In some areas of the Lower Mississippi Valley, the severe weather threat is predicted to persist through Monday. Strong storms are likely to form ahead of and alongside an eastward-moving cold front. Supercell thunderstorms capable of producing all types of severe weather will be supported by conditions with MUCAPE values between 2000 and 3000 J/kg and 40 knots of deep-layer shear. The weather on Sunday will have an impact on the exact location, quantity, and strength of these storms. More favorable conditions such as higher CAPE and steeper lapse rates may be present for thunderstorms in the Lower Mississippi Valley on Monday if widespread convection does not form across the Southern Plains on Sunday. This could result in a more severe weather threat.

The Storm Prediction Center has already issued a 15% chance for western Kentucky in their 6-day outlook.

I will keep a close eye on this situation.

 

 

 

 

 

 

 

 

 

A potent storm system brings a threat of strong to severe storms Monday (4/27). The most likely time for severe weather is Monday afternoon and evening. Timing will likely change as the forecast evolves. The western half of Kentucky and most of southern Indiana are currently under the greatest risk. Severe weather could still be possible outside of the highlighted area. All severe threats are possible: damaging winds, large hail, and tornadoes.

 

A high-impact severe weather event is predicted for Monday, April 27, 2026, over the Tennessee Valleys, lower Ohio, and middle Mississippi.

 models are showing some potential for significant surface cyclogenesis across the Upper Midwest and Great Lakes region. A strong shortwave and 50-70 kt 500 mb jet streak will drive this process, setting the stage for widespread severe thunderstorm development during the afternoon and evening. The target area is southeastern Iowa, central and southern Illinois and eastern Missouri, with activity moving into the lower Ohio and Tennessee Valleys late in the day.

The main threat is tornadoes with potential for strong, long track and damaging tornadoes if discrete storm modes can persist. The first storms are likely to be individual supercells, but will probably grow upscale into clusters or lines later in the evening. These lines will continue to have embedded supercell structures that will be a significant tornadic threat.

Large, clockwise-turned low-level hodographs (see picture below in white circle*) are a key ingredient for strong, tornadic supercells. Also, a modifying outflow boundary may provide a focus for enhanced differential surface heating. A dryline in eastern Missouri is expected to provide a focus for discrete development ahead of the advancing cold front, which will push the activity southeastward.

It is important to keep an eye on your local National Weather Service office for the latest watches and warnings due to the potential for strong, long-track tornadoes. If you are in the impacted area, be sure to have multiple ways to receive severe weather alerts throughout the day.

 

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The state’s weather forecast is calling for mid- and upper-level dynamics to bring a major storm system to Kentucky, especially Monday afternoon and evening. This is mainly due to a strong 500 mb jet with southwest winds greater than 70 kts that will promote upward motion near the triple point low and dry line.

As the system approaches from Missouri and Illinois, Western Kentucky will be in the focus for strong storm development in the late afternoon. The environment will be supportive for some severe weather with strong low-level wind shear and instability. This environment could favor the development of isolated supercells capable of large hail and strong tornadoes. Storms will push east across the state and may consolidate along an outflow boundary that will be pushing into the Lower Ohio Valley by evening. As the storm moves into a squall line, the threat of tornadoes, especially embedded tornadoes, and damaging wind gusts will continue.

Elsewhere, the threat for severe weather in Kentucky moves east through the period, with storms potentially remaining supercell in nature into the evening hours. With the front pushing south, the structure of the storm will change, and the threat of tornadoes will increase, including the possible development of meso-vortices and strong wind gusts. 

A mesovortex is a small, intense, rotating whirlwind that forms within larger convective weather systems such as hurricanes or squall lines. These features often develop along squall lines and can produce extreme localized winds, tornadoes, and sudden wind shifts. 

The exact amount of tornado potential will depend on how long discrete supercells can survive before merging into a larger complex and if outflow boundaries across Iowa and Illinois can help boost tornado potential. There is still some uncertainty on the tornado threat, but the threat could increase as more data becomes available.

Be ready for quickly changing weather conditions and stay informed as conditions may change.

 

 

 

 

This now has the potential to become a multiday event. Here’s the latest information I just got from NWS-Louisville office.

