Tuesday, April 2, 2024

Update on Today's Severe Weather Potential

Today: Thunderstorms likely. Possibly severe. High 79, Low 67

Wednesday: Mostly sunny. Cool and breezy. High 60, Low 46

Thursday: Sunny. Sort of cold. High 59, Low 37

Friday: Sunny. Widespread frost possible in the morning. High 60, Low 33

Saturday: Sunny. Patchy frost still possible in the morning. High 64, Low 35

Sunday: Sunny. Cool. High 70, Low 39

Monday: Mostly sunny. High 74, Low 46

Tuesday: Partly cloudy with a 20% chance of showers/thunderstorms. High 76, Low 54

All right, that's all the forecast I'm doing again for a while. Just rehashing the basics above. 

Because later today will get really active. Not sure if I'll be able to cover any of it on this blog or not. But before I nod off, here is the latest from the SPC. 

There has not been much change except to expand some of the higher threat categories. It looks like a pretty bad severe weather outbreak for much of the Ohio Valley. I feel for the people who get hit hardest today in advance. It is likely that some people will. 

But look, things are bad enough around here. We are under the Enhanced Level 3 out of 5 severe weather risk Tuesday and Tuesday night. 

Our potential for severe thunderstorms with large hail and damaging winds is more than average, 30% chance of seeing such an event within 25 miles of a given point. I'm a little surprised there is no hatching for the hail risk, but we may not see hail to the size of golfballs with this, even if supercells can form during part of the event. It would probably max out at about the size of ping-pong balls, which is 1.5 inches in diameter. 

Unfortunately all of us do now have the hatching for the 10% tornado risk. This means there is a 10% chance of seeing a tornado within 25 miles of any given point in the Tennessee Valley with this event. And that includes a risk for tornadoes with a longer track, that do fairly significant damage. Those tend to come from supercells, sometimes out by themselves, but can also be part of a squall line, especially if the line if broken. 

The timing of this event is not high-confidence. We could potentially see some stuff starting in far Northwest Alabama or adjacent parts of Tennessee (like Hardin and Wayne Counties) as early as Noon. Some time between them and 4 PM, I think will be the onset time. And the storms will gradually spread East. Things may not wind down in Northeast Alabama completely until 10 PM or close to midnight. 

Since all modes of severe weather are possible with this, a quick review of tornado safety.

Have a better way to get warnings than an outdoor siren. Wireless emergency alerts on a cell phone are good, but leave out most Severe Thunderstorm Warnings. They do get you Tornado Warnings. 

A NOAA Weather Radio with battery backup is best, and WeatherCall is a good second layer if you can afford it. 

But at least do the WEA, have that enabled on a cell phone. Don't wait to try to hear an outdoor siren. Of course with this starting during daylight, you may get all the information you need from regular media. 

You can't stay in a mobile home during a tornado, and you don't need to get caught in a car either. Plan ahead, at least three or four places along your route you could pull over and get in a building. Leave a mobile home for sturdier shelter in enough time, before the storms get to you. 

A last resort instead of a mobile home would be lying in an unflooded culvert or ditch, or even flat on the ground, covering your head and neck as best you can. But hopefully you can get to a safe structure. Don't try to shelter up under a bridge, because that is a very old myth from a misleading video. 

If you are in a sturdy house or other strong building:

* Stay away from windows.

* Get to the lowest floor. 

* Get in a small room like a bathroom, closet, or hallway.

* Make it as near the center of the structure as possible - walls between you and outside. 

* Shield your body from falling or flying debris, especially protect your head. 

And as a footnote, if you do have access to an actual storm shelter, of course that is best. If you know you can trust people, please consider sharing that shelter with others who need it. 

If you live in a mobile home or other weak structure you can't stay in, like an apartment up on the top floor, you may need to rely on a public shelter. I hope most of you have some family or a friend you can count on instead, who has a sturdy house or something like a basement or cellar. 

Everybody stay safe, and remember that whatever it does today in our neck of the woods, it is our last severe weather in a while. We won't see any more rain until at least next week. It may be a rough ride for some of us today or into the night, but it will probably be somewhere between a lower-end severe weather threat and an actual outbreak. Now from about Nashville up through Kentucky into Ohio, it does look like a tornado outbreak. So if you know anybody up there, make sure they know this is cooking up. Wishing us all the best for a somewhat unpleasant situation.  

SPC AC 020600

   Day 1 Convective Outlook  

   NWS Storm Prediction Center Norman OK

   0100 AM CDT Tue Apr 02 2024

   Valid 021200Z - 031200Z




   A potentially substantial severe weather outbreak -- possibly

   including a few significant/long-track tornadoes -- is anticipated

   this afternoon and evening, with the highest probability centered

   over the Ohio Valley.  Severe risk exists as far south as the Gulf

   Coast, and as far east as western portions of Virginia and the



   Strong northern-stream upper low, currently located over southern

   MB, is forecast to drop south across MN into northern IL late in the

   period. This evolution is driven in part by a 500mb speed max that

   will translate across the central Plains, increasing to near 100kt

   over eastern KS/OK by 03/12z. Intense 12hr midlevel height falls are

   forecast across much of the Great Lakes, OH/TN Valley, and the

   northern Gulf States, where values in excess of 200m are expected

   during the latter half of the period. Synoptic front that is

   currently draped across the OH Valley will be encouraged to

   gradually advance north due to the digging trough; however, an

   extensive corridor of convection currently extends across the MS

   Valley into the OH valley, which is maintaining cool boundary-layer

   conditions north of I-70.

   Latest water-vapor imagery suggests a southern-stream short-wave

   trough is progressing across eastern KS/eastern OK. This feature

   will progress downstream and likely aid early-day thunderstorm

   development near the confluence of the MS/OH Rivers. Seasonally high

   PW airmass currently extends across northern AR/southern MO into

   southern IL. NAM forecast sounding for JBR at 15z exhibits 60kt

   surface-6km bulk shear with SBCAPE on the order of 1500 J/kg.

   Discrete supercells may evolve ahead of this feature then

   spread/develop northeast across southern IN/KY into OH. Some

   uncertainty exists across northern OH/IN regarding destabilization.

   It's not entirely clear if ongoing convection will allow the warm

   front to lift appreciably north of its current position. However,

   large-scale pattern is quite dynamic and favors surface low

   deepening over southern Lake MI during the latter half of the

   pattern. NAM struggles to reflect this scenario, thus weaker

   instability is forecast at higher latitudes. Tornadoes, damaging

   winds, and large hail are expected with supercells that evolve

   across the warm sector. Some tornadoes may be long-lived and strong.

   Farther south, a bimodal severe threat may ultimately evolve with a

   secondary corridor of more concentrated severe across portions of

   the northern Gulf States. 500mb speed max is forecast to eject

   across northern Mexico into TX by 03/00z. This feature will

   intensify as it translates across LA into eastern TN by the end of

   the period. There is some concern that severe probabilities may need

   to be increased across this region to account for this low-latitude

   speed max during the evening/overnight hours. Strong shear will

   support supercells along with a threat for tornadoes, damaging

   winds, and hail.

   ..Darrow/Bentley.. 04/02/2024

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