Area Forecast Discussion
Issued by NWS Portland, ME

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897
FXUS61 KGYX 260448 AAA
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1248 AM EDT Fri May 26 2017

.SYNOPSIS...
A broad area of low pressure from the Ohio Valley through the
mid Atlantic coast will slowly lift northeast tonight...reaching
Cape Cod by Friday morning. Low pressure will continue
northeast into the maritimes through Friday night. Weak high
pressure will build over the area on Saturday and will shift
offshore on Sunday. Weak low pressure over the eastern Great
Lakes will lift north into western Quebec Sunday night and will
drive a cold front toward the region on Monday. The front will
slowly cross the area Late Monday night and Tuesday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Update...Have introduced thunder to the grids based on latest
trends and near term forecasts. Lightning detection is still
showing plenty of activity in the convection moving Nwd...less
than an hour from our Srn border now. SPC mesoanalysis shows
around 500 J/kg MUCAPE lingering along the coast. This is
supported by forecast soundings showing a nice area of CAPE
available just above the LLJ. Heavy rain continues in the
forecast as well...with Srn New England ASOS/AWOS reports
showing 0.50 to 0.75 inches in an hour.

I will also let the coastal flood headlines expire on time.

1045PM UPDATE...
Initial batch of rain has developed and begun pushing onshore
over much of Maine this evening, while another more substantial
area of rain is finally taking shape to the south of Rhode
Island. HRRR model is handling both areas of rain quite well,
and based the forecast update largely on this. Precipitation
from the heavier band to the south should be arriving in
southern New Hampshire around midnight. Thunderstorms are
currently noted with this activity as it is forming. As this
wraps around the low, expect the thunderstorm activity to
decrease a bit, but there could still be some rumbles of thunder
across the southern part of our area overnight as this low winds
up. Have increased precipitation amounts as well, as even this
earlier area of rain forming along the coast of Maine has
produced some decent rainfall rates. Area moving in from the
south could produce rates up to about an inch per hour, though
the heaviest rain should only last an hour or two before
becoming light and drizzly.


945PM UPDATE...
Getting a few reports of high, gusty winds. Have increased wind
forecast for the overnight hours, especially through 06Z where
best wind fields will be in place from the northeast.

Otherwise, have updated the forecast based on current
conditions and latest set of mesoscale models. Rain continues to
spread north and east, however it remains fairly light and
fragmented in most areas. Heaviest precipitation remains over
Upstate New York well to our west. However, satellite imagery
continues to show a large plume of moisture forming off the Mid
Atlantic coastline and moving quickly to the north. Mesoscale
models have this heavier precipitation arriving from south to
north within the 06Z and 12Z time frame.

Have made minor adjustments to pops and temperatures for the
next 6 hours. Areas of light rain will continue with downsloping
over the northern Connecticut River Valley.

ORIGINAL DISCUSSION...
Higher pressure and easterly winds have kept much rain from
intruding into northern New England by retarding the advancement
of precipitation into Maine and northern and central NH until
the last couple of hours. The flow has intensified along the
coast as the pressure gradient increases/low pressure nears.
Temperatures have been kept down in this marine airmass while
northern sections were able to break out into the 60s.

CAM models have been correct in showing a weakness this
afternoon in precipitation fields over NH and especially Maine
as energy diverges both towards northern NY State as well as
offshore. We`ll see a break in most shower activity more or
less this afternoon and evening...however there will be widely
scattered showers still around...mainly over the mountains.
Around midnight a stronger short wave associated with this
system will pivot into the area and precipitation will increase
both in intensity and areal coverage. This is when we will see
the bulk of the 1-2 inches with this event. We`ll see some heavy
downpours for the overnight period into Friday morning.

Winds are picking up as mixing deepens today and expect ESE
winds to gust to 25 kt through the night. Continued with
drizzle tonight mainly in between the two systems as the onshore
flow intensifies. Lows will be in the upper 40s to around 50.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
After the heavier rain expected during the morning
hours...precipitation tapers off to showers by Friday afternoon.
Again the heavier rain will be along the coast with some
enhancement over terrain. The long duration of this event should
preclude any flooding issues but poor drainage areas may see
some brief issues in heavier rainfall that occurs through
tomorrow. Expect temperatures to warm only about 5-10 degrees
from overnight lows tonight to highs Friday. Tomorrow night
clouds will begin to decrease across the region. The upper low
will be engulfed in another circulation south of Greenland while
the surface cyclone fills. Overnight lows Friday night will
drop farther in a drier airmass with lows in the 40s most
locations and perhaps up to 50 degrees in warm spots.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Mean long wave trof position will remain over the Great Lakes, this
will mean a general cool wet pattern can be expect for the
outlook period with a few dry periods between systems.

Starting with Saturday, the system that exits into the maritimes
allows weak high pres over the area and a drier north to
northwest flow to develop for Saturday into Sunday with cool
temps. By late Sunday into Monday, the next short wave that
rotates around the base of the Great Lakes trof then moves
northeast bringing another period of wet weather with a
developing onshore flow that keeps temps cool. With the mean
upper trof remaining over the Great Lakes through mid week a
continue unstable southwest flow with embedded short waves with
keep unsettled conditions through Wednesday. It appears we may
finally get rid of the onshore flow by midweek so temps may
actually get back to near normal high temps reaching into the
70s.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Short Term...IFR/LIFR ceilings developing today and persisting
through tomorrow. ESE winds will gust to 25 kts most terminals
through tomorrow. Early on LLWS will affect HIE and LEB tonight.
Drizzle and fog will affect most TAF sites outside of HIE and
LEB tonight before the moderate to heavy rain arrives.

Long Term...Winds and seas generally light.  No flags.

&&

.MARINE...
Short Term...Continuing SCAs through Friday afternoon. At that
point we may need a SCA just for high seas for the outer waters.

Long Term...Conditions become VFR Sat into Sun before returning to
MVFR conditions for Sun night and Monday and possibly through
midweek in scattered showers.

&&

.TIDES/COASTAL FLOODING...
Highest astronomical tides of the year on tap for tonight and
Friday night. A Coastal Flood Advisory remains in place the
Midcoast region of Maine.

The astronomical tide in Portland is 11.8 feet near midnight
tonight. Expect around a foot of storm surge overnight. Flood
stage in Portland is 12 feet and a storm tide will likely be
near 13. Areas of flooding are expected with pockets of
moderate flooding. Have therefore upgraded the Coastal Flood
Advisories from Portland south to warnings.

We may need a Coastal Flood Statement for the tide tomorrow
night despite the absence of an onshore wind as astronomical
tides will be at the flood stage of 12.0 feet in Portland.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Coastal Flood Advisory until 1 AM EDT early this morning for
     MEZ025>028.
     Coastal Flood Warning until 1 AM EDT early this morning for
     MEZ023-024.
NH...Coastal Flood Warning until 1 AM EDT early this morning for
     NHZ014.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ150>154.

&&

$$

NEAR TERM...Legro



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