NWS Gray, Maine Area Forecast Discussion

FXUS61 KGYX 291136

Area Forecast Discussion
National Weather Service Gray ME
736 AM EDT Thu Jul 29 2021

Low pressure approaches from the west today and crosses
tonight, bringing widespread rain and embedded thunderstorms to
the area into Friday morning. Scattered showers and gusty winds
are expected behind the system through Friday evening. High
pressure briefly builds Saturday into Sunday with seasonably
cool and comfortable temperatures for the foreseeable future.
The next showery system crosses Sunday into Monday.


Made minor adjustments to sky cover forecast as cloud cover
associated with the arrival of low level moisture in NH has been
a bit more extensive. Otherwise no significant changes in
forecast thinking.

High pressure moves east today opening up a southerly flow
across our area. After quite a cool morning in this dry air
mass, we`ll see moisture levels increasing in the low levels of
the atmosphere with cloud cover increasing as well. Some cooling
aloft associated with the approaching trough may combine with
the low level moisture advection to produce some showers or even
a thunderstorm by midday, but the better chances will be in the
late afternoon. Temperatures will be quite cool by late July
standards, peaking in the low to mid 70s.


The general idea of a trough approaching from the west leading
to increased chances for showers and thunderstorms through the
night tonight is well agreed upon by all the models. However,
there`s still a wide array of possibilities on where the heavier
rainfall may occur as well as some differences on the timing of
it as well. Thus for this forecast I tried not to get too
precise with timing or location of high PoP or QPF, although I
did try to show the best estimate on timing and locations of
greater rain chances based on a synthesis of the model guidance.
At this point it seems there may be an initial area of showers
and thunderstorms affecting northern NH and northwest ME this
evening while synoptic forcing then transitions to a focus on
southern NH and through the coast of Maine during the overnight
and into Friday morning as low pressure develops near the coast.
All of this rain will be convective in nature and thus highly
variable and occasionally heavy, especially where it persists.
Total rainfall amounts are likely to range from about 0.5 to 1.5
inches with the possibility for amounts over 2 inches where
convective enhancement persists. Temperatures remain fairly mild
overnight tonight, in the low 60s to upper 50s.

On Friday the developing surface low moves east while the upper
trough moves in overhead. Cool air within this trough will move
in ahead of the drier air advecting in the low levels, and as a
result we will likely see the resulting instability bubble up in
the form of showers and a few thunderstorms on Friday even well
after the low has departed to the east. However, as the day goes
on, the dry advection will win out and shut off the showers and
thunderstorms. The northwest flow behind the low will also
promote better mixing in the low levels and support wind gusts
of 20 to 30 mph. The warmest temperatures will be along the
coast where mid to upper 70s will be seen, but north of the
mountains it may stay in the 60s.


Upper level troughing and a Canadian airmass remain entrenched over
eastern NOAM through this weekend and into the next work week,
although signs of this pattern breaking down are starting to appear
later next week. In the meantime we`ll continue to enjoy
seasonably cool conditions with occasional bouts of rain shower
activity, but overall an enjoyable stretch of weather for what
is typically the warmest time of year for this region.

Starting Friday night...low pressure departing to the east will be
rapidly deepening over the Gulf of Saint Lawrence. Thus northwest
winds in cyclonic flow overhead will ramp up, continuing upsloping
clouds/showers along with gusty winds in cold advection. Ensemble
analysis yields wind gusts in the 20-25 mph range... however BUFKIT
soundings suggests strongest wind gusts Friday evening will be
closer to 30 mph, so have trended the forecast in that direction.
Will have to keep an eye on locally stronger winds to near 40 mph in
the downslopes of the Whites and western Maine Mountains with
some modeled soundings suggesting an inversion forming just
above the peaks... assuming we keep mixed.

Besides the wind... a thermal trough will descend through Quebec and
into New England with h850 temperatures dipping to +3-7C by Saturday
morning. Overnight lows remain a bit of a conundrum with uncertainty
in humidity and mixing due to the PGF; I remain skeptical that we`ll
cool much more than the 50s over the lakes region and coastal plain,
40s toward the north and west, in spite of the impressive airmass
arriving. The rock pile (MWN) however may flirt with freezing at its
6288` peak with wind chills certainly coming below freezing above
treeline over the Whites. Thus remaining upsloping showers may
actually produce some wet flakes at the very top of the CWA.
Breezy northwest flow continues into Saturday with partly cloudy
skies and highs in the 70s, except limited to the 60s in
portions of the western Maine mountains. That night, high
pressure builds by to the south with a weak southwest flow
developing amid otherwise quiet and calm conditions... and lows
just a touch warmer than the previous night.

The next short-wave pivoting down through the larger trough brings
increasing clouds and showers starting Sunday with system passage
centered Sunday night into Monday morning. Early looks at this
system show some potential for stronger moisture ingest, and there
is certainly favorable dynamic forcing with the upper level wave,
which leaves some potential for convection at least toward the
west. Questions with this system mainly concern how well it
will phase between northern (near the international border) and
southern (near the Carolina or Mid- Atlantic coast) components.
This system exits east by the end of Monday with high pressure
briefly building in through Tuesday.

After what will be several days of cool, Canadian airmass
reinforcement, a Bermuda high is expected to build sometime next
week, blocking downstream flow and pushing the upper level trough
upstream over the central CONUS. Thus am expecting the storm track
associated with deeper southwesterly moisture feed and warmer
temperatures to lift closer to the region with increasing shower
chances and a warm trend during the second half of the week.


Short Term...Early morning fog at LEB and HIE burns off quickly
this morning with VFR for all areas. Expect increasing clouds
and lowering ceilings over the course of the day from south to
north with an increasing chance for showers and thunderstorms by
late in the afternoon. The better chance of showers and storms
and IFR conditions will be during the overnight period,
especially along the coast. This should improve for most areas
on Friday as northwest flow clears out the coastal plain. Lower
ceilings may linger in the mountains through the day Friday.

Long Term...VFR with gusty northwest winds up to 25-30 kts
Friday evening, tapering overnight, then back up to around 20-25
kts on Saturday. High pressure builds to the south late Saturday
into Sunday with light winds turning southwesterly. The next
opportunity for restrictions comes with a system crossing late
Sunday into early Monday with SHRA expected.


Short Term...Southerly flow increases today as high pressure
moves east and a trough approaches from the west. Gusts to 25 KT
are likely over the outer waters where a Small Craft Advisory
has been issued. Low pressure develops as the trough arrives at
the Gulf of Maine tonight and then tracks northeast through
Friday. Behind the low, winds shift to the northwest and
strengthen again. As a result, we will likely see a break in the
advisory level winds before they ramp back up again out of the
northwest on Friday.

Long Term...Gusty offshore/NWerly winds around 20-25 kts into
Saturday keep wave action over the outer waters elevated with
3-5 ft seas expected. Thus a SCA from Friday may need to be
extended through the overnight and into Saturday. After that,
high pressure builds to the south into Sunday with winds turning
out of the southwest... then the next low pressure system
crosses Sunday night and Monday. The storm track remains active
near the Gulf of Maine through next week.


MARINE...Small Craft Advisory from noon today to 6 AM EDT Friday for



NEAR TERM...Kimble

NWS GYX Office Area Forecast Discussion