NWS Gray, Maine Area Forecast Discussion

FXUS61 KGYX 192239 AAA

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
639 PM EDT Sun May 19 2019

A warm front will set up across New Hampshire and southernmost
Maine tonight and move north of our region on Monday. Showers
and thunderstorms are expected this evening, some possibly
strong across western New Hampshire. Increasingly warm and humid
air moves into the area on Monday. A cold front moving into the
region late Monday will bring showers and thunderstorms, some
possibly severe, to the area before much cooler and drier air
works back into New Hampshire and western Maine for midweek.


630 PM Update...
Storms are making their way across the CT River Valley this
evening, but are losing steam as they encounter a less
favorable air mass. Will continue to watch these cells as they
approach from the west. Much of the region has temperatures in
the 70s with dew points in the upper 50s/lower 60s which will
not do much to help sustain convection, much less support severe
weather. Adjusted PoPs and thunder chances for this update,
bringing the threat into southern NH for the next couple of

Previous discussion...
Warm front extends in a west-east fashion from north of KLEB in
NH southeastward to around KSFM in Maine as of 230 PM. This
front will only move very slowly northward overnight. Conditions
are currently dry as of mid afternoon as larger scale forcing
moved off to the east this morning. However, a weak short wave
trough rounding the mean upper level ridge over the eastern
Great Lakes will continue to move our way late this afternoon
and evening.

Thunderstorms developing in the vicinity of the warm front east
of Lake Ontario should continue to organize and spread eastward
for the balance of the afternoon. These are expected to make it
into the CT River Valley zones in NH after 6 PM. Several CAMs
are in general agreement with this scenario, with marginally
strong storms affecting mainly Grafton and Coos Counties this
evening. Less instability will be available in our forecast
area than points west, so we expect a weakening trend by the
time they get into the CT River Valley. However, a few storms
may be strong with strong wind gusts and small hail. The storms
will continue to weaken as they move eastward into the rest of
the CWA overnight with heavy downpours and lightning being the
main threats.

Coverage of showers and thunderstorms should decrease after
midnight as short wave energy moves off to the east. However,
sct activity should remain present overnight in the general WAA

North of the warm front tonight there will likely be areas of
fog, especially across central and Midcoast Maine. Not out of
the question that it could become dense fog a time.


Warm and humid conditions are expected on Monday as the warm
front lifts north of the forecast area. The exception will be
the Mid Coast of Maine where marine stratus and fog will likely
last into the afternoon hours. Temperatures are expected to top
out in the 70s most areas, with 80s across the far south. It
will feel muggy.

The main forecast concern will be the coverage and strength of
thunderstorms Monday afternoon. At this time, 12z guidance
members are in pretty good agreement with convection initiation
occurring in the western ME mountains and far western NH around
18z as a short wave trough and associated forcing for ascent
moves eastward from the Great Lakes. The activity will then
sweep toward the coast by late afternoon and early evening. As
long as low level moisture doesn`t mix out too much, the
combination of CAPE and deep layer shear will support scattered
severe thunderstorms. Convective mode is a bit uncertain right
now as some CAMs are quick to develop a line of storms, but some
are keeping cells more discrete longer. Mixed modes will
probably be the case, with a few supercells possible along with
clusters and line segments. If LCLs remain below 800-1000m and
SFC winds remain relatively backed, a couple of brief tornadoes
will be possible. However, wind damage will be the main overall
threat. Weak mid level lapse rates will be the main mitigator
of overall storm strength. The threat should end around 00z as
the storms move off the coast.

Clearing occurs Monday night and winds become gusty from the
northwest late as low pressure strengthens off the coast.


Upper air pattern remains largely stationary through the coming
week as a blocking pattern becomes established over western
North America. A trough remains across the southwestern US with
a ridge on top of it over the Canadian northwest. This causes a
downstream trough over Hudson Bay and a downstream ridge over
the southeast US. Our area will primarily be on the northern
periphery of the southeast ridge. We will thus be in the line of
fire for any waves ejecting out of the southwest trough as well
as any which might sneak down out of the Hudson Bay low.

