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KEY MESSAGES

* SIGNIFICANT SEVERE STORM THREAT THIS EVENING INTO TONIGHT

* LIFE-THREATENING FLOODING POSSIBLE FROM TONIGHT INTO THE WEEKEND, WITH ADDITIONAL CHANCES FOR STRONG TO SEVERE STORMS LATER THIS WEEK AND INTO THE WEEKEND.

MESOSCALE

Issued at 1056 PM EDT Wed Apr 2 2025

Mature QLCS continues to push into the middle Ohio Valley. Impressive bowing structures have developed with strong RIJs and bookend vortices. Several strong circulations have developed in areas of curling segments, cell mergers, and reflectivity tags, leading to tornado warnings and reports of tornadoes and damage. Tops have cooled over the last few hours as the convection continues to deepen.

North domain of WoFS shows high probabilities of tornado activity between now and 2am EDT along and northwest of a line from Hartford to New Albany to Madison. Mesoanalysis shows tongue of SBCAPE ahead of the storms co-located with eSRH of 500-700 m2/s2 and a 70kt 850mb jet.

This line of powerful storms will continue to be capable of damaging wind gusts and occasional tornadoes. The tornadoes will likely be rain-wrapped, and of course will be occurring in the dark of night, making this set-up especially dangerous.

Issued at 915 PM EDT Wed Apr 2 2025

Supercells this evening have moved from middle Tennessee into southern Indiana but as the sun has set and CIN has increased the storms have struggled under weak capping. A storm that slipped into Simpson County developed an impressive wall cloud, but high LCLs may have discouraged tornadogenesis.

Attention now turns to the approaching squall line extending from Indiana to Arkansas. Those high LCLs have been lowering along and just ahead of the line of storms. Low level jetting will increase overhead this evening with increasing bulk shear. There is expected to be a narrow corridor of SBCAPE along/ahead of the line, and the last few hours of SDF ACARS soundings have shown increasingly favorable hodograph traces and increasing low level SRH. The line is expected to maintain good organization as it pushes east into the middle Ohio Valley and attain bowing structures capable of enhanced intense wind gusts, especially across southern Indiana and north central Kentucky. Cell mergers continue to occur on the leading edge of the line, and these cell mergers plus the expected bowing segments will continue the tornado threat with eSRH around 400 m2/s2 possible. The most favorable synoptic set-up for tornado activity appears to be over the southern half of Kentucky, but tornadoes will be possible anywhere along the length of the QLCS.

Torrential downpours can also be expected with the line. Upstream precipitable water values along the line have increased over the course of the evening from 1.50" to 2". Values around 1.50-1.75" are expected to continue as the line moves into the region. The line should push through the region fairly cleanly, and models have backed off some on laying the line out east-west, which is good for reducing the likelihood of flooding. Nevertheless, flooding chances will increase at least slightly between midnight and dawn, especially over eastern and southern parts of central Kentucky.

SHORT TERM /THROUGH FRIDAY/

Issued at 316 PM EDT Wed Apr 2 2025

****SIGNIFICANT SEVERE STORM THREAT THIS EVENING****

An occluded 988mb low pressure system is centered over IA as of 02/18Z with a warm front extending west through IL/IN/OH and a cold front extending SW into TX. Current conditions attest to our area being well situated within the warm sector as KY Mesonet shows current temps in the upper 70s to low 80s and dew points in the low to mid 60s. Strong LLJ is also evident on area radar VWPs with 65KT noted at 6kft. Strong southerly winds will continue through the afternoon with gusts in the 40 to 50 mph range possible. In fact, peak winds of 52 mph have already been measured by KY Mesonet in Nicholas and Clark counties, KY. With that said, the Wind Advisory will continue through 03/05Z as planned.

Ahead of the main line of storms, some showers will likely push through the area. ACARS soundings out SDF show a rather impressive subsidence inversion at around 800mb, which will likely cap any convective growth and thus limit any severe hazards this afternoon.

