571 
FXUS63 KLMK 010621
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
221 AM EDT Sat Apr 1 2023

.Mesoscale Update...
Issued at 219 AM EDT Sat Apr 1 2023

Ongoing convection has evolved into a broken line of strong storms 
along and just west of I-75, with a second line of weaker showers 
along the river at this hour. Severe weather is not expected with 
this second line of convection; therefore, have dropped counties 
behind the leading line from the tornado watch. Expect a continued 
downward trend in convection over the coming hours as instability 
continues to dwindle and drier air pushes in from the west. At this 
time, expect to end the tornado watch for all remaining counties at 
the top of the hour.


Issued at 1200 AM EDT Sat Apr 1 2023

Two convective clusters, one along the Ohio River within our CWA and 
another farther south stretching from Hopkinsville into west TN 
appear to be in the process of growing upscale into a larger quasi-
linear system as new convection has started within the last half 
hour over Ohio and Muhlenberg County in between the two lines. 
Environmental shear remains strong ahead of the current convection; 
however, the instability will become less conducive for severe 
storms (according to mesoanalysis CAPE fields and sfc obs) as storms 
approach the I-65 corridor. Appears that while tornado threat will 
still continue in the immediate near term, it is decreasing at this 
hour in favor of a damaging wind threat.

Latest watch update has included Henry and Shelby County to account 
for severe threat translating eastward.

Issued at 1005 PM EDT Fri Mar 31 2023

Recent radar trends to the west of our region suggest that 
convective mode is currently transitioning from a more discrete mode 
to a predominantly quasi-linear one. The first cluster of storms 
which looks to impact our area stretches from just north of Paducah 
to around Evansville, and looks to reach Dubois/Perry County just 
after 1030 PM EDT. VAD wind profiles from VWX show very large low-
level helicity values (500+ m2/s2 0-1 km SRH), so from a dynamics 
perspective, this cluster of storms is moving into a favorable 
environment. Now that we've lost diurnal heating, any 
destabilization ahead of ongoing convection will have to be done by 
low-level theta-E advection and encroaching reduced heights aloft. 
Compared to latest RAP mesoanalysis, convection to our west may be 
slightly outrunning the best instability, but with the amount of 
dynamic support that we've got, still expect storms to maintain 
strength over the next few hours.

The main area of concern over the next 1-2 hours looks to be a 
corridor from extreme northern Ohio County KY north to southern 
Dubois County IN eastward to the I-65 corridor (mainly along and 
north of the Ohio River). This area has been keyed on by Warn on 
Forecast simulations consistently over the past 1-2 hours.

Issued at 830 PM EDT Fri Mar 31 2023

As was mentioned in the previous update concerning the watch 
potential over the CWA, Tornado Watch 98 has been issued for all of 
our southern IN counties along with western and central KY until 3am 
EDT/2am CDT. Very strong 60-70kt LLJ will work over the Ohio Valley 
now through 07z. This along with the approaching 80-100kt mid-level 
jet will increase the deep layer shear over the Ohio Valley and 
increasing the potential development of severe weather out ahead of 
the approaching cold front. Latest 2330z update of the WoF continues 
to show this split dynamic over western/central KY with a favorable 
low-level updraft helicity track coming the current storms over the 
Boot Heel of MO and extending it northwestward along the Ohio River 
and reaching Hancock Co. KY/Perry Co. IN between 03/04z as it shows 
the cells currently over western TN weakening as they approach or 
southwestern CWA. 

Hi-res model soundings continue show a ramp up of instability and 
shears after 02/03z across the CWA. The threat remains strong 
damaging winds and spin up tornadoes. 

Issued at 720 PM EDT Fri Mar 31 2023

Current Radar imagery from KLVX WSR-88D has a broad area of 
stratiform thundershowers moving over Butler, Logan, Simpson and 
Warren counties as it continues to move eastward. Satellite imagery 
generally shows Broken to overcast cloud cover over most of western 
KY with a few breaks in the clouds over Evansville IN. The main show 
continues to be in the warm sector just behind the warm front that 
stretches from around Davenport IA to Evansville, IN to around 
Nashville, TN while the cold front stretches from about Cedar Rapids 
IA southward through central MO into eastern TX. Activity currently 
stretching from near St. Louis across south central MO into central 
AR is where our focus is for what is expected to push through 
western KY into central KY and southern IN later tonight. 

Cloud cover and slightly cooler temperatures have helped keep 
instability levels down but per the KY Mesonet, we have dew points 
in the low/mid 60s and temperatures in the upper 60s/near 70. This 
still remains the focus for the highest risk of severe weather later 
this evening with a gradual diminishing of that severe threat as it 
works eastward into central KY. WoFs or Warn on Forecast guidance 
this evening has been doing an extremely good job on placement and 
severity of activity through the afternoon and early evening. If 
this trend continues, the WoF brings the current storm just 
northeast of Memphis to just south of BWG by around 0130z but with a 
much lower severe threat. This is likely due to the aforementioned 
stratiform thundershowers taking place across the area as of the 
writing of this update. 

