Central/Southern Plains Severe Weather Palooza (4/29 - 05/05)

[andyhb]

So far the HRRR has the best handle on current convective evolution, with the NAM 3 km and NSSL WRF being far too bullish on early elevated convection. The environment close to the warm front later looks pretty dangerous from CDS towards OKC. Seems like a low-level flow has ramped up in forecasts as well the closer we've gotten to verification.

[SmokeEater]

Going moderate next outlook, unknown it it's hail or tornado driven.

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[Quincy]

46 minutes ago, andyhb said:

So far the HRRR has the best handle on current convective evolution, with the NAM 3 km and NSSL WRF being far too bullish on early elevated convection. The environment close to the warm front later looks pretty dangerous from CDS towards OKC. Seems like a low-level flow has ramped up in forecasts as well the closer we've gotten to verification.

It’s concerning that HRRR is not showing much of any convective initiation through mid-afternoon. Some elevated activity races north with the warm front, but it looks like the WF is going to be draped close to the I-40 corridor. 

Right now, low level lapse rates are pretty bad (< 5 C/km across all of Oklahoma) and capping will probably limit CI for a while. Not really sure how convection evolves, but any discrete/semi-discrete cells initiating after 3-4 PM will need to be watched very closely.

Based on near term trends, those cells coming out of the panhandle later will probably remain at least semi-discrete as they move into southwestern Oklahoma. Looks like odds are increasing for at least 1-2 long-track, intense supercells, with other tornadic supercells possible in the warm sector and near the warm front. 

[cincy.wx]

moderate for tornadoes and hail, spc seems to think that nw texas and sw oklahoma will see some discrete supercells due to lack of convection this AM

 

 

Quote

 ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
   NORTHWEST TEXAS AND THE SOUTHEAST TEXAS PANHANDLE...SOUTHWEST
   OKLAHOMA...

   ...SUMMARY...
   Numerous severe thunderstorms are expected across parts of the
   southern Great Plains this afternoon through tonight.  A few strong
   tornadoes and giant hail is most probable across the southeast Texas
   Panhandle into portions of southwest Oklahoma and north Texas.

   ...Southern Great Plains...
   Complicated forecast today/tonight as a broad/destabilizing warm
   sector enlarges as a warm front advances northward today. 
   Considerable forecast uncertainty remains evident for a multitude of
   possible scenarios, some of which differ both spatially in terms of
   severe hazard and intensity.  Nonetheless, with the lack of morning
   convection across northwest TX into the TX Panhandle, thinking is
   this area will remain void of convection through the midday/early
   afternoon.  Consequently, it seems a categorical Moderate Risk is
   warranted for dryline/triple point storms. 

   Visible-satellite imagery late this morning shows a cirrus canopy
   across much of the outlook area.  A warm front is rapidly moving
   northward across north TX with upper 60s F dewpoints reaching the
   Red River as of 16z.  A destabilizing boundary layer beneath a
   capping inversion, which seems likely to hold through the early
   afternoon, will become quite unstable by peak heating with 3000-4000
   J/kg MLCAPE forecast over northwest TX by 4pm.  The RAP/HRRR seems
   to have the best handle on morning storm activity compared to the
   ARW and associated CAM models.  In general, model guidance indicates
   storms will develop over the TX Panhandle during the mid-late
   afternoon with more widely spaced thunderstorms farther south along
   the dryline.  Very steep 700-500 mb lapse rates, enlarged low-level
   hodographs via easterly component to low-level flow, and long
   hodographs all suggest discrete supercells will be the preferred
   mode over the TX Panhandle into northwest TX late this afternoon. 
   Very large to giant hail (potentially 3+ inches in diameter) and a
   few strong tornadoes are possible during the late afternoon into the
   early evening as this activity moves into parts of western OK/far
   western north TX.  Less certain but a plausible scenario involves
   free warm sector development farther east across parts of OK and
   perhaps north TX.  A potentially significant tornado risk could
   develop if discrete supercells were to develop within an
   increasingly moist/strongly sheared environment during the late
   afternoon/early evening.  

   By early to mid evening, the strengthening of a southerly LLJ and
   coalescing of storms/outflow will probably lead to the development
   of a severe MCS moving east across parts of OK.  Severe gusts,
   possibly greater than 65 kt, and tornadoes will become the primary
   severe hazards with time.  As this activity approaches the western
   part of the Ozarks, a lessening in the severe risk is anticipated
   late overnight.

   ...Southeast VA and the Carolinas...
   Not much change from the previous forecast in the overall
   thunderstorm scenario for VA/Carolinas.  A low-amplitude shortwave
   trough over the Lower Great Lakes will move east into southern New
   England this evening. To the south of this wave, a cold front will
   push southeast across the Lower Mid-Atlantic into the Carolinas.
   Convergence along the cold front and coastal sea breezes should
   support scattered thunderstorms this afternoon. While deep-layer
   shear will be modest, it should be adequate for multicells capable
   of isolated severe hail and damaging winds. Convection should
   largely shift offshore and/or weaken after dusk.

