Scientific Forecaster Discussion
fxus61 kbgm 211027
Area forecast discussion
National Weather Service Binghamton New York
627 am EDT Fri Jul 21 2017
high pressure will bring rain free weather today, along with
seasonably warm, humid conditions. An approaching warm front,
will bring unsettled weather back to the region this weekend.
Near term /through tonight/...
245 am update... a mixture of low stratus clouds and fog cover
much of cny/nepa early this morning, in the wake of yesterday's
rainfall. The lower clouds and fog should burn off towards 8-9
Today looks like a tranquil day, with a fair amount of sunshine,
amidst a patchy fair weather cumulus field. This is owing to
weak high pressure ridging southward from Ontario and Quebec. It
will still feel rather Summer-like, with afternoon highs well
into the 80s for most areas, along with fairly sticky dew points
in the 60s.
Under partly cloudy skies tonight, we think at least patchy
valley fog will form again, given all the available soil
moisture, and a fairly humid air mass. Lows by daybreak will
range from the upper 50s-mid 60s.
Short term /Saturday through Sunday night/...
345 am update...
active weekend foreseen, with concerns for locally heavy
rainfall and perhaps strong to severe thunderstorms. Main
periods to worry about will be late Saturday afternoon into
night, and then Sunday afternoon into evening.
We will have to watch for convective complexes upstream which
could gum up the works in terms of timing, but right now,
Saturday morning through at least early afternoon appears
pretty quiet due to mid-level ridge and a fairly dry boundary
layer. Increasing moisture in the upper levels, including
blowoff cirrus from storms in the western to central Great
Lakes, will cause the sky to turn mostly cloudy with time while
also holding temperatures back in the upper 70s-lower 80s for
highs. Lower elevations of northeast PA-Sullivan County New York may
manage mid 80s with longer window of sunshine early to midday.
Mid afternoon Onward and especially Saturday night itself, warm
frontal boundary will lift into our region in tandem with well
marked shortwave embedded within zonal flow aloft. Low level
jet, especially prominent in the NAM and Gem models, surges
precipitable water values to at least 1.75 inches and perhaps 2
inches. Front will slow down and probably even stall awaiting
wave of low pressure coming in from Michigan, with low level jet
nearly parallel to that boundary. This will promote
backbuilding and/or training. Add forced ascent via right
entrance region of 300mb upper jet, and of course antecedent
moist conditions from a very wet several weeks, and this means
several worrisome ingredients are coming together for
potentially heavy rainfall including possible localized flash
flooding. There is somewhat of a severe weather threat as well
due to increasing shear, though this may be displaced further
south where better surface-based instability will reside. Much
of our convection will take on an elevated nature, at least
initially, and so main issue is heavy rain potential.
All told, for late Saturday into Saturday night, a heavy
rainfall risk appears to be increasing for The Finger lakes-
southern tier-Catskills areas in central New York, and for
northeast Pennsylvania. The severe weather risk will be more
focused on Pennsylvania.
More uncertainty exists on Sunday. Initial lull in activity
expected early, in the subsidence behind the wave from Saturday
night as per NAM-Gem-ECMWF. GFS delays wave passage into Sunday
itself. Then Sunday afternoon through evening, non-NAM models
lift frontal boundary back north through the area with
additional convection. At this point, storm-level flow will no
longer be boundary-parallel and thus showers-storms should be
more progressive and so heavy rainfall threat is less clear.
However, there may be significant instability and a good amount
of shear in the atmospheric column as warm sector gradually
overtakes the region southwest to northeast. So potential for
severe thunderstorms definitely cannot be ignored. Also there
will be large-scale ascent ahead of upper level trough axis. If
the 00z NAM solution wins out, the threat will be lower, but the
balance of other guidance is pointing to another possibly
significant event. Monitor the forecast closely the next couple
Long term /Monday through Thursday/...
215 PM update...
a final upper trough will roll through the region Sunday night
and Monday morning with precipitation lasting through the day
Monday. Weak ridging will develop behind this trough and allow
conditions to dry out. Temperatures will remain on the cool side
with highs in the 70s and lows in the upper 50s and lower 60s.
Aviation /12z Friday through Tuesday/...
residual restrictions this morning (particularly at kelm, kbgm,
and kavp) should burn off by around 14z.
Thereafter, VFR should prevail for the rest of the day. Fog is
likely to form again later tonight, particularly at kelm. At
this early juncture, we've gone with IFR restrictions at kelm,
with MVFR at kbgm and kavp.
Saturday through Monday...periodic restrictions in
showers/thunderstorms expected, especially Saturday night-