Tuesday we will be in a post-frontal northwest flow regime
which yields warmest temperatures in the south and coast while
cooler conditions and possibly a few showers occur in the north.
Temperatures will range from the 60s near the coast to the low
50s or even upper 40s in northern areas. Cold advection on
Tuesday is strong enough to bring cooling 850mb temperatures
through the day in spite of strong mixing. Winds at this level
peak at around 50 KT. With strong cold advection expect a good
portion of this wind to mix down to ground level. This could
possibly be a Wind Advisory scenario but for now have increased
wind gusts to the 35 to 45 MPH range just about area wide.
Downsloping component southeast of the mountains on the coastal
plain could enhance the downward transport of higher winds.

Pressure gradient begins to relax Tuesday night and especially
on Wednesday as high pressure builds in from the west. This air
mass will have modified after several days of transit across the
northern tier of the US, so high temperatures will only be a
couple of degrees below normal... mainly in the 60s. Could see
some patchy frost in northern areas especially Wednesday night,
though confidence is a bit low due to the possibility of cloud
cover spilling over the top of the southeast ridge. Temperatures
will be a few degrees warmer on Thursday generally in the 60s to
low 70s.

The next low pressure area moves out of the Great Lakes on
Thursday and tracks southeast through southern New England
Thursday night. It is not particularly well organized in part
due to its track through the subsident northwest periphery of
the ridge. However, it could trigger a few showers as it crosses
the region. Some intensification is possible as it reaches the
coast, though the track is uncertain enough that it`s not clear
whether the most likely area of rain will be over northern or
southern New England. It moves out of the area on Friday with
high pressure building in from the north behind it.

The next larger scale low pressure and frontal system moves out
of the northern plains on Friday and through Canada on Saturday.
We will see a southerly low level wind flow behind departing
high pressure and ahead of the approaching front which will
bring warmer, more humid air into the area with an increased
chance of showers. All the models are in agreement that the
parent low tracks to our north in Canada, though just how far
north is not clear. Some models have the southeast ridge pushing
this wave far to the north and thus the trailing cold front
moves through without much upper support for showers. However,
if it moves through a bit closer we could see more widespread
showers across the area. Either way it seems clear the front
will move through our area Saturday night, with a post-frontal
northwest flow expected on Sunday. This would be similar to
Tuesday except warmer and not as windy, likely a nice day for
the coastal plain.


Short Term...MVFR to IFR conditions develop tonight in low
clouds and some fog (mainly coastal plain). Showers and
thunderstorms are also likely this evening, especially in the CT
River Valley. VFR conditions return Monday morning except for
the mid coast of Maine where IFR conditions last into the
afternoon. Showers and thunderstorms with gusty SFC winds are
expected to move through NH and ME Monday afternoon...generally
from west to east between 18z and 00z.

Long Term...Northwest winds gust to 30-35KT on Tuesday behind
a cold front. Could see some showers linger in the mountains but
otherwise expect it to be VFR. Winds relax Tuesday night into
Wednesday. There could be a period of MVFR or IFR conditions and
showers late Thursday into Thursday night with improving
conditions on Friday.


Short Term...Very marginal SCA remains in effect through
tonight for gusts up to 25 kt and seas building to around 5 ft.
Gusty NW winds will occur behind low pressure starting later
Monday night.

Long Term...Northwest winds behind the cold front will gust to
30 to 35 KT on Tuesday. Although this should for the most part
fall within the range of a Small Craft Advisory, it`s possible
that some gale force gusts occur especially near the coast.
Winds diminish through Wednesday with high pressure building in
from the west and cresting over the Gulf of Maine Thursday
morning. A weak area of low pressure tracking southeast through
southern New England could bring some showers and an increase in
winds, but for now it looks like this will remain below advisory


MARINE...Small Craft Advisory until 8 AM EDT Monday for ANZ150-152-154.



LONG TERM...Kimble

NWS GYX Office Area Forecast Discussion