Severe WX Severe Risk 2/23-2/24

[andyhb]

Honestly not impressed by CAPE values at this point. First sniff of the NAM came in even less than the GFS. Think a forced squall line with damaging winds, maybe a few embedded tornadoes in the most likely outcome.

The NAM is probably lowballing surface temperatures a bit in the warm sector looking at the models that also have relatively solid cloud cover getting them to 72-74˚F, with the NAM holding them at 68-70˚F. I have a hard time believing temperatures aren't going to rise at least a bit Saturday afternoon from 12z given the strong southerly flow in the warm sector.

One thing to take away from the NAM though, adding southerly/slightly backed surface winds (like what should happen in this scenario) to this is making the low level hodographs very large.

 

[Kory]

The euro is supercells in warm sector...

 

[SilentShadow87]

I think everyone is gun-shy because of how many apparent threats have fizzled as it got close to go time recently lol

And by recently we mean "pretty much for the past 2 years". Seriously, the last decent severe weather event was probably 5/18/17 and the last one that I'd call a "major" event was 6/16/2014. Granted, the Euro does look interesting for this one but there's a lot of time left for it to Forecasted Convective Amplification Deficiency.

 

[warneagle]

And by recently we mean "pretty much for the past 2 years". Seriously, the last decent severe weather event was probably 5/18/17 and the last one that I'd call a "major" event was 6/16/2014. Granted, the Euro does look interesting for this one but there's a lot of time left for it to Forecasted Convective Amplification Deficiency.

19 March last year really had the potential to get ugly had the storm mode not gotten messy early. The SRH values on the 18z balloon launches were major outbreak levels.

 

[Daryl]

 

[Gail]

Rather large hatched area on Day 3.

 

[Tennie]

Reading the SPC discussion, it seems that the primary threat is damaging winds from an MCS, though it's also possible we could get some discrete supercells and perhaps even a few tornadoes.

 

[tennessee storm chaser]

Reading the SPC discussion, it seems that the primary threat is damaging winds from an MCS, though it's also possible we could get some discrete supercells and perhaps even a few tornadoes.

Some strong tornadoes also mentioned ... agree with the wind fields model showing

 

[Xenesthis]

The more I am looking at this.. the soundings are less then impressive. Anyone else notice this?

 

[warneagle]

Some strong tornadoes also mentioned ... agree with the wind fields model showing

We’ll have to see when get closer to time on this but the 3 km NAM keeps things semi-discrete south of I-40 which could be trouble. At minimum we’re probably going to get a significant damaging wind event, especially further north, but if things stay discrete further south or we get some cells popping out in front of the line with that kind of wind shear we’re gonna have some problems.

 

[warneagle]

The more I am looking at this.. the soundings are less then impressive. Anyone else notice this?

Where and on what model? The models are in pretty good agreement on there being enough wind shear for a significant wind event and a conditional tornado threat. The instability isn’t eye-popping, but it’s not going to be in late February. This looks like a pretty typical cool season event with strong wind fields and the usual caveats about destabilization and storm mode.

 

[rolltide_130]

The more I am looking at this.. the soundings are less then impressive. Anyone else notice this?

Shear is plentiful and instability is creeping up as especially the NAM has been underdoing instability values. I'd argue the exact opposite.. that this is trending up with time.

 

[warneagle]

Shear is plentiful and instability is creeping up as especially the NAM has been underdoing instability values. I'd argue the exact opposite.. that this is trending up with time.

Exactly. If the NAM and GFS are underestimating the instability even a little, this event could be trouble. I’ll be curious to see what the HRRR has to say; it was on point with the event that produced the Wetumpka EF-2 but swung and missed on yesterday’s event.

 

[MichelleH]

With all the rain we've had and will still get, it's not going to take very high winds for trees to start falling all over the place.

 

[Xenesthis]

Where and on what model? The models are in pretty good agreement on there being enough wind shear for a significant wind event and a conditional tornado threat. The instability isn’t eye-popping, but it’s not going to be in late February. This looks like a pretty typical cool season event with strong wind fields and the usual caveats about destabilization and storm mode.

I was looking at several different ones off pivotalweather. I am not arguing the shear will be there. It seems more of a straight line wind event to be honest. And I realize we don’t need high Cape values however the models I was looking at weren’t even bringing 500 j/kg into TN

 

[Kory]

Not sure how you're gonna get a solid squall line for damaging winds when the shear vectors are oriented WSW to the boundary. This will be mostly cellular.

 

[warneagle]

Not sure how you're gonna get a solid squall line for damaging winds when the shear vectors are oriented WSW to the boundary. This will be mostly cellular.

Yeah, the shear vectors from about Memphis southward in particular (i.e. where the strongest destabilization will be) favor a more cellular mode and the convective products at present (on the 3km NAM for example) reflect that.

 

[rolltide_130]

Not sure how you're gonna get a solid squall line for damaging winds when the shear vectors are oriented WSW to the boundary. This will be mostly cellular.

I've been watching forecasts, and its a CLASSIC trap mets here fall into and they're doing it once again... looking at precip/sim reflectivity and immediately saying QLCS without paying an ounce of attention to the wind fields.

 

[Kory]

Now, one trend I'm seeing in the models is developing a mass of convection over the mid-South (Western/Central TN and even into Northern MS). This is something that should be monitored for enhancements and reductions of severe threats over the current outlooked area.

 

[rolltide_130]

Now, one trend I'm seeing in the models is developing a mass of convection over the mid-South (Western/Central TN and even into Northern MS). This is something that should be monitored for enhancements and reductions of severe threats over the current outlooked area.

That appears to be being lifted north along the warm front so I'm hoping that doesn't contaminate the warm sector. Granted those models aren't always the most accurate at the end of their range so we'll see if they keep up that trend. They have significantly more rainfall than the other models do as the WF lifts north.