Short-Term Severe/Flooding Discussion

[cheese007]

Looking like DFW proper might thread the needle and make it out unscathed, aside from the far northern exurba

[Jim Martin]

2 minutes ago, Indystorm said:

Yes, it is instructive to watch the DFW composite loop over time and see the storms coalesce into five cells from ne to sw as they move in a southeasterly direction.

 

[Santa Clause]

Storm mode remained impressively discrete, definitely had potential to be worse. Still think significant severe reports are still likely and already is happening for hail.

[Indystorm]

Yes, baseball size hail reported at Prosper with that Collin county cell.

[Santa Clause]

1 minute ago, Indystorm said:

Yes, baseball size hail reported at Prosper with that Collin county cell.

Wow, incredible stuff. 

[Jim Martin]

This severe storm could pay a visit to Fort Worth later this evening. The one north of Decatur, that is, moving southeast.

[Santa Clause]

Boy, these cells are impressive, just lucky they aren't producing TOR.

[jojo762]

4 minutes ago, Wmsptwx said:

Boy, these cells are impressive, just lucky they aren't producing TOR.

Wind-profile highly favors supercell structures... But low-level winds are fairly weak speed-wise, resulting in 0-1KM SRH that just isn't quite good enough, per 00Z FWD sounding. Believe the cap may be playing some role in limiting tornadogenesis as well.

[Santa Clause]

4 minutes ago, jojo762 said:

Wind-profile highly favors supercell structures... But low-level winds are fairly weak speed-wise, resulting in 0-1KM SRH that just isn't quite good enough, per 00Z FWD sounding. Believe the cap may be playing some role in limiting tornadogenesis as well.

Nice input! Bet they make incredible pictures though.

[jojo762]

Supercell in Wise Co./ moving into Denton Co TX/ needs attention... Exhibiting some low-level rotation, and its moving into a populated area. Appears that it actually has two areas of rotation.

[cheese007]

2 minutes ago, jojo762 said:

Supercell in Wise Co./ moving into Denton Co TX/ needs attention... Exhibiting some low-level rotation, and its moving into a populated area. Appears that it actually has two areas of rotation.

Even without that it looks to move into areas that were hailed on before. Two rounds of the stuff :/

[Sydney Claridge]

16 minutes ago, jojo762 said:

Supercell in Wise Co./ moving into Denton Co TX/ needs attention... Exhibiting some low-level rotation, and its moving into a populated area. Appears that it actually has two areas of rotation.

That storm does seem to be post-frontal, so I wonder if that might temper any potential threat for tornadic activity?

[jojo762]

9 minutes ago, BrandonC_TX said:

That storm does seem to be post-frontal, so I wonder if that might temper any potential threat for tornadic activity?

Oops. Forgot to check SFC obs in a while to see where the front was, given that we have a crashing CF today. Tornado potential is pretty much NIL in that case, storm is elevated. 

[cheese007]

Storm was supposedly dropping tennis balls in Plano. UTD got some brief hail. Biggest stones I found

 

[cheese007]

Just got about 5 minutes worth of these with literallly no warning. UTD area

 

[andyhb]

Surprised there hasn't been a bit more discussion for tomorrow in SE TX and LA. The GFS, Euro and NAM variants are all suggesting a relatively high end (particularly in the low levels) parameter space in place centered on the Sabine Valley and then shifting E towards the Lower MS Valley later on, especially nearer to the warm front. Assuming the MCS along/ahead of the southeastward moving front doesn't completely take over, seems like there would be potential for tornadoes out ahead in the open warm sector. 00z NCAR ensembles did show a number of members with more discrete cells going up out ahead of this feature.

[monsoonman1]

SPC goes Enhanced for tomorrow from east Texas into Louisiana and Mississippi, which seems to be for tornado potential. 

[andyhb]

12z CAMs, particularly the NSSL WRF, highlighting the possibility of intense supercells INVOF the I-10 corridor through the afternoon tomorrow.

[1900hurricane]

Guidance had been developing an instability-clearing MCS along the advancing warm front during the earlier runs. The fact that they have largely backed off on this is rather concerning.

[jojo762]

Wednesday (5/10) continues to look more and more interesting on the models. 12Z EC depicts a classic 500mb jet timing, and shows a 30-35kt LLJ developing by 00Z across western OK/TX PH and into southern KS, with moderate instability. Potential for morning convection throws some uncertainty into the mix, and VBV wind profiles also throw a wrench into what the dominant storm-mode will be. Thinking a mixed storm-mode of supercells and clusters seems probable, with all severe hazards possible.

