Mid to Late May 2019 Severe Threats

[jpeters3]

Currently progged to be a bit more deep layer shear (0-6 km ~ 65-75 kt) than the 4-13 gulf coast event, which could help keep things discrete for longer.

[Sydney Claridge]

It looks like a storm is trying to go up south of Mineral Wells, TX, west of DFW, within a recovered airmass behind the MCS.  Not severe at the moment, but there seem to be some good parameters in place there per SPC Mesoanalysis (supercell composite, EHI, CAPE, shear), and it's not even within the general thunderstorm outline area.  It would probably encounter some issues as it reaches the more stable air over DFW though.

I'm getting sunshine in west Fort Worth now so there's definitely instability building ahead of this new cell.

EDIT: SPC has issued an MD regarding the possibility for large hail in the DFW area:
 

Quote

   Mesoscale Discussion 0676
   NWS Storm Prediction Center Norman OK
   0637 PM CDT Sat May 18 2019

   Areas affected...portions of north Texas

   Concerning...Severe potential...Watch unlikely 

   Valid 182337Z - 190030Z

   Probability of Watch Issuance...20 percent

   SUMMARY...A storm or two may pose a brief threat for large hail this
   evening across the MCD area.

   DISCUSSION...An isolated thunderstorm has developed in Palo Pinto
   County TX this evening amidst strong low level convergence along the
   dryline. Earlier convection has generally resulted in surface
   inhibition, though latest surface observations have shows some
   recovery across a small area from near MWL toward Collin, Dallas and
   Ellis counties. Temperatures have rebounded from the mid 60s into
   the low and mid 70s and dewpoints were in the upper 60s to near 70
   as of 23z. As a result, a narrow corridor strong instability atop a
   weakly capped boundary layer exists just downstream from the surface
   dryline. While convection is not expected to be widespread, a couple
   of storms could pose a threat for large hail in the short-term
   across the MCD area. At this time, a watch is not expected, but
   trends will be monitored closely.

   ..Leitman/Guyer.. 05/18/2019

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...FWD...

   LAT...LON   33549770 33659750 33659724 33609695 33379678 33029672
               32709673 32599686 32479707 32439752 32489790 32639816
               32809820 33119802 33429784 33549770 

EDIT 2: The cell seems to be struggling to strengthen, so I'm not sure if it will amount to anything.

[Sydney Claridge]

Severe thunderstorm warning now up for eastern Parker and western Tarrant counties in Texas:

 

Quote

Severe Thunderstorm Warning
TXC367-439-190100-
/O.NEW.KFWD.SV.W.0185.190519T0007Z-190519T0100Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Fort Worth TX
707 PM CDT Sat May 18 2019

The National Weather Service in Fort Worth has issued a

* Severe Thunderstorm Warning for...
  Eastern Parker County in north central Texas...
  Western Tarrant County in north central Texas...

* Until 800 PM CDT.

* At 706 PM CDT, a severe thunderstorm was located over Willow Park,
  or near Weatherford, moving east at 15 mph.

  HAZARD...60 mph wind gusts and quarter size hail.

  SOURCE...Radar indicated.

  IMPACT...Hail damage to vehicles is expected. Expect wind damage
           to roofs, siding, and trees.

* Locations impacted include...
  Fort Worth, Weatherford, Benbrook, Saginaw, White Settlement, Azle,
  River Oaks, Sansom Park, Lake Worth, Eagle Mountain, Willow Park,
  Aledo, Westworth Village, Hudson Oaks, Annetta, Lakeside, Westover
  Hills, Annetta South and Annetta North.

This includes the following highways...
 Interstate 20 between mile markers 410 and 433.
 Interstate 30 between mile markers 1 and 11.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection get inside a sturdy structure and stay away from
windows.

&&

LAT...LON 3265 9774 3284 9776 3292 9738 3262 9737
TIME...MOT...LOC 0006Z 267DEG 13KT 3276 9767

HAIL...1.00IN
WIND...60MPH

$$

05/

And it's a slow mover indeed.  Minimally severe at the present moment though.

