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May 15-20 Severe Weather Obs/Discussion (Part 2)

SmokeEater

By SmokeEater,
in Central/Western States

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tornadotony

tornadotony

Posted
Posted

One thing that does not at all sit well with me is the residual outflow from the MCS.  It is fairly washed out and retreating N.  That outflow, though, is going to provide an area for pooling of water vapor and locally backed flow (both of which are evident in current sfc obs), as well as potentially create a pseudo-triple-point setup.  Watch that boundary because that could be the focus for a very localized but extremely dangerous violent tornado threat this afternoon wherever it ends up.

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Ian

Ian

Posted
Posted

One thing that does not at all sit well with me is the residual outflow from the MCS. It is fairly washed out and retreating N. That outflow, though, is going to provide an area for pooling of water vapor and locally backed flow (both of which are evident in current sfc obs), as well as potentially create a pseudo-triple-point setup. Watch that boundary because that could be the focus for a very localized but extremely dangerous violent tornado threat this afternoon wherever it ends up.

Yeah we've been watching that too. Buddy of ours who lives in TX that we are going to try to chase with again today wants to try to play it. See where it goes thru the day.
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Stebo

Stebo

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Posted

One thing that does not at all sit well with me is the residual outflow from the MCS.  It is fairly washed out and retreating N.  That outflow, though, is going to provide an area for pooling of water vapor and locally backed flow (both of which are evident in current sfc obs), as well as potentially create a pseudo-triple-point setup.  Watch that boundary because that could be the focus for a very localized but extremely dangerous violent tornado threat this afternoon wherever it ends up.

 

You can see this boundary very evident on the surface vorticity/0-3km MLCAPE map on the SPC mesoanalysis, it lifts northward toward the I-35 corridor in KS then stalls there as instability pools on it  over the next 4hr.

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Chicago Storm

Chicago Storm

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LCLs on forecast soundings across much of KS and OK not really where I would personally like the see them. Would not be surprised to see a couple quick touchdowns like we saw yesterday instead of what you would normally expect from a 15 hatched SPC day.

This makes no sense given what happened yesterday.

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soonertrey

soonertrey

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LCLs on forecast soundings across much of KS and OK not really where I would personally like the see them.  Would not be surprised to see a couple quick touchdowns like we saw yesterday instead of what you would normally expect from a 15 hatched SPC day.

I think LCL's look fine for most of the MDT risk area.

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thunderbird12

thunderbird12

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The 12Z NAM seems more bullish on today's potential in the area bounded by I-35 to the west and I-44 to the south as it has mostly backed off its drier solutions from earlier runs. Temps will probably warm into the 90s in the immediate vicinity of the dryline and initial storms may be high based, but anything that initiates would move into a lower LCL environment after it matures. 

 

 

While the 12Z NAM looks better for today, its solution for tomorrow looks pretty messy and disorganized. 

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CT Rain

CT Rain

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Pretty evident the difference between the 12z NAM and 12z GFS with the lower BL flow.

 

With the existing outflow boundaries from last night's MCS you're going to have a number of small perturbations in the flow which may locally enhance the odds of tornadogenesis as well.

 

The GFS solution would certainly favor long-track tornadoes IMO while the NAM solution is more run of the mill.

 

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OUGrad05

OUGrad05

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I'm starting to wonder just a bit if things aren't going to fall apart.  Dewpoint here (just NE of Tulsa) is 66* air temp 75.  I just finished mowing the lawn and it's certainly nowhere near as sticky as yesterday.  Unless the DP's jump back up to the 70ish range LCL's may indeed be a bit of an issue.

 

It's overcast and breezy here with a thick blanket of low clouds.

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Ground Scouring

Ground Scouring

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Posted

I'm starting to wonder just a bit if things aren't going to fall apart.  Dewpoint here (just NE of Tulsa) is 66* air temp 75.  I just finished mowing the lawn and it's certainly nowhere near as sticky as yesterday.  Unless the DP's jump back up to the 70ish range LCL's may indeed be a bit of an issue.

 

It's overcast and breezy here with a thick blanket of low clouds.

Dews are already hitting 72˚F at JWG (Watonga), with a very pronounced moisture depth and convergence line developing in just a few hours, resulting in a +4˚F upward jump. The mixing ratio in this area is rapidly going positive, meaning that dews should rise quite steadily in the next hour over S KS / N OK, especially with the THETA-E advection supporting low cloud development preceding the initiation later today. I think dews will get to about 70˚F in your area once the advection spreads to the NE before 00Z.

