Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 141349
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
949 AM EDT Fri Aug 14 2020

.Mesoscale Update...
Issued at 949 AM EDT Fri Aug 14 2020

...Localized Flash Flooding A Threat Through This Evening...

Decided to go ahead and lift a Flash Flood Watch over a good portion
of the CWA to cover the afternoon and evening threat of additional
localized heavy rain. The Flash Flood Watch will go until 10 PM EDT
and covers the almost all of central KY. Decided to leave our NW CWA
out as the data suggests that the bulk of activity will be on the S,
E, and NE quadrants of the MCV. This area also matches up with the
2"+ PWAT axis and where WPC has the Marginal Risk for excessive
rainfall. Given the nearly stationary MCV, and slow/training storm
movement combined with efficient rainfall rates decided a Watch was
the right call. Not overly confident that we will see real
widespread coverage, but the localized threat of 2-3"+ could lead to
some additional significant flooding in areas like we saw earlier
this morning.

Debated on whether to include our NW CWA in the watch also because
FFG values will be quite low given the recent heavy rainfall.
However, hi res model data and the fact that this area will have
trouble destabilizing later today was enough to hold off in this
area. If it becomes apparent that more coverage of storms is
expected later today, we can easily add that area into the watch.

Issued at 835 AM EDT Fri Aug 14 2020

A cluster of persistent moderate to heavy rainfall continues across
southern IN and north central KY. Strong moisture convergence into
the region has been driven by a nearly stationary MCV, and this
feature is expected to continue to drive new convection as we move
through the day. So far, areas of 2 to 3 inches with locally higher
amounts have occurred along with some closed roads across the west
central CWA and a couple of submerged vehicles on the west end of
Louisville.

The latest IR satellite imagery has shown some warming cloud tops
along with a drop off in lightning, so things have at least shown a
trend in slackening in the hardest hit areas around Louisville and
west central KY.

It does look like the focus will gradually shift a bit south through
the day more to central KY. Already seeing an uptick in
intensity/lightning over Taylor/Marion/Larue. May consider trying to
place a Flash Flood Watch for later today if enough confidence can
be gained for a particular region. Updated products out shortly with
higher coverage precipitation chances and rainfall totals.

Issued at 548 AM EDT Fri Aug 14 2020

Widespread heavy rainfall with embedded thunderstorms continues
across southwest Indiana and across portions of north-central
Kentucky this morning.  Radar mosaics show a well defined MCV out
near Santa Claus, IN this morning.  Moderate to heavy rainfall
continues just east of the MCV across portions of Meade and Hardin
Counties in Kentucky.  This activity should rotate north and
northwest and gradually move into Perry, Crawford, and portions of
Harrison counties in Indiana over the next hour.  Dual pol estimates
of 3-4 inches of rain were noted across portions of Hancock,
Breckinridge and southern Perry county (IN).  In addition, areas of
convection were moving through the Louisville Metro area, mainly in
the I-65 corridor and points west.  This activity should slowly
rotate northwestward into Floyd and southern Clark counties over the
next hour.

In general, the moisture flux convergence has decreased a bit, but
the high resolution models will likely continue to struggle with
this over the next few hours.  In the meantime, heavy rainfall looks
to be concentrated along the I-64 corridor from Louisville westward
through Evansville.


Issued at 436 AM EDT Fri Aug 14 2020

Strong moisture flux convergence continues over portions of NW
Kentucky and SW Indiana this morning.  Cluster of showers and
thunderstorms with heavy rainfall has been ongoing for the last few
hours primarily affecting Hancock and Breckinridge counties.  Dual
pol radar estimates instantaneous rainfall rates of 2-3 inches per
hour with a few scans showing up to 4 inches/hr.  Dual pol rainfall
estimates that 2-3 inches of rainfall has fallen across much of
Hancock and western Breckinridge counties in the last few hours.
This matches up pretty good with some private weather station precip
measurements.

Decent southerly inflow on the southern flank of convection should
maintain convection for the next several hours, even though most of
the high resolution guidance suggests that the moisture flux
convergence should weaken in the 5-6 AM time frame.  Training of
heavy rainfall over Hancock, western Breckinridge, and southern
Perry County (IN) has necessitated the issuance of Flash Flood
Warnings for those areas.

Convection may develop a little more eastward with time, but should
mostly remain generally west of the I-65 corridor through sunrise.
Heaviest rainfall concentration looks to remain over
Perry/Crawford/Dubois counties in IN and in western portions of
Meade and much of Breckinridge in KY.