[Misstertwister]

Hello my favorite weather casters. As I’ve always mentioned many of you have helped me overcome a lot of my severe weather anxiety by showing me how to look at wind fields, EHi, dew points and various other parameters to look ahead and prepare for potential weather days.

 

howevwr, one thing I’m not good at is looking at possible where initiation may begin. 

 

My question is about Monday. As it looks there could be some significant weather and I will be out of town. I live in Edmond OK and my kids will be in school. I’ve arranged for their grandma to possibly get them out early just in case things get bumpy earlier than normal. 

 

Is there a way to analyze where initiation may start and if there will be time for them to finish school?  

 

This is not a question like will it hit XYZ at 5:30  

 

just more of being prepared and not getting congested at school if grandma does need to get them early 

 

 

 

 

[Indystorm]

23 minutes ago, Misstertwister said:

Hello my favorite weather casters. As I’ve always mentioned many of you have helped me overcome a lot of my severe weather anxiety by showing me how to look at wind fields, EHi, dew points and various other parameters to look ahead and prepare for potential weather days.

 

howevwr, one thing I’m not good at is looking at possible where initiation may begin. 

 

My question is about Monday. As it looks there could be some significant weather and I will be out of town. I live in Edmond OK and my kids will be in school. I’ve arranged for their grandma to possibly get them out early just in case things get bumpy earlier than normal. 

 

Is there a way to analyze where initiation may start and if there will be time for them to finish school?  

 

This is not a question like will it hit XYZ at 5:30  

 

just more of being prepared and not getting congested at school if grandma does need to get them early 

 

 

 

 

Hopefully the school already has a policy in place to cover issues such as this....like early dismissal or no school if the day starts out as high risk in the outlook.  Initiation and timing are almost always day of sort of decisions with only educated guesses this far out in advance.

[cheese007]

Warning for the rogue storm in TX has been extenxed into Dallas county

[Misstertwister]

10 minutes ago, Indystorm said:

Hopefully the school already has a policy in place to cover issues such as this....like early dismissal or no school if the day starts out as high risk in the outlook.  Initiation and timing are almost always day of sort of decisions with only educated guesses this far out in advance.

Does this look like typical Tx panhandle/ western ok initiation first like usual on the DL? I’ve noticed there might be some earlier initiation further east possibly

[Sydney Claridge]

Severe thunderstorm warning cancelled for the DFW area as that storm has weakened below severe limits.

[Indystorm]

9 minutes ago, Misstertwister said:

Does this look like typical Tx panhandle/ western ok initiation first like usual on the DL? I’ve noticed there might be some earlier initiation further east possibly

18z NAM 3k has initiation in the TX/OK panhandles in the morning and moves to central OK by late afternoon.  But this is one run of one model.  Keep alert to future forecasts.

[Misstertwister]

15 minutes ago, Indystorm said:

18z NAM 3k has initiation in the TX/OK panhandles in the morning and moves to central OK by late afternoon.  But this is one run of one model.  Keep alert to future forecasts.

Do you look at composite reflectivy dbz?

 I use pivotal weather. 

[Indystorm]

1 minute ago, Misstertwister said:

Do you look at composite reflectivy dbz?

 I use pivotal weather. 

I like looking at the various parameters on pivotal weather from different models.  It is a good site.  But I rely on professional mets for interpretation in the affected areas because things can and do change rapidly in volatile situations like this.  Soundings are intense for the evening in much of the affected region.

[Southern stream]

Definitely still looking like a dangerous setup. Will it be our first High risk of the year? This is a parameter space that supports one, but Ive seen lots of people on twitter thinking we could even see a D2 high. 99.9% chance that will not happen. Seeing how careful and conservative they have been on pulling the trigger for a higher risk this year, they will much more likely wait (the smart thing to do), until the morning of, to get a much better idea of mesoscale details. Not to mention the idea of a D2 high occuring is extremely uncommon and last I checked, only has happened on 2 other days. Me personally, I think D2 outlooks having a max ceiling of MOD would do just fine and get the message out just as effectively. In general though it is looking like potentially the biggest event in the southern plains in several years should parameters hold.