 

By the way, current hourly observations and surface data indicate that the timing of the LLJ's strengthening is proceeding just as the GFS indicated, if not earlier. I would expect the LLJ to be cranking as early as 22-23Z based upon the likelihood of a mesoscale low forming over W OK. This is suggested by the net convergence in the region and the stretching of the PVA lobe due to a perturbation at 850-400 mb. This should allow the LLJ to strengthen a bit earlier than shown on the GFS, which is still more realistic than the NAM.

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OUGrad05

OUGrad05

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Dews are already hitting 72˚F at JWG (Watonga), with a very pronounced moisture depth and convergence line developing in just a few hours, resulting in a +4˚F upward jump. The mixing ratio in this area is rapidly going positive, meaning that dews should rise quite steadily in the next hour over S KS / N OK, especially with the THETA-E advection supporting low cloud development preceding the initiation later today. I think dews will get to about 70˚F in your area once the advection spreads to the NE before 00Z.

That's a good point, if dews get to 70 then the potential for strong and violent tor's goes up significantly.  I don't envy the folks at SPC having to eval this next update.

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baroclinic_instability

baroclinic_instability

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The 12Z NAM seems more bullish on today's potential in the area bounded by I-35 to the west and I-44 to the south as it has mostly backed off its drier solutions from earlier runs. Temps will probably warm into the 90s in the immediate vicinity of the dryline and initial storms may be high based, but anything that initiates would move into a lower LCL environment after it matures. 

 

 

While the 12Z NAM looks better for today, its solution for tomorrow looks pretty messy and disorganized. 

 

If the NAM verifies, I agree, tomorrow would be a messy and unimpressive event. GFS slightly backed off too and sinks the surface low too far S...which effectively places a large COL that extends into the warm sector. We will see, interested in what the morning day 2 goes with. As for today, I think the best threat is across southeast KS where the progged LCL-LFC RH's are progged to be much more reasonable. The best kinematic environment farther S near OKC may end up being too dry/possibly capped, but we will see. Some of the convection allowing guidance (namely HRRR) tries to initiate a few discrete supercells down that way.  

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CUmet

CUmet

Posted
Posted
Based on the latest high res models not really showing the secondary low and backed surface winds, I'm leaning against this reaching its major tornado outbreak ceiling.  However, given the impressive instability, deep layer shear, and sufficient helicity, I do still expect a few supercells to develop that are capable of producing quite a few tornadoes, some strong.

Like some others have noted, I'm definitely interested in that boundary currently located along a line from near Wichita, KS E/ENE to just north of Nevada, MO.  The latest HRRR and RAP runs indicate that this should settle along the I-35 corridor from Wichita-Emporia-Ottawa, KS.  Since convection further north will likely initiate early due to the weaker capping and strong forcing, it will not have as much access to the LLJ enhancement that comes near sunset, so the boundary up there will be crucial for locally backing the winds and enhancing the helicities there.

 

A second potential target is with the more southernmost cells, since it will have some access to the LLJ intensification later.  Tough to say where that'll be right now, but if I had to take a stab at it, maybe somewhere along a Stillwater-Bartlesville, OK line or so.

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CUmet

CUmet

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Just for clarification: Which models are you referring to? The GFS shows the secondary low and the backed surface winds...

 

The HRRR runs, the RAP (which isn't really a high res model I guess), and the 4km NAM.  Also, the 00Z ECMWF did back off somewhat on the surface winds backing.

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ZackH

ZackH

Posted
Posted

I am starting to think I missed a storm (was in and out) ...

 

We watched the Rozel storm for a while. It was clearly a strong tornado and the first time it touched down it was down for at least 15-20 minutes.  The 3rd touchdown also lasted about 10-15 mins.  It was an impressive tornado and LCLs were fine.

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brettjrob

brettjrob

Posted
Posted

 

Based on the latest high res models not really showing the secondary low and backed surface winds, I'm leaning against this reaching its major tornado outbreak ceiling.  However, given the impressive instability, deep layer shear, and sufficient helicity, I do still expect a few supercells to develop that are capable of producing quite a few tornadoes, some strong.

 

Beat me to it. I was just looking at the HRRR and noting there's very little backing of sfc winds, even as late as 00z. It's very difficult to get tornadic supercells in the Plains with sfc winds due S. I wouldn't be surprised to see relatively poor storm organization through much of the afternoon until the low-level shear eventually ramps up closer to sunset. The tricky part is that mesoscale processes can locally back sfc winds, and when/where that happens in the presence of a storm, all bets are off. But TBH, I'm beginning to lean back toward the "floor" for today's potential being quite low in terms of tornado count and strength/longevity. Will just have to keep a very close eye on the obs.

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