FXUS61 KGYX 211850

Area Forecast Discussion
National Weather Service Gray ME
250 PM EDT Sat Jul 21 2018

Low pressure will move northward off the Mid Atlantic coast
tonight and Sunday and bring rain to northern New England,
possibly heavy at times Sunday morning. Thereafter, a tropical
air mass will remain in place through mid week with scattered
tropical showers and thunderstorms each day. A cold front
crosses the region Friday and moves offshore next Saturday.


Stratus and areas of fog off the coast will rapidly develop and
spread west along the coastal plain on the light east to
southeast low level flow this evening. Otherwise clouds will
spread north from south to north overspreading western and
northern areas later this evening.

Meanwhile a sub-tropical short wave will rotate negatively
around the base of the digging Ohio valley upper low and develop
as is races north up the east coast. This system will be
speeding north toward the area toward morning spreading rain and
convection into southern areas toward morning. Models in fairly
good agreement on timing. Stayed close to RFCQPF. Considering
the tropical nature of its source region would not be surprised
to see some locally higher amounts than forecast. Overnight
temps will be milder as the tropical air mass slowly advects


The sub-tropical wave is progged to move well west of the
forecast area into western New York by Sunday morning leaving
us in the east quadrant and very unstable tropical southerly
flow. Expecting heavy rains and convection through the morning,
some of which may be strong. Considering the northward speed of
the system, strong sheer creating convection may allow some
strong gusts making their way to the surface through the more
stable light boundary layer east-southeast flow. Models agree on
heaviest QPF to be in the morning into early afternoon before
tapering to scattered showers. Once again, due too the tropical
nature and very high PWATS, QPF amounts may end up higher than
forecast which is generally in the .75-1.5 inch range.

Sunday night the tropical southerly flow continues with
scattered tropical showers. Very muggy conditions will prevail.

Fog will also plague the coastal plain Sunday through through
Sunday night as the very high dewpoints move over the cool ocean


Deterministic models and ensemble members are in above average
agreement on the pattern for this upcoming week. The trough
parked from the Great Lakes to Georgia will continue to weaken.
To the east, blocking high pressure over the Atlantic will
build downstream farther inland over the northeast. A northern
stream short wave in Manitoba will begin to dip slowly into the
northern Plains and eventually the northern Great Lakes and New
England by week`s end.

A warm and tropical air mass remains in place throughout the
week with temperatures in the 80s and dew points in the 60s and
70s, making for a very muggy and uncomfortable time. PWATs and
specific humidity values remain anomalously high for much of the
week. Showers and thunderstorms will be in the forecast each
day, especially during the afternoon when diurnal heating and
CAPE values are highest, and especially over the mountains and
foothills, where differential heating boundaries exist. Heavy
downpours and/or flash flooding will be possible under any
shower or thunderstorm, especially if cells train.

After several days of tropical-fueled convection, the approach
and passage of a northern stream short wave, mentioned earlier,
could trigger flash flooding, or additional flash flooding. A
pre-frontal trough will arrive on Thursday, providing a sharp
focus for showers and a few strong embedded thunderstorms.
Heavy downpours are likely, especially over the higher terrain,
and flash flooding is a real possibility. The cold front
arrives Friday into Saturday and makes a slow traverse of
northern New England, pushing offshore next Saturday. A few
scattered showers and thunderstorms are expected. The good news
is beyond this beneficial rainfall this week, drier air will
filter in behind next weekend`s front.


Short Term...VFR conditions will lower to IFR/LIFR conditions
on the coast this evening then spread inland overnight...mainly
low clouds and fog. Showers are expected to arrive across
southern NH after midnight tonight and expand to the rest of NH
and ME by early Sunday morning. IFR conditions in showers and
possibly thunder are expected during the day on Sunday.
Generally IFR conditions will continue with stratus, showers,
and fog through Sunday night.

Long Term...All terminals will have MVFR/IFR conditions possible
Monday through Wednesday in -TSRA and -SHRA with heavy
downpours...but most likely at HIE and LEB. Fog and stratus is
also likely everywhere at night and in the early morning hours.


Short Term...Winds and seas remain light tonight. The prolonged
light southeast onshore flow will allow seas to build Sunday so
a SCA for the outer waters for building seas has been issued
for Sun and Sun night.

Long Term...Waves remain AOA 5 ft Monday into Tuesday morning
for the outer waters...therefore requiring a SCA still. The
bays should drop below 5 ft by Monday morning sometime. Winds
will be southerly 10-15 kts Monday and Tuesday, and may increase
to near gales for the outer waters on Wednesday, which would
require another SCA or a gale warning.


Some smaller rivers and streams may need to be monitored Sunday
as bursts of heavy rains and scattered thunderstorms produce
locally up to 1.5 inches of rain with some higher amounts


ME...Beach Hazards Statement until 8 PM EDT this evening for MEZ027-
MARINE...Small Craft Advisory for hazardous seas from 11 AM Sunday to 8
     AM EDT Monday for ANZ152-154.
     Small Craft Advisory for hazardous seas from 7 PM Sunday to 8
     AM EDT Monday for ANZ150.



NEAR TERM...Marine

NWS GYX Office Area Forecast Discussion

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