Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 220830

Area Forecast Discussion
National Weather Service Wilmington OH
430 AM EDT Tue Aug 22 2017

A cold front pushing through the Ohio Valley will bring
organized showers and thunderstorms today, then drier and
cooler air moves in for the rest of the week.


Varying scenarios playing out via the CAMs, with HiRes NMM/HRRR
slowly diminishing the early morning convection over Indiana as
it pushes toward forecast area. What precipitation that does
work into western forecast area expected bring enough clouds to
inhibit destabilization in the western forecast area for the
afternoon, so have generally kept severe potential wording
further east where enough heating combined with 40kts+ of 0-6km
bulk shear will be present as the prefrontal trough pushes
through the eastern forecast area in the 18-22z timeframe. Main
severe threat will be damaging winds. Greatest confidence in
thunderstorm coverage south/east of I-71, along with greater
confidence in at least a few severe storms this area. NW of I71,
expecting most scattered coverage and less likely to be severe,
though a narrow line of storms indicated by numerous CAMs
associated with the frontal passage itself.

In addition to severe threat essentially east of I-71 corridor,
as the progression of the trough slows slightly especially
along and south of the Ohio river, concern is an East-West
oriented line segment which could pose a more favorable pattern
for training storms and a localized flood threat. While ample
deep moisture available over nearly all of area in the form of
PWs at 1.75-2" and warm cloud depths of 3.5-4k, central Ohio
storms likely to be more N-S oriented line segments, which will
produce heavy rain but storms should be fairly progressive.


Cold front to push through the region in the 00-03z timeframe
Wednesday, with some lingering showers in the far southeast as
the surface boundary will be less progressive in nature.

Below normal temperatures through this period with the strong
cold frontal passage and then surface high pressure building in
under an upper level trough where NW flow will dominate the
region through Wed.



Beautiful weather is in store for most of the long term as below
normal temperatures, dry conditions, and lower dewpoints take hold
across the region. Overall, the long term will be characterized by
below normal height anomalies as well as below normal 850 mb
temperatures. This will be in large part due to a longwave trough
axis that looks to remain in close proximity to the region through
the weekend.

Wednesday evening will open up with an upper level low pushing east
across Quebec. At the same time a potent shortwave will drop south
out of Saskatchewan/ Manitoba. This shortwave will drop down
towards Michigan Thursday afternoon acting to reinforce the longwave
trough axis west. As this happens low level CAA will continue with
an expansive cu field likely forming in the afternoon. 850 mb
temperatures Thursday fall to around 8 degrees C (GFS slightly
cooler than the ECMWF) with 1000/ 850 mb thicknesses around 1375 m.
500 mb heights on the NAEFS are around 1 to 2 standardized anomalies
below normal for this time of year with 850 mb temperatures
following suite. Even with it being August still thinking high
temperatures will struggle a bit Thursday given the likely cu
development. Have gone ahead and lowered high temperatures Thursday
into the mid 70s with thicknesses alone supporting highs in the
lower 70s (esp northern zones).

Thursday night into Friday morning the trough axis will begin to
modulate and nudge east allowing the best ageostrophic convergence
to push closer to the area. Friday afternoon thicknesses and 850 mb
temperatures remain similar to Thursday, with the only difference
being less cu probably (thanks to PWATs falling to around 0.60").
Saturday morning looks to be the coolest as surface high pressure
and ageostrophic convergence settles overhead. Winds will also
likely decouple. GFS forecast soundings are hinting at some cirrus
moving in but we will likely see some upper 40s in rural zones
Saturday morning. Saturday afternoon the trough axis will slowly
pull east allowing low level thicknesses and temperatures to ever so
slowly recover. By Sunday surface high pressure will be off to the
east with temperatures approaching the 80 degree mark. The area also
looks to remain dry through Sunday as PWATs hover around 0.50" (or
near record low values for this time of year).

By Monday models begin to diverge as an upper level disturbance is
forecast to dive south into the plains with an upper level jet at
250 mb amplifying. As this occurs the ILN forecast area will fall
into a LFQ which means rain chances will likely be on the increase.
There still remains uncertainty though on how everything will play
out so have just trended towards chance PoPs at this time.


VFR conditions expected through the period, with current
thinking of convection in 2 rounds, first the prefrontal trough
in the 15-18z timeframe, then redevelopment closer to the actual
front with most likely affected locations the KCMH/KLCK sites
where instability and forcing more favorable. Could be
occasional MVFR in moderate rain in especially these locations.

OUTLOOK...No significant weather.




LONG TERM...Haines
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