Area Forecast Discussion
Issued by NWS Binghamton, NY

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FXUS61 KBGM 181451

Area Forecast Discussion
National Weather Service Binghamton NY
1051 AM EDT Mon Jun 18 2018

Heat and humidity will both reach their peak today with heat
index values well into the 90s. Thunderstorms will be possible
beginning this afternoon, and especially into evening as a cold
front drops out of Canada. Some storms could contain gusty winds
and very heavy downpours. Tuesday will be dry, and temperatures
through midweek will be quite a bit cooler.


1045 am update... An eventful afternoon and evening may be in

A fair amount of sunshine, along with increasingly hot, humid
conditions prevailed as of late morning. Temperatures were
already well into the 80s to near 90 over portions of the
forecast area as of this writing, with dew points in the lower
70s. Incoming 925 mb temperature/dew point combinations of
25C/20C from the west, continue to support highs in the lower
90s, and heat indices locally near 100 this afternoon. Our Heat
Advisory statement was just refreshed to reflect such.

As for convective potential, isolated storms are already
beginning to fire near Lake Erie/Ontario convergence boundaries
as of late morning. As we destabilize this afternoon, and
potentially get impacted by a convectively induced short-wave
from MI/southern Ont, we expect showers/thunderstorms to
increase in coverage across CNY/PA`s northern tier. Initially,
localized strong winds/hail would be the main threats.

After perhaps a brief lull in the 5-8 pm time frame, we still
expect a second round of showers/storms this evening, just ahead
of the main surface cold front and upper-level short-wave. Given
the incoming anomalously high precipitable water values
(2.25"-2.5") and potential for repeat development (prevailing
flow becoming increasingly parallel to frontal orientation),
heavy rainfall would be the greater threat with the latter round
of storms.

A briefing will be issued this morning to address all near-term
hazards (heat, possible severe storm development, and also
potential heavy rainfall this evening/tonight).

Previous discussion... 405 AM Update... A fairly active period
is anticipated in the very near term; first the combination of
heat and humidity, and then afternoon- evening thunderstorms
capable of gusty winds and very heavy downpours including
possible isolated flash flooding. Things quiet down considerably
after tonight.

Temperatures are starting off mainly in the 60s to lower 70s at
the surface, but anomalously hot and humid air mass has
continued to advect into the region. Rapid warming will occur
after sunrise dissipates the paper-thin surface inversion, and
in pretty short order it will feel rather oppressive. Areawide
Heat Advisory remains in effect 10AM to 8PM, due to combination
of upper 80s-lower 90s temperatures and lower 70s dewpoints
producing heat indices topping mostly in the 95 to 100 degrees
range. The only silver lining on this, will be increasing cloud
cover blowing off from convection well upstream - and eventually
our own convection - as well as a west-southwest wind picking up
to take some of the edge off of the heat.

Thunderstorms late today through this evening will pose a threat
for both gusty winds and locally heavy rainfall, though of those
two the potential for isolated flash flooding appears to be the
larger concern. The atmosphere is streaming a plume of
extremely high precipitable water values exceeding 2 inches,
currently from Wisconsin to northern Michigan. This will advect
across the Saint Lawrence Seaway today, ahead of a cold front
that will drop south through our region this evening. These
precipitable water values are well above the 90th percentile
for even midsummer let alone mid June. Models depict 850mb
moisture transport late today is 5-6 standard deviations above
normal over our region. While areal average rain amounts will
not be excessive, the individual storms will be very efficient
downpour producers to the point that an inch of rain could very
easily occur in a half hour or less. Progressive nature of the
front should limit coverage of problems, but isolated flash
flooding is a distinct possibility and indeed will probably
occur somewhere within our region. It should be noted and
respected the history of this upstream air mass that will now
move over our area; several instances of flash flooding have
already occurred in the Upper Midwest-Northwestern Great Lakes

One complicating factor for the evolution of things today, will
be a shortwave that runs out ahead of the front. Several higher
resolution convection-allowing models are allowing a line of
scattered thunderstorms to develop in early afternoon, which
will then sweep east across the area through mid-late
afternoon. There will still be some dry midlevel air in the
column at this time, which along with modest unidirectional flow
could result in gusty strong to marginally severe gusts under
those cells. Coverage of these cells will be limited, but storms
are nevertheless a possibility this afternoon with this initial

