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000
FXUS61 KILN 290603
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
203 AM EDT Thu Oct 29 2020

.SYNOPSIS...
Expect widespread rain tonight through Thursday as copious
moisture enters the Ohio Valley ahead of Hurricane Zeta
remnants. Cool and dry weather is forecast to accompany high
pressure on Friday and Saturday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Rain will continue to overspread the region. As the surface low
from remnants of Zeta translate northeast along the
Appalachian`s spine, the pressure gradient over the Ohio Valley
and much of forecast area will increase. The result of this will
be strong northeast winds and periods of heavier rainfall
beginning in the predawn hours.

Steady temperatures in the upper 40s to lower 50s will be the
rule through daybreak, with only a slight rise expected during
the day.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/...
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 NIGHT 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 /06Z THURSDAY THROUGH MONDAY/...
Prevailing MVFR rain will be found for the bulk of the forecast
with a slight improvement as rain ends from west-east at the
tail end of the forecast. VFR cigs in northern TAF sites will
quickly drop to the lower MVFR range and then drop below 1kft,
lingering here for the majority of the day with a steady rain.

Some heavier rain elements will bring IFR cigs and vsbys through
the course of the day, particularly as winds gust to 20kt in the
late morning/early afternoon. Conditions will improve later in
the day but a light rain and MVFR cigs/vsbys will stick around
until the tail end of the precip exits beginning in the west
late in the evening.

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

&&

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

&&

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