Weather Blog: Friday's severe weather potential ramping up

Weather Blog: Friday's severe weather potential ramping up
Storm chances go up during the morning, but severe weather arrives later in the day
Storm chances go up during the morning, but severe weather arrives later in the day
Supercell storms are possible initially on Friday afternoon & evening before they merge into lines of storms
Supercell storms are possible initially on Friday afternoon & evening before they merge into lines of storms
Faster-than-normal winds aloft for this time of year are part of the reason why we have a severe weather threat on Friday
Faster-than-normal winds aloft for this time of year are part of the reason why we have a severe weather threat on Friday
A cutoff upper low pressure system will plague the weekend forecast with rain, clouds, and cooler temperatures
A cutoff upper low pressure system will plague the weekend forecast with rain, clouds, and cooler temperatures

All eyes are on Friday's severe weather threat as the Storm Prediction Center has put WAVE Country in an Enhanced Risk of severe weather, which is a 3 out of 5 on their scale. Damaging winds are the main threat with these storms, but hail and isolated tornadoes are definitely on the list too. In fact, the isolated tornado potential looks to be highest early on in the afternoon/evening round of severe weather when individualized supercell storms are possible before they merge into one or more lines of storms. There is so much atmospheric instability at play here that hail is definitely something to watch for as well. The main timing for severe weather looks to be from 2pm to 10pm, but please stay updated with our latest forecasts for any changes that may take place over the next 36 hours.

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Let's back up for a moment, because what happens early on Friday will have a BIG impact on how the severe weather threat for the latter part of the day will go. A line of storms looks to traverse our counties early Friday morning, likely before sunrise. With that said, some of the latest runs of the RPM and NAM models are delaying this line of storms until just after sunrise and even strengthening it somewhat, potentially bringing some brief severe weather earlier in the day. Should the later timing of these storms play out, the afternoon would be pretty dry due to stable air, preventing storms from forming again until the evening. This would not only delay the severe weather threat, but also lessen it. We've seen this happen time and again in WAVE Country, so we'll need to keep a very close eye on how this plays out.

The reason we're seeing the severe weather potential at all is because of abnormally fast winds aloft for this time of year moving in with an area of low pressure. That's going to really crank up the wind shear Friday afternoon and evening, especially along and west of I-65 closer to those faster winds aloft. Bulk wind shear values between 30 and 45 kt are possible, but low-level winds may back and come more out of the southeast or east as storm outflows interact with one another, driving these values closer to 50 or 55 kt. You need roughly 40 kt of bulk wind shear as a baseline for sustained severe storms, so the criteria will likely be met. Instability with this setup, should the morning storms plow through earlier than later, will also be insane, to put it bluntly. CAPE (Convective Available Potential Energy) values may top 5,000 J/kg if some of the NAM model runs are correct. Very high dew points in the 70s and warm temperatures in the upper 80s are the reason why we'll see these crazy instability values. Being in summer as opposed to spring gives us more of these ingredients, so when you pair them up with spring-like faster winds aloft you get a bad combination!

This weekend's forecast continues to unravel as well. The low pressure center responsible for Friday's severe weather is going to not only slow down and meander around the Ohio Valley for the weekend, but it now looks like it will make an even closer pass to us as it tries to drift south toward the Gulf Coast. That trend is increasing our storm chances on Saturday and rain chances on Sunday. Saturday afternoon's storms could be stronger in Central and Southern Kentucky as some instability gets going down there, but wholesale severe weather chances look low. Sunday's rain will be more of a gentle rain deal as the energy for storms gets pushed south. It will NOT be a washout for the complete weekend as we will see rain chances that are far lower during the mornings and evenings. Storms and cooler air aloft will keep the afternoons cooler though, so expect highs in the 70s and lower 80s this weekend! Cooler-than-normal weather looks to continue through next week and into the end of July.