 

 

 

 

Here is how the setup for western Kentucky is as of now for Monday evening. A negatively tilted trough will be positioned around Iowa. Downstream of the trough, upper jet winds are forecast to be out of the west at 62 mph, and the lower jet is out of the south at around 46 mph. The lower jet will also bring in Gulf moisture with dew points in the mid 60s. These ingredients, along with CAPE values of around 2200 J/kg, could be enough for the formation of supercell storms that could produce tornadoes. The optimal period appears to be between 5 and 8 pm EDT.

I wouldn't be surprised to see an upgrade in the threat level tomorrow. Those in the affect area should be going over their emergency action plan today. Also make sure you have more than one source to get severe weather notifications. 

 

Currently, there is a 15% chance of seeing tornadoes with an EF3+ rating and a level 2 intensity level in areas mostly north of I-64 in Illinois. This is within a 25-mile radius of a specific location.

Within a 25-mile radius of a point in western Kentucky, there is a 5–14% chance of EF2+ tornadoes forming at a level 1 intensity.

I'm not liking the latest model data from the euro concerning western Kentucky. It displays CAPE values greater than 2300 J/kg. I anticipate that the threat level for western Kentucky will rise if the trend continues.

 

@theguru

12 minutes ago, nWo said:

I'm not liking the latest model data from the euro concerning western Kentucky. It displays CAPE values greater than 2300 J/kg. I anticipate that the threat level for western Kentucky will rise if the trend continues.

Would you please expand on this?

12 minutes ago, theguru said:

Would you please expand on this?

C.A.P.E., or convective available potential energy, means that there is sufficient energy in the atmosphere to fuel the formation of severe storms. In simple terms this means fuel for thunderstorms. The level of 1000 J/kg is usually considered the baseline for severe storms. The higher the level, the better the chance of stronger severe storms developing or a more volatile atmosphere.

Thanks and wow, the more you know. ?

5 minutes ago, theguru said:

Thanks and wow, the more you know. ?

Here's some more info on what it could mean. I got this from the NWS website. Oh, I forgot to mention I'm using mixed layered cape, which is more accurate than an SB or surface-based cape. 

 

May 16, 2025: Extreme Instability Outbreak
A highly volatile environment with extreme instability led to multiple violent tornadoes across the Ohio and Mississippi Valleys.
Surface-Based CAPE (SBCAPE) peaked between 3,500 and 4,500 J/kg across central Kentucky and southern Indiana. Mixed-Layer CAPE (MLCAPE) exceeded 2,500 J/kg region-wide. Downdraft CAPE (DCAPE) was noted at a high 1,200–1,500 J/kg, contributing to significant straight-line wind threats.
Tornado Ratings:
EF4: Somerset–London, KY (170 mph winds).
EF4: Marion, IL (190 mph winds).
EF3: St. Louis, MO (152 mph winds).
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April 2, 2025: Rare High-Risk Event
A rare High Risk (Level 5/5) was issued due to perfect overlap of strong wind shear and significant instability.
Mixed-Layer CAPE (MLCAPE) exceeded 2,000 J/kg by 4:00 PM as Gulf moisture surged northward. In some frontal zones, values reached 2,500 to 3,500 J/kg.
Tornado Ratings:
EF3: Jeffersontown, KY (145 mph winds).
EF3: Lake City, AR; Selmer, TN; and Potosi, MO.
EF2: Multiple confirmed in Indiana and western Kentucky.
________________________________________
These CAPE values reflect the intensity of the severe weather, with the highest instability leading to the most violent tornadoes, particularly during outbreaks with extreme CAPE.
 

The values keep increasing and the fancy terms are endless. 

I just finished checking the bulk shear, which is the wind speed and direction difference between different levels of the atmosphere. It is approaching 49 kts. This means the area will be highly favorable for severe weather with supercells and potentially tornadoes. A section of Kentucky from around Owensboro to Louisville is showing 60-67 kts. This is why my concern is growing. 

12 minutes ago, theguru said:

The values keep increasing and the fancy terms are endless. 

Yes, I know. I spent a good deal of time in the winter studying this. There is still a lot more.