&&

.Short Term...(Today and tonight)
Issued at 306 AM EDT Fri Aug 14 2020

Early morning satellite and obs reveal partly to mostly cloudy skies
across the region.  Temperatures were generally in the lower 70s.
Showers and thunderstorms have been developing out across western KY
this morning.  SPC mesoanalysis shows an area of deep surface
moisture flux convergence from roughly Bowling Green northwestward
into the Owensboro area.  This area is also on the upshear side of a
general broad low level circulation over SE MO.  Rainfall has been
heaviest over Hancock county where dual pol precipitation estimates
that 1-1.5 inches has fallen in the last hour.   Latest high res
guidance suggests that this moisture flux convergence should weaken
over the next few hours and shift slightly westward.  For now, have
increased PoPs substantially out across our western sections.  Will
continue to monitor this area for flash flood concerns over the next
few hours.

Moving into the daylight hours, upper level wave out to the west of
the region is forecast to move eastward and into the region.  With
daytime heating, expect convective coverage to increase through the
mid-late morning hours.  Overall coverage will vary across the
region, but at least 60-70% coverage looks likely.  Coverage looks
to be more centered on KY than IN at this time.  Overall
environmental shear parameters remain rather weak and steering flow
will be generally light.  With PWAT values remaining in the 1.75-2.0
inch range, these storms will be capable of producing
torrential/tropical rainfall.

Similar to yesterday, these storms should develop rather quickly but
are likely to be short lived due to the precipitation loading and
resultant precipitation cutting off the updrafts.  Isolated gusty
winds look likely in the scenario, in addition to the torrential
rainfall threat.  Some localized flooding will also be possible
where these heavy cores dump their precipitation.  In cases like
this, very localized rainfall amounts of 2-3+ inches can`t be ruled
out.  Highs on the day look to top out in the mid 80s.

For tonight, upper wave looks to shift eastward and convection
should take a noticeable downturn by early-mid evening.  Some
lingering convection may be seen over our eastern areas in the late
night hours.  Overnight lows are forecast to drop into the upper 60s
and low 70s.

.Long Term...(Saturday through Thursday)
Issued at 245 AM EDT Fri Aug 14 2020

A few waves of upper level troughs are expected to pass over the
region which will continue to bring unsettled weather to the Ohio
Valley for the weekend. For Saturday, the slow moving trough axis
that has been a topic of discussion for the past week will be moving
eastward over the region. By Saturday afternoon, the accompanied
850mb low and 500mb trough axis should be east of our CWA, and
current guidance is suggesting the best precip chances could be east
of the I-65 corridor. While sufficient SBCAPE will be present during
the afternoon hours, PW values look to remain under 1.2" for areas
west of I-65. Looking at the I-75 corridor and further east, there
is greater moisture content with PW values generally above 1.6" and
K-Index values in the mid 30s, which would suggest some potential
for heavy rain producing thunderstorms.

There will be another chance for showers and storms on Sunday as the
secondary upper level tough and associated sfc cold front pass
through the Ohio Valley. Model soundings reveal that tall, skinny
CAPE will be present, but with virtually no wind shear and a lack of
deep moisture, organized severe weather is not expected. Can`t
completely rule out a few storms to produce heavy rain and gusty
winds, but this frontal passage should move out of our region rather
quickly. Following behind the front will be cooler and drier air.
Forecast lows for Monday AM are in the upper 50s to low 60s.

For late Monday/early Tuesday, another upper trough and weak sfc
front looks to swing through the region. This should limit
temperatures to the upper 70s and possibly low 80s for urban areas.
While guidance suggests this weak front will be limited on the
amount of available moisture, can`t rule out a few stray showers.

The upper trough could deepen during the Wed/Thu time frame, which
would keep precip chances around for the later half of the work
week. Otherwise, temperatures look to remain cooler than normal
through next week with low to mid 80s.

&&

.Aviation...(12Z TAF Issuance)
Issued at 633 AM EDT Fri Aug 14 2020

Remnant MCV over southern IN is forecast to drift northward this
morning.  Widespread convection is expected on the eastern side of
this feature which will affect mainly KHNB/KSDF this morning.
Thunderstorms will be likely at the beginning of the period for KSDF
but this activity should diminish by mid-morning.  Elsewhere, still
expect scattered showers and storms to redevelop by mid-late morning
and continue into the afternoon hours.  Convection is expected to
diminish by evening.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...Flash Flood Watch through this evening for KYZ026>043-045>049-
     053>057-061>067-070>078-081-082.

&&

$$

Mesoscale...MJ/BJS
Short Term...MJ
Long Term....CJP
Aviation...MJ



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