Severe Weather April 6th-10th 2021

[Powerball]

And 1 new SPC outlook later, DFW has gone from being in the enhanced risk area to barely being in the slight risk area, lol..

[cstrunk]

I guess they decided that the Euro wasn't the model to follow after all (or maybe the Euro caved)? This update lines up with what the NAM and HRRR are showing.

[Powerball]

15 minutes ago, cstrunk said:

I guess they decided that the Euro wasn't the model to follow after all (or maybe the Euro caved)? This update lines up with what the NAM and HRRR are showing.

The EURO was already an outlier when they issued the outlook this morning.

[Powerball]

Pretty insane sounding at 22z over the eastern half of DFW.

Cap is virtually gone too.

[WhirlingWx]

16 minutes ago, Powerball said:

Cap is virtually gone too.

 

Still doesn't really convect here in the metro though (not that I want a supercell with baseball-sized hail roaring through DFW), so I'm just wondering what's up with that. Upper 80s surface temps, >4000 CAPE, and little CINH, is there something I'm missing? Of course, have to see what other CAMs say, but HRRR has been the most notorious at bombing areas with convection, so I feel like there's at least some significance in it not really showing much here for multiple runs.

Edit: flow is pretty bleh, but I'm not knowledgeable enough to know if it's typical for that to just suppress convention entirely.

[Powerball]

15 minutes ago, TexMexWx said:

Still doesn't really convect here in the metro though (not that I want a supercell with baseball-sized hail roaring through DFW), so I'm just wondering what's up with that. Upper 80s surface temps, >4000 CAPE, and little CINH, is there something I'm missing? Of course, have to see what other CAMs say, but HRRR has been the most notorious at bombing areas with convection, so I feel like there's at least some significance in it not really showing much here for multiple runs.

Well technically, it still shows the tiniest bit of mixed level CINH, but I've seen storms break through that easily. So it's understandable why FWD has been so ominous in their discussion, especially with the strong surface convergence from the dry line. The 3km NAM does make a valiant attempt at breaking the cap though.

I just took a look at the HRRR's forecasted sounding where this evening's supercell in Central TX originated, and it had similar CINN values to what the HRRR's advertising for tomorrow afternoon/evening. 

 

 

[cheese007]

Meanwhile Bryan is under a tornado warning...

[WhirlingWx]

5 minutes ago, Powerball said:

Well technically, it still shows the tiniest bit of mixed level CINH, but I've seen storms break through that easily. So it's understandable why FWD has been so ominous in their discussion, especially with the strong surface convergence from the dry line. The 3km NAM does make a valiant attempt at breaking the cap though.

I just took a look at the HRRR's forecasted sounding where this evening's supercell in Central TX originated, and it had similar CINN values to what the HRRR's advertising for tomorrow afternoon/evening. 

Well, yeah, I do agree. It wouldn't surprise me if we have a Wylie 2016 repeat or a cap bust at this point. Both seem well within the realm of possibility lol. Definitely is a nasty supercell pounding College Station right now, and many HRRR runs earlier showed like nothing firing up there until the storm had formed pretty much, iirc

[WhirlingWx]

3 minutes ago, cheese007 said:

Meanwhile Bryan is under a tornado warning...

Lots of reports of golf ball sized hail there

[Powerball]

6 minutes ago, cheese007 said:

Meanwhile Bryan is under a tornado warning...

 

2 minutes ago, TexMexWx said:

Lots of reports of golf ball sized hail there

Between the tragic incident earlier and now this, it's just not their day.

[Chinook]

for those interested:

DAY 1 CONVECTIVE OUTLOOK    
NWS STORM PREDICTION CENTER NORMAN OK  
0109 AM CDT FRI APR 09 2021  
  
VALID 091200Z - 101200Z  
  
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR PARTS OF  
EXTREME SOUTHEAST ARKANSAS INTO FAR NORTHEAST LOUISIANA INTO CENTRAL  
MISSISSIPPI...  
   
