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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KILN 170757
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
357 AM EDT Tue May 17 2022

.SYNOPSIS...
A weak, but dry cold front will push south into the region
overnight. This front will then sag south toward the Ohio River
Valley on Tuesday where it will eventually stall. The weather
pattern will then quickly become more active by Wednesday, with
periods of showers and storms expected through the end of the
work week and into the start of the next weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
A dry, weak cold front is moving through the fa early this
morning. The primary result of this front will be a shift in
near-surface winds out of the northwest, as well as keeping a
reasonably comfortable (and generally unmodified) airmass in
place for the day Tuesday.

With persistent northwesterly flow aloft, model soundings show
another day with steepening low-level lapse rates and even some
weak instability forming. This will help with some cu
development again by the afternoon, but cloud coverage should be
limited as the troposphere remains fairly moisture-starved.
Breezy conditions expected once again as sufficient BL mixing
occurs, allowing for some periodic wind gusts of around 20-30
mph.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
-- Changed Discussion --
Flow aloft starts to breakdown and become more quasi-zonal
Tuesday night. Models agree in a shortwave trough developing
within this flow pattern across the Midwest overnight, but the
timing and placement still has some differences. In our CWA, we
are likely to remain dry overnight with cloud coverage
increasing from the west. Due to some differences in the timing
of the shortwave however, decided to keep slight chance PoPs in
the grids for late Tuesday night/early Wednesday morning just
touching our far western counties as some pcpn may occur ahead
of the main system.

Coverage in pcpn will increase late Wednesday afternoon from
west to east as an MCS moves along the shortwave feature. Hi-
res models such as the NAM3K/HRRR even show an MCV present in
portions of Missouri/Illinois, with it beginning to lose some
of its characteristics as it moves eastward into our CWA.
Destabilization will help support thunderstorm potential across
our entire fa, but lower instability is expected in central and
west-central OH. Thus, have only kept a slight chance thunder
mention near/north of I-70 for the day. The potential does exist
for severe thunderstorms - mainly near/south of the OH River
where the atmosphere destabilizes more and is also supported by
sufficient speed shear (~30-40 kts). However, global and hi-res
models seem to keep most of the instability elevated during the
day, with SBCAPE struggling to build in until later in the
evening. This should help limit the severe potential, but will
still be something to closely monitor with additional model
guidance.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
-- Changed Discussion --
The transition from the near term into long term period will be an
active one, as will the start of the long term period, as there is
an expectation for an MCS/MCV to be racing ESE through the region
sometime in the Wednesday afternoon to evening time frame. This will
occur, in part, due to a potent S/W translating E through the quasi-
zonal/NW flow aloft that will be entrenched across the OH Vly.

Guidance has come into a bit better agreement regarding the
evolution of the weather situation during the day on Wednesday,
although there are still plenty of questions regarding how
quickly/far N low level destabilization efforts are able to evolve
late in the day. It does, however, seem that most of the convective
activity with the MCS -- including renewed development during the
afternoon into early evening near/S of the OH Rvr -- will be
primarily elevated in nature locally as the best pooling of richer
LL moisture will be just off to the SW of the ILN FA across
central/NW KY and s-cntrl IN by 00z. And while there is still some
uncertainty regarding the latitudinal variability of the MCS/MCV,
and more importantly the flanking boundary on its southern
periphery, do feel like we have enough confidence to suggest that
once the SHRA/TSRA moves through areas near/N of I-70, the
subsidence in the wake of the complex, as well as the LL moisture
boundary that will settle to the south of these areas, will yield
increasingly dry conditions later into the evening Wednesday for
the northern 2/3 or so of the ILN FA.

Further south, however, closer to the OH Rvr, it may be a far
different story. Confidence remains reasonably high in the MCS
laying out a quasi W-E oriented boundary on its southern flank
Wednesday evening, even as the initial MCS continues to track E.
This is due, in part, to the maintenance of the convergent H8
baroclinic zone/LL moisture axis stretching from WNW to ESE across
far southern IN/OH and N KY. Although the best H8 LLJ will be
pulling E toward later Wednesday evening/night, there will still be
some subtle convergence along the LL boundary amidst an environment
of increasing LL moisture convergence/theta-e advection. And as the
initial S/W energy pulls E, a better northward surge of deeper
moisture will commence, yielding moisture and mass convergence along
the quasi-zonal boundary.

