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Severe Weather October 10th-12th 2021


BrandonC_TX
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Mesoscale Discussion 1838
   NWS Storm Prediction Center Norman OK
   0229 PM CDT Tue Oct 12 2021

   Areas affected...Portions of southwest Kansas into northwest
   Oklahoma and far northeast Texas Panhandle

   Concerning...Outlook upgrade 

   Valid 121929Z - 122000Z

   SUMMARY...An upgrade to Category 4/Moderate risk will be introduced
   in the 20Z Day 1 Convective Outlook to reflect a greater risk for
   strong tornadoes.

   DISCUSSION...The latest high-resolution/convection allowing model
   guidance consensus has been generally trending upward in the
   intensity and longevity of deep, moist convection over portions of
   the southern High Plains. Potential exists for multiple
   discrete/semi-discrete supercells to develop ahead of a Pacific
   front late this afternoon/evening. These storms are expected to
   progress eastward into an ambient environment characterized by very
   strong low-level shear, resulting in large, curved hodographs and
   effective SRH values exceeding 400 m2/s2, especially across portions
   of southwest KS/northwest OK/far northeast TX Panhandle. Here,
   potential exists for at least a few intense, cyclical tornadic
   supercells to develop, and a long-tracked tornado or two cannot be
   ruled out. As such, portions of the central Plains will be upgraded
   to Category 4/Moderate risk in the upcoming 20Z Day 1 Convective
   Outlook.

   ..Squitieri/Grams.. 10/12/2021

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

   ATTN...WFO...OUN...DDC...AMA...
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Seems to have a bit more potential than Sunday night. Still think the storm mode may get messy, but even with those concerns, I’d expect at least a few noteworthy tornadoes after dark. 

Moisture return has been steadily occurring with mid/upper 50s dew points already into the OK/TX panhandles. Placement and timing remind me a bit of 11/16/15. Can’t overlook the intensity of the low level jet tonight. 

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ay 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0246 PM CDT Tue Oct 12 2021

   Valid 122000Z - 131200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS NORTHEAST TEXAS
   PANHANDLE...FAR NORTHWEST OKLAHOMA AND THE EASTERN OKLAHOMA
   PANHANDLE...AND SOUTHWEST KANSAS...

   ...SUMMARY...
   Scattered to numerous severe thunderstorms are expected to begin
   late this afternoon, peak this evening, and continue into tonight
   across parts of the central and southern Great Plains. Several
   tornadoes, some of which may be strong, along with destructive hail
   and wind are possible.

   ...Discussion...
   Forecast thinking from the previous outlook is on track regarding
   the overall scenario, and confidence has increased for several
   long-track supercells capable of a couple strong and perhaps an
   intense tornado this evening/tonight.  As a result, this outlook
   update is introducing a 15-percent tornado probability and an
   associated Moderate Risk for portions of the northeast TX Panhandle
   and far northwest OK, and areas to the north-northwest into
   southwest KS.  Storm-simulated model guidance continues to show
   quasi-discrete convective mode with storms that develop initially
   near the dryline and move east into richer low-level moisture and
   high SRH this evening.  Forecast soundings strongly favor discrete
   supercells and long-track, fast-moving supercells appear likely to
   traverse across the Moderate Risk.  Linear forcing and slightly
   drier/less unstable air will probably favor upscale growth into a
   band of storms in northwest KS and northeast CO, limiting the
   tornado risk.  Have adjusted the southeastern bound of the
   10-percent tornado area to be farther northwest and mainly be
   confined to western and northwestern OK.

   ..Smith.. 10/12/2021
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Mesoscale Discussion 1840
   NWS Storm Prediction Center Norman OK
   0314 PM CDT Tue Oct 12 2021

   Areas affected...eastern Texas Panhandle into far western Oklahoma

   Concerning...Severe potential...Tornado Watch likely 

   Valid 122014Z - 122245Z

   Probability of Watch Issuance...80 percent

   SUMMARY...A few supercells may develop through evening, from the
   eastern Texas Panhandle into far western Oklahoma. Tornadoes,
   perhaps strong, and very large hail will be possible.

   DISCUSSION...Surface analysis shows a front extending from northern
   TX into southwest OK which is becoming more diffuse with heating.
   This boundary separates a cooler/capped air mass over much of OK
   from a destabilizing air mass over northwest TX and into the TX
   Panhandle. Meanwhile, a dryline stretches from north to south across
   the TX Panhandle and South Plains.

   Visible satellite shows stable billow clouds north of the boundary,
   but these are gradually eroding from south to north as temperatures
   warm into the lower 80s F. A growing CU field is also evident over
   northwest TX, where MLCAPE is in the 1500-2000 J/kg range. Backed
   surface winds on the cool side of the boundary are contributing to
   100-150 m2/s2 0-1 km SRH per FDR VWP.

   Although convergence is currently weak, it is expected to increase
   around 00Z and into the evening as the dryline eventually pushes
   east with the upper trough. A few more hours of air mass
   modification will occur, including moistening. In addition, the
   low-level jet will continue to increase to over 50 kt, further
   enhancing shear.

   Assuming a cell or two can form, they should quickly acquire
   rotation, with tornadoes and hail likely. Any lone cells that can
   maintain access to the warm side of the boundary will have the
   potential for a strong tornado.

