365
FXUS61 KILN 161753
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
153 PM EDT Thu May 16 2024

.SYNOPSIS...
A return to southerly flow will occur today ahead of a cold
front in the Midwest. An upper level ridge of high pressure will
break down and move east this afternoon, setting the stage for
the next system and rainfall moving in tonight. Surface low
pressure with this system will remain west of the CWA as it
tracks northeast into MI on Friday, with more shower activity
noted during the day.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Went into the overnight period with regards to precip
overspreading the region from west-east. While the overall
message of overspreading showers is pretty uniform, some
differences in the models bring an element of uncertainty to the
table. This is more concerning the timing of the leading edge
but to a lesser extent coverage and placement.

Looking at forecast soundings, the pre-storm environment shows
steep low level lapse rates. These rates are found in the yet
unmixed layer below the LFC and quickly become less favorable as
the moisture becomes deeper with the mixing found on the
leading edge of this activity. Likewise, most unstable CAPE
values under 400 J/kg are only briefly found at the onset of
precip. This is indicative of an atmosphere that does not have a
forcing mechanism in the lower levels such as tonight. Mid
level vorticity is largely the driving force for upward motion
in this forecast from what I am able to discern. The relatively
small waves in the height fields and brief time the best
vorticity maxima cross are a favored indicator of storms
producing lightning. Conversely, it doesn`t help pin down with
any reliability the timing/placement of thunderstorms.

The leading edge of this rain tonight has been slowed with this
update, but it did not make a significant decrease in the
overnight probability at any one location. Given the lack of
indicies supporting discrete thunderstorms, expect this to be
more of a showers with some thunder flavoring for the overnight
hours. Used pops >40% to include a slight chance of thunder and
pops >50% for a chance of thunderstorms.

Previous Discussion:
Have decreased cloud cover for today though kept high
temperatures unchanged in the upper 70s to near 80. Temperature
trace in the hourly forecasts have bumped up a bit is more
cosmetic and will largely be unnoticed.

Cu rule over the CWA does not support development today, and
what slight bit of increased moisture 5-6kft will be late this
afternoon. Some cirrus blowoff from upstream system will
generally be thin, and any noticeable opaque cloud cover is not
expected to enter the CWA until this evening and primarily be
along and west of the IN/OH border.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
A S/W embedded within the midlevel zonal flow draped across the
OH Vly will serve as a focus for a few SHRA/TSRA to move into
the ILN FA around/after sunset this evening. This being said,
the environment should be slightly less favorable for
maintenance of storm activity with eastward extent, so would
expect that any clusters that make it into the local area this
evening should be on a weakening trend and pose little to no
severe threat. But, a few rumbles can`t be ruled out from time
to time, with a gradual /increase/ in coverage of SHRA expected
past midnight as the S/W progresses E and a subtle LLJ impinges
to the NE into the ILN FA, providing a bit of speed/convergence
and lift amidst a saturating LL profile.

The activity tonight should be largely non-impactful, with
questions even on whether it will contain any lightning/TS.
Additionally, although the steering-layer flow is still somewhat
weak, the activity should be moving and is not likely to be
stationary, meaning that the potential for prolonged heavy rain
in one location is also rather low through Friday morning. But
conditions should be increasingly wet/soggy toward daybreak
Friday as temps dip into the lower 60s area-wide.

Periods of SHRA/TSRA should continue about the area during the
day Friday, with the best instby focusing around any larger area
of SHRA activity (where instby should be more convectively-
contaminated/limited). So we will probably end up with a larger
area of steady SHRA (likely near/S of the OH Rvr) surrounded
(especially on the nrn periphery in the local area) by a
slightly better instby profile and ISO/SCT cellular/disorganized
TSRA activity. The steering-layer flow will become increasingly
weaker late into the day/evening and beyond, suggesting that
storm motions should slow and could become a bit more erratic by
late day, especially along a weakly-convergent axis stretching
across nrn parts of the area. This could lead to some very
isolated localized heavy rain/flooding, but confidence on a
favored location at this juncture is very low.

Highs on Friday will be tempered quite substantially by
prevalence of clouds/pcpn, with temps only reaching into the
lower/mid 70s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
On Friday evening, the Ohio Valley will be just upstream of a broad
mid-level trough, which will extend from Illinois through the
southern plains. As this trough slowly moves east, displacing
ridging over the east coast, a continued feed of moisture will bring
showers and storms into the region. With the forcing and moisture
transport involved, it does appear that some nocturnal convection
may occur on Friday night, with additional diurnal development on
Saturday afternoon. Still seeing some timing differences in how
quickly this slow-moving trough makes it out of the area, but this
forecast will have to keep some PoPs in on Sunday, especially in the
eastern and southeastern sections of the CWA.

In terms of hazards through this part of the forecast period, narrow
CAPE profiles and a lack of shear will preclude a threat for severe
weather. However, the moist profile and slow motions could lead to a
threat for some flooding, especially on Saturday.

A narrow ridge will move into the area late Sunday into Monday,
providing a brief period of dry weather. However, this respite will
not last long, as the flow pattern over the region will turn to
something a bit more progressive. As it looks now, some
precipitation chances may return on Tuesday, with no significant
forcing but a gradual increase in instability. By the middle of the
week -- although timing is far from certain at this distance in the
forecast cycle -- a stronger trough and a cold front will likely
move into the region. Whenever this occurs, it may provide the next
chance for strong storms.

A gradual warming trend is expected from Saturday through the middle
of next week, as the upper trough moves away, and warmer air moves
into the region behind it. Highs are likely to reach the 80s by
Sunday for most of the ILN CWA, and for the whole area by Tuesday
and Wednesday.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
Weakening/disorganized showers will approach from the west
after 06z, possibly including some embedded thunder without
organization of cells, clusters, or line segments. Have held any
prevailing -shra/-ra until just before daybreak, and only
restrict vsbys during the morning in a tempo group. While
thunder could be present, several uncertainties described in the
near term forecast remain in play. Best forecast right now is to
include thunder when it can be reliably indicated as moving in
from upstream, which should not happen until later tonight.

Expect a lot of the -ra/-shra to be VFR and fall from a mid
level deck 8-10kft. There will be stronger elements in a
scattered nature on Friday that would be expected to drop vsbys
into MVFR. Cigs may briefly appear in MVFR category but all
indications attm are for lower cloud cover to be the outlier.

Light/variable wind will become ssw late tonight and then wsw
during the day, increasing to 7-10kt.

OUTLOOK...MVFR CIGs/VSBYs are possible with showers and possible
thunderstorms on Friday into Friday night.

&&

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

&&

$$
SYNOPSIS...Franks
NEAR TERM...Franks
SHORT TERM...KC
LONG TERM...Hatzos
AVIATION...Franks