[lokee]

2 hours ago, Indystorm said:

Hopefully the school already has a policy in place to cover issues such as this....like early dismissal or no school if the day starts out as high risk in the outlook.  Initiation and timing are almost always day of sort of decisions with only educated guesses this far out in advance.

There are districts in the Okc metro area that have severe weather policy. I know MId Del School district has a policy that states if a severe weather event is likely to occur during school hours then the district will not be in session. Also, if school is in session and there are weather threats then the student can be check out by parents and it is excused.  This is both with spring and winter weather.

[jpeters3]

00 UTC NAM NEST shows a tornado outbreak, albeit a brief one.  CI is between 22-00 UTC, and then upscale growth pretty quickly follows by 3-4 UTC.

Simulated radar shows numerous discrete cells with high UH at 02 UTC.  Widespread STP > 10 in the region where cells initiate.  I attached two forecast soundings: one in OK near the northern discrete cells and one in the TX panhandle near the southern group of cells.  Both profiles are, needless to say, impressive.

I'm still curious about the deep low-level saturated layer shown in the NAM and NAM nest.  This may be a result of strong low-level ascent associate with warm air advection earlier in the day, though warm air advection ramps down into the afternoon.  This same feature was present in soundings from the 4-13 event, which turned into widespread messy/grungy convection in the MOD risk region.  Really, the feasible only bust scenario is widespread junk and/or upscale growth that happens too quickly.  I wouldn't discount this scenario, and it's certainly enough to hold back a day 2 High risk.  That sort of call really needs close to 0 uncertainty in day 1, and I don't think we're anywhere close to 0 uncertainty right now.

If we do manage to get discrete cells, they are going to produce numerous ground wedges and ground scraping mesos, in the style of gulf mega outbreaks.

 

[jpeters3]

FYI, the 00 UTC initialized CSU WRF is another model to look at, available here:

http://schumacher.atmos.colostate.edu/weather/csuwrf_4km.php

This is run with the GFS (rather than the NAM) as ICs and LBCs.  Tonight's run should be available soon.

[jojo762]

High-end event certainly appears to be evolving across the Texas Panhandle, western Oklahoma, and southern Kansas... Forecast soundings on both the GFS (and especially the NAM) are ludicrous across much of the warm sector... but for one, I’m not sure how much value I’d put into the NAM nest’s storm mode over the next two days tbh, It’s notorious for going insta-linear. It did so on Friday, and we saw how that went. 

[Misstertwister]

Is that low slowing down some slightly? Seems like some new thinking might have it lagging a little further west now and I-35 corridor more of a late evening threat or MCS

[bjc3395]

27 minutes ago, jpeters3 said:

00 UTC NAM NEST shows a tornado outbreak, albeit a brief one.  CI is between 22-00 UTC, and then upscale growth pretty quickly follows by 3-4 UTC.

Simulated radar shows numerous discrete cells with high UH at 02 UTC.  Widespread STP > 10 in the region where cells initiate.  I attached two forecast soundings: one in OK near the northern discrete cells and one in the TX panhandle near the southern group of cells.  Both profiles are, needless to say, impressive.

I'm still curious about the deep low-level saturated layer shown in the NAM and NAM nest.  This may be a result of strong low-level ascent associate with warm air advection earlier in the day, though warm air advection ramps down into the afternoon.  This same feature was present in soundings from the 4-13 event, which turned into widespread messy/grungy convection in the MOD risk region.  Really, the feasible only bust scenario is widespread junk and/or upscale growth that happens too quickly.  I wouldn't discount this scenario, and it's certainly enough to hold back a day 2 High risk.  That sort of call really needs close to 0 uncertainty in day 1, and I don't think we're anywhere close to 0 uncertainty right now.

If we do manage to get discrete cells, they are going to produce numerous ground wedges and ground scraping mesos, in the style of gulf mega outbreaks.

 

In my honest opinion, what sets this apart from the 4/13 "bust" is a prominent focus for surface-based convective initiation: the dry line. If you had a surging dry line into eastern TX with favorable shear orientation, I imagine that day plays out much differently.

