FXUS61 KGYX 180959

Area Forecast Discussion
National Weather Service Gray ME
559 AM EDT Sat Aug 18 2018

Low pressure over northern New England will exit into the
maritimes later today pulling a trailing cold front across the
area. Ahead of this front we`ll see a few showers and
thunderstorms into this evening. High pressure and drier air
will build in from the northeast tonight through Sunday and
then hold over the region Monday and Tuesday. Low pressure will
move in from the west Tuesday night and Wednesday. High pressure
follows this system for Wednesday night and Thursday.



559 AM...Minor ESTF update to reflect the current mesonet in
near term grids.

Prev Disc...
At 06z...a 1008 millibar low was near Sherbrooke with a warm
front extending through central and downeast Maine and a
trailing cold front through the lower Great Lakes. NWS Doppler
Radar mosaic showed widespread convection with some embedded
thunder. For today...the surface low will race east and offshore
near the Bay of Fundy during the afternoon with the surface cold
front settling slow southward across the forecast area. We`ll
continue to see scattered to broken convection traverse the
area along and ahead of this boundary and associated upper
impulse. The 00z raobs revealed an extensive plume of
precipitable water values near 2 inches across the area and
this will continue to produce tropical downpours with localized
flooding potential. There will be some heating in the warm
sector ahead of the cold front...particularly over southeast
New Hampshire and extreme southwest Maine yielding CAPES near
1500 J/KG with forecast soundings suggesting a few stronger
multicell storms and line segments with gusty winds to accompany
the tropical downpours. highs today will be mainly in the 70s
with some lower 80s for southeast New Hampshire and adjacent
southwest Maine.


High pressure and drier air begins to build into northern
sections and the international border area late today. This
drier air and clearing trend will gradually work south with any
lingering showers ending overnight. We`ll see some fog and
stratus develop overnight...especially across the northern
valleys. On Sunday....a few clouds will linger along the New
Hampshire/Massachusetts border with a low chance for a spot
shower...otherwise high pressure and drier air will dominate
northern New England. The easterly flow will keep us on the cool
side...especially close to the coast. Highs will be in the 70s.


With the ECMWF trending weaker and farther S with the S/WV trof
Sun into Mon...the extended is basically two periods of high
pressure punctuated by the passage of a deeper trof.

High pressure and generally gradient/flow Mon should allow for
sea breezes to develop with seasonable and comfortable
temps/dewpoints. Return flow begins in earnest the second half
of Tue. A warm front S of Srn New England will surge Nwd thru
the day. With the return of deeper moisture we may see
fog/stratus develop Tue night. With a seasonably strong surface
low pressure and H8 jet...an area of rainfall will also approach
from the W late Tue into Wed. Both the jet and associated S/WV
trof are weakening with time...so precip character may become
more scattered with time. However...enough forcing remains for
likely PoP showers...and embedded thunder with the lingering 30
kt H8 jet taking advantage of weak instability. PWATs do look
like they will surge back towards 2 inches ahead of the
front...and while embedded convection may be capable of heavy
rain...the threat does not look widespread enough to include
wording in the forecast at this time.

High pressure returns behind the front Thu...and a trailing
secondary cold front will move Swd thru Canada. At this time it
looks like return flow will prevent that trailing front from
moving S of the St. Lawrence Valley in Quebec...and keeping much
cooler air at bay.


Short Term /through Sunday/...Areas of MVFR/IFR ceilings/vsby
persisting through Saturday. Gradually becoming VFR with areas
of IFR/LIFR ceilings/vsby in valley fog tonight. Becoming VFR
through aft 13z Sunday.

Long Term...VFR conditions prevail until midweek. An approaching
front will bring SHRA and embedded TSRA late Tue into Wed. Local
IFR or lower conditions will be possible in the heaviest
convection. Ahead of the front we will also have to watch for
marine fog and stratus moving into coastal terminals.


Short Term /through Sunday/...Winds and seas remain below SCA
threshold. However...winds shift into the northeast behind the
cold front for tonight and Sunday. The winds and seas outside
the bays will increase and cold briefly approach SCA`s in the
northeast flow.

Long Term...NE flow behind the cold front may allow some seas
S of Cape Elizabeth to near 5 ft into Mon. Otherwise...winds and
seas are expected to remain below SCA thresholds. The next
chance for 25 kt gusts and 5 ft seas will be Wed...as a LLJ
lifts across the waters.






NWS GYX Office Area Forecast Discussion

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