Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 250318 AAD
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1118 PM EDT Mon Jul 24 2017

.SYNOPSIS...
Low pressure tracking through the Gulf of Maine tonight will
keep rain in the forecast through the evening with lingering
showers tapering off Tuesday morning. High pressure builds in
from the west on Tuesday and shifts offshore on Wednesday. Some
warmer air moves in on Wednesday, bringing temperatures back up
to near normal. But a cold front pushes toward the area on
Thursday, with low pressure possibly forming along the front
bringing another chance of rain and cooler temperatures.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
1117 PM Update...
Minor changes to account for current observational trends.
Rain has transitioned to heavy drizzle along the coast with any
bona fide showers relegated to the mountains and foothills.
Shower activity may pick up again as upper level support arrives
shortly.


959 PM Update...
Shower activity still ongoing across the region as both the 700
and 500 mb lows have yet to cross New England. Expect weak
showery activity overnight as this occurs. Euro and GFS20 are
more bullish with precip overnight with the HRRR and RAP models
much more spotty. The latter models have a better handle on the
situation attm and have kept only slight chance or chance PoPs
in where warranted.

Regardless plenty of low level moisture is still lingering and
stratus will continue to be an issue as well as patchy fog and
drizzle over southern sections. Temperatures are not going to
change much through daybreak with overnight lows just a few
degrees lower than they are now. Adjusted the forecast for these
broad points.


605 PM Update...
PoPs were adjusted as well as stratiform vs. shower wording as
rain shield moves to the east and is slowly replaced by lighter
and more showery activity. This will also be the case overnight.
Also added drizzle over southern portions of NH and SW Maine
near the coast where ceilings are around 200-800 ft and not
expected to lift for a while.


Previous discussion...
The large area of steady, moderate rains will continue to exit
to the east this evening. This will leave the region with
pockets of mainly light rainfall and patchy fog. The latest HRRR
continues to show most of the precipitation exiting eastern
areas during the 03Z to 06Z range.

With the cloud cover and a northeasterly gradient, temperatures
will not move all that much from their current readings.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
Much of the precipitation will be east of the region on Tuesday.
Low level winds will back to the north during the day, allowing
for limited drying. However, the upper level low pressure system
will remain overhead during this period. Scattered showers will
develop as lapse rates increase and surface temperatures reach
milder conditions than today, about 70 degrees for many
locations. This precipitation will be mainly away from the
coastline.

The scattered showers will diminish around sunset on Tuesday
evening as high pressure builds over northern New England. This
will leave the remainder of Tuesday night rainfree. However,
plenty of low level moisture will linger over the region,
allowing patchy fog to form once again.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
High pressure crosses the area Tuesday night, bringing decent
radiational cooling conditions with a dry air mass in place.
Temperatures will fall into the 40s and 50s overnight, rather
cool for this time of year.

High pressure shifts offshore on Wednesday with a return
southerly flow developing. This will bring warmer and more humid
conditions back into the area, though we will still see
temperatures near normal for late July.

Models diverge a bit on the handling of the next trough. The GFS
sends most of the energy with this trough eastward in
progressive fashion to our north, sliding a cold front through
our area on Thursday. This would bring a chance of showers and
thunderstorms as the front moves through, with less humid but
still seasonable temperatures behind the front for Friday. The
ECMWF and CMC models, however, are in agreement that the better
energy will linger near the base of the upper trough, spinning
up a rather strong surface low which tracks across southern New
England on Friday. This would send a good chunk of rain headed
our way, with temperatures staying quite cool on Friday. Given
the newly upgraded GFS is the outlier, it would seem that the
ECMWF/CMC might be on to something here. Have tilted the
forecast in favor of this scenario for Friday, though
uncertainty remains.

High pressure builds in behind the departed front/low for the
weekend, bringing fair weather and temperatures near seasonal
normals but with only moderate humidity.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Short Term...Pockets of light rain and fog will continue
overnight, bringing some areas of IFR and LIFR conditions.
Ceilings will be lowest along the coast. A gradual lifting of
the clouds will occur on Tuesday, but there will still be
scattered showers.

Long Term...There will be a chance of thunderstorms on Thursday
and a chance of more widespread IFR to LIFR conditions in rain
on Friday.

&&

.MARINE...
Short Term...Prolonged northeasterly flow over the waters will
allow waves to build into the 4 to 7 foot range. Increased
gradient will allow for wind gusts to 25 to 30 knots along the
outer waters. Seas will be slow to subside on Tuesday.

Long Term...Winds and seas remain fairly calm over the waters
for the next several days as high pressure crosses the Gulf of
Maine. A return southerly flow begins on Thursday, with a cold
front or low pressure passing through on Friday. Depending on
the track of this low, it is possible that advisory level
conditions could occur.

&&

.TIDES/COASTAL FLOODING...
The astronomical high tide in Portland Harbor is 11.5 feet
tonight. Northeasterly winds will allow for a half foot or more
storm surge overnight, bringing the storm tide to between 12 and
12.5 feet. Flood stage is 12 feet. Minor flooding is expected
along the wharfs and wharf side streets in Portland, Granite
Point Road in Biddeford and the Backbay area of Hampton.

Nearshore waves building to 4 to 7 feet may allow for some
splash-over in Saco tonight.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Coastal Flood Advisory until 3 AM EDT Tuesday for MEZ023-024.
NH...Coastal Flood Advisory until 3 AM EDT Tuesday for NHZ014.
MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ150-152-154.

&&

$$

NEAR TERM...Hanes
SHORT TERM...Cannon
LONG TERM...Kimble



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