Flash Flood Warning 10, NWS Wilmington, OH

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
938 PM EDT Thu May 16 2019

.SYNOPSIS...
Northwest flow aloft and southwest flow at the surface will
bring together moisture and lift over the Ohio Valley this
evening, resulting in an enhanced threat for thunderstorms
tonight.

A frontal boundary will sag slowly south across the Great Lakes
region tonight into Friday, leading to a chance for showers and
thunderstorms. High pressure and drier conditions will build
into the region for Saturday before another front brings a
chance of showers and thunderstorms on Sunday. Temperatures will
continue to moderate into the weekend.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
A challenging forecast scenario continues to play out this
evening, as one round of convection has exited the ILN CWA, and
another is about to enter.

Current surface analysis indicates that the ILN CWA remains
within a general regime of SSW boundary layer flow, disrupted in
part by the MCS that moved through the southwestern sections of
the forecast area in the past few hours. The area is also on the
edge of a significant increase in 925mb/850mb theta-e, which is
advecting ENE on the southern periphery of a slightly-elevated
trough over the Great Lakes. Convergence developing in this area
(at the nose of the strengthening 850mb flow) has led to storm
development in the IWX CWA, with storms quickly becoming strong
to severe.

These storms will behave much differently than the storms
earlier in the day. The previous storms developed within a
favorable boundary layer air mass, with overall propagation
along the edge of the surface-based instability to the south,
though individual storm motions were more toward the ESE. While
one bowing segment was able to persist into the less favorable
air mass and move into Ripley County IN (prompting a warning)
eventually these cold-pool driven storms ran out of energy to
tap, leading to their weakening with eastward extent. To
contrast, the storms developing now are not tied at all to
surface-based instability, and are instead being fed by a
significant amount of theta-e advection a few thousand feet off
the surface. Despite a stable layer under an inversion near the
surface, these storms are realizing a decent bit of elevated
instability (SPC Mesoanalysis suggests 500-100 J/kg, though it
may be slightly higher given the intensity of the updrafts).
Further, they are also being aided in organization by favorable
shear in the 0-3km layer.

It is difficult to use a model to try to project these storms,
because the models simply do not have these storms developing
this soon. The RAP seems to be slightly ahead of the HRRR in
terms of development, which is good because it would be
charitable to describe the performance of the HRRR today as
poor. Nonetheless, the expectation is for overall storm motions
to the E / ESE and a gradual propagation more to the SE as the
LLJ continues to feed elevated instability into Ohio. The
northern half of the ILN CWA will be favored (especially along
and north of a line from Darke County OH to Ross County OH) with
more question marks regarding any further southward propagation
into an increasingly stable air mass. The primary threats appear
to be large hail (with deep rotating updrafts) and heavy rain
(potential training) with a much lesser threat for damaging
winds (stable boundary layer).

Previous discussion >
Upper level energy upstream that is firing convection in nw IN
will race over the CWA this late day and early evening,
outpacing the low level forcing in place in western IN and IL.
Near 70 dewpoints running s-n through IL will continue to get
wrung out on the leading edge of this convective complex, but
the upper energy outpacing it and the relative unreceptive
surface features currently over ILN CWA does not favor this
complex to continue to hold together as it pushes into the CWA
on northwest flow aloft.

This is just a mashup of a couple of vastly differing model
solutions this evening, most of which keep convective initiation
at bay and more northwest of the CWA through this evening.
Expect some storms in northern Ohio to lay out a boundary wnw to
ese over the CWA and another round of storms possible early in
the overnight period northwest of metro Dayton. Any storms
overnight will be on the decrease in both coverage and
intensity, dying out towards daybreak.

Storms that are present will have enough shear to maintain a
presence for at least a few hours early tonight, and possibly
but less likely through the overnight period. This shear
increases the threat of these storms to produce large hail if
they are present, which remains in high question at this time.

Overnight lows were raised, particularly in the western third of
the CWA where dewpoints in the mid 60s should be working in and
inhibiting any rapid temperature decreases.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
A relative minimum in thunderstorm activity is expected to start
the day on Friday, but this could ramp up into some storms by
late morning given the boundary that is expected to cross the
CWA and potentially act as a focus for more storms to fire on.
The bulk of the model solutions push the area of rain to the
northeast sections of the CWA while the CAMs fire more robust
activity along the boundary by later afternoon. Played the
middle ground here and had a brief uptick in the potential for
thunderstorms running from nw of Dayton to se of Columbus late
in the day, decreasing sharply with the setting sun tomorrow.
Any activity tomorrow night will lift well northeast of the CWA
overnight.

Highs on Friday were cut slightly everywhere given the expected
cloud cover and potential rain, but by 3-4 degrees in the north
where these conditions are more likely. Overnight lows will
again be mild - 60-65 with the warmer readings southwest of
Cincy and coolest northeast of Columbus.

Forecast probabilities of thunderstorms are unusually low
confidence starting in the immediate near-term and lasting
through Friday given the wholesale differences between models,
until the upper ridge finally begins to build into the region
and southwest flow aloft turns more westerly overnight.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
A mid level ridge will continue to build northward across the
region on Saturday. This will place our area in a somewhat humid
and warm airmass. There could be a low chance of a PoP up
shower or storm during the afternoon, but that's around 10
percent so have kept the forecast dry. Highs will be in the
lower to mid 80s.

