Friday Morning, July 20, 2018
Chief Meteorologist Jason Simpson/Meteorologist Christina Edwards/Meteorologist Ben Smith

Unusually high-end risk of severe weather Friday into Saturday

It’s warm and muggy with temperatures in the lower 70s this morning.  Today looks hot and humid, and it will get stormy before the day is done.

Larger view of the SPC Outlook for Friday. (Updated 12:34am CDT Friday morning)

We expect an unusually high-end risk of severe storms for this time of year today, tonight, and early Saturday morning: very high wind gusts, large hail, heavy rain, intense lightning and even a risk of brief tornadoes.

The afternoon outlook from the Storm Prediction Center shows a *SLIGHT* to *ENHANCED* risk of severe weather in North Alabama and Southern Middle Tennessee in the Friday/Saturday timeframe; that’s a statistical outlook. The *enhanced risk* expands a little east with a *moderate risk* just to our north.  The derecho we had on June 28th with wind gusts as high as 100 miles per hour came in a SLIGHT RISK as well (just for reference).

*Enhanced Risk* expanding a little further east. (12:34am CDT Friday morning update)

TIMELINE:

  • Precise timing down to when a storm would hit a neighborhood cannot be determined yet; however, we do expect the first heavy storms of the day (Friday) to begin in Tennessee in the early afternoon and move south-southwest into North Alabama between 2 PM and 8 PM.  This is more of a ‘chance’ than a certainty.  The more widespread, significant wave blows in later Friday night.
  • The ‘main’ wave that has the highest potential for severe storms likely comes in between 10 PM Friday and 5 AM Saturday.

WHAT WE EXPECT:

  • High wind gusts: a ‘severe’ storm has to have wind gusts at 58 miles per hour or higher.  Some model guidance suggests isolated 70-80 mile per hour gusts.
  • Tornado risk: it’s low but not zero.  You may see charts floating around on social media showing ‘STP’ (significant tornado parameter) that look scary; that modeled severe weather parameter is not extremely useful for this kind of weather pattern.  Think of it this way: a crescent wrench is a great tool unless the job requires a Phillips head screwdriver.
  • Flash flooding: a few areas may see more than 2-3” of rainfall Friday and Friday night.  That could produce some localized flooding.
  • Lightning: we know of at least four lightning strike victims in North Alabama this summer.  We have seen house fires from lightning, trees damaged, and a lot of power outages from it.  Lightning will be a danger from these storms, so stay indoors and be aware of the risks if lightning strikes your property.

Track heavy storms with WHNT.com’s Interactive Radar or swipe over to the radar feature on Live Alert 19!

Heat builds before the storms: 

We would be remiss if we did not mention the heat that will build on Friday afternoon before the storms’ arrival.

 

Temperatures are expected to climb into the low to mid 90s west of I-65 on Friday, and with the high humidity, it will feel rather oppressive. A heat advisory will be in effect from 12pm through 6pm Friday for counties west of I-65.

Sunday into next week: There’s not much change in the day-to-day from Sunday through the first half of next week. Each day features highs in the upper 80s to low 90s with a chance of some scattered afternoon and evening thunderstorms each day.

The forecast looks rather gloomy at first glance, but the good news is that it won’t rain every single hour of every single day over next several days. And this is no guarantee that everyone will receive rain: A 40-50% chance of rain means that we are confident that it will rain somewhere, but not necessarily that it will rain everywhere!

You may notice an increase in cloudiness Sunday into next. The reason? An upper level low is retrograding — or moving backwards — from the Ohio River Valley towards the Mississippi Valley.

As it does so, it will continue to kick up scattered afternoon showers and thunderstorms, keeping the area covered in a little more cloud cover than we would otherwise expect for mid-July. These clouds may seem gloomy, but there is a silver lining to them: They will provide a little bit of cooling in the effect that afternoon highs will stay in the upper 80s/low 90s as opposed to the sweltering upper 90s that would occur during full sunshine!

Tennessee Valley Forecast:

TODAY: Partly cloudy and hot. Scattered storms becoming more likely in the late afternoon/evening; many storms could be strong to severe with damaging winds, large hail, and frequent lightning. High: 90. Wind: S 7-12. Rain: 60%.

TONIGHT: Scattered storms, many of which could be strong to severe with damaging winds, large hail, and frequent lightning. Low: 73. Wind: WSW 15-25. Rain: 60%.

SATURDAY: Strong to severe storms likely through sunrise, becoming partly cloudy with scattered showers and storms throughout the day. Some storms could be strong to severe, potentially producing damaging winds. High: 89. Wind: W 15-25. Rain: 50%.

SUNDAY: Mostly cloudy, hot and humid with scattered afternoon thunderstorms. High: 88. Wind: NW 10-15. Rain: 40%.

MONDAY: Partly to mostly cloudy with scattered afternoon thunderstorms. High: 87. Wind: ENE 3-5. Rain: 40%.

TUESDAY: Partly cloudy to mostly cloudy and humid. Scattered storms in the afternoon. High: 89. Wind: E 7-12. Rain: 50%.

WEDNESDAY: Partly to mostly cloudy, hot, and humid. Scattered storms in the afternoon. High: 90. Wind: SSE 7-12. Rain: 50%.

THURSDAY: Partly to mostly cloudy with widely scattered storms in the afternoon. High: 88. Wind: SW 5-10. Rain: 50%.

FRIDAY: Partly cloudy with a few afternoon showers and storms. Where the rain does not fall, temperatures will rise into the low 90s. High: 92. Wind: SW 5-10. Rain: 30%.

SATURDAY: Mostly cloudy with scattered afternoon showers and storms. Where the rain does not fall, temperatures will rise into the low 90s. High: 91. Wind: SW 5-10. Rain: 50%.

SUNDAY: Partly cloudy with isolated afternoon showers and storms. Where the rain does not fall, temperatures will rise into the low 90s. High: 90. Wind: NE 5-10. Rain: 20%.