 

Instead we didn't exactly have that and storms were initiating but not exactly well-rooted into the surface, nor organized. I think that is a key difference, and the CAMs across the board are depicting varying solutions that all kind of converge on a mixed-mode severe weather outbreak by/after 00z. Agree that a day 2 high is too much. But don't think a day one high is out of the question yet.

 

Threat for supercells producing significant or violent tornadoes should carry well into dark with the strong theta e advection. Boundary layer stabilization should be offset some.

[MUWX]

I doubt they go high, but it will be interesting to see what kind of day 2 tornado probabilities they put up. 

[Quincy]

It's still early to call boom or bust. The linear mode (especially up north) advertised on some models might be right. Remember in 2017 when a few of the high shear/high CAPE setups in May across Oklahoma failed to meet expectations? Just because there's substantial instability with strong wind shear does not equal a supercell tornado outbreak. That 5/18/17 tornado-driven high risk busted hard, especially when CAMs were in good agreement about messy storm modes. There was a moderate risk later in the month that was very junky from eastern Oklahoma into the Ozarks.

With that said, this event has a higher ceiling than most we've seen over the past 4-5 years across the Southern Plains. Aside from storm mode, I'd also be concerned about a mass of convection moving from the panhandles into Oklahoma during the morning. This is advertised on the GFS/Euro/RGEM and to a lesser extent, then 3km NAM.

I have the most confidence in the dryline lighting up with a potentially significant tornado threat. The instability progs ahead of the dryline are pretty ridiculous, on the order of 3,000-4,000+ J/kg MLCAPE by peak heating and that's across relatively high terrain, in the Lubbock-Midland-Fort Stockton zone. Speed shear is substantial and directional shear is good with plenty of veering with height. There is a southwesterly component to the upper level winds and although the angles with respect to the dryline probably won't be 90 degrees, it will still get things done with S to SE near-surface winds.

The biggest question mark is up north, in my view, from the panhandles/northwest Texas into western/central Oklahoma. That's where the parameter space is maxed out, but where there could also be convective overturning earlier in the day. Another scenario is a reinforced boundary being left somewhere between the Texas panhandle and the Red River Valley from morning convection, but it's early to speculate where that might setup, if such a boundary does get laid down.

[lokee]

One of the tv stations in Okc 

[jojo762]

With the wave trending slower and slower (wrt energy/lift ejecting into the warm sector), I see no reason to not expect discrete/semi-discrete modes to be prevalent and dominant (owing to ridiculous shear profiles throughout the entire column). As with almost any “big troughs,” the evolution of morning convection will be a question, but that’s not exactly the most profound question wrt a significant severe setup.

With how these things (big time trough setups) have worked in the past, mixed modes with tornadic supercells and some messier clusters will probably exist across the warm sector/near the dryline/warm front. It is notable that it only takes one or two cyclic tornadic supercells to totally change the perspective of a setup (see Friday, 5/17). We don’t need, let’s say,  7 discrete tornadic supercells, for a higher-end risk to verify.

Perhaps my biggest question for this setup is the evolution/location of the warm front. Pattern recognition (intense moisture advection, aided by a strong low-level jet throughout the entire day) would tell you that the warm front will lift north significantly, but models don’t show that, owing to potentially significant amounts of convection north of the front. Generally think it’ll lift a bit more north than currently shown, but that’s just a hunch. Generally it’s smart to trust NWP, but it hasn’t been the most stellar lately. ( for example see UH tracks/storm mode from Friday, and initiation south along the DL and sustainability thereafter).

Next big question is the impact on supercell modes, and low-level mesocyclones of having a deep-moist layer extend to ~3km. Shear profiles would tell you that you shouldn’t have to worry about grungy supercells, but doubt that’ll be the case if moisture of that level verifies. Ground-scraping, grungy, fast moving high-precipitation supercells may be the result of all that. This, of course, would provide its own significant threat. Any tornadoes that form would likely tend to be shrouded by rain/ rain-wrapped well into the evening.

Important to note that details will certainly change to some degree!

[jojo762]

SPC maintained MDT risk @ 06Z update. Mostly concerned about where/when initiation will occur, doesn’t appear to be any concern regarding storm mode or morning convection. 