..SUMMARY  
  
A COMPLEX SEVERE-WEATHER SCENARIO IS EXPECTED TO UNFOLD ACROSS THE  
MID-SOUTH INTO THE SOUTHEAST LATE THIS MORNING THROUGH THE AFTERNOON  
AND OVERNIGHT HOURS. SIGNIFICANT SEVERE STORMS, INCLUDING WIDESPREAD  
DAMAGING WINDS, AND AT LEAST A FEW TORNADOES ARE EXPECTED ACROSS  
PORTIONS OF NORTHEAST LOUISIANA INTO MISSISSIPPI, ESPECIALLY  
OVERNIGHT. LARGE HAIL IS ALSO EXPECTED TO BE A CONCERN, MAINLY  
DURING THE DAY ACROSS PARTS OF EASTERN OKLAHOMA INTO THE ARKLATEX  
REGION.  

 

[cheese007]

Forecast for this one has been all over the place. Curious to see what actually pans out+

[janetjanet998]

New day 1

 

ACUS01 KWNS 091252  
SWODY1  
SPC AC 091251  
  
DAY 1 CONVECTIVE OUTLOOK    
NWS STORM PREDICTION CENTER NORMAN OK  
0751 AM CDT FRI APR 09 2021  
  
VALID 091300Z - 101200Z  
  
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF  
SOUTHERN ARKANSAS...NORTHERN LOUISIANA...CENTRAL MISSISSIPPI...AND  
WESTERN ALABAMA...  
  
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SEPARATELY OVER  
PARTS OF SOUTHERN VIRGINIA AND NORTHERN NORTH CAROLINA...  
   
..SUMMARY  
  
MULTIPLE EPISODES OF SEVERE THUNDERSTORMS ARE EXPECTED TODAY FROM  
PARTS OF EASTERN OKLAHOMA AND NORTH-CENTRAL/NORTHEAST TEXAS, ACROSS  
THE MID-SOUTH AND MISSISSIPPI DELTA REGIONS, TO PARTS OF ALABAMA AND  
GEORGIA.  THIS INCLUDES A THREAT FOR A SWATH OF SEVERE WIND FROM   
ARKANSAS ACROSS THE LOWER MISSISSIPPI VALLEY.  LARGE, DAMAGING HAIL  
AND TORNADOES ALSO ARE POSSIBLE.  
   
..SYNOPSIS  
  
IN MID/UPPER LEVELS, A SPLIT-FLOW PATTERN WILL BE MAINTAINED OVER  
THE CENTRAL CONUS, AS ONE CYCLONE EJECTS OUT OF A BROADER-SCALE  
TROUGH CAUSING THE SPLIT, AND ANOTHER TAKES ITS PLACE.  THE LEADING  
CYCLONE -- INITIALLY CENTERED NEAR LSE -- IS FORECAST TO WEAKEN  
GRADUALLY TO AN OPEN-WAVE TROUGH AND HEAD NORTHEASTWARD OVER UPPER  
MI AND LAKE SUPERIOR OVERNIGHT.  UPSTREAM, A STRONG SHORTWAVE TROUGH  
WAS APPARENT IN MOISTURE-CHANNEL IMAGERY FROM EASTERN MT SOUTHWARD  
TO CENTRAL CO.  THIS FEATURE WILL DIG SOUTHEASTWARD ACROSS THE  
CENTRAL PLAINS TODAY AND THIS EVENING, BEFORE PIVOTING EASTWARD  
TONIGHT AS A CLOSED CYCLONE, ACROSS PARTS OF THE LOWER MISSOURI  
VALLEY.  BY 12Z, THE ASSOCIATED 500-MB LOW SHOULD BE LOCATED NEAR  
THE KS/MO LINE SOUTH OF MKC.  
  
FARTHER SOUTH, A BROAD AREA OF STRONG CYCLONIC FLOW ALOFT WILL  
SPREAD EASTWARD ACROSS THE OUTLOOK AREA, WITH EMBEDDED, CLOSELY  
SPACED PERTURBATIONS NOW EVIDENT OVER SOUTHWESTERN/CENTRAL NM AND  
THE TX PANHANDLE.  THESE PERTURBATIONS WILL MOVE ACROSS OK AND SOUTH  
TX TODAY.  TONIGHT, THEY SHOULD REACH PARTS OF TN/MS/LA, LIKELY  
BLENDING INTO CONVECTIVELY GENERATED VORTICITY FIELDS.  THE BROAD  
LEFT-EXIT REGION OF A CYCLONICALLY CURVED, 250-MB SUBTROPICAL JET,  
ALSO EXHIBITING PRONOUNCED DIFLUENCE, ALSO WILL SHIFT EASTWARD OVER  
MUCH OF CENTRAL/NORTH TX AND LA TODAY AND TONIGHT TOWARD THE DELTA  
REGION.  
  
