Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 240753

Area Forecast Discussion
National Weather Service Wilmington OH
353 AM EDT Thu Aug 24 2017

High pressure and a seasonably cool airmass will be in place
across the region through the end of the week.


Skies are mostly clear across the area this morning although
there are still some patchy areas of higher based stratocumulus
clouds floating around. This will likely continue through mid
morning before the daytime heating combines with a mid level
short wave to produce some late morning and afternoon cu. The
combination of some slightly deeper moisture across the
northeast and the mid level energy may be enough to produce a
few showers across mainly central Ohio later today. In a
continued weak low level CAA pattern, temperatures will be
seasonably cool today with highs mainly in the low to mid 70s.


The cu and any lingering showers should quickly dissipate as we
head into this evening and lose the daytime heating. As the
winds decrease, good radiational cooling is expected again
tonight with lows mainly in the upper 40s to lower 50s.

Surface high pressure will build slowly east across the
southern Great lakes through th day on Friday. With a dry
airmass in place, expect just some sct cu development through
the afternoon with daytime highs generally in the mid 70s.


Friday night into Saturday temperatures will again be below normal
with the upper level longwave trough axis centered across eastern
Canada. Good ageostrophic convergence moves overhead Saturday
morning on the convergent side of the trough axis and with winds
decoupling lows could fall into the upper 40s in some rural zones.
The only uncertainty here remains whether or not cirrus will move
in. Latest run of the GFS has forecast soundings remaining sky clear
until Saturday evening. Saturday into Sunday 850 mb temperatures
will slowly warm above 10 degrees C and with PWATs being low for
this time of year high temperatures could warm up slightly more than
guidance. We will probably end up hitting 80 degrees by Sunday
afternoon across the southwest.

Sunday night through Thursday model confidence quickly decreases as
a complex scenario appears to be taking stage. Across the Mountain
West mid-level ridging will begin to amplify with a shortwave diving
south into Illinois from Canada. At the same time Harvey is forecast
to stall across southern Texas and be caught on the southeastern
periphery of the mid-level ridge. The overall trend had been for
Harvey to be pulled northeast into the shortwave diving south into
Illinois on Monday. Now the ECMWF and GFS are quicker and slightly
further north with the shortwave compared to previous runs. If this
solution pans out Harvey will likely remain stalled across southeast
Texas. Finally towards the end of extended a deeper trough axis will
push east and pick up Harvey. This means that the ECMWF and GFS now
have the remnants of Harvey pulling northeast towards the CWA next
week Friday/ Saturday (the beginning of September). Any slight track
change in the shortwave diving south on Monday (e.g., further south)
could act to pick up Harvey sooner. Either way have kept PoPs at
chance or less through the extended given the uncertainty. To put
the model spread in perspective the GEFS 24.00z run has a low member
in the accumulated QPF spread of 0.00" for KILN with a high member
of 1.38" (by September 1st).

As of now delaying Harvey being picked up in the main flow appears
to be the way to go. This means Monday the shortwave diving south
will slowly approach the area from the west with rain chances
increasing Monday afternoon. The ILN forecast area appears to fall
in a LFQ with a splitting jet. PWATs at this time climb to around
1.30" (via GFS) with forecast soundings destabilizing by the
afternoon. For now have just nudged PoPs up, but this will likely
need to be raised in future forecast packages.

Monday night into Wednesday morning the shortwave will begin to wrap
up into an upper level low allowing shower and thunderstorm chances
to continue. The upper level low will be slow to exit east and more
uncertainty exists here as both the ECMWF and GFS then shear the
low out and pull the energy east into another tropical system moving
northeast off the east coast of the United States. Towards the end
of the extended the remnants of Harvey will finally be approaching
the area from the southwest.


We are seeing a few higher based sc floating across the area
early this morning and this will likely continue through
daybreak. Otherwise, short wave energy will pivot down across
the region through this afternoon. Moisture is fairly limited
so think the main result will just be an increase in cu later
this morning and into this afternoon. However, it will be tough
to rule out a few showers across central Ohio but chance
appears low enough to leave mention out of KCMH/KLCK at this
point. The cu and any lingering shower activity will dissipate
as we head into this evening.

OUTLOOK...No significant weather.




LONG TERM...Haines
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