 

 

[Quincy]

HREF ensemble probability for intense (>150 m2/s2) helicity tracks. Keep in mind these don’t explicitly/necessarily indicate tornado potential, but given low level moisture and wind fields today, there is a bona fide tornado threat. 

The cluster near/NE of OKC is mostly FV3 driven, but still plausible near the warm front, IF low level thermodynamic fields improve enough to support supercells rooted near the surface. 

[Powerball]

 

[Powerball]

 

[Quincy]

Trying to save data, so embedding tweets instead of uploading more images. 

Low level lapse rates look to be a noteworthy limiting factor for central Oklahoma, in terms of tornado potential this afternoon. Not all that much different from 5/20/19. If lapse rates stay low, as is expected through 6-7 PM, the tornado threat may be limited to closer to the Red River. 

This doesn’t mean that tornadoes can’t happen, but that the threat with northward extent may be more marginal and could hold off until after 00z/7 PM.

 

[Amped]

The infamous Texas panhandle cell that the HRRR has been insisting on has formed and is headed towards Amarillo.  Not Tornadic yet but could be pretty soon.

[Powerball]

 

[Powerball]

 

[Powerball]

 

[SmokeEater]

Moderate is being extended into OK, will include OKC.

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[Quincy]

18z sounding from OUN is ugly if you want tornadoes. At least for the next several hours, as there’s a stable near surface layer.

 

[yoda]

22 minutes ago, SmokeEater said:

Moderate is being extended into OK, will include OKC.

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Expanded quite alot eastward

[Chinook]

The Texas panhandle is warming up, with southeasterly winds at some spots. The SPC mesoanalysis shows a lot of areas up to 3000-3500 J/kg of CAPE near the Red River now

[Chinook]

another unbelievable tweet- this sped-up video shows the American flag nearly getting ripped off the flagpole and small trees bending as the tornado moves perhaps less than 1/2 mile away. It kind of looks like it's across the street, but I'm not sure.

[Quincy]

Relatively quiet this far. Panhandle storms appear to be overrunning the warm front and ingesting cooler air. Low level lapse rates are still unfavorable across most of Oklahoma. A cell tried to go up near Abilene, but weak forcing seems to be the issue there. 

Focus moves toward a dryline bulge, just east of Lubbock. It looks like we may have convective initiation now after a failed attempt earlier. 

[WhiteoutWX]

Warm front is evident on Frederick radar in SW OK. Nearly stationary. Think that area east of Lubbock and whatever develops on the warm front will be the main show. Clearly the cells that were near Amarillo early are north of the boundary and the stuff the HRRR was blowing up in central OK is likely just the usual HRRR shenanigans where it takes warm advection showers and creates a cluster of supercells. Seems way overdone there at this point, though I guess something could still get going across south central OK where better surface heating is occurring. 

[Powerball]

As the FWD sounding that was posted above implied, storms are struggling to develop in Texas (outside the panhandle) because, while weak, the cap remains just strong enough with the nebulous forcing to surpress updrafts.

We'll see if that changes in the next few hours. But the better dynamics/forcing won't shift SE into North/Central Texas until tomorrow morning.

 

[Santa Clause]

1 minute ago, Powerball said:

As the FWD sounding that was posted above implied, storms are struggling to develop in Texas (outside the panhandle) because, while weak, the cap remains just strong enough with the nebulous forcing to surpress updrafts.

We'll see if that changes in the next few hours. But the better dynamics/forcing won't shift SE into North/Central Texas until tomorrow morning.

 

Couldn’t this cause a less messy storm mode?

[weatherextreme]

Reed Timmer is live

 

 

 

[Powerball]

8 minutes ago, Wmsptwx said:

Couldn’t this cause a less messy storm mode?

If a storm can manage to sustain itself, yes.

Time is of the essence though, because the later we get into the evening and surface temps fall, the cap will strengthen again.

[Quincy]

21z FWD sounding still shows a cap holding on. Warm front is basically stalled just north of the Red River. Thinking OKC is going to be spared the worst, but we’ll see how it continues to evolve. 

[Calderon]

1 hour ago, Chinook said:

another unbelievable tweet- this sped-up video shows the American flag nearly getting ripped off the flagpole and small trees bending as the tornado moves perhaps less than 1/2 mile away. It kind of looks like it's across the street, but I'm not sure.

The core of the vortex is directly across the street, but it was within the damage envelope, so it counts as a strike. 

[weatherextreme]

Reed just mentioned that he saw a funnel. On stream

[MNstorms]

Reed Timmer has a tornado near Dumont TX. Not even tornado warned yet.

[Chinook]

Seeing some chasers show a tornado, most likely same thing as Reed Timmer is seeing. This is at some of those county borders southwest of Paducah, Texas.

[mob1]

3 minutes ago, MNstorms said:

Reed Timmer has a tornado near Dumont TX. Not even tornado warned yet.

Someone's asleep at the wheel, at least 2 cells east and southeast of Amarillo have tight couplets. 

 

Edit: now TW'd. The 2 cells to it's north also look pretty healthy. 

[schoeppeya]

The storm SE of OKC looks like it’s latched on to the warm front and could probably use a TW as well

ETA: There it is