[WhiteoutWX]

Some of the CAMs are hinting at discrete activity along the lifting warm front tomorrow morning. Shear is good through the morning so if these cells could become surface based the tornado threat could start early and extend eastward into central OK. HRRR probably looks most concerning regarding this possibility but taken verbatim it appears the cells cross the warm front and are elevated. Lifting warm front scenarios can be sneaky tho and this should be watched IMO.

Overall though I agree with SPC basically leaving the risk area as is given some uncertainty with storm mode/initiation.

[jpeters3]

9 hours ago, bjc3395 said:

In my honest opinion, what sets this apart from the 4/13 "bust" is a prominent focus for surface-based convective initiation: the dry line. If you had a surging dry line into eastern TX with favorable shear orientation, I imagine that day plays out much differently.

 

Instead we didn't exactly have that and storms were initiating but not exactly well-rooted into the surface, nor organized. I think that is a key difference, and the CAMs across the board are depicting varying solutions that all kind of converge on a mixed-mode severe weather outbreak by/after 00z. Agree that a day 2 high is too much. But don't think a day one high is out of the question yet.

 

Threat for supercells producing significant or violent tornadoes should carry well into dark with the strong theta e advection. Boundary layer stabilization should be offset some.

I should probably stop calling 4-13 a "bust," since it verified in terms of SPC D1 probabilities.  I guess the reason I think of that event as a "bust" is because it looked to have high-end potential 1-2 days before, but a high end event never came to fruition. 

[jpeters3]

0000 UTC CSUWRF (GFS based) shows quite a bit of early-day convection through the panhandle and OK (this generally agrees with the GFS solutions), along with widespread upscale growth by 03-04 UTC.  Some notable UH streaks throughout the region, but this early CI scenario would substantially reduce the warm front risk.

CSUWRF: http://schumacher.atmos.colostate.edu/weather/real_time_wrf/radar_1km_4km/anim.php?

SPC outlooks have harped on the lack of synoptic scale forcing as a factor in keeping cells discrete; however, with such saturation at low levels, it doesn't take much lift to get parcels to their LFCs and not much large-scale ascent is needed to make widespread CI, and the large CAPE and relatively moist mid-level environment in soundings will readily facilitate intense cold pool production and upscale growth.

[jpeters3]

Another crazy eye candy sounding from the NAM at 03 UTC.  STP of 19..., 0-3 km SRH of 860 J/Kg. 

[WhiteoutWX]

1 hour ago, jpeters3 said:

0000 UTC CSUWRF (GFS based) shows quite a bit of early-day convection through the panhandle and OK (this generally agrees with the GFS solutions), along with widespread upscale growth by 03-04 UTC.  Some notable UH streaks throughout the region, but this early CI scenario would substantially reduce the warm front risk.

CSUWRF: http://schumacher.atmos.colostate.edu/weather/real_time_wrf/radar_1km_4km/anim.php?

SPC outlooks have harped on the lack of synoptic scale forcing as a factor in keeping cells discrete; however, with such saturation at low levels, it doesn't take much lift to get parcels to their LFCs and not much large-scale ascent is needed to make widespread CI, and the large CAPE and relatively moist mid-level environment in soundings will readily facilitate intense cold pool production and upscale growth.

Definitely looks messy but I don’t know if I would characterize that look as totally upscale or linear. Looks like line segments with probable embedded supercells. With that environment I’d still think there would be plenty of tornado risk, just maybe not pristine and clean for chasers.

[jpeters3]

12 minutes ago, WhiteoutWX said:

Definitely looks messy but I don’t know if I would characterize that look as totally upscale or linear. Looks like line segments with probable embedded supercells. With that environment I’d still think there would be plenty of tornado risk, just maybe not pristine and clean for chasers.

Right.  I'm definitely not calling "bust" at this point, or even saying this won't be a high-end historic outbreak. I just think the upscale growth potential, and/or the potential for mixed storm modes **might** keep this from being a historic tornado outbreak.  But it might not...  Hard to tell at this point.

There will almost certainly be tornadoes somewhere, and probably a few EF-2 + tornadoes.

[jpeters3]

FWIW, the 12 UTC HRRR is pretty much all discrete storm mode.