April 17-18 Severe Weather

[wotan]

Out of curiosity, what are the thresholds for a PDS Severe Thunderstorm Watch? I hadn't previously really thought about it for this, but the newly updated Day 2 Outlook has the following probabilities:

Edited to correct Warning to Watch.

Quote

...MAXIMUM RISK BY HAZARD...
   Tornado:   5%     - Slight
   Wind:     30%     - Enhanced
   Hail:     30% SIG - Enhanced

 

[jojo762]

21 minutes ago, wotan said:

Out of curiosity, what are the thresholds for a PDS Severe Thunderstorm Warning? I hadn't previously really thought about it for this, but the newly updated Day 2 Outlook has the following probabilities:

 

 

There is no such thing as a PDS Severe Thunderstorm warning... What are you referring to?

[wotan]

1 minute ago, jojo762 said:

There is no such thing as a PDS Severe Thunderstorm warning... What are you referring to?

I meant watch.

[Superstorm93]

 

Just now, wotan said:

I meant watch.

 

 

Usually reserved for widespread damaging wind events.

Here's an example https://www.spc.noaa.gov/products/watch/2017/ww0280.html

[wotan]

Just now, Superstorm93 said:

 

 

 

Usually reserved for widespread damaging wind events.

Here's an example https://www.spc.noaa.gov/products/watch/2017/ww0280.html

Ahhh. I was thinking very large hail could also trigger one. 

[jojo762]

This setup in some aspects is reminiscent of 4/26/16... Thermodynamics are impressive... Mid-level support is there (trough strength/orientation and degree of moisture tell you severe outbreak from a pattern standpoint) ... But hodographs are just really funky. Could see some initially discrete storms produce a tornado or two anywhere from southern KS to northern TX, but the prospects we get a discrete supercell for more than an hour, maybe two hours max seem pretty slim with that disgustingly messy wind profile. Even if we do get discrete storms for longer than I or others anticipate (owing mainly to lingering CIN), that hodograph between 1-4km is really going to hold back low-level mesos from attaining the necessary strength to produce tornadoes. 

[CheeselandSkies]

So what is it about this trough that's making the wind profiles so wonky?

[Msalgado]

45 minutes ago, jojo762 said:

This setup in some aspects is reminiscent of 4/26/16... Thermodynamics are impressive... Mid-level support is there (trough strength/orientation and degree of moisture tell you severe outbreak from a pattern standpoint) ... But hodographs are just really funky. Could see some initially discrete storms produce a tornado or two anywhere from southern KS to northern TX, but the prospects we get a discrete supercell for more than an hour, maybe two hours max seem pretty slim with that disgustingly messy wind profile. Even if we do get discrete storms for longer than I or others anticipate (owing mainly to lingering CIN), that hodograph between 1-4km is really going to hold back low-level mesos from attaining the necessary strength to produce tornadoes. 

That day had a long lived supercell that went up through Central OK though.  What ruined the action own in Texas was ongoing elevate convection that eventually made it to the target area and just grew immediately upscale into an MCS.  After that initial convection passed I remember getting a rotating supercell after dark in N Central TX.

There are plenty of days where VB profiles still cause supercells.  I'd agree that they generally look less than favorable and we probably won't see more than an isolated weak tornado tomorrow though.

[WhiteoutWX]

14 minutes ago, Msalgado said:

That day had a long lived supercell that went up through Central OK though.  What ruined the action own in Texas was ongoing elevate convection that eventually made it to the target area and just grew immediately upscale into an MCS.  After that initial convection passed I remember getting a rotating supercell after dark in N Central TX.

There are plenty of days where VB profiles still cause supercells.  I'd agree that they generally look less than favorable and we probably won't see more than an isolated weak tornado tomorrow though.

Tomorrow’s problems aren’t only just VBV related as there is a distinct weakness in the low-mid level flow that will likely inhibit updraft rotation/longevity and will make it harder for tornadic activity than VBV alone would suggest. Could this weakness be overdone in the models? Perhaps. But at this point we need wholesale changes to the mid level synoptic pattern to support more than just a very isolated/brief tornado threat.

[MoistWx]

Interesting. Wasn't really expecting to see a mid-day day 3 update come out.

 

Quote

   ....Louisiana and Mississippi upgraded to Enhanced Risk for
   Thursday...
   Models are in good agreement with the general setup for Thursday,
   indicating a deepening upper trough across the lower MS Valley. Wind
   profiles will increase throughout the period, ahead of a developing
   squall line. Models indicate substantial low-level moisture will
   surge northward early through midday across LA, with cells possibly
   developing ahead of the ongoing frontal convection to the west. Any
   cells ahead of the line could be supercells capable of tornadoes.
   With time, a consolidation into a severe QLCS is expected.
   Hodographs will be supportive of supercells and/or embedded
   corridors of significant wind and a few tornadoes. A strong tornado
   is possible. 

