Area Forecast Discussion
Issued by NWS Portland, ME

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765
FXUS61 KGYX 221527
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1127 AM EDT Mon Jul 22 2019

.SYNOPSIS...
A front stalls across southern New England today. Low pressure
will track along it to our tonight and Tuesday bringing
potentially heavy rain to the area. Localized amounts of an inch
or more are possible. Showers diminish late Tuesday. High
pressure will build over New England Wednesday into the weekend
with temperatures and humidity slowly increasing.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1130 am Update...
Have updated the forecst to increase high temperatures for
the midday hours, before temps drop during the afternoon. Upped
pops for this afternoon for western areas per latest surface
observations and radar images.

908am Update... Will only make minor changes
with this update to account for ongoing diurnal trends. The
latest high resolution short term models are much slower in
bringing precipitation into Maine this afternoon and evening.
Both the RAP and the HRRR have backed off on the start time of
precipitation in Maine until around/after 00z. However, the 06z
GFS and NAM still had precipitation coming in by late afternoon.
Will need to wait and see some of the 12z guidance before
making wholesale changes, but it is looking like we may need to
adjust the onset timing of precipitation a little bit for this
afternoon and evening.

6 AM Update...
Made a few minor changes to the sky cover as well as
temperatures and dew points. Temperatures in the mountains have
dropped into the upper 50s, with upper 60s to lower 70s across
the foothills and the coastal plain this morning.


Previous discussion...
A front which moved through yesterday has moved south of the
Gulf of Maine and stretches from the Ohio River Valley to
Pennsylvania to the Atlantic south of Cape Cod. A wave of low
pressure is forecast to move off the coast near Long Island
today as the front becomes active again and begins to lift north
as a warm front.

The best ingredients for a potential flash flood event will be
to our south, including deeper moisture and instability,
multiple forcing mechanisms, and a right entrance region of the
upper jet crossing the region. We still have high PWATs on the
order of 175% of normal, but southern areas have been
noticeably absent from precipitation the last 7-10 days during
the heat wave. Current flash flood guidance indicates portions
of southern NH can handle 2-2.5 inches of rainfall. The most
recent storm total QPF grid currently estimates about 1.5 inches
may fall in this area over the next 36 hours.

So while heavy rain is likely for mainly the southern and
coastal areas, and have reflected this in the forecast, it
appears we should be able to avoid major flooding except for
perhaps urban and small stream.

Rainfall will begin around noon in NH and push east into Maine
by early afternoon. Highs will be much cooler with all the
clouds and rainfall and range from the lower 70s north to lower
80s south. Have removed thunder as it does not look likely for
our area.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
The first low races by the coast overnight tonight, with rain
chances diminishing as it does so. We`ll see fog form offshore
and over the islands, and perhaps inland. Overnight lows will
drop into the mid 50s north to lower to mid 60s south.

Right behind the first storm another impulse will cross the
Gulf of Maine maybe 12 hours later. This will keep showers
primarily along the coast on Tuesday before coming to an end.
The only concern is if this second impulse arrived faster or
farther north, we could see some flooding issues. Highs will be
in the lower 70s to mid 70s area wide.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Models continue to support a re-established wrn Atlantic ridge
after brief bout of troughing moves through around mid-week,
with a trend back to above normal temps and humidity late week
into the weekend, but little in the way of any rain.

The cold front will finally shift well to the south tue and Wed
and temps return to around normal with more comfortable
humidity Wed into Thu. Highs Wed will be in the mid 70s N to low
80s S, and a few degrees warmer on Thu, with mostly sunny
skies. Sea breezes will keep the coast a little cooler.
Overnight lows both days will range from 50-60, coolest in the
north and warmest in srn NH.

Sfc ridge will gradually shift off shore Fri-Sun and t/Td will
be on the rise each day eventually reaching into the mid 80s to
around 90 by Sunday.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
Short Term...There may be some brief fog in the mountain
valleys in the next few hours as moisture increases. Otherwise
expect VFR conditions even once rain begins towards mid morning
over NH and in the afternoon over western Maine. Ceilings will
eventually lower to MVFR and possibly lower in heavier areas of
rain this afternoon and evening with some fog developing. KHIE
and KLEB may have higher ceilings. Rain chances decrease from
the northwest tonight with coastal as well as KMHT/KCON/KAUG
seeing chances for rain and MVFR ceilings continue through
Tuesday.

Long Term...There could be some lingering flight restrictions
on the coast Tue evening, but should see a return to VFR by Wed
morning, which will hold at all terminals thru Friday.

&&

.MARINE...
Short Term...Low pressure tracks along a stalled front to our
south today and Tuesday bringing rain and fog to the waters.
Winds will stay below advisory levels, but wave heights could
approach 5 ft for a couple hours today in the western Gulf of
Maine.

Long Term...Winds and seas remain below SCA thresholds Tue night
thru Friday.

&&

.CLIMATE...
Portland tied its warmest low temp on record yesterday /7-21/
only dropping to 76 F early Sunday morning. The only other time
this happened was 7-22-2011.

&&

.EQUIPMENT...
The Sugarloaf NWR transmitter is off the air until further
notice. This will be an extended outage as the tower, which was
severely damaged in a winter storm, is rebuilt.

&&

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

&&

$$



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