Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 221014

Area Forecast Discussion
National Weather Service Gray ME
614 AM EDT Sun Apr 22 2018

High pressure centered over the Great Lakes will build east into
the region today...then stick around through Tuesday with fair
weather and seasonable temperatures before exiting into the
maritimes. By mid week, unsettled weather returns with the
approach of our next storm system.



614 AM...For this ESTF update only minor adjustments to near
term grids to reflect the current mesonet.

Prev Disc...
At 06z...a 1031 millibar high was centered over the
Great Lakes. GOES imagery showed widely scattered clouds across
the area pivoting around a decaying storm system centered
northeast of Newfoundland. For today...the building surface high
and rising heights bring a mostly sunny and mild day with a
diminishing northwest flow to round out the weekend. Highs will
range from the upper 40s and lower 50s across the
mid 50s to lower 60s elsewhere.


Clear and cool tonight under the building surface high and I
undercut machine temperatures a bit in the dry airmass. On
Monday...the high will be centered to our south. After a chilly
start...temperatures will rebound to the mid 50s to lower 60s
under the strong late April sunshine. The light synoptic flow
will give up the ghost by afternoon in favor of a strong
seabreeze with the mercury dropping off during the afternoon
near the coast.


The trend in model guidance has been to slow the advance of
upper low pressure...allowing for one more dry and mostly clear
day Tue. H8 temps around +5C will support widespread 60s across
much of the forecast area.

But all good things must come to an end...and so will our
warming trend by Wed. Upper low pressure will lift into the
Northeast as it is picked up by a trof digging across the
central CONUS. SEly LLJ will develop and help transport PWAT
values around 2 standard deviations above normal towards the
forecast area. The 22.00z GFS and CMC feature a stronger
interaction with the approaching trof...and thus higher QPF
across the forecast area...while the 22.00z ECMWF keeps forcing
more separate and lighter QPF amounts. ECMWF EPS shows nearly
half of the members on the more robust side of some
support to the North American solutions. That being said...this
will be lighter than the last QPF event for the region. It will
be worth keeping an eye on the headwaters the
gradual warm up and around an inch of QPF will bring some river
forecast points to near flood stage. Ensemble river guidance
using the NAEFS QPF does bring several points...including on the
Saco...Swift...and a 30 to 50 percent chance of
flooding. So I will continue to mention the threat in the HWO.

Beyond the midweek system...Ern CONUS trofing looks to hang
around. This will mean unsettled wx continues as we will be on
the downstream side of the trof...but the pattern will also not
be overly cold either.


Short Term /through Monday/...VFR.

Long Term...VFR conditions prevail thru early Wed. Developing
onshore flow will see lowering CIGs by Wed afternoon...and
precip moving in from the SW. Areas of MVFR/IFR are likely in
RA thru early Thu. IFR CIGs will be most likely near the
coast...but rainfall will be fairly widespread across the area.


Short Term /through Monday/...Quiet on the waters with winds and
seas below SCA under building surface high. For Monday mid day
and afternoon...developing seabreeze along the coast will bring
gusts to 20 kt and briefly building seas.

Long Term...Persistent Sly flow by Tue may allow seas outside
the bays to build to 5 ft. As flow becomes more Ely and LLJ
increases into Wed and Thu...more widespread SCA conditions are
likely with gusts to 25 kts and seas over 5 ft.





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