Area Forecast Discussion
Issued by NWS Binghamton, NY

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FXUS61 KBGM 171052

Area Forecast Discussion
National Weather Service Binghamton NY
652 AM EDT Thu Aug 17 2017

Valley fog will lift to reveal partly sunny skies this morning,
with increasing clouds during the rest of the day. Muggy
conditions along with showers and scattered thunderstorms
develop tonight, and continue at times through Friday. Locally
heavy rain will be possible in thunderstorms. Cooler, but still
somewhat unsettled weather continues on Saturday.


345 AM Update...
Fairly routine mid-August weather today with early morning
valley fog expected to lift during the usual hours. High
pressure then retreats to the east with warm frontal clouds
approaching the rest of the day. Not seeing much lift, or
instability increasing prior to 00Z Friday, therefore, we nudged
a blended PoP downward a tad early this evening. Model consensus
agrees on sweeping a warm front through the region tonight with
a healthy surge of deep layer moisture. PWAT values get into the
1.5-2.0 inch range by 12Z Friday. Strongest forcing sweeps
across southern Canada, but frontal boundary and elevated
instability will be enough to produce showers and thunderstorms,
especially overnight. Simulated reflectivity on several of the
high resolution runs did not seem to be as emphatic about
widespread coverage tonight, but did trend at least with an
increase after 04Z. Given this, can`t really justify several
hours of categorical PoPs in our area tonight, so have tamed
predictions into the likely range. Although QPF and simulated
radar trends don`t jump out with a potential for heavy rainfall,
the anomalous PWATs of 2-3 standard deviations along with some
of the other Maddox flash flood ingredients do suggest potential
for locally heavy rain in the pattern. The system seems fairly
progressive, but given dewpoints surging above 70F, the risk of
excessive rainfall rates is something to monitor closely.

Blended guidance today and tonight for highs in the upper 70s-
low 80s and overnight lows in the mid-upper 60s.


345 AM Update...
The passage of the surface warm front early Friday morning will
likely bring a brief respite from the bulk of any widespread
precipitation. Surface based destabilization is expected to
occur Friday afternoon with plenty of moisture still available,
and a shot at breaking out of the cloudiness within the warm
sector. Therefore, another round of convection is expected to
initiate during the afternoon and push east into the evening
hours. The intensity of the convection will depend on how much
clearing occurs. Latest BL CAPE values appear to be considerably
lower than yesterday`s model runs with values possibly reaching
about 1000 J/kg, maybe a little higher. Deep layer shear still
looks to become sufficient in the 30-40 kt. A drying of the mid
levels is also noted by mid-late afternoon, particularly across
our northern and western areas which would contribute to
steepening low level lapse rates and the potential for strong
updrafts leading to a chance for severe thunderstorms with hail
and strong winds. Deepest moisture may linger across our
southern-eastern areas where flash flooding could occur in the
late afternoon. SREF probabilities in excess of 2 inches/6 hours
were hovering around 10-20 percent from the Poconos to
Catskills. GEFS/GFS moisture parameters look like they slide
east a little faster.

Chances for shower activity diminish Friday night, but can`t
rule out all the potential for rain with broad cyclonic flow
aloft and minor ripples noted in the flow. Will pin slightly
better risk of instability clouds and showers during the day
Saturday with heating and a secondary, amplified wave moving
through the area. Subsidence and drying in the low levels will
help to mitigate coverage, but there certainly remains
opportunity for hit and miss activity.


4 AM Update...
Forecast adjusted towards latest multi-model blend, with very
little change to prior thinking. Though flow is generally zonal
Monday-Tuesday, enough ridging and warm air advection occur to
create a rather warm couple of days. Tuesday in particular looks
a bit uncomfortable, considering highs in the mid to upper 80s
at lower elevations combined with dewpoints in the mid to upper
60s. Though above normal, readings like that are not very
unusual for August, but this year we have not had much heat
since the first few days of this month.

Previous discussion...
Medium range models are in good agreement through the extended
period. Saturday night through Monday night looks dry and warm
with zonal flow aloft and high pressure in the vicinity.
Tuesday through Wednesday the next upper level trough moves
through the northeast with surface low pressure moving through
eastern Canada. The best chance for showers and thunderstorms
will be Tuesday night into Wednesday when the trailing cold
front crosses the region.

Temperatures through the period will run about 4 to 8 degrees
above seasonal normals.


VFR conditions generally expected 12Z Thursday through 06Z
Friday, except for lingering valley fog/low ceiling issue at
KELM 12Z-13Z. Patchy high thin clouds today will become thicker
while lowering this evening as warm front approaches. Showers
will start to spread across the area 06Z-12Z Friday, with
ceilings eventually lowering into fuel alternate required
levels. Light and variable winds early this morning, will become
generally southeast or south 4-8 knots late morning onward.


Friday through Friday night...Periodic restrictions from
showers/thunder as system moves through area.

Saturday through Monday...Mainly VFR, though a few showers and
brief restrictions still possible Saturday.




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