 

 

[Msalgado]

32 minutes ago, WhiteoutWX said:

Tomorrow’s problems aren’t only just VBV related as there is a distinct weakness in the low-mid level flow that will likely inhibit updraft rotation/longevity and will make it harder for tornadic activity than VBV alone would suggest. Could this weakness be overdone in the models? Perhaps. But at this point we need wholesale changes to the mid level synoptic pattern to support more than just a very isolated/brief tornado threat.

Yeah I don't disagree at all, which is why I don't think there's going to be much more than an isolated threat unless they're completely wrong on that front.  The S shape occuring below 700 mb is never good for low level rotation.  

[Sydney Claridge]

18z and 00z HRRR runs have discrete storms forming up near DFW at around 6-7pm or so:





NAM and NAM3K (0z) have the storms moving through DFW about 3 hours later (and more linear on the 3K).  Texas Tech's model also shows storms for DFW around the 7pm timeframe as well.  Not total agreement among the CAMs shown on Pivotal Weather (including the HRW models) though; that said, I'm getting a bit concerned about the possibility of another damaging hailstorm in/near DFW if one of the models showing discrete storms does verify.  I know there were some issues about VBV brought up with respect to the tornado threat though, but some of the models I've been looking at seem to lessen that a little bit (I believe).

[DanLarsen34]

I know most of this thread has focused on the threat tomorrow/today, but SPC amended their day 3 outlook to an enhanced risk during the afternoon (which is very rare) and mentioned the threat of a strong tornado. Will be interested to see if they stick with that for Thursday when the day 2 outlook comes out in a little bit.

What do people on this thread think about the Thursday threat?

[Chinook]

The Rio Grande region--Eagle Pass, TX to the Dallas area may have some severe storms, but I don't think the models are particularly amazing, given the 3000 J/kg of CAPE. Several areas of severe wind/hail should exist with the cold front in Kansas/Oklahoma. The 00z HRRR is more aggressive with severe storms, in a broad area south of Dallas, including Austin and San Antonio.

 

Day 3 - Thursday. Models look impressive from eastern Louisiana to Jackson, MS. Overall, there might be a bit of veer-back-veer in the soundings, and maybe  *too* much convection. Even so, if you have a big line of storms those storms still could produce tornadoes, given some 400 m2/s2 of SRH and 65 kt of deep layer shear.

[cstrunk]

Models are showing supercells/convection firing in the warm sector across east Texas... mainly along and north of the US 79 corridor (the hard hit area last Saturday) region later this afternoon. Definitely something to keep an eye on.

 

 

[wotan]

Interesting thread:

 

 

[cheese007]

Still pretty cloudy here in far north Dallas but there was some clearing happening out by Farmer's Branch 

EDIT: https://www.spc.noaa.gov/products/md/md0365.html Some storms trying to fire out in the panhandle 

[lokee]

5 minutes ago, cheese007 said:

Still pretty cloudy here in far north Dallas but there was some clearing happening out by Farmer's Branch 

EDIT: https://www.spc.noaa.gov/products/md/md0365.html Some storms trying to fire out in the panhandle 

One of the storms has already gone severe.

[Sydney Claridge]

Got some good clearing (partly cloudy) here in Fort Worth.  Now it’s just a matter of waiting for the storms to fire up I guess.

[cstrunk]

Clouds are socked in pretty thick across east Texas. We'll have to see if that affects what the models are showing with storms firing out this direction.

[Sydney Claridge]

Surface CAPE has also rapidly increased (3000-3500 J/kg) and so has the MLCAPE (2000-2500 J/kg) per SPC Mesoanalysis for Fort Worth and Tarrant County.  Once this cap breaks I have a feeling there could be some big storms.

[cheese007]

Clearing here in far north Dallas and UTDallas just cancelled everything after 3PM due to the threat of severe weather 

[cstrunk]

If storms fire in east Texas, they currently have up to 300-400 ESRH to work with.

Foggy/misty currently here in Longview, TX.

[aggiegeog]

4 minutes ago, cstrunk said:

If storms fire in east Texas, they currently have up to 300-400 ESRH to work with.

Foggy/misty currently here in Longview, TX.

Very dreary with light rain and drizzle around Tyler. It is around 70 throughout E TX. As of now it is in the mid 80s west of I-35 and low 70s east of I-35. It doesn't look like the NE quadrant of TX will warm enough for much isolated supercell activity this evening, but closer to I-35 it may be possible.

[jpeters3]

So the VORTEX SE teams that are launching sondes near college station are finding much more CIN and less CAPE than what the HRRR/RAP/MESO analysis are showing... 

[lokee]

Weather Service lin Norman putting up a balloon at 3pm 4 /17 

[tornadoguy11]

Weather Service lin Norman putting up a balloon at 3pm 4 /17 

Do we know if Ft. Worth is doing a special balloon about the same time?

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[CryHavoc]

Awfully quiet today...

[cheese007]

2 minutes ago, CryHavoc said:

Awfully quiet today...

No tornadoes = no interest for most

[Weatherdemon]

OUN sounding indicates cap almost eroded and temps rising. Wind fields indicate linear mode with hail and wind threat per MD 369.