Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 270128

Area Forecast Discussion
National Weather Service Gray ME
928 PM EDT Thu Apr 26 2018

Low pressure exits into the maritimes tonight allowing clearing
that will last into early Friday. A large upper trough will move
east from the Great Lakes and become centered over the region
Friday night through the weekend bringing cool and unsettled
conditions at times in the form of scattered showers that will be
most numerous in the afternoon and evenings both Saturday and
Sunday. The system will begin to exit the region late Monday. A
warming trend is expected to begin Tuesday on a developing
southwest flow.


930 PM Update...Just a few minor adjustments to the going
forecast for the overnight hours. Skies are clearing as planned
for the coastal plain and southern zones as a short wave trough
is moving eastward and away from the region. Showers have ended
across the area. However, upslope clouds and some showery wx is
expected in the mountains for the next several hours.

610 PM Update...Have indeed added thunder to portions of central
and Midcoast Maine where convective showers have grown enough to
produce lightning. Storms should weaken enough to stop producing
thunder by 8 pm.

515 PM Update...Have updated PoPs and weather for the next
couple of hours based on latest radar trends. Convective
showers, possibly with small hail and/or graupel continue to
move eastward across southern Oxford and Androscoggin Counties
as of 5 PM. A few heavy downpours are expected. These will reach
the Augusta area by 6 PM then gradually weaken as they approach
the Midcoast. Have not added thunder to the forecast at this
time as this activity remains low-topped. However, we cannot
rule out an isolated strike or two through 7 pm.


As weakening 500 MB trough crosses New England this afternoon
could set off a few scattered showers, especially across the
foothills and coastal plain of western and central ME, where
lingering surface Tds in the 50s and some sun could spark some
convective showers through around sunset. So an isolated heavy
downpour, and even some graupel, are possible as temps aloft are
cool and freezing level is low. These will diminish with the
sunset, as we lose daytime heating and the wave shifts to our

For tonight, any lingering showers will end quickly, with skies
clearing out this evening. Temps should fall off into the upper
30s N to mid 40s S. Could see some patchy fog develop especially
in the sheltered valleys as skies clear, winds subside and low
level moisture lingers.


Friday morning will start mainly sunny but sun fades during the
morning from SW to NE as a wave cruises around the base of a
trough to our SW, and weak sfc low develops. Highs will be in
the 60-65 range most places, but only in the mid-upper 50s on
the coast as onshore flow develops in response to approaching
system early in the day. Some showers will develop ahead of the
system Friday afternoon, but a period of steady rain is likely
to hold off until late in the day and mostly Friday night. The
system is being sheared out in the SW 500 MB flow, so it will
not be impressive, with QPF mainly around a quarter to a third
of an inch or less. Low will mostly be in the 40s.


Uncertainty on arrival of warmer temps next week... Models
showing a deep upper trof over the Great Lakes region digging
southeast and becoming a broad closed upper low over New England
over the weekend and into Monday. This will provide cool and
unsettled weather. The most numerous showers will be in the
mountains and foothills although all areas will have sct showers
at times especially in the afternoon/evening hours each day.
Any partial clearing during the daytime hours allowing surface
heating will only steepen lapse rates and cause showers to
become more numerous and enhanced, possibly causing some graupel
in a few of the heavier afternoon showers. This is very common
with upper low systems during late April into May across the
Northeast. The euro is much slower in moving the upper low east
and keeps it over the area through Tuesday while some other
models are quicker in moving it east. Prefer the solutions that
move it east by Tuesday allowing the ridge to the west to become
progressive. With this all in mind will push back any warmer
temps to Tuesday and best warming waiting now until at least Wed
where h85 temps warm to +12C to +14C. If the Euro ends up
correct then the warming trend will have to hold off even
longer. For now will stick with the superblend guidance for
temps which is a good hedge and does bring the warmer temps with
the developing southwest flow on Tue.


Short Term...VFR expected at all but KHIE this evening, with the
possibility of some fog at KLEB/KHIE. VFR likely through most
of Friday with MVFR or IFR returning in some light rain Friday

Long Term...Variable conditions from VFR to MVFR in scattered
showers over the weekend and thru Mon.


Short Term...The SCA has been converted for a SCA for seas only
for the ocean waters through Friday as winds are diminishing.

Long Term...Seas over the weekend will be slow to subside over the
outer waters so a SCA for seas may be needed Sat into Sun.


Most rivers have or are cresting, and will be subsiding thru
tonight. The Kennebec is the only exception with minor flooding
expected at Skowhegan, and an outside chance for minor flooding
at Augusta on Friday.


MARINE...Small Craft Advisory for hazardous seas until 5 PM EDT Friday
     for ANZ150-152-154.



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