain snow showers the
area looks to remain dry. Thus...from a weather impact
standpoint...looking rather quiet through the long term period.

--Daily Details--

Wednesday - Thursday: High pressure centered south and east of the
New England coast will allow broad southwesterly flow to overspread
the region taking T8s from just above freezing Wednesday afternoon
to above +5C by Thursday afternoon.  Model soundings suggest mixing
to around H9 both afternoons...which would allow temperatures into
the lower 50s for southern areas on Wednesday...and upper 50s/lower
60s on Thursday.  These late winter/early spring warm ups tend to
over-perform...particularly on the first day...but even more have employed the warmer MEX guidance at this range
to boost model consensus temperatures.

Thursday Night / Friday: Cold front moves through the area as low
pressure passes well north of the region Thursday night.  While
there are differences at this range in the actual strength/position
of the surface low...there is good agreement that the vast majority
of mid an upper level forcing for ascent will be well north of the
region with flow increasingly parallel to the surface boundary
limiting convergence. PWATs briefly push to around 1 inch ahead
of the boundary which...despite the weak forcing...should allow
for at least a broken line of showers reaching the northern
zones late Thursday night or early Friday. Ensemble QPF
probabilities drop markedly south of the mountains and don/t
expect more than a few hundredths of liquid regardless.

Saturday - Sunday: Cold front settles south of the region with some
degree of Polar or even Arctic air pushing back into the
region. Some of the deterministic runs have been rather
cold...and generally near the bottom end of the ensemble
envelopes. So...while a return to more seasonable temperatures
is a near certainty...whether we go significantly cooler than
this is still less certain. If we were to go well below normal
for temps...Sunday would be the most likely day. There are
signals that snow showers would be possible due to impulses in
the northwest flow aloft...but following climatology this would
be most likely in the mountains.

Monday:  There is reasonable ensemble support that as we end the
forecast period early next week that the Canadian high pressure over
the Northern Plains and Great Lakes region this weekend will settle
east and overhead with the coldest of temperatures aloft moving east
of our region and the period ending on a seasonable note.  Will not
move temperatures far from climatological norms at this range.


Short Term...Light westerly to northwesterly winds expected
with VFR conditions through the short term; looks like there
was a weak seabreeze this afternoon as well at the coastal
terminals. HIE could see a snow shower or two tonight with
associated MVFR/IFR conditions possible, but confidence remains
low. Clear skies will gradually become broken overnight, but
ceilings should remain VFR; skies clear again on Tuesday, except
at HIE.

Long Term...
VFR should dominate conditions through the period with the
potential for some brief MVFR restrictions Thursday night and
early Friday as a cold front brings a few showers to the region.
Gusty northwest winds are likely Saturday as the cold front
departs the region.


Short Term...High pressure briefly gets pushed to the side
tonight ahead of an approaching shortwave. This will allow
northwest winds to increase tomorrow behind the shortwave. While
there could be a few gusts to 25 kts over the outer waters on
Tuesday, expected coverage and duration did not warrant an SCA.
The northwest winds will decrease Tuesday night.

Long Term...
Southwesterly winds will increase to SCA levels on Wednesday
night with SCAs likely needed through cold frontal passage on
Friday. Behind this front on Saturday...northwesterly winds will
strengthen with SCAs likely needed again...particularly for the
outer waters.




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