AT THE SURFACE, 11Z ANALYSIS SHOWED AN OCCLUDED, ELONGATED AREA OF  
LOW PRESSURE ACROSS NORTHWESTERN WI TO NORTHERN IA.  AN OCCLUDED  
FRONT WAS DRAWN FROM THE NORTHERN PART ACROSS LAKE SUPERIOR AND  
LOWER MI, WITH WEAKENING/QUASISTATIONARY FRONT ACROSS WESTERN OH,  
EASTERN PORTIONS OF TN/KY, AND NORTHERN AL.  A WARM FRONT EXTENDED  
ACROSS LAKE ERIE, EASTERN WV, AND SOUTHWESTERN/SOUTHERN VA NEAR THE  
NC LINE.  THIS BOUNDARY WILL MOVE SLOWLY NORTHWARD OVER SOUTHERN/  
CENTRAL VA TODAY.  A COLD FRONT EXTENDED ACROSS SOUTHERN IA,  
NORTHWESTERN MO, CENTRAL/WESTERN KS, AND SOUTHEASTERN CO.  A  
MARINE/WARM FRONT EXTENDED FROM A LOW OVER NORTHWEST TX ACROSS  
NORTH-CENTRAL TX, CENTRAL LA, AND SOUTHERN PORTIONS OF MS/AL. THIS  
BOUNDARY WILL MOVE NORTHWARD ACROSS SOUTHERN /EASTERN OK, AR, AND  
CENTRAL MS/AL THROUGH THE DAY.  
  
THE NORTHERN LOW SHOULD CONSOLIDATE IN FORM BUT CONTINUE TO FILL,  
AND MOVE NORTHEASTWARD OVER ON.  MEANWHILE, A SECOND LOW IS EXPECTED  
TO DEVELOP ALONG THE FRONT TODAY NEAR THE DRYLINE INTERSECTION,  
PERHAPS EVOLVING OUT OF THE INITIAL/PREFRONTAL LOW OVER NORTHWEST  
TX.  THE RESULTING LOW SHOULD DEEPEN AS THE NEXT MID/UPPER CYCLONE  
APPROACHES, AND MOVE NORTHEASTWARD TO NEAR STL BY 12Z TOMORROW.  BY  
THAT TIME, THE COLD FRONT SHOULD EXTEND FROM THE LOW SOUTHWARD DOWN  
THE MISSISSIPPI VALLEY TO NEAR BTR, THEN SOUTHWESTWARD ACROSS  
MID/UPPER TX COASTAL WATERS TO DEEP SOUTH TX.  
   
..SOUTHERN PLAINS TO ARKLATEX/MID-SOUTH/DELTA REGIONS  
  
EPISODES OF SEVERE THUNDERSTORMS ARE EXPECTED TODAY INTO THIS  
EVENING BETWEEN EASTERN OK, NORTH TX AND MISSISSIPPI, RESULTING IN  
LARGE (LOCALLY VERY LARGE) HAIL, SEVERE GUSTS AND SEVERAL TORNADOES.  
  
THIS IS A COMPLEX SCENARIO WITH AN ASSORTMENT OF MESOSCALE  
POSSIBILITIES MORE DIVERSE THAN THE NUMBER OF MODELS AND ENSEMBLE  
MEMBERS AVAILABLE.  PROGS SOMEWHAT INCONSISTENTLY DEPICT EARLY  
INITIATION AND EVOLUTION OF THE CONVECTION ACROSS THIS REGION,  
WHETHER NEAR THE FRONT IN OK (A VERY PLAUSIBLE CONSENSUS THEME), ON  
THE DRYLINE (MORE ISOLATED/CONDITIONAL DUE TO STRONG CAPPING), AND  
IN THE WARM SECTOR (HIGHLY VARIABLE).  MULTIPLE EPISODES OF  
STRONG-SEVERE THUNDERSTORMS MAY MOVE OVER ANY GIVEN SPOT THROUGH  
TONIGHT.  THIS OUTLOOK REPRESENTS BOTH:  
1.  THE POTENTIAL FOR OVERLAPPING AREAS OF SEVERE AT DIFFERENT TIMES  
THROUGH THE DAY AND EVENING AS DIFFERENT AREAS OF CONVECTION EVOLVE,  
BUT ALSO:  
2.  A SCENARIO THAT MOST PROGS REASONABLY DO CONVERGE UPON DESPITE  
EARLY DIFFERENCES:  A DOMINANT QLCS/MCS EVOLVING OUT OF CONVECTION  
INITIATING IN OK AND/OR NORTHEAST TX, THEN MOVING EAST-SOUTHEASTWARD  
TO SOUTHEASTWARD OVER THE ARKLATEX TO DELTA REGIONS, ORGANIZING A  
WELL-DEVELOPED COLD POOL, AND PRODUCING A SWATH OF SEVERE WIND.  
  