It should be noted that there are considerable convectively-driven
uncertainties regarding not only the placement of renewed convection
Wednesday night, but also the potential coverage of such
development. A stronger afternoon/early evening MCS/MCV may be
enough to shunt the best convergent axis completely S of the ILN FA
for Wednesday night, rendering a solution in which most of the local
area trend drier during this period. A weaker midday MCS/MCV,
however, is not likely to augment the placement and orientation of
said axis quite as much, suggesting that the renewed convective
activity late Wednesday evening may be squarely across the southern
third of the ILN FA. Or it could be any number of scenarios even
between the two laid out here. The primary takeaway is that
confidence is high in a corridor of renewed TSRA activity late
Wednesday evening into early nighttime, in which heavy rain and
localized flooding will be the primary concerns, but lower in
exactly where this may set up. Training storms with very efficient
rain rates may translate into pockets of very heavy rain during this
period. As of right now, this is favored near and south of a
corridor from near the vicinity of Ripley Co IN to Pike Co OH,
although confidence in exact location remains quite low at this
time.

The WNW-ESE oriented axis of TSRA Wednesday night, wherever that may
actually line up, will gradually weaken/dissipate during the predawn
hours as the LL convergence weakens and the axis shifts S subtly.
This will commence a brief window -- perhaps on the order of 12 to
18 hours or so -- in which the LL and deep-layer shear weakens
considerably over the region. This will coincide with the best
pooling of LL moisture pivoting across southern parts of the region,
perhaps even S of the immediate ILN FA through the first half of the
day on Thursday. Again, latitudinal variations exist in where the
instby axis will drift, but it seems plausible at this juncture that
locales N of the OH Rvr will remain in a relatively stable regime
through midday as the instby builds further S across KY. But by
Thursday evening, however, the LL wind fields will once again be on
the increase from the W/SW as the moisture boundary pivots about the
region and begins to make a more concerted movement N. This will
coincide with broad/large-scale height rises, which should help keep
a cap in place for most spots, or even keep any renewed convection
slightly elevated in nature. There remains a signal, however, for
some convective redevelopment along the northward-advancing frontal
boundary late Thursday evening. Model soundings vary on whether this
is likely to be surface-based or slightly elevated. But the overlap
of LL instby and better deep-layer shear may re-establish itself
Thursday evening into early night before the area becomes more
solidly warm-sectored by daybreak Friday. Considerable questions
remain at this juncture in whether the lift will be enough to 1)
generate convection as the boundary moves N, and 2) whether it will
be slightly elevated due to an intruding warm bulge aloft, making
the threat highly conditional. If it does in fact evolve to be more
surface-based, a strong to severe storm potential may also evolve
Thursday evening into early Thursday night across the central part
of the ILN FA as this boundary pivots N.

Friday will offer the only real quiet day of the stretch, with warm
and humid conditions early before a tightening pressure gradient
allows for an uptick in S winds, yielding an increasingly well-mixed
environment toward the afternoon. Do think we will mix down sfc DPs
fairly well Friday afternoon into the evening as S winds at around
20 MPH and gusts to around 30-35 MPH will be possible at times,
especially near/W of I-71. Highs will top out in the upper 80s to
maybe lower 90s, depending on afternoon/early evening DP trends.

Guidance has come into better agreement regarding timing of the
front coming through the region more to during the day/evening
Saturday, which would suggest another warm and humid day for most
spots locally with the slightly slower timing than was previously
indicated. The overlap of instby and shear parameter spaces suggest
that a severe weather episode may also be possible Saturday
afternoon into Saturday night across parts of the ILN FA, depending
on exact timing. Will hold off for now on in-depth discussions
regarding this potential until details come into a bit better focus.

Cooler/drier air settles into the region in the post-frontal
environment for Sunday into early the next week.
-- End Changed Discussion --

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
Skies remain mostly clear overnight even with a dry cold front
passing through. Winds not expected to deviate from the west-
southwest flow for majority of the night, remaining around 5
kts or less. Winds will eventually switch towards the northwest
Tuesday after sunrise, increasing in magnitude with diurnal
heating/mixing. Northwesterly gusts of 20-25 kts will be
possible through the late afternoon hours Tuesday.

VFR conditions expected through the period. There will be some
~6000 ft CIGs that develop with diurnal heating on Tuesday.
Tuesday night, cloud coverage will increase from the west
(generally mid-level clouds).

OUTLOOK...Thunderstorms possible at times Wednesday into
Thursday and again Saturday.

&&

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

&&

$$
SYNOPSIS...Hickman
NEAR TERM...Clark
SHORT TERM...Clark
LONG TERM...KC
AVIATION...Clark