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Area Forecast Discussion (AFD)

Issued by Louisville, KY (LMK)

                            
000
FXUS63 KLMK 202227
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
627 PM EDT Tue Aug 20 2019

.Mesoscale Update...
Issued at 620 PM EDT Tue Aug 20 2019

Strong to severe storms continue mainly east of I-65.  East central 
KY is mostly worked over from sct convection this afternoon. 
However, south central KY may still have around 1000 j/kg DCAPE and 
2000 j/kg CAPE with current radar showing healthy convection in that 
area which should continue for the next 1-2 hrs before diminishing. 
Damaging winds will be the primary threat for south central KY and 
brief heavy rain and possible minor flooding may threaten east 
central KY. 

Cancelled a portion of SVR Watch 604 over southern IN and north 
central KY as the severe threat has ended with some light rain to 
follow this evening. 

Issued at 450 PM EDT Tue Aug 20 2019

Even as the MCS looks completely outflow-dominated, there remains a 
tongue of 1500 J/kg of downdraft CAPE ahead of the line, and cells 
that develop along the outflow are quickly approaching SVR limits. 
Pop-up storms out ahead of the line are quite active and have 
prompted a few warnings on their own. After coordination with SPC, 
we will do a local extension of SVR Watch 604 to include the rest of 
the Louisville CWA. Will clear behind the convective line in 
Indiana, which knocks out a handful of counties.

&&

.Short Term...(This evening through Wednesday)
Updated at 315 PM EDT Tue Aug 20 2019

...Strong to Severe Storms Through Early Evening...

Outflow-dominated MCS entering SW Indiana will be the main player 
through this evening, but we are also seeing more popcorn-type 
convection out ahead of that line as a result of differential 
heating at the edge of the MCS anvil. A few of these storms east of 
I-65 have pulsed up to marginally severe levels, but organized SVR 
is not expected with this activity. The main line will push across 
southern Indiana and north-central Kentucky through sunset, and 
downdraft CAPE approaching 1500 J/kg will support a continued 
damaging wind threat. SVR Watch 604 is in effect until 9 PM but 
expect to chip away at it from the NW once the main line passes. The 
line should really weaken once it gets solidly into Kentucky is it 
quickly runs out of instability. 

Hi-res models suggest redevelopment is possible overnight, 
especially heading north into Indiana, so we'll hang on to a 20-30 
POP through the night. Wednesday will be the last day for this 
tropical air mass, with hot and humid conditions once again. Temps 
solidly in the 90s and dewpoints in the lower/mid 70s will push heat 
index values very close to advisory thresholds. However, precip 
chances will again ramp up in the afternoon and that could limit the 
window for any dangerous heat, so we'll just mention the triple-
digit heat indices in the Hazardous Weather Outlook. Primary storm 
threats will be cloud-to-ground lightning, and heavy rainfall given 
slow storm motion.

.Long Term...(Wednesday night through Tuesday)
Updated at 250 PM EDT Tue Aug 20 2019

Wednesday Night - Friday...

An active pattern looks in store through the end of the work week. A 
cold front will move into the Ohio Valley and linger providing focus 
for multiple rounds of storms Wed night through Friday. While no 
organized severe threat looks likely at this time, cannot rule out 
some strong storms with gusty winds, lightning, and brief heavy 
rainfall.  

Temps will cool down through the end of the week into the upper 
70s/lower 80s for highs by Fri.  Lows Fri night should be in the 60s.

Saturday - Tuesday...

We should see a drier trend for the weekend, although some data 
still hangs some showers up along our southern border through the 
weekend. Will keep some mention of precipitation chances in the 
forecast, but overall should expect a mostly dry and pleasant 
weekend as surface high pressure tries to take hold north of the 
front. Highs should top out in the low and mid 80s, with pleasant 
lows in the low to mid 60s.

Small shower and storm chances continue into the new work week, 
although the lack of a notable trigger will likely keep coverage 
pretty low. Temps start to trend back closer to normal with highs in 
the mid to upper 80s returning.

&&

.Aviation...(18Z TAF Issuance)
Updated at 105 PM EDT Tue Aug 20 2019

Main concern is the timing and impact of incoming convective 
complex. Fairly high forecast confidence for HNB, where we expect 
storms with IFR cig/vis and gusts hitting a solid 30 kt around 20Z. 
Still think the worst weather will be fairly brief, so will carry a 
TEMPO to show some wiggle room. Expect the line of storms to push on 
into SDF around 21Z, and BWG/LEX after 22Z. There is a split 
starting to form in the line, which has the most impact on forecast 
confidence for LEX, but we have included VCTS for pop-up cells 
forming ahead of the main line. 

By mid/late evening, even the trailing stratiform showers should be 
tapering off, and a mid-level ceiling overnight will be the worst-
case scenario. If any of the terminals pick up heavy rain, that 
could drive some fog potential for Wed morning, but will not include 
restrictions in any of the TAFs.  SW winds and scattered Cu expected 
by late Wed morning as mixing picks up again.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Mesoscale...RAS/AMS
Short Term...RAS
Long Term...AMS
Aviation...RAS