WHETHER OR NOT THIS EVENT WILL QUALIFY AS A DERECHO IS A SEMANTIC  
EXERCISE, AND LIKELY REGULATED BY MESOSCALE CONVECTIVE/BOUNDARY  
PROCESSES YET TO BECOME APPARENT.  REGARDLESS, HURRICANE-FORCE  
CONVECTIVE GUSTS ARE A THREAT WITH ANY SUCH COMPLEX, IN THE ENHANCED  
AND MODERATE AREAS.  ALSO, BECAUSE BOTH THE PROBABLE QLCS AND ANY  
PRECEDING SUPERCELL(S) WILL ENCOUNTER AN ENVIRONMENT OF MODERATE-  
STRONG BUOYANCY, STEEP MIDLEVEL LAPSE RATES AROUND THE EASTERN RIM  
OF AN EML, ENLARGED LOW-LEVEL HODOGRAPHS, AND FAVORABLE VERTICAL  
SHEAR, TORNADOES ALSO ARE EXPECTED.  PEAK PRECONVECTIVE MLCAPE  
ACROSS THE WARM SECTOR COMMONLY SHOULD BE IN THE 2000-3000 J/KG  
RANGE, AMIDST 40-55-KT EFFECTIVE-SHEAR MAGNITUDES.  AS ONE OR MORE  
MCSS PLOW COLD POOLS INTO THIS ENVIRONMENT, THEY SHOULD BE  
MAINTAINED SOUTHEASTWARD TOWARD SOUTHERN MS/AL TONIGHT, CONTINUING A  
WIND-DAMAGE AND SPORADIC TORNADO THREAT.  
   
..CENTRAL GULF COAST TO AL/GA THIS MORNING/AFTERNOON  
  
WIDELY SCATTERED TO SCATTERED THUNDERSTORMS SHOULD DEVELOP FROM  
MID/LATE MORNING THROUGH THIS AFTERNOON, WITH A THREAT FOR SPORADIC  
LARGE HAIL AND DAMAGING GUSTS.  A CONDITIONAL, LOCALIZED TORNADO  
THREAT ALSO MAY DEVELOP.  FOR NEAR-TERM COVERAGE, PLEASE SEE SPC  
MESOSCALE DISCUSSION 338.  
  
MIDLEVEL LAPSE RATES WILL BE LESS THAN IN THE MORE EML-INFLUENCED  
AIR MASS OF THE PLAINS/DELTA AREA.  STILL, RICH LOW-LEVEL MOISTURE  
SPREADING INLAND, COMBINED WITH AREAS OF DIURNAL HEATING (TEMPERED  
IN PACE BY MID/UPPER CLOUD COVER FROM UPSTREAM CONVECTION), WILL  
WEAKEN MLCINH AND YIELD FAVORABLE SURFACE-BASED BUOYANCY.   
MEANWHILE, LOW-LEVEL SHEAR WILL BE MAXIMIZED NEAR THE MARINE FRONTAL  
ZONE, THOUGH WEAK ABSOLUTE SPEEDS WILL LIMIT HODOGRAPH SIZE  
SOMEWHAT.  MODIFIED 12Z RAOBS AND FORECAST SOUNDINGS FROM MIDDAY  
THROUGH AFTERNOON INDICATE AROUND 1500-2000 J/KG MLCAPE IS POSSIBLE,  
WITH 35-45 KT EFFECTIVE-SHEAR MAGNITUDES. EFFECTIVE SRH WILL RANGE  
FROM AROUND 200-250 J/KG ON THE FRONT TO AROUND 100-1-50 J/KG  
COASTWARD IN THE WARM SECTOR.  WITH UPPER SUPPORT MEAGER IN THIS  
AREA, BUT ALSO MODEST MLCINH, CONVECTIVE COVERAGE ALONG AND SOUTH OF  
THE FRONT IS UNCERTAIN.  