Also been noticing a trend in recent CAM updates of a north/south 
split in the main line of activity as it works across 
western/central KY later this evening. General timing looks good 
with the strongest activity working into our western southern IN 
counties by around 02-03z then to the I-65 corridor between 03-04z 
then into the Bluegrass, including Lexington between 04z-06z. Given 
the model soundings showing good shear and SRH values ahead of the 
boundary this evening the pervasive thought in the office is we 
could still see a watch issued at some point later this evening.

&&

.Short Term...(Today and tonight)
Issued at 330 PM EDT Fri Mar 31 2023

Satellite imagery still shows the majority of the region remains 
under cloudy skies. A few holes are allowing some sunshine to reach 
the ground through the CWA, but the cloud cover is keeping most of 
our temperatures near the mid 50s which is below what was forecast 
earlier. Western Kentucky and southwest Indiana are seeing 
temperatures in the 60s to almost 70. Southern winds ahead of the 
approaching cold front will continue to lift temperatures and dew 
points. Dew points are currently in the 50s and are expected to 
climb into the upper 50s to low 60s ahead of an advancing cold 
front. A lot of the precipitation in the CWA has drifted off to the 
east, but scattered showers remain across our southern counties with 
isolated pockets to the north. A few rumbles of thunder continue, 
but precipitation through the afternoon hours is expected to remain 
elevated.

Tonight, the aforementioned cold front moving east towards southern 
Indiana and central Kentucky continues to be the focus of concern. 
The CAMs have fairly good agreement in timing and general overall 
environmental parameters. Strong wind shear will be the driving 
force that will make severe weather possible. Most models have the 
low level jet around 70 to 75 knots. Hodographs show large areas of 
low level wind shear. Bulk shear values between 0-6 km will likely 
be in the 60-80 knot range, which can easily support severe weather. 
Storm relative helicity between the 0-1 km level could see values in 
the 500-600+ m2/s2 range, so even with the mediocre low level lapse 
rates, shear values this strong can overcome near surface stability. 
MLCAPE values remain fairly high for a cool season system. Values 
could range from a couple hundred J/kg to 500 or 600. So with this 
environment, the main threats will be gusty winds and possible 
tornadoes. The threat of severe weather will be the higher to the 
west and diminish as the system moves east. Believe the threat will 
noticeably drop off east of Interstate 65. 

Behind the front, the threat of severe weather will be over. Skies 
will clear as surface high pressure begins moving into the region. 
Gradient winds will remain gusty for the rest of the night. 
Southwest winds around 10-20 mph with gust to near 30 mph before 
winds begin increasing again on Saturday. Gusts on Saturday are 
expected to reach into advisory levels with gusts over 40 mph 
because of this and windy conditions today, the wind advisory 
already in place will remain from 8 PM this evening until 5 PM 
Saturday.

&&

.Long Term...(Sunday through Friday)
Issued at 209 PM EDT Fri Mar 31 2023

Winds will begin to taper down Saturday night as the pressure 
gradient relaxes and nocturnal inversion sets in. High pressure is 
expected to settle over the region by Sunday morning, so winds will 
likely go light to calm by then. The surface high will push toward 
the Appalachians during the day Sunday, and southerly return flow 
will pick up across southern Indiana and central Kentucky. With 
sunny skies and light southerly winds, highs should top out in the 
upper 50s to low 60s. 

Upper level flow becomes amplified going into early next week as a 
trough moves into the western CONUS and ridging develops in the 
eastern CONUS. A surface warm front will lift from the Gulf Coast 
states into the Ohio Valley during this time, engulfing us well 
within the warm sector ahead of a developing low pressure system and 
surface cold front. Models still vary on the timing of various 
perturbations within the flow of the trough and the passage of the 
cold front, but the Tuesday - Wednesday timeframe could feature 
periodic active weather given the co-location of favorable 
thermodynamics and kinematics for strong/severe thunderstorms. 

The front will likely push through the region by Thursday with 
surface high pressure building in behind it, though some ensembles 
suggest the frontal passage could be delayed or even held up, so 
have included low-chance PoPs through the end of the week.

&&

.Aviation...(06Z TAF Issuance)
Issued at 155 AM EDT Sat Apr 1 2023

Thunderstorms will be clearing area terminals within the next 1-2 
hours as drier air begins to work into the area. The main impact to 
operations over the next 12-24 hours will be due to strong winds and 
wind gusts as winds are expected to pick up out of the west tomorrow 
morning. The strongest gusts, approaching or slightly above 40 
knots, are expected at SDF and LEX after sunrise today through mid-
afternoon, although BWG and HNB are also expected to gust above 30 
knots through early afternoon. Winds will gradually ease during the 
mid-to-late afternoon hours, with gusts subsiding after sunset from 
west to east. MVFR ceilings are most likely at HNB, although SDF and 
LEX could also see brief periods of MVFR ceilings this afternoon 
into the evening. VFR conditions are expected to return for all 
toward the end of the forecast period, with much quieter conditions 
expected as we head into Sunday.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Wind Advisory until 5 PM EDT /4 PM CDT/ this afternoon for 
     KYZ023>043-045>049-053>057-061>067-070>078-081-082.

IN...Wind Advisory until 5 PM EDT /4 PM CDT/ this afternoon for 
     INZ076>079-083-084-089>092.

&&

$$

Mesoscale...CSG
Short Term...KDW
Long Term...DM
Aviation...CSG