Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 271108 AAB
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
708 AM EDT FRI MAY 27 2016

.SYNOPSIS...
Warmer air will continue moving into the region through the first
part of the weekend...with the hottest temperatures expected for
Saturday. Upper level high pressure will be in control...so any
showers or thunderstorms are expected to be scattered at best.
Moist tropical air will move in Sunday night brining rain showers.
A cold front pulls through Monday night clearing out the rain.
Tuesday will be warm with a chance for afternoon thunderstorms.
High pressure will move in for the remainder of the week yielding
dry and mild weather.

&&

.NEAR TERM /THROUGH TONIGHT/...
Update...Coastal fog and stratus is beginning to form...mainly in
an arcing band parallel to the coastline. Have adjusted Wx and Sky
grids to account for this into mid morning.

Previous discussion...Warm front is moving into the area this
morning. Showers and a couple rumbles of thunder have formed on
the leading wing of WAA...captured well by the GFS convergence at
900 mb. GFS transitions focus from ENEwd moving band of showers to
more general scattered showers in the background WAA across Nrn
zones thru the rest of the morning. Do not think thunder will be
widespread...but will keep isolated mention as there have been a
few CG and IC flashes detected.

Heights aloft rise thru the day...which should continue to keep
any shower activity scattered in nature. Onshore flow will limit
warming for much of coastal ME...but much of NH will get quite
warm again this afternoon. S/WV trof moves thru Quebec this
afternoon...shearing out as it does so. The decaying front
attendant to it will approach Nrn zones during peak heating.
Convection allowing models show the potential for some storms
mainly in the mtns during this time. Have removed enhanced wording
from the thunder forecast for the afternoon time period based on
latest trends in guidance. Strongest forcing remains well N of the
area...and lapse rates are rather poor with weak mid level flow
across our forecast area. A gusty storm or small hail isn`t out of
the question...but organized convection doesn`t appear likely.

&&

.SHORT TERM /SATURDAY/...
Dominated by upper ridging tonight looks quiet. Winds look to veer
a bit thru the column...which despite a moisture increasing may
help to limit coastal stratus development. For now will leave any
fog mention out of the forecast.

Sat then looks like the hottest day of the bunch. H9 temps
climbing above 20C and Wly low level flow should mean low 90s
across much of Srn NH. Could see some heat index values creep
at or above 95. Given the hot and increasingly humid air mass...at
least modest instability should be in place by afternoon.
However...we lack a coherent trigger for convection. Modeled
QPF is seemingly following terrain features...which makes sense
given the lack of other background forcing. For now will keep PoP
at chance or slight chance.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
High impact weather: Heavy rain showers Sunday night into Monday
bring a chance for flash flood threat.

Overview: Summer makes its long awaited return for Memorial Day
weekend. A broad upper level ridge builds from Bermuda into the
northeastern United States through much of the next week. Tropical
moisture will move in for the start of the week before a brief
shortwave will yield falling heights on Tuesday only to quickly
return to the strong ridge on Wednesday.


Sat night warm air advection continues with ongoing convection from
Saturday afternoon.  Warm air continues to build in for Sunday as
the high crests overhead. On shore flow will keep temperatures at
the shore cooler.

Sunday night showers will develop ahead of a front pushing through
on Monday. Southerly flow around a Bermuda high will push an
exceptionally moist airmass into northern New England. The moisture
transport will be further enhanced from a weak tropical
system moving into South Carolina. Forecast soundings show tropical
airmass characteristics with about 4km of above freezing and
saturated air by 00Z Sunday. Furthermore, current deterministic
guidance suggest PWAT as high as 2 inches is possible...which would
put this at the 99th percentile. That moisture will depend largely on
how the tropical system is able to develop over the next several
days. Even with more modest PWATS /around 1.5 inches/ the storm
motion vectors are less than 10kts across much of our area which
would bring concerns of flash flooding with any cell training. Have
added isolated thunder and heavy rainfall wording for Sunday night
and Monday.

Monday evening the front pushes through leaving the heavy moisture to
our east. While the widespread rain will come to an end
thunderstorms remain a possibility for Tuesday afternoon as steep
lapse rates combine with upper level support from the right
entrance of the jet.

Wednesday the upper level ridge returns and remains in place through
the end of the week. Highs will be seasonable in the 70s with
overnight temperatures in the 50s. Dry and seasonable conditions
continue for Thursday with the next rain moving in on Friday.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
Short Term...Coastal fog/stratus is beginning to develop at this
hour. Instead of a widespread fog bank...it appears to be related
to coastal convergence and thus an arcing band has set up along
the coast. Will include in the TAFs to persist into the mid
morning before lifting with daytime heating.

Widely scattered SHRA or an isolated TSRA will be possible thru
morning in background WAA pattern. A decaying front will approach
Nrn zones later this afternoon...and HIE may see an increased
chance for TSRA during that time. Again confidence is low in that
scenario...with SPC SREF only showing around 40 percent prob for
TSRA this afternoon. As moisture increases tonight...coastal
stratus may again be a problem...though models are forecasting a
more offshore wind component.

Long Term...Sunday night into Monday will see periods of IFR in
rain showers. IFR is most likely along the coast through Sunday
night, where fog may develop, but inland areas may also see the
rain yield IFR. Conditions will return to VFR by late Monday
night. Thunderstorms are possible on Tuesday afternoon.

&&

.MARINE...
Short Term...Winds and seas expected to remain below SCA
thresholds thru the first half of the weekend.

Long Term... Quiet period on the waters as the high pressure keeps
winds and seas calm.

&&

.FIRE WEATHER...
Very warm and increasingly humid conditions are expected for much
of the area through the holiday weekend. Precipitation will be
scattered for the first half of the weekend...with showers and
storms becoming more widespread Sun into Mon.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$

NEAR TERM...Legro
SHORT TERM...Legro
LONG TERM...Curtis
AVIATION...Curtis/Legro
MARINE...Curtis/Legro
FIRE WEATHER...Legro


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