Tid Bit from DDC AFD: 

Quote

On Wednesday, the threat of severe thunderstorms increases. 40-50 kt
bulk shear suggests supercells. CAPE is forecast 1500-3000 J/kg, depending
on which model you use. Feel that the NAM is probably overdoing BL
moisture and CAPE. Both the GFS and EC suggest less morning convection
with mainly afternoon and evening convection now. So, the forecast
CAPE above may be realized. The threats for Wednesday will be 2-3"
hail, 60-75 mph winds, and even a few tornadoes. The highest tornado
threat will be across the southern zones, where low level flow will
be backed more and thus increasing 0-1 km shear. There is still large
uncertainty in how this will play out, but there is a trend in the
last 24 hours of models to suggest a higher threat of severe on Wednesday
compared to yesterdays runs. Something to watch and keep updated as
the smaller mesoscale details become more clear.

 

[Jim Martin]

Southwest Oklahoma Wednesday Evening off this afternoon's GFS.

[brettjrob]

Wednesday is definitely worth watching. It's a flawed synoptic setup, but rejoice ye all, for it is May and such things can be overcome! If morning crapvection persists across the warm sector into the afternoon, as suggested by the Euro and GFS, then the most interesting threat may be confined to the Red River and NW TX. The NAM's idea opens the whole dryline up to SW KS for fun, but I don't trust its handling of CI, especially at this range. Either way, low-level shear appears to be the main limiting factor right now, primarily due to a weakness around H7 (not surprising for a closed low). Again, though... it's mid May now, and nothing with adequate moisture and 35 kt of bulk shear can be written off.

[jojo762]

2 hours ago, brettjrob said:

Wednesday is definitely worth watching. It's a flawed synoptic setup, but rejoice ye all, for it is May and such things can be overcome! If morning crapvection persists across the warm sector into the afternoon, as suggested by the Euro and GFS, then the most interesting threat may be confined to the Red River and NW TX. The NAM's idea opens the whole dryline up to SW KS for fun, but I don't trust its handling of CI, especially at this range. Either way, low-level shear appears to be the main limiting factor right now, primarily due to a weakness around H7 (not surprising for a closed low). Again, though... it's mid May now, and nothing with adequate moisture and 35 kt of bulk shear can be written off.

Yeah that weakness in low-level flow above 850mb is really dampening this from looking much better, quite disappointing given that we actually have an appreciable LLJ with moderate instability and impressive moisture by 00Z... Regardless, as you said, its mid-may now so really anything could happen, wouldn't be surprised to see a few tornadic supercells, but also wouldn't be surprised if we just got clusters and very large hail-producing non-tornadic supercells. Thursday, however, could be more interesting... across north Texas and perhaps the arklatex. 

[the ghost of leroy]

Best city on earth

 

 

[Jim Martin]

Beckham County, Oklahoma Wednesday Evening off the 12z NAM. 

[monsoonman1]

5% tornado risk today for east CO into NM.

[Quincy]

Chased New Mexico today and some of the better structure was just southwest of Tucumcari:

 

[Quincy]

Convective evolution late tonight into early tomorrow across the OK/TX panhandles will be critical with supercell potential in the region Wednesday afternoon. 

There's a fine line between an MCS that leaves a significant cold pool and early day convection that lays down one or more outflow boundaries. There are some similarities to 5/16/15 as mentioned. 

As it stands now, CAMs and ensembles, including 12z HRRRX, show at least some discrete storm development from the panhandles into western OK. That remains to be seen. If there is at least modest airmass recovery, significant severe will be possible with any isolated storms as they mature, but it's also plausible that most of the area gets heavily disrupted by morning convection. It is May, so even the latter solution would still suggest some severe potential, even if it is shunted south a bit. (Again, similar to 5/16/15) 

Backing up to today, it looks like a better-than-yesterday setup across the southern target. Modest height falls, better quality low-level moisture and stronger shear profiles suggest a relatively high likelihood for a few robust supercells from southeastern NM into West Texas. The northern target (northeastern NM into eastern CO) looks messy with marginal low-level moisture, but you can't rule up a local-terrain driven spinup or two. This could also be an event that supports an intense rogue tail end Charlie cell going up down near I-20 in southwest Texas (near sunset and/or into the evening) with large CAPE and shear vectors nearly perpendicular to a dryline. 

[Drz1111]

Man, the HRRR loves that SE NM / West Texas zone around dusk, when the SE low level flow amps up.  SPC seeing it too, of course, but that's a pretty interesting setup.

[jojo762]

SPC added a 10% TOR and 30% hatched hail area to SE NM/W TX... kiss of death to the setup.