Severe WX Severe Threat 17-18 March 2021

[Fred Gossage]

The 6z NAM, 6z operational GFS, and 6z parallel GFS are all coming in with a solution that maxes the 850mb jet in the 60-65 kt range from central Alabama into Tennessee during the evening/overnight Wednesday. This is not a good trend...

 

[CheeselandSkies]

I'll have to take a look at the latest runs, but some of the forecast hodographs on the NAM yesterday afternoon were the most impressive I've seen in a long time.

 

[tennessee storm chaser]

Appears latest overnight n early morning trends not good ... 850 mb wind fields seems be increasing toward supporting strong to perhaps even a violent tornado... seems warm frontal boundary getting further into Tennessee also

 

[Clancy]

Curious what caliber of threat those in here think the west/northwest Atlanta metro will be facing with this. It seems like we may be on the weakening end of it, but it's hard to tell, and it's certainly no reason to let our guard down.

 

[Fred Gossage]

Curious what caliber of threat those in here think the west/northwest Atlanta metro will be facing with this. It seems like we may be on the weakening end of it, but it's hard to tell, and it's certainly no reason to let our guard down.

Those are always tricky, but the 850mb jet ramps up into the 50-60 kt range as it moves into west central Georgia during the late overnight, and that makes me really nervous with the retreating wedge warm front near by. Deep-layer shear vectors would support at least a semi-cellular storm mode way over into north central Georgia. I think the higher threat is ultimately north central AL up into southern TN and then westward, but I could easily see a few tornadic supercells, and can't rule out a significant tornado, over into west central or north central Georgia either.

 

[Clancy]

Those are always tricky, but the 850mb jet ramps up into the 50-60 kt range as it moves into west central Georgia during the late overnight, and that makes me really nervous with the retreating wedge warm front near by. Deep-layer shear vectors would support at least a semi-cellular storm mode way over into north central Georgia. I think the higher threat is ultimately north central AL up into southern TN and then westward, but I could easily see a few tornadic supercells, and can't rule out a significant tornado, over into west central or north central Georgia either.

Gotcha. Thanks!

 

[KG4KBU]

Looks like KGWX radar will be down for at least part of the event as well

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[Fred Gossage]

Looks like KGWX radar will be down for at least part of the event as well

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They were stating through yesterday that although that is the timeline for the part, they would have the capability of bringing the radar back into operation if needed. Has that changed?

 

[GA Stormchaser]

Looks like KGWX radar will be down for at least part of the event as well

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Saw this posted on another site. This is a glaring example of why trained storm spotters are still important. They rarely go down for maintenance.


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[GA Stormchaser]

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[KG4KBU]

Let's hope they can bring it back up for the event. That is another reason it's good for tv stations to have their own radars. They don't have to rely on the nws radars if they go down. A lot of tv stations use the nexrad radars now due to the cost of operations and maintenance for their own radars.

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[Marshal79344]

Man if we could have a stronger LLJ to enlarge those photographs a bit more, the tornado threat would be much more significant. We will probably still see significant tornadoes, but I've heard all of this talk about an "Easter V2" or "Bassfield V2," not gonna happen without that stronger LLJ.

 

[Fred Gossage]

Man if we could have a stronger LLJ to enlarge those photographs a bit more, the tornado threat would be much more significant. We will probably still see significant tornadoes, but I've heard all of this talk about an "Easter V2" or "Bassfield V2," not gonna happen without that stronger LLJ.

Every single model has locked onto a 50-55+ kt 850mb jet developing near sunset and continuing into the overnight, and the 06z runs all had a 60-65 kt 850mb max. This trend upward in the models started with the upper trough starting to get observed in the upper air network last night.

 

[warneagle]

The thing that concerns me the most is that the significant tornado threat continues well after dark. There's still plenty of instability in the 03z to 06z timeframe when the LLJ is really peaking in central Alabama. We saw how devastating just one or two sigtors could be after dark with Nashville/Cookeville last year, so a nighttime threat in a more "traditional" severe setup is...concerning.

 

[Richardjacks]

GFS ramping back up significantly. 55kts at 850 in the late evening. NAM ramps up overnight for a nocturnal tornado event across Central AL.

The is the trend I feared. I haven't had a chance to look at everything this morning g due to work, but will later today, after the 12z stuff is in. I just wonder if we might see a little more slowing today and tomorrow.

 

[Fred Gossage]

The is the trend I feared. I haven't had a chance to look at everything this morning g due to work, but will later today, after the 12z stuff is in. I just wonder if we might see a little more slowing today and tomorrow.

I wouldn't rule it out, but I've also noticed that the trough trajectory is now due east across the area instead of to the northeast and glancing us. That more direct ascent across the warm sector is going to increase the chances for open warm sector development instead of having to wait for the cold front or dryline or whatever crosses to get here. I think we're still looking at a mid-afternoon start time in Alabama, but I do definitely think the end time is trending deeper into the overnight.

Oh, and since Matt's post there last night, UKMET, Euro, and Canadian 00z runs all had a 50-55+ kt 850mb jet max, and the 6z runs of the NAM, op GFS, para GFS, and even the RGEM that has been crap the whole time, have ramped the overnight 850mb max into the 60-65 range.

 

[Richardjacks]

I wouldn't rule it out, but I've also noticed that the trough trajectory is now due east across the area instead of to the northeast and glancing us. That more direct ascent across the warm sector is going to increase the chances for open warm sector development instead of having to wait for the cold front or dryline or whatever crosses to get here. I think we're still looking at a mid-afternoon start time in Alabama, but I do definitely think the end time is trending deeper into the overnight.

Oh, and since Matt's post there last night, UKMET, Euro, and Canadian 00z runs all had a 50-55+ kt 850mb jet max, and the 6z runs of the NAM, op GFS, para GFS, and even the RGEM that has been crap the whole time, have ramped the overnight 850mb max into the 60-65 range.

Ouch, I am hoping to take a look at everything later this morning after my first appointment. All of that is very concerning.

 

[CheeselandSkies]

Jackson, MS has a 68 degree dewpoint at 00Z Thursday on the 06Z NAM. Even if that's overdone by a few degrees, that's plenty of moisture for March.

 

[keithGA]

I hate for my first post here to be an "in my backyard" question, but what about ~40 miles east of ATL?

 

[Fred Gossage]

I hate for my first post here to be an "in my backyard" question, but what about ~40 miles east of ATL?

The deeper you go into Georgia, the farther away you are from the higher impact area. However, this low-level jet does migrate eastward through Georgia, and the Thursday risk goes through the Carolinas. I think a lot of the Georgia threat, especially I-75 and east, will come down to how long the storms are cellular or semi-cellular. You still need to be alert for a severe storm/tornado risk, but the higher threat is definitely west of you.