The line of strong to severe thunderstorms is currently advancing across AR/MO and is expected to reach our westernmost counties by as early as 7PM EDT this evening. Ample kinematic energy and instability will result in an especially ripe environment for severe weather, with all hazards in play: damaging winds, large hail, flash flooding, and tornadoes. The severe threat should diminish as the line pushes east of the I-65 corridor, and is expected to become mostly non-severe by 03/08Z. The line is forecast to slow down once entering the OH Valley with the frontal boundary eventually stalling somewhere over central KY. At this point, the stalled boundary will serve as the focus for continued rainfall as we transition from a severe threat to more of a flood threat as embedded convection trains along the boundary.

Hyetal pattern continues throughout Thursday as the stalled boundary anchors over central KY. Light rain is expected for most of the area with moderate rain possible at times. The flood threat will continue as soils saturate and rivers become full. The ongoing Flood Watch will continue as planned.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 316 PM EDT Wed Apr 2 2025

**** MAJOR FLOODING (POTENTIALLY LIFE THREATENING) EXPECTED****

Thursday Night and Friday...

Quasi-stationary boundary over central KY and southern IN will be the main focus for our active weather Thursday night into Friday. LLJ coming up from the south will help to enhance lift along and north of the boundary. This will provide good moisture transport increasing PWAT values between 1.50-1.75" along and just south of the boundary through central KY into southern IN. Significant heavy rainfall will be the main threat leading to significant flash flooding across our area, especially where the heaviest corridor of rain occurs. Forecast rainfall amounts range from between 1-2.5" in the heaviest precipitation corridor, which currently looks to be along and north of the Parkways into northern KY and southern IN but will be dependent on where the boundary sets up. Model soundings continue to show a limited severe threat with most convection being mainly elevated. Even with this, any training elevated convection could produce localized higher amounts of 3-4" of rainfall.

Rainfall and rain amounts will be determined by placement of the meandering sfc boundary over the region. There is growing guidance that the boundary will start to lift northward into central IN late Friday into early Saturday as mid-level ridging increases over the area. This may give us a slight break from the heavy rain with just some scattered showers and storms mainly across southern IN/northern KY late Friday into early Saturday.

Saturday and Sunday...

During the day on Saturday, the upper trough to our west finally gets picked up by a northern stream disturbance and begins to eject off to the northeast. This will push the sfc boundary back to the south and east as a cold front leading to one final push of strong storms and heavy rainfall Saturday afternoon into Sunday morning, with the sfc front finally crossing through the area on Sunday. Ahead of the front, moisture indices like PW and IVT once again surge to near the maximum of climatology, with several more inches of rain likely with this final wave. Rain should end from west to east during the day on Sunday, with cooler air rushing in for the end of the weekend and the start of next week.

Early Next Week...

Much quieter weather is expected during at least the first half of next week, with a much-needed reprieve from heavy rainfall and severe storm chances. The upper flow pattern over North America will be rather amplified, but will take on an inverse phase with deep ridging out west and troughing across the east. This should place our region within a NW flow regime aloft, and sfc high pressure will gradually sink into the region by the middle of next week. This flow regime will be supportive of cold and dry air advection, with ensemble mean PW and temperatures below climatological normals. Light precipitation from transient clipper systems can't be ruled out, and we'll have to watch for potential frost/freeze conditions; nevertheless, this pattern shift will support a much calmer period of weather.

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1249 AM EDT Thu Apr 3 2025

A large and slow moving line of thunderstorms will blanket central Kentucky through much of the TAF time period. TEMPOs for KBWG, KSDF, and KLEX through 10Z will take into account strong thunderstorms with heavy rains and gusty winds that could lower surface visibilities to 2-4 SM. Cloud ceilings will fall through the night to MVFR category by 09Z and fluctuating between MVFR and IFR categories during the day and then becoming likely IFR around 00Z. Winds should also diminish during the night from 10-20 kts and occasional gusts over 30 kts with the stronger thunderstorms to light and variable during the day on Thursday.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Flood Watch through Sunday morning for KYZ023>043-045>049- 053>057-061>067-070>078-081-082. Wind Advisory until 1 AM EDT /midnight CDT/ early this morning for KYZ023>043-045>049-053>057-061>067-070>078-081-082. IN...Flood Watch through Sunday morning for INZ076>079-083-084- 089>092. Wind Advisory until 1 AM EDT /midnight CDT/ early this morning for INZ076>079-083-084-089>092.