574
FXUS61 KGYX 051951
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
351 PM EDT Thu Jun 5 2025

.SYNOPSIS...
A weak cold front will approach from the northwest this
afternoon and evening with a hot and humid airmass in place.
The front will bring chances for scattered strong to severe
storms, mainly from the foothills northward. The front will
stall over the region Friday with humid conditions continuing
and chances for strong storms again Friday afternoon, with an
isolated flood threat due to heavy rain showers. Additional
waves of low pressure will track along the front through
Saturday with another round of potentially heavy showers posing
an isolated flooding risk. High pressure then builds in Sunday
to Monday.


&&

.NEAR TERM /THROUGH TONIGHT/...
Hot weather continues...but aside from near the sea breeze
dewpoints have been dropping as the mixing height increases. So
we are not getting the humidity to go along with the heat. That
will be less true overnight...as sustained moisture advection
will allow dewpoints to creep up. That will leave overnight low
temps quite warm for this time of year.

The main story continues to be the threat for convection. Widely
scattered showers continue to percolate along the prefrontal
trof...but have yet to take off. This is likely because there is
significant dry air still in place. It will take a sustained
period of forcing to drive a robust updraft and I just do not
think we have a strong enough lifting mechanism for that today.
If we cannot get the elevated heat source of the higher terrain
to pop a storm late this afternoon or early this evening...that
is likely the end of the severe threat for today anyway. If we
were to get a storm the 05.18z GYX sounding shows ample
CAPE...and marginal shear...so gusty winds and small hail would
be the most likely hazards.

Hi-res guidance also wants to develop marine fog and stratus
tonight. I opted to hold off on that until Fri as there is
currently no visible fog bank on satellite. Confidence would be
higher if the fog bank already existed.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
Most model guidance now agrees that Fri will be the more
convectively active day.

On the severe front...we now have a slight risk for parts of
southern NH and marginal risk bordering it to the north. While
CAPE may ultimately be a little lower than today...the shear
will be stronger and more supportive of organized updrafts.
Machine learning guidance supports the SPC upgraded risk to
slight across the southern portions of the forecast area. Wind
would likely be the primary hazard...but I cannot rule out
small hail in any stronger storm. I maintained the enhanced
wording of gusty winds/small hail primarily for the southern
half of the forecast area.

On the flash flood front...WPC has placed much of the area in a
marginal risk for excessive rainfall. I think this makes sense
given the hi-res guidance. HREF forecasting a prob matched mean
of around 2 inches across central NH...and max values for 6
hours Fri afternoon are approaching 3 to 4 inches. Local
research has demonstrated that while location may be off...the
max values are usually achieved somewhere in the vicinity. So
the threat is there for someone to get 3 to 4 inches of rain in
a short window.

Convection will weaken overnight but showers will linger into
Sat morning. Temps will also remain near 60 as clouds blanket
the area.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Pattern Overview: A northern stream trough will provide forcing
for showers on Saturday as it swings through the region.
Afterward our weather pattern becomes more dominated by the
Bermuda High as it strengthens in the central Atlantic during
the first part of next week. This will advect moisture into the
region creating more unsettled weather heading into mid-week.

Impacts and Key Messages:
* An isolated flooding threat exists on Saturday as another
  round of potentially heavy showers and a few thunderstorms
  move through ahead of a cold front.

Details: Saturday: A northern stream upper trough aligned with
a surface stationary front is going to provide the forcing for
another round of widespread showers that will be ongoing
Saturday morning. A very moist airmass with PWATs 1.25-1.50" and
warm cloud depths 10- 11kft suggest efficient rain rates that
combined with weak low level flow may lead to slow moving heavy
showers that could pose an isolated flooding risk, especially in
areas that see heavy rainfall from an expected initial round on
Friday. While individual storms may not cause issues by
themselves, training of these storms might. With the frontal
boundary being mostly stationary and forecast soundings showing
short corfidi vectors, this is looking like how any isolated
flooding could come about. Heading into the afternoon hours the
front begins to get pushed out as an upper trough digs into the
region, so showers would begin to clear from west to east
through the evening hours. The latest NAM Nest suggests an
additional line of showers may develop as forcing increases
again with the trough moving overhead, but this is also toward
sunset so timing will be a large factor on this actually coming
to fruition, and even so it is likely short lived and/or weaker
than the preceding showers with waning instability. Drier air
fills in behind the front slowly clearing clouds overnight. The
cloud cover will last most of the night so low temperatures
remain mild, in the low to mid 50s.

Sunday and Monday: The first part of next week looks mostly dry
as the general pattern supports upper level ridging with a
surface high pressure building in to our north. However, with
the Bermuda High also strengthening over the Atlantic our region
gets locked into southwesterly flow which means upper level
moisture will remain present and with high temperatures climbing
into the 70s both days, sufficient instability to support
isolated showers could develop. Sunday certainly looks like the
drier day with a fresh airmass overhead, with moisture beginning
to increase and be more supportive of isolated showers on
Monday.

Tuesday-Thursday: Southwesterly flow continues into mid-week
increasing moisture over the region once again. This will be our
next best chance for widespread precipitation after Saturday as
low pressure moving out of the Great Lakes Region may drag a
front through on Tuesday or Wednesday, with additional forcing
from an upper trough. As usual, timing varies between model
suites at this point, so its worth a mention as a period to
watch, but the finer details will have to wait.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
Short Term...I anticipate mostly VFR conditions tonight. Any
convection will be capable of brief local IFR or lower
conditions...but HIE is the only TAF site really with any
appreciable chance of rain. SHRA/TSRA will be more widespread
Fri with areas of MVFR spread southwest to northeast and local
IFR or lower conditions in the strongest cells. In addition fog
and stratus may develop near the coast during the day. That will
continue thru the overnight.

Long Term...Looking at mainly VFR ceilings through the long term
with a period of showers and thunderstorms Saturday. Winds
remain generally light outside areas of convection, through
Tuesday.

&&

.MARINE...
Short Term...Winds and seas expected to remain below SCA
thresholds. Continued moisture advection Fri may lead to areas
of fog developing and continuing into Sat morning. Some
thunderstorms Fri may contain gusty winds.

Long Term...Low pressure tracking over the region will bring
showers and thunderstorms to the waters Saturday. This will also
build seas to 3-5ft on Sunday. Afterward, a strengthening
Bermuda High will bring tranquil conditions to the waters for
the first part of the week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Air Quality Alert until 11 PM EDT this evening for MEZ023>028.
NH...Air Quality Alert until midnight EDT tonight for NHZ014.
MARINE...None.

&&

$$

NEAR/SHORT TERM...Legro
LONG TERM...Baron