Forecast Blogs

Unsettled, Severe Weather Potential Explained

Flood Advisory Continues For the Stones River

The river is expected to remain at the same level or barely recede by the weekend. If you come across a flooded road, turn around don’t drown.

Stormy Pattern Ensues, Doesn’t Mean We All Get Thunder

Ingredients are coming into play for multiple rounds of showers and thunderstorms, some with heavy rainfall and severe potential, today through the weekend.

Updated Round 1: Midday-Afternoon

NWS Nashville reiterated late Thursday night:

“Friday afternoon/evening continues to be a difficult forecast.”

The following is a checklist for severe weather ingredients Friday. Will we have…

→ Moisture?

Definitely, yes. Latest HRRR Model guidance says that moisture will surge rapidly north after noontime, providing more than enough “juice” for the atmosphere.

→ Instability?

This measures how easily/quickly an air parcel, or imaginary volume of air, will rise through the troposphere. Why does this matter? The faster a parcel can rise, the more unstable an atmosphere will be. One way to measure this is through a composite value called “C.A.P.E.” The newest HRRR indicates we will have impressive values for this ingredient surge northward, too (on the order of 2000-4000 J/kg^-1).

Zoomed in at 5PM CDT

Do I think these data could be showing too much gumption? Yes. I’m not yet convinced instability will get this high…but it’s not impossible.

→ Lifting Mechanism?

Well, this is where we may lack. While every other component lines up, there will be one factor that remains uncertain until later today.

Example: If you place a cap on a Pringles can and dump it over, not a Pringle will fall out. But what if you put a super-heavy rock inside? The “cap” will likely break, and now whatever remains inside the can will fall out.

The atmosphere works similarly. Today, we will have a “cap” in the mid-levels (~6,500 feet up). Eventually, this could erode, allowing for thunderstorms to freely develop in the afternoon. Models still suggest this feature will play a large role in storm coverage (or not) across Davidson/Williamson Counties today.

→ Wind Shear?

Kind of. Turning of the winds with height is wind shear. Based on the latest forecast sounding information, we will have “okay” wind shear by the time storms decide to pass through. This is one thing we worry about for tornado potential. Plus, the other ingredients have to line up for tornadoes, too.

Bottom line…why does this all matter?

Timing: 11AM-6PM…keeping an eye on lunchtime!

Hazards: Damaging Winds, Large Hail, Isolated Tornado

This is a lower-than-normal confidence forecast. Why? One or two ingredients may lack, whereas further northwest, conditions may be more favorable for severe weather. Please remain abreast to any and all changes that may (will) occur between now and later today.

Round 2: Saturday Afternoon

Hot, humid, and pop-up storms….sounds like Nashville summertime! If you’re outside during the day, be sure to stay hydrated as heat indices approach 90ºF.

Running in the Rock ‘n’ Roll Marathon? The latest forecast models have shoved the morning rain away to our northwest. We hope this trend continues, but still have a rain plan just in case.

A few afternoon storms are possible during the afternoon, any of which could become severe. The main threats will be large hail and damaging winds.

Otherwise, Saturday is a great day for the pool. But remember…“When thunder roars, go indoors!”

Round 3: Sunday thru Sunday Night

GFS Loop for Sunday

A line of strong storms appears possible on Sunday night (post-sunset), maybe even stretching into the overnight hours and into Monday morning. Damaging straight line winds will be the main threat, although large hail and an isolated tornado cannot be ruled out. Also, heavy rain will exacerbate flood concerns, so let’s keep a watchful eye on rain totals Sunday.

Essentially, folks west of I-65 have the best chance of seeing bumpy weather Sunday.

*Caroline will be online later this morning with any new information regarding today and Sunday’s severe weather chances. Follow @NashSevereWx for more information!*

5-Day Forecast

Categories: Forecast Blogs