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000
FXUS61 KILN 282334
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
734 PM EDT Wed Oct 28 2020

.SYNOPSIS...
Widespread rain is expected tonight into Thursday before drier
and cooler conditions return to the region Friday into this
upcoming weekend. A reinforcing shot of seasonably chilly air
will arrive Sunday into early next week, with mainly dry
conditions past the next 36 hours.

&&

.NEAR TERM /THROUGH THURSDAY/...
Quite a lot to unpack with the forecast here, so let`s get
right to it.

This afternoon, the Ohio Valley finds itself in a quasi-zonal
midlevel flow regime with the impressively and anomalously
deep/stacked low over the south-central plains into north Texas
and Hurricane Zeta coming onshore the northern Gulf. With the
broad and seasonably strong southwesterly midlevel flow between
these two features, moisture transport aloft from the northern
Gulf into the TN/southern OH Valleys will only increase as we
progress further into the evening.

Midlevel energy pivoting N/NE into the region late this evening
will allow for a blossoming of light rain progressively from
south to north late this evening, with a subtle signal for some
light rain developing near the I-70 corridor late this evening
(past 00z) along a lingering and weakening H8 convergent axis
stretched west to east near I-70 across the region during this
time period.

Attention will quickly turn to a much stronger elevated frontal
boundary pivoting in from the SW past midnight. This pivoting
elevated (H8-H9) baroclinic zone will undergo
frontogenesis/tightening tonight as a seasonably potent LLJ
streams northward into the WSW-ENE oriented boundary. This will
create tremendous moisture and mass convergence in the H8-H9
layer beginning in the predawn hours initially to the SW of the
local area before working its way ENE into the far SW part of
the ILN FA -- perhaps southeast IN into southwest OH -- by
sunrise. This will be particularly stout across south-central IN
Thursday morning as the H8 low tracks from western TN into NW
KY, maximizing convergence in this layer and creating ample lift
for heavier rain rates to develop.

Although rain will undoubtedly overspread the entire ILN FA
tonight -- warranting 100 PoPs for the entirety of the CWA --
there will likely be an enhanced axis of heavier rates
coincident with the H8 front developing and pivoting into the
Tri- State area beginning around 09z. This will mark the
beginning of a 6-8 hour period where rain rates will be the most
robust, with pockets up to 0.5 in/hour possible in SE
IN/northern KY/SW OH until late morning when the H8 low begins
to jog east, allowing the convergent axis to subtly shift to
the south and decrease in magnitude the amount of convergence/lift
over the immediate ILN FA.

Lows tonight will range from the lower 40s in the NW to the mid
50s in the SE with the overcast conditions and widespread rain.
Winds will gradually go northeasterly and pick up toward
daybreak. Sustained winds of 15-20 MPH will be possible Thursday
morning.

&&

.SHORT TERM /THURSDAY NIGHT/...
Widespread rain -- with an enhanced axis of heavier rates from
SE Indiana into southwestern/south-central OH -- will be ongoing
at daybreak Thursday. Even by 12z, we may see some spots nearing
1" in total rainfall already, especially near/south of the Ohio
River. This steady/heavy rain will continue through the morning
hours before the magnitude of LL convergence/ascent begins to
gradually decrease by the afternoon (as the LLJ pulls to the
east), yielding a trend toward lighter rainfall rates for the
afternoon. This is not to say it is going to clear up by the
afternoon -- because it won`t. We will, however, see a trend
toward lighter rainfall rates as the LL convergence decreases
and begins to pivot a bit further to the east/southeast. For the
afternoon hours, we will see a deformation axis of rain linger
back well to the west, with steady /but lighter/ rain continuing
well into the evening before tapering off late evening from
west to east.

