-- Discussion containing changed information from previous version are highlighted. --
668
FXUS61 KBGM 202347
AFDBGM

Area Forecast Discussion
National Weather Service Binghamton NY
747 PM EDT Fri Sep 20 2024

.SYNOPSIS...
Dry conditions are expected tonight through Saturday morning
before a chance of showers and thunderstorms mainly west of
Interstate 81 during the afternoon and evening hours. Dry
conditions return on Sunday, but more showers will be possible
Monday night into Tuesday.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
635 PM Update...
Forecast on track. There remains quite a bit of uncertainty
Saturday for how long it will take for clusters of convection to
work their way into the area. Quite a gradient will exist
Saturday afternoon-early evening, from stable air with
significant dryness in our eastern zones, to more moisture and
instability west of I-81 and especially towards the Finger
Lakes-Central Southern Tier of NY. The 18Z NAM is the most
aggressive with instability and earlier timing, however, it has
also been overdoing convection during the last week or so.
Indeed, it even has some convection this evening, as in right
now; which is comical. At this point we are figuring that the
NAM is overdoing the boundary layer moisture. Other guidance,
including the 3km NAM and other convection-allowing models
(CAMS), support holding back the timing to 2-6 PM for
development west of I-81, then making its way across the I-81
corridor in early evening but with loss of diurnal heating
weakening activity as it also tries to work into a drier air
mass.

Previous discussion...
A nice, quiet evening is shaping up across the area with
scattered clouds. Mid and high level clouds will gradually
increase across the area tonight, but despite the increase in
clouds, some areas of valley fog are still expected to form
overnight and early tomorrow morning as winds remain pretty
light. Lows tonight will be in the 50s and low 60s.

The day will start off dry tomorrow before a vigorous shortwave
moves out of southern Ontario and across CNY which will lead to
the chance of showers and thunderstorms for the afternoon and
evening hours, mainly west of I-81, as the shortwave drifts south-
southeast. Most models do depict an increase in instability
values from earlier this morning with CAPE values between 500-1000
J/kg during the afternoon and early evening west of I-81 with
even a pocket of 1200 J/kg over far western portions of the CWA.
Shear values are low, generally capped at 20 knots, but there
are some decent low-level lapse rates and SRH values are shown
to be anywhere from 75-120 m2/s2. Dew points are in the low to
mid 60s and PWAT values climb to 1.25-1.50 inches, so there
could be an isolated robust thunderstorm, and some localized
downpours are possible. Any lingering showers are expected to
diminish during the overnight hours. Highs tomorrow are expected
to be in the 70s with valley areas near or into the lower 80s.
Lows Saturday night will be in the 50s to near 60 degrees.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
230 PM update...
Main concerns in the short term are focused on the slightly and
relatively cooler conditions Sunday with dry/quiet weather
expected, and even cooler air moving in on Monday with
increasing clouds and eventually rain showers from the west.

The synoptic pattern across the Northeast US will be defined by
a narrow ridge of high pressure extending from Nova Scotia
southwest into the mid Atlantic region bordered by an area of
low pressure 300 mi off the coast and an incoming upper trough
getting cut off over the Great Lakes. A narrow corridor of
leftover warm air will be aligned with the ridge along with some
residual low-level moisture. So, as temperatures climb well
into the 70s Sunday afternoon, there will likely be a robust
area of cumulus blossom across the region. However, there should
be enough dry air aloft to limit the vertical growth of
convection, but cannot completely rule out a stray shower in and
around Steuben County.

The surface ridge axis moves slowly to the east Sun night and
Monday as the developing low pressure system in the Great Lakes
starts to inch farther to the east. There is some uncertainty
regarding the onset of rain on Monday, so kept PoPs around 15-20
pct in the morning and 20-35 pct in the afternoon mainly east
of I-81. High temperatures on Monday are expected to be at or
slightly below normal...topping out in the mid 60s to lower 70s.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
230 PM update...
Several rounds of rain showers and isolated weak thunderstorms
are expected Monday night, through the day Tuesday and into
Wednesday as a slow moving/evolving low pressure system over the
mid MS Valley region phases with the Great Lakes low/trough and
lifts northeastward through the GL and into Ontario and Quebec
by Wednesday. The air mass associated with this system is
expected to be fairly mild with 850mb temperatures around +8 to
+11 deg C and plenty of clouds and rain around keeps surface
temperatures mostly in the 60s for highs Tue and Wed and into
the 50s for overnight lows. PWs during this 2 day window are
progged to reach up to 1.5 inches or higher at times, which
could prove supportive for some locally heavy rain. There is
quite a bit of uncertainty when Thursday roles around as the
synoptic pattern is not well agree upon by the model guidance so
there are still a lot of unknowns with respect to both
thermal/moisture profiles and chances for precipitation.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
VFR conditions are expected through the TAF period other than
some valley fog at KELM in the several hours up to and
including dawn. Increasing high clouds, along with milder
forecast minimum temperatures, will tend to limit valley fog
production compared to prior nights. It will take longer to get
going at KELM, but most likely scenario is that it will still
ultimately happen even if delayed by several hours. However,
actually reaching to airport minimums will be a challenge.
Whatever valley fog we get will mix out quickly after dawn,
leaving mainly VFR conditions areawide during the day Saturday.
Showers and a chance of thunder may occur prior to 00Z Sunday
west of KSYR-KBGM-KAVP; especially KELM and perhaps KITH.

.Outlook...

Saturday night through early Sunday morning...Scattered showers
and chance of thunder with associated restrictions possible,
especially for ELM-ITH-AVP. After rain ends, shallow deck of
clouds may cause ceiling restrictions for same terminals and
perhaps KBGM into early Sunday.

Sunday midmorning through midday Monday...Mainly VFR.

Late Monday through Wednesday...Multiple chances for showers
and isolated thunderstorms with associated potential
restrictions as disturbances pass through the region.
-- End Changed Discussion --

&&

.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...None.

&&

$$

SYNOPSIS...DK/MDP
NEAR TERM...DK/MDP
SHORT TERM...BJT
LONG TERM...BJT
AVIATION...MDP