Topsham, Maine 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

903
FXUS61 KGYX 312341
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
641 PM EST Fri Jan 31 2025

.SYNOPSIS...
Light snow will continue to slowly spread north through tonight.
The heaviest amounts will mostly stay south of the mountains,
while some rain and mix this evening will cut down on totals
over southern New Hampshire. By morning 2 to 4 inches will be
possible between these two areas. High pressure will build in
and set up another very cold night Saturday night. Another weak
system will arrive late Sunday with more light snow
accumulation.

&&

.NEAR TERM /THROUGH SATURDAY/...
635 PM Update... Latest correlation coefficient data from KBOX
indicates that the rain/snow line has now moved south of the
MA/NH state line with ASOS and webcams supporting this data.
Webcams and traffic reports indicate that the cold roadways are
quickly becoming snow covered this evening with rapidly
deteriorating road conditions expected through the remainder of
the commute. As a result, went ahead and issued a special
weather statement to highlight this potential hazard. Otherwise,
just tweaked PoPs based on latest trends and loaded in the
latest sfc observations.

Previously...
500 MB wave to our W this afternoon has sfc low reflection
tracking across OH/PA this afternoon, while a weak wave comes
down from the N and shows some very mild signs of [phasing as it
moves across the CWA. Forcing is most evident in the mid
levels, especially around 850 MB as that trough deepens from the
N overnight /It shows up at 700 MB too, but is weaker. This
should be where the best forcing as a secondary sfc low forms E
of the first one, in response to the deepening mid level system.
This should be enough to produce enough deformation for some
broad banding to occur well N of the sfc low, and allow for
precip tonight, especially this evening and for a few hours
after midnight. While we won`t see exceptional snowfall rates
should be enough to produce a swath of 2-4 across central NH
into SW ME, where the forcing will be best, and SLRs should be
in the 10-15:1 range. To the south across S NH, precip has begun
as RA, and may take a a few more hours to start accumulating
amounts will be lower, around 2 inches, while further E into
central ME and the mid coast as well as the ME mtns, 1-3 is
forecast. Actually 12Z models 10-1 snowfall forecasts are fairly
well aligned, including the Euro operational, the EPS mean, the
NAM3, and the latest run of the HRRR, and adjusting these based
on the geographically varying ratio seems like a good bet for a
forecast.

There should be a drop in temps at precip onset for
wet bulbing, and then temps settle in through the evening before
they drop again, as flow picks up from the NNE later tonight
with lows 10-15 in the N and the mid to upper 20s in the S. All
snow should be done before or right around sunrise Sat.

&&

.SHORT TERM /SATURDAY NIGHT/...
Sfc high builds in from the W Sat afternoon and night, as 500 mb
flow gradually shifts zonal to weakly anticyclonic. Breezy
conditions in the morning should gradually diminish in the
afternoon, but temps will likely not rise much during the day
despite fast clearing as CAA persists through Saturday and highs
range from the mid teens in the N to 25-30 in the S.

Winds will die off as the sfc high shifts right across the CWA
Tuesday night. And should be a good rad cooling night with
little or no winds, so look for lows -20 to -10 below in the
mtns ranging to the single digits below zero to around zero in
the south.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Message: Temps in the extended are still expected to be a
rollercoaster of above normal at times and below normal at times
and not so much in between. Precip chances will also be above
normal thru the extended...with at least two maybe as much as
three chances for accumulation.

Impacts: Primary hazard will be wintry precip. Sun night into
Mon some light snow is likely across the area. This will linger
into the Mon morning commute. Another chance of snow and mix
will arrive towards the middle of the week.

Forecast Details: High pressure will be departing Sun allowing
clouds and eventually precip to invade from the southwest by
evening. Ensemble guidance is in fairly strong agreement that
this event will be both light and primarily all snow. QPF is
generally a quarter inch or less. At this time that sort puts
the high end goalpost around 4 inches of snow...but there
remains some risk on the southern end of a mix depending on
storm track. I have once again opted for the cooler
guidance...where cold air damming hangs on longer than currently
modeled. Some freezing rain is possible mainly across southern
NH.

Colder air will filter in behind this system followed by another
cold front Mon night into Tue. Some gusty winds will result
during the day as that colder air advects in.

There is still a very strong ensemble signal mid to late week
for a higher QPF storm...generally half inch or more liquid.
This storm has more room for track errors west than previous
events...so snowfall has more spread. We could see a range from
mostly rain like the GEFS to mostly snow like the GEPS. But
overall ensemble guidance suggests snow is most likely from the
Lakes Region NH and points northeast...which is pretty standard
climatology for cold air damming. I am fine with the higher NBM
PoP despite the long lead time given the strong signal.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Short Term...All terminals should go IFR this evening, with a
period of LIFR in SN at KMHT/KCON/KPSM/KPWM. Will see
improvement early Saturday with VFR at all terminals by mid
morning. VFR will persist through Sat night.

Long Term...VFR to begin the day Sun but precip will move in
during the evening and areas of IFR or lower are expected to
develop in low CIGs and snow. Conditions will improve around
midday Mon....though some MVFR CIGs may linger in the mtns
around HIE. That will continue into the middle of the week. Some
surface gusts Mon and Tue afternoons may approach 25 kt or
higher.

&&

.MARINE...
Short Term...SCA was extended through this evening due to high
seas in the open waters E of Casco Bay, but these will gradually
diminish as well. Will likely need an SCA again Sunday morning
for NNE winds shifting NW during the day, and continuing into
Sunday night.

Long Term...Southerly winds increase Sun night and SCA
conditions are expected at least outside of the bays thru Mon
morning. Wind direction shifts to more west southwest and will
remain gusty thru midweek. Overall SCA conditions will be likely
most days thru the end of the period.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 11 PM EST this evening for ANZ150-
     152.

&&

$$

NEAR TERM...Tubbs
SHORT TERM...Cempa
LONG TERM...Legro
AVIATION...Tubbs/Cempa/Legro
MARINE...Cempa/Legro