Area Forecast Discussion
Issued by NWS Portland, ME-- Highlight Changed Discussion --
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FXUS61 KGYX 271635
Area Forecast Discussion
National Weather Service Gray ME
1235 PM EDT FRI MAY 27 2016
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 bringing 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 /TODAY/...
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Clouds hanging tough across much of Maine today south of the
mountains. This has kept temperatures in the 50s. Should continue
to see this erode from west to east through the remainder of the
afternoon. As it does so temperatures will finally begin to warm
up. Hourly temperatures and high temperatures were updated with
this update to account for cooler conditions where the cloud cover
will linger the longest. Otherwise no significant changes were
Clouds and isolated showers associated with an initial shortwave
trough are moving through central and eastern parts of the area
now. Have adjusted cloud cover forecast to better match current
trends and to try to paint a picture of decreasing clouds as the
morning goes on along the coastal plain while clouds advance into
northern areas through the day. Area of showers and storms in
Quebec will move eastward and may clip the northern part of
western Maine late this morning or early afternoon. Instability
generally decreases as these storms move toward our area, so they
could lose their punch as they get here. Isolated to scattered
convection expected to develop this afternoon over New York,
Vermont, and possibly bleeding over into western New Hampshire as
well where better heating and instability exist. Further east, an
onshore southerly flow will limit instability over Maine.
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.
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.
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.SHORT TERM /TONIGHT AND 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.
Saturday then looks like the hottest day of the bunch. H9 temps
climbing above 20C and westerly low level flow should mean low
90s across much of southern 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.
Saturday 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
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 /13Z FRIDAY THROUGH TUESDAY/...
Deck of clouds at about 1000 to 1500 feet persists across the
coastal plain from Concord/Manchester eastward to Augusta. This
will gradually move east and dissipate through the morning. Could
see some afternoon showers/thunderstorms develop over western New
Hampshire. Most likely areas impacted will be Whitefield and
Lebanon though the chances are quite low. 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.
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.
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.
NEAR TERM UPDATE...Kimble