With all of this in mind, quite a bit of consideration was given
to issuance of a Flood Watch for at least a part of the ILN FA.
Although for the month thus far many spots are fairly close to
normal for rainfall, it has been a bit wetter-than-normal over
the past 10 days, with multiple heavy rain events moving through
the region during this span. Additionally, the 12z guidance came
in a bit more aggressive/further north with the strip of heavier
QPF (aligning with that potent/tight H8 baroclinic/convergent
axis), with spots near the Tri-State area most likely to
receive in excess of 2 inches of rain by the time the rain
tapers off late in the evening Thursday. This uptick in QPF was
particularly noticeable amongst the hi-res CAMS as well as a
subtle shift further north in the GEFS and GEPS QPF means --
with both ensemble suites showing 2 inches of rain into the
southeast IN/northern KY/southwest OH by the time rain ends
early Thursday night. With all of this being said, there are
several factors that will work against widespread flooding
issues, most notably the extended timeline for which we are
expecting the rain to fall. It will be raining for the better
part of 18-20 straight hours for many spots, with about half of
the rainfall coming in just a 4-hour span or so centered around
daybreak. So even with this, our soils should be able to handle
1-1.25" of rain over a 4-hour span. That would equate to about
1/3" of rain per hour, which is well below prevailing FFG. If we
see a setup favoring this rate to continue for most than just a
handful of hours over any one location, it is feasible that a
short-term flood advisory will be required to handle lowland
flooding and higher water in "typical" trouble spots. But
anticipate that this will be the exception rather than the rule.
There is no doubt that it will be soggy on Thursday. There will
be standing water in fields and in low-lying spots in yards by
the afternoon. But it appears unlikely at this juncture that
there will be any widespread threat of flooding to inundate
structures or do anything more than just fill up local
creeks/waterways. The biggest threat to flooded streets will be
the potential for leaf debris to temporarily clog typical
drainage spots, delaying and/or slowing the drainage of water in
some isolated spots. We will certainly be monitoring the
evolution of the rain rates Thursday morning and will be
watching for any training scenario where those 1/3"-1/2" rates
train over the same locales for any extended period of time.
But right now, will continue to highlight the potential for
isolated flood issues in the HWO.

Storm total rainfall will range from less than 1 inch in west-
central Ohio to 1-1.5" near the I-70 corridor to 1.5-2.5" near
the Tri-State area and near the Ohio River. Rainfall of 1.5-2"
in the far south is expected.

Rain will end from west-to-east late Thursday evening, with
sustained NE winds of 15-20 MPH during the morning and afternoon
tapering slightly by Thursday night as much colder air begins to
filter in from the NW. Lows Thursday night will range from the
mid 30s in west-central OH to the mid 40s in the lower Scioto
Valley and NE KY.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
West-northwest flow aloft with surface high pressure building into
the area Friday. Low level CAA along with flow off the lakes may
result in a few showers into central Ohio on Friday. Have elected to
go with dry fcst with any impacts very low due to limited coverage
and probability. Temperatures look to be 10 to 15 degrees below
normal with highs on Friday generally from 45 north to 50 south.

With the sfc high pressure building across the area Friday night
expect mainly clear skies and light winds. This will lead to
Saturday morning temperatures at or below freezing, with frost
likely. Will continue this mention of freezing in the HWO product.

Mid level flow backs westerly with sfc high pressure moving off to
the east on Saturday. After a cold start -- a low level southerly
flow will only bring modest warming to temperatures. Expect highs on
Saturday of 50 to 55.

Shortwave and sfc low to track thru the Great lakes with an
associated sfc cold front to sweep east across the region on Sunday
morning. A few showers are possible, mainly acrs northern and
eastern counties. In the wake of the cold front, winds will become
gusty Sunday afternoon into Sunday evening. Wind gusts of 30 to 35
kts will be possible.

Northwest flow aloft develops with another surface high to build
across the area Monday and Tuesday. Dry conditions to continue with
below normal temperatures early in the week. Highs look to be around
15 degrees below normal Monday in the lower and middle 40s. Some
moderation Tuesday with fcst highs of 50 to 55. Southerly flow looks
to bring temperatures close to normal at midweek with Wednesday`s
fcst highs in the upper 50s to lower 60s.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Aviation will be affected by plentiful moisture ahead of the
remnants of Hurricane Zeta. MVFR ceilings to start will drop to
IFR tonight as rain begins. Rain will become heavy Thursday
while the remnants track across Kentucky, causing IFR
visibilities. Wind gusts over 20 knots out of the northeast will
be common on Thursday in the rather tight pressure gradient on
the north side of the system. Some improvement back to MVFR
along with subsiding winds may be observed near the end of the
forecast as the remnant low moves east of the Appalachians.

OUTLOOK... IFR ceilings possible Thursday night through Friday.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.

&&

$$
SYNOPSIS...KC
NEAR TERM...KC
SHORT TERM...KC
LONG TERM...AR
AVIATION...Coniglio