Area Forecast Discussion
Issued by NWS Portland, ME

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KGYX 151431 AAA
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1031 AM EDT Wed Aug 15 2018

.SYNOPSIS...
A weakening upper low and associated weak surface system will
exit the coast this morning. A cold front over Quebec will
advance southeast into the region later today accompanied by
scattered showers and thunderstorms. Behind this front, high
pressure and noticeably less humid air will briefly build into
the area for Thursday. By friday, another area of low pressure
will approach from the west and bring more unsettled weather
that will last into the start of the upcoming weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1019 AM Update: Generally minor changes to the forecast this
morning as previously cutoff low opens and moves east of our
longitude...and we await a secondary shortwave which is helping
spawn convection north of upstate New York ahead of a surface
front. Between these features we have a slow moving band of
showers over north Northeast Kingdom of Vermont that are
fighting mid level height rises as they slowly sink south in an
airmass of 500-750 J/kg of MLCAPE. While a pop up shower/storm
is possible over northern areas through early afternoon...expect
that...outside of producing locally heavy rain...these will not
be all that strong. Expect that we/ll have to await the front
further to the north and west...which recent HRRR runs as well
as the HREF suggest will not arrive until later this evening.
Certainly another warm and humid day with dewpoints near 70 and
temps about ready to take off as morning llevel cloud cover
scatters. T8s around +14C suggest low-mid 80s...in line with
the warmer /and better performing of late/ MET guidance.

600 AM...minor ESTF update to reflect the current mesonet in
near term grids.

Prev Disc...
At 06z...a broad weak area of low pressure was over the region.
A cold front was draped across central Quebec and central
Ontario and into the northern Great Lakes. Widespread clouds
with areas of fog were across the area in humid airmass. NWS
Doppler Radar mosaic showed scattered convection spiraling
around the rapidly weakening upper low situated over west
central New England on current GOES water vapor imagery. For
today...the weakening upper low will accelerate offshore by dawn
as the system finally opens up and take the current scattered
shower activity with it. Behind it...clouds and fog should lift
for at least a partly sunny day. Meanwhile a shortwave impulse
approaching from eastern Canada will nudge a cold front towards
the international border late today. Ahead of this feature and
with some daytime heating...we should see scattered convection
develop by afternoon with the most abundant coverage across the
higher terrain of northern New Hampshire and western Maine.
Forecast soundings suggest 1500 to 2000 j/kg potential with
heating...and given wind field this looks to be a multicell day
with potential for a few line segments with locally damaging
wind gusts. Precipitable water values remain between 1.50 and
1.75 inches based on the 00z raobs...so we will see some
tropical downpours with these quick moving cells as well. Highs
today should be mainly in the 80s...but with the dewpoints in
the 60s it`ll feel even warmer by several degrees.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
The cold front will cross the area tonight and be offshore by
morning. Convection should quickly weaken in coverage and
intensity during the evening with loss of daytime heating before
ending overnight with the frontal passage. We`ll see some patchy
fog and stratus overnight...especially across interior valley
locations. On Thursday...a near picture perfect summer day with
highs in the upper 70s to mid 80s as high pressure traverses
the area. Dew points will drop into the 50s across much of the
area with the exception of southern New Hampshire and coastal
Maine where dew points are likely to remain in the lower 60s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
The extended begins with the approach of the next S/WV trof from
the Great Lakes. It will try and push a warm front Nwd thru the
forecast area. Now while our forecast area is typically where
surface warm fronts languish...the lack of appreciable high
pressure to the N or E and some of the warmest water of the year
should allow for less push back than normal. Assuming the front
works its way thru at least part of the area and
ongoing/decaying convection does not retard
destabilization...the afternoon forecast looks interesting. A
warm and moist air mass characterized by temps climbing towards
80...and dewpoints increasing into the upper 60s/low 70s will be
in place S of the boundary. At this time...NAEFS guidance is
suggesting a seasonably strong Sly LLJ at H8 will move into the
region Fri as well. While winds veer with height...deep layer
shear remains just marginal for storm organization.
However...low level shear is quite strong featuring plenty of
turning...sufficient for transient or shallow supercellular
structure. Thermodynamic trends will need to be monitored over
the next 24-36 hours...as this is a low confidence but
potentially high impact event. SPC has introduced marginal risk
for most of the Srn half of the forecast area...and I agree that
this is the highest risk area at this time.

The trof axis does not cross the forecast area until Sat...so
convection will be possible into the first half of the weekend.
Will also have to watch for persistent forcing along the warm
front and possible higher rainfall totals there. I tried to
limit heavy rainfall wording to those areas most at risk based
on latest guidance...mainly in the higher terrain. High
pressure looks to hold thru the rest of the weekend...and into
early next week. A much deeper trof is forecast to approach the
East Coast for the middle of next week.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Short Term /through Thursday/...Mainly IFR with conditions
improving to MVFR and briefly VFR btw 12 and 16z. Scattered
shra/tsra develop aft 16z with MVFR and brief lcl IFR
conditions. This activity will end tonight with passage of a
cold front with areas of MVFR and lcl IFR in cigs and fog. Bcmg
VFR throughout aft 13z Thu.

Long Term...Will have to watch for low CIGs Fri ahead of an
approaching cold front. A warm/moist air mass drawn Nwd ahead of
the front may bring marine stratus into coastal areas during the
day. SHRA/TSRA along the front may also bring local IFR or lower
conditions. Behind the front high pressure should bring several
days of VFR conditions during the day...with the possibility of
valley fog at the usual locations.

&&

.MARINE...
Short Term /through Thursday/...Winds and seas expected to
remain below SCA criteria.

Long Term...With generally weak surface flow...winds and seas
are expected to remain below SCA thresholds. Ahead of an
approaching cold front Fri...areas of fog are probable over the
waters as a warm/moist air mass is advected N.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...Arnott
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.