Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 291935

Area Forecast Discussion
National Weather Service Gray ME
335 PM EDT Mon May 29 2023

A ridge of high pressure will build over the region through the
middle of this week with moderating temperatures to well above
average. High pressure is also expected to bring in some smoke
and haze from Nova Scotia wildfires, at least on Tuesday. A
cold front will then cross late Friday, bringing the potential
for scattered showers and thunderstorms. Cooler more seasonable
temperatures will then return behind this front for the upcoming


Pressure rises, slackening gradient flow, and subsidence are
expected tonight as surface high pressure anchored over the Gulf
of Maine into Nova Scotia phases with an upper level ridge
pushing in from the Great Lakes region. Combined with clear
skies and a dry column, this will set up an excellent
radiational cooling night. Thus, dew points from today will be
the key to overnight low temperatures... with coolest
statistical guidance and MOS indicating widespread 30s to
low-40s can be expected. This is tricky WRT the potential for
frost... since using these values indicate potential for patchy
frost in most places, but without the coverage to necessitate an

Based on a tendency for nights like this to cool well past even
the coolest guidance, especially recently, and in spite of the
limited night time with sunrise around 5 AM... have decided to
take temperatures down further in valleys that climatologically
tend to do so, including the upper Androscoggin and Connecticut
River Valleys and the sandy/low-lying Saco River Valley. Thus
have gone with a Frost Advisory for these locations. Evening
shift will have to monitor trends in model guidance and observed
dew points for potential expansion.


High pressure remains entrenched over the Gulf of Maine and
southern New England on Tuesday, building and sinking south
through the day to overnight and producing a southerly flow
over the forecast area. Other than a few high level clouds from
a weak wave dropping toward the southeast over eastern
Canada/northern New England... we`ll have another sunny day
leading to nice mixing, at least to start, before the sea breeze
pushes ashore. Highs will depend on how quickly the sea breeze
arrives, with western locations warming to around 80 but the
coast quickly plateauing or reversing the diurnal trend in the
60s. Steady gradient of 70s reading separates these two.

A quick glance at visible satellite (and news stations) today
shows significant fire activity ongoing to our east in Nova
Scotia. Examining HRRR- and RAP-Smoke fields... subsidence and
anticyclonic flow from the high pressure circulation in the
Gulf is forecast to bring smoke to the surface and advect toward
into New England Tuesday morning. The stable air in the sea
breeze is presently modeled to bring the smoke ashore. Impacts
are uncertain right now, but at least a smell and/or thicker
haze may be noticeable.

For the overnight forecast... anticyclonic flow eventually
advects in higher dewpoints from the South by way of the Ohio
Valley, resulting in somewhat warmer low temperatures in the
40s. Subsidence and decoupling may cause smoke to hug surface...
but again, the impacts are uncertain.


Overview: A large dome of high pressure will remain over the region
through much of the week before a cold front crosses on Friday.
Moderating temperatures to well above average are expected ahead of
this front with more seasonable temperatures returning behind the
front for the upcoming weekend.

Impacts: Near record high temperatures possible on both Wednesday
and Thursday. The lack in appreciable rainfall may result in an
expansion of abnormally dry conditions.

Forecast Details: Surface high pressure will be centered to our
south on Wednesday, promoting warm southwesterly flow as 925mb
temperatures climb to around +21C. Large scale subsidence will allow
for another day of mainly sunny skies with above average
temperatures into the middle to upper 80s away from the coast.
Closer to the coast developing onshore flow will keep high
temperatures into the 60s across the Mid-Coast to the 70s from
Portland and points south. Clear skies and light winds on Wednesday
night will allow for some radiational cooling with lows bottoming
out into the upper 40s to lower 50s. The peak of the warmth then
looks to arrive on Thursday with WAA allowing 925mb temperatures
to approach +24C. This combined with sunny skies and afternoon
mixing will result in near record highs into the lower to
perhaps middle 90s away from the coastline with 70s and low 80s
along the coast. Heat indices do not look to be a factor,
however, as Tds are likely to largely remain below 60 degrees
but it may feel a little humid. Thursday night will be very warm
with readings likely not falling below 60 degrees across the
urban corridors and perhaps even portions of the interior.

One more unseasonably warm day is then expected on Friday ahead of
an approaching cold front from the north. Ahead of this front,
highs will once again reach the middle to upper 80s with
readings into the lower 90s likely across south-central NH.
Current guidance indicates the aforementioned cold front may
cross after peak heating but depending on the timing of this
front thunderstorms will be possible given the very warm
preceding airmass. A return to more seasonable temperatures is
then expected for this weekend with dry weather conditions.
Another frontal system may then approach the area early next


Short Term...VFR all terminals with very few clouds to speak of
and flow veering southeasterly at all terminals through this
evening. Most places go calm tonight. Southerly flow on Tuesday
will be most pronounced along the coast and over eastern
terminals peaking around 10-15 kts, with lighter flow for
western terminals. Smoke from fires in Nova Scotia may impact
visibility with the sea breeze through the afternoon, but the
degree of impact is uncertain. Light and variable or calm flow
is expected Tuesday night with some potential for valley fog.

Long Term...Widespread VFR conditions expected through Thursday
with daily sea breeze chances across coastal TAF sites including
KPSM, KPWM, and KRKD. A cold front will then arrive late on
Friday, bringing scattered SHRA and perhaps TSRA. VFR conditions
will then return for the upcoming weekend.


Short Term...High pressure builds over the Gulf of Maine through
tonight and shifts just south Tuesday into Tuesday night...
allowing southeasterly winds today to veer southerly to
southwesterly, except for in sea breeze circulations. Winds and
seas are expected to remain below SCA thresholds.

Long Term...Winds and seas will largely remain below SCA
thresholds through Thursday. A cold front will then cross over
the waters either late Friday or Friday night, perhaps bringing
a period of SCA level winds along with scattered showers.


Record high temperatures are possible on both Wednesday and
Thursday of the upcoming week. Below are the respective high
temperature records for each day.

SiteWednesday RecordThursday Record
Portland, ME        94 (1987)               90 (2013)
Augusta, ME         91 (2013)               92 (2013)
Concord, NH         94 (2013)               94 (2013)


ME...Frost Advisory from midnight tonight to 7 AM EDT Tuesday for
     Beach Hazards Statement until 8 PM EDT this evening for
NH...Frost Advisory from midnight tonight to 7 AM EDT Tuesday for
     Beach Hazards Statement until 8 PM EDT this evening for NHZ014.



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