NWS Gray, Maine Area Forecast Discussion



000
FXUS61 KGYX 200826
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
426 AM EDT Sat Jul 20 2019

.SYNOPSIS...
A hot and humid air mass which has been baking over the Midwest
will move into the area today. Expect the temperature to top 90
degrees just about everywhere with some places getting close to
100 degrees. With the humidity it will feel even hotter. A cold
front drops down from the northwest on Sunday with one more hot
and humid day before the front cools things down. The front
stalls south of the region and low pressure is forecast to track
along this front, bringing showers to the region Monday into
Monday night. An upper level trough may bring a risk for a
shower through midweek.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Heat and Humidity: A very warm moist airmass in place across the
region. Dewpoints are in the 70s across southern New Hampshire and
overnight temperatures remain in the 80s along the mass border. This
will provide a very warm starting point for a day that will just get
warmer. Have not made substantial changes to the forecast as at this
point the forecast highs from various models are all quite closely
clustered with the consenus being highs near 100 and 90s
extending clear up to the Canadian border. This will push the
heat index up to 110 across southern New Hampshire and well into
the mid 90s through the north. Only change to the headlines was
to expand the Excessive Heat Warning into interior York county.
This area saw some of the warmest temperatures today and
overnight giving it a slight edge up to heat up for today. The
other area of concern is the lower Connecticut River valley and
Keene NH. Here the topography will help to trap the low level
moisture which may allow the heat index to climb above the 105
threshold. While the valleys may bake, the rest of Cheshire and
Sullivan counties will not be quite as hot due to the
topography and thus have opted to leave the heat advisory in
place for this region.

Convection: While the main story of the day will likely be the heat,
some attention needs to be paid to the potential for convection to
move through the area, especially along the Canadian border and
into central Maine. As the ridge axis crests to our west that
leaves open a path for a ridge roller MCS to move down into our
area from southern Quebec. Here the source of the trigger would
be remnants of the ongoing convective complex over northern
lower Michigan. Upstream soundings from Maniwaki Quebec show a
much weaker 500mb capping inversion and thus this ridge running
trigger may be able to initiate convection over the
Ontario/Quebec border later this afternoon. If such convection
develops, nothing in our environment will be able to stop it as
a layer of mid level steep lapse rates remains overhead. With
40kts of shear to assist in the organization any convection that
forms would be capable of producing damaging winds. This is a
conditional threat, dependent on the upstream trigger and thus
hard to really express in the gridded forecast. Have opted to
increase PoP through the mountains with mention of gusty winds
however anything which does occur will be capable of extending
further south, and this threat will need to be monitored this
morning.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Overnight temperatures will remain very warm, and even warmer if
any convection impacts the region leaving us with some residual
cloud cover. Some patchy fog is again likely as valleys will
not be able to mix out very well.

Sunday the southwesterly flow continues ahead of a cold front
approaching from the west. This southwesterly flow will continue to
drive up the heat and humidity which will just build again on the
already warm overnight temperatures thus expect some regions of
southern NH to be even hotter on Sunday than today and the excessive
heat warning remains in effect.  The cold front will cross the
region in the late afternoon bringing welcome relief from the heat
and humidity but also showers and thunderstorms. With such a humid
airmass and high PWATs expect heavy downpours in any storms. These
downpours will in turn mix down some gusty winds.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Beginning Monday we will see an end to the oppressive heat and
humidity we have been experiencing. Highs Monday will be in the
mid 70s north to mid 80s south, with temperatures areawide
Tuesday in the 70s under cloud cover, precipitation, and
northerly winds. Readings rebound slightly for the remainder of
the week, but should only get as high as the mid 80s at the
warmest.

Gentle troughing will remain the general upper level pattern for
the first part of the work week. A significant open trough
over the eastern Canadian Provinces will be digging into the
Great Lakes region earlier in the week and will make its way
towards the northeastern states by midweek.

At the surface, the frontal boundary which moved through
northern New England Sunday will shift just offshore Sunday
night and will remain there through Tuesday night. Lee troughing
along this boundary will stretch from southern New England into
the Piedmont region. Recent model runs have been deepening low
pressure as it ejects into the Gulf of Maine Monday night into
Tuesday. This would bring us our most significant rainfall of
the long term period as the low tracks just off the coast along
the stalled front. Along with PWATs about 150% of normal, the
stalled boundary and forecasted slow storm motion will
contribute to heavy rain and possibly training which may lead to
heavy rain concerns.

Wednesday into Thursday subtropical ridging builds in from the
south. This will bring mostly dry conditions with some chances
for showers over the mountains as weak waves pass to the north.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
Short Term...Some patchy fog in the northern valleys will give way to
sunshine today. Expect hot and humid VFR conditions across the
region. Some thunderstorms are possible across the northern
mountains this evening.

Long Term...Scattered thunderstorms expected to continue into
Sunday night into Monday morning as a cold front crosses the
region. Areas of MVFR or IFR conditions developing in low clouds
and locally heavy rainfall for all terminals. Conditions
gradually improve Monday morning. Lowering cloud cover possible
later Monday into Monday night as low pressure brings showers
to the region...mainly for the southern terminals.

&&

.MARINE...
Short Term...Areas of fog will linger through the day east of Casco
bay through the morning. Southwesterly flow will bring more hot
and humid air into the region.

Long Term...A front drops south of the area Sunday night and
stalls south of the area through early next week as low
pressure tracks northeast along it. There will be periods of
heavy rain and fog over the waters during this time.

&&

.CLIMATE...
It will be hot this weekend and record high temperatures and
record warm low temperatures may be challenged. The records
are as follows:

July 20
CONCORD: 101 in 1977 and 72 in 1975
PORTLAND: 96 in 1949 and 70 in 2013, 1991, and 1949

July 21
CONCORD: 101 in 1977 and 74 in 1876
PORTLAND: 99 in 1977 and 72 in 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...Heat Advisory from 11 AM this morning to 7 PM EDT Sunday for
     MEZ012>014-018>028.
NH...Heat Advisory from 11 AM this morning to 7 PM EDT Sunday for
     NHZ002>007-009-011-014.
     Excessive Heat Warning from 11 AM this morning to 7 PM EDT
     Sunday for NHZ008-010-012-013-015.
MARINE...None.

&&

$$

NEAR TERM...Curtis
SHORT TERM...Curtis
LONG TERM...Hanes

NWS GYX Office Area Forecast Discussion