The bigger heavy downpour threat will be this evening as the
cold front pools the highest precipitable water values and
harnesses instability for additional thunderstorms. At this
point it is difficult to tell if the initial shortwave takes
away some energy from the frontal convection, or if instead
exacerbates the potential for isolated flash flooding from some
locations getting more than one heavy downpour. But as
mentioned before, the history and the very anomalously high
moisture of this set up heightens concern that the event could
exceed expectations. If confidence in flooding problems were to
increase, a short-fuse Flash Flood Watch could be hoisted later
today for the most prone locations. At a minimum, urban and poor
drainage water problems can reasonably be expected with the
storms that pass through this afternoon into especially evening.

Strong upper wave in Eastern Canada, will ultimately drive the
front through the region to the point that for Tuesday, we are
now confident in a dry day with much cooler temperatures. After
lows of mostly 60s-near 70, highs of 70s-lower 80s are
anticipated. More importantly in terms of comfort; dewpoints
will crash into the lower 50s as daytime mixing occurs. Post-
frontal clouds may initially hang around from Twin Tiers
southward, but trend will be for a mostly sunny sky to overtake
the region from north to south during the day.


415 AM Update...
High pressure lingers over the region Tuesday night, then becomes
more diffuse on Wednesday. Medium range models are now suggesting a
bit of a wrinkle in what looked to be a mainly dry week. The frontal
boundary sitting just to our south develops a weak surface wave
along it and surges slightly further north during Wednesday as the
favored entrance region of a 300 mb jet streak dives into the back
side of the upper trof over New England. Not prepared to completely
believe the wettest GFS model, but the EC and Canadian NH are also
in some agreement that showers/thunderstorms could develop across
NEPA, and possibly as far north as the Southern Tier NY. Will
introduce low probabilities for now just to allude to this


415 AM update...
A reinforcing high pressure center drops out of east-central Canada
on Wednesday night, which is likely to force the frontal boundary
well to our south with no further shower, or thunderstorm problems
through Friday. Seasonable, to slightly under the average June
temperatures are expected during this time. A more pronounced low
pressure area is forecast to lift out of the Plains states and into
the Northeast this weekend. Influence from the leading warm front
should be reaching CNY/NEPA by early Saturday morning, but there are
timing differences among the big 3 models at this range. Isentropic
lift may bring some leading showers in during the morning, but will
lean with the better chances for storms in the afternoon after some
heating. General slow movement of this system will keep conditions
unsettled through Sunday with the cold front expected to swing
through from Sunday-Sunday night. Temperatures in the upper 70s to
low 80s during the day with 50s-60s at night.


12Z Update...
VFR conditions will persist through the morning, with variable
or light south wind becoming west-southwest 8-12 knots during
the day including gusts approaching 20 knots. Heat and humidity
will cause instability this afternoon, and while not in TAFs due
to lack of confidence/coverage, a scattered line of
thunderstorms may cross the area between 17Z-23Z as a weak wave
passes. Watch for amendments should confidence increase. However,
higher likelihood for convection exists along a cold front
dropping southward across the NY terminals between 23Z Monday-
04Z Tuesday, and thus thunder was included in the TAFs during
that period. For KAVP, timing more likely to be 03Z-06Z. A
period of MVFR/some fuel alternate ceilings will occur for a
time behind the front, but improvement will not be far behind.


Tuesday through Friday...Mainly VFR, though a small chance for
a thunderstorm/brief restriction at KAVP Wednesday.


High temperatures are expected today to fall a few degrees
below records at all three climate sites. The forecasted high at
Avoca is 92 where the record is 93 set back in 1994. At
Binghamton, the record is 92 set back in 1957 and at Syracuse
the record is 96 set back in 1957. High temperatures at
Binghamton and Syracuse are forecasted to be around 90.


PA...Heat Advisory until 8 PM EDT this evening for PAZ038>040-043-
NY...Heat Advisory until 8 PM EDT this evening for NYZ009-015>018-


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