[mob1]

I wonder if that large area of convection offshore will put a bit of a lid on things later. Either way, most mesoscale models show a decent nocturnal tornado threat, though they're likely to be embedded in a line. 

[cheese007]

Morning cloudyness probably keeps storms at bay in DFW

[jojo762]

1 hour ago, cheese007 said:

Morning cloudyness probably keeps storms at bay in DFW

I'm not going to pull the trigger on saying there will for sure be N TX dryline storms today... But SFC temps sure seem to be running at-forecast or even a smidge above 12z HREF mean temps for 15z. The cloud cover doesn't seem to be having much of an impact -- and it looks like the LLVL clouds could clear out a bit more.

[Powerball]

1 hour ago, cheese007 said:

Morning cloudyness probably keeps storms at bay in DFW

A cluster of storms (which will likely become severe for the Arklatex region later) did blow up just to the NE, on the nose of the LLJ.

[cheese007]

Most of DFW back under the sign hail hatch 

[Powerball]

11 minutes ago, cheese007 said:

Most of DFW back under the sign hail hatch 

The cloud deck has finally moved to the east, so now it's just waiting to see what happens as temps surge.

[Santa Clause]

Looks like active severe evening ahead, not big tornado threat but hail and wind threats look high end.

[Powerball]

Dry line is already entering the western half of DFW.

We'll see if it does slows down, or if it moves through and sets up shop just east of the Metroplex like the GFS has been showing. 

[Powerball]

18z 3km NAM does pop one lone cell over parts of Dallas County later today.

 

[Powerball]

18z sounding from FWD.

They're going to do another sounding at 21z

 

[cheese007]

What does the sounding indicate re: capping? 

[WhirlingWx]

Also a 10% hatched TOR added for parts of MS/AL in the updated SPC outlook

[cheese007]

Mesoscale Discussion 0345
   NWS Storm Prediction Center Norman OK
   0314 PM CDT Fri Apr 09 2021

   Areas affected...central and eastern Oklahoma/western Arkansas/North
   Texas

   Concerning...Severe potential...Watch likely 

   Valid 092014Z - 092115Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Eventual storm development expected across this region
   will likely require WW issuance late this afternoon.

   DISCUSSION...Midday RAOB from KOKC revealed stout capping just above
   850 mb, supporting persistent low cloud cover across central
   Oklahoma.  While the low clouds persist, a slight change in
   character toward more cumuliform elements is occurring --
   particularly over portions of western/southwestern Oklahoma.

   As a cold front continues to advance southeastward across this area,
   ahead of a mid-level vort max shifting southeastward out of the High
   Plains, ascent will continue to allow the cap to weaken -- resulting
   in eventual storm development.  Intensity of the initial cells over
   far western Oklahoma will likely remain limited, but with 2000 J/kg
   mixed-layer CAPE now indicated within the very steep lapse rates
   within the elevated mixed layer above the cap, robust storms will
   likely evolve.

   Storm intensity will be aided by a belt of stronger mid-level flow
   expected to spread across the region south/southeast of the upper
   system.  Along with potential for locally damaging wind gusts, very
   large hail will also be possible with the strongest/rotating storms.

   ..Goss/Thompson.. 04/09/2021

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

   ATTN...WFO...LZK...SGF...SHV...TSA...ICT...FWD...OUN...

   LAT...LON   35389873 36389838 37019704 37019488 36089383 34429374
               33199511 33479796 34439850 35389873 

[Powerball]

33 minutes ago, cheese007 said:

What does the sounding indicate re: capping? 

Yes. A very strong one at that.

[WhirlingWx]

NOW the HRRR wants to fire storms off in/near the Metroplex, so I guess we should watch for that. I remember hearing yesterday that the monster supercell that ended up going through Bryan/College Station didn't really start getting picked up by the models until only a couple hours before, so I'm wondering if the same thing happens again.

[Powerball]

The area circled below (the line of agitated CU ) is going to be the place to watch for any storms that first initiate along the dry line...

[cheese007]

4 minutes ago, TexMexWx said:

NOW the HRRR wants to fire storms off in/near the Metroplex, so I guess we should watch for that. I remember hearing yesterday that the monster supercell that ended up going through Bryan/College Station didn't really start getting picked up by the models until only a couple hours before, so I'm wondering if the same thing happens again.

What timeframe would this be?