For Saturday night into Sunday, a mid level trough with embedded
short wave energy will pivot northeast from the central/southern
Plains toward the western Great Lakes and middle Mississippi River
Valley. This system now seems to have a stronger surface low and
overall stronger wind field. The mid level ridge will move east on
Sunday while the mid level trough/embedded energy pushes a cold
front east. The timing of the front and associated instability will
play an important part as to whether we see much severe weather
Sunday afternoon and evening. For now, it looks like the slower
progression of the cold front and max diurnal instability favor
points just to our west, and that is where SPC has a slight risk for
scattered severe storms. But given strong wind field and at least
early on low end moderate instability across our west, there will
likely be a marginal risk for isolated severe. A little early to put
in the HWO for now. Otherwise, given the strong wind field and
diurnal mixing, it will be breezy to windy with the windier
conditions slated across the western CWFA.  After lows in the 60s,
Highs will range from the upper 70s northwest to the mid 80s east.

As the mid level trough pushes northeast across the remainder of the
Great Lakes Sunday night into Monday, the cold front will push east
as well. Instability wanes fairly quickly overnight, such that only
some scattered showers are expected across the east by morning. Any
lingering pcpn should move out of eastern locations by afternoon
with skies becoming partly cloudy. After lows from the upper 50s
northwest to the mid 60s east, highs will range from the lower 70s
northwest to the lower 80s southeast on Monday.

High pressure at the surface and aloft is expected to move into the
region Monday night, then move east on Tuesday. This should provide
a window of dry weather with near or slightly above normal
temperatures.

The remainder of the extended is still muddled with uncertainty (in
terms of timing) as we head into mid to late week next week. A warm
front will likely move into the region on Wednesday followed by a
cold front Wednesday night into Thursday. Have kept a chance of
showers and thunderstorms in the forecast during this period. Highs
will remain in the 70s to the lower 80s.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
In the next hour or two, some rain (possibly with embedded
thunder) will impact the KCVG/KLUK airports. However, prevailing
conditions should remain VFR. There may also be some brief wind
gusts out of the west at about 25-30 knots.

VFR conditions should prevail for all TAF sites going into the
overnight hours, but there will be another chance of storm
development after 04Z at KDAY and especially KCMH/KLCK. For
now, it remains unclear if the storms will actually impact the
airports, but some MVFR/IFR conditions will be possible if they
do. A period of VCTS has been included at these TAF sites for
the most likely timing. Also, some MVFR ceilings may get into
KCMH/KLCK during the morning hours, but these should dissipate
by early afternoon.

Thunderstorms will again be possible on Friday afternoon for
KILN/KDAY/KCMH/KLCK, mainly from 20Z onward. Otherwise, VFR
conditions are expected, with westerly winds of 10-12 knots and
SCT/BKN cumulus.

OUTLOOK...Thunderstorms may continue into Friday evening.
Thunderstorms will be possible again on Sunday.

&&

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

&&

SYNOPSIS...Franks
NEAR TERM...Franks/Hatzos
SHORT TERM...Franks
LONG TERM...Hatzos
AVIATION...Hatzos

Hazardous Weather Outlook
National Weather Service Wilmington OH
421 AM EDT Thu May 16 2019

INZ050-058-059-066-OHZ026-034-035-042>046-051>056-060>065-070>074-
080-082-171100-
Wayne-Fayette IN-Union IN-Franklin IN-Hardin-Mercer-Auglaize-Darke-
Shelby-Logan-Union OH-Delaware-Miami-Champaign-Clark-Madison-
Franklin OH-Licking-Preble-Montgomery-Greene-Fayette OH-Pickaway-
Fairfield-Butler-Warren-Clinton-Ross-Hocking-Highland-Pike-
421 AM EDT Thu May 16 2019

This Hazardous Weather Outlook is for East Central Indiana,
Southeast Indiana, Central Ohio, South Central Ohio, Southwest Ohio
and West Central Ohio.

.DAY ONE...Today and Tonight.

Occasional showers and thunderstorms will be possible tonight. A few
of the storms may become severe with damaging wind and large hail the
primary threat. In addition, locally heavy rainfall may result in
isolated flooding concerns.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

There will be a chance of showers and thunderstorms Friday into
Friday night. A few of the storms may become severe later Friday
afternoon and evening with damaging wind and large hail the primary
threat. In addition, locally heavy rainfall may result in isolated
flooding concerns.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be required this evening.

INZ073>075-080-KYZ089>100-OHZ077>079-081-088-171100-
Ripley-Dearborn-Ohio-Switzerland-Carroll-Gallatin-Boone-Kenton-
Campbell-Owen-Grant-Pendleton-Bracken-Robertson-Mason-Lewis-Hamilton-
Clermont-Brown-Adams-Scioto-
421 AM EDT Thu May 16 2019

This Hazardous Weather Outlook is for Southeast Indiana, Northeast
Kentucky, Northern Kentucky, South Central Ohio and Southwest Ohio.

.DAY ONE...Today and Tonight.

Occasional showers and thunderstorms will be possible tonight. A few
of the storms may become severe this evening with damaging wind and
large hail the primary threat. In addition, locally heavy rainfall
may result in isolated flooding concerns.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be required this evening.

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