   ..Jewell/Grams.. 10/12/2021

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

   ATTN...WFO...OUN...LUB...AMA...
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Mesoscale Discussion 1839
   NWS Storm Prediction Center Norman OK
   0308 PM CDT Tue Oct 12 2021

   Areas affected...portions of the central High Plains

   Concerning...Severe potential...Tornado Watch likely 

   Valid 122008Z - 122145Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Strong ascent ahead of an advancing upper low will support
   rapid destabilization and storm development late this afternoon and
   into this evening. Supercells with all hazards including tornadoes
   are possible. A tornado watch is likely late this afternoon.

   DISCUSSION...As of 1955 UTC, a well-defined upper low was located on
   WV imagery near the Four Corners region moving east. To the south of
   the low, an 80-100 kt mid-level speed max was observed rounding the
   base and ejecting into southern CO. To the north and east of the
   low, strong ascent (90-120 DM 12 hr H5 height falls) is supporting
   widespread precipitation across the central and northern Rockies. In
   response to the powerful dynamics aloft, already strong low-level
   pressure gradients are forecast to strengthen rapidly allowing a
   relatively warm/moist surface airmass to advect ahead of the
   dryline/surface trough supporting destabilization late this
   afternoon.

   Mid and lower 50s F surface dewpoints at the nose of deeper surface
   moisture, have already been observed across southwestern KS as far
   north as TQK. Continued warm/moist advection beneath the cold-core
   of the upper low will support rapid destabilization (MLCAPE values
   of 500-1250 J/kg) by 23-01z given steep mid-level lapse rates near
   8.5 C/km. Late afternoon/early evening model soundings also show
   very strong and veering wind profiles developing beneath the
   mid-level jet, with largely boundary-normal effective shear values
   of 60-70 kt supportive of discrete supercells. Low-level shear is
   also likely to be strong beneath a 50-60 kt low-level jet. Model
   soundings show large looping hodographs (ESRH 300-400 M2/s2)
   favorable for strong low-level mesocyclone development. Given the
   overall parameter space and potential for strong supercells, a risk
   for tornadoes (some significant), large hail, and damaging winds
   appears likely to develop by 22-00z. 

   Latest observational trends suggest hi-res guidance remains too cool
   and dry across much of the High Plains where rapid
   warming/moistening is occurring. This lends high confidence in
   eventual destabilization of the airmass as the upper low approaches
   late this afternoon. Deep convection should gradually evolve out of
   the initial updrafts ongoing in the elevated cumulus field across
   eastern CO. Weaker buoyancy and storm motions more parallel to the
   northern sections of the dryline suggest initial storm mode may
   remain linear, though a gradual transition to more isolated
   convection is expected with southern extent. Fast-moving long-track
   supercells capable of all hazards should evolve rapidly and
   intensify as they move through the narrow, but unstable and strongly
   sheared warm sector after dark. Given the potential for significant
   severe weather, a tornado watch will likely be needed late this
   afternoon.

   ..Lyons/Grams.. 10/12/2021

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

   ATTN...WFO...LBF...DDC...GLD...AMA...PUB...BOU...
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Great AFD out from NWS Amarillo…

Area Forecast Discussion
National Weather Service Amarillo TX
314 PM CDT Tue Oct 12 2021

.MESOSCALE UPDATE...
...Severe weather likely tonight...

* Synoptic Overview: The much-ballyhooed strong western CONUS
  upper low is finally knocking at our doorstep. Strong upper
  level forcing will overspread an increasingly juicy surface with
  the best dynamics set to impinge on the area beginning around
  sunset. Trends in the synoptic scale have been a little slower
  and a little further west with the best sfc moisture, meaning a
  few more folks in the Panhandles could get in the action. The
  rest of this discussion predominately applies to the eastern
  half of the combined Panhandles.

* Mesoscale: So much to unpack in the mesoscale, we`ll break it
  down into PROS and CONS for a significant severe event...

  PROS:
  - Very strong vertical wind shear with bulk and effective shear
    values 60-70 kts among a near-perfectly turning profile. In
    addition to promoting a supercell storm mode with any discrete
    convection, shear-induced buoyancy will increase the strength
    of updrafts.
  - Some of the best shear is in the low levels, with 0-1 SRH values
    exceeding 400 m2/s2.
  - Surface moisture has been underestimated in the models so far
    today, and even so, model forecasts for MLCAPE this evening
    are in excess of 2500 J/kg.
  - Strong surface moisture advection will allow sfc theta-e values
    to INCREASE after sunset in spite of falling temperatures.
  - Low level forcing for ascent is pretty weak until a cold
    front sweeps through very late tonight, not clearing the
    eastern Panhandles until nearly 3 AM. This will likely help
    foster at least a quasi-discrete storm mode. As we like to say
    in the Panhandles, when in doubt, discrete wins out.
  - For any rooted storms, LCLs are basically scraping the
    ground. That`s not common around here.
  - There are more PROS but we`ll keep it to these for now.

  CONS:
  - A strong (though not deep) isothermal layer bordering on an
    inversion is forecast by all models to develop after sunset
    around h8. Resulting low level lapse rates are expectedly
    putrid in this narrow layer and will almost certainly hamper
    weaker convection and even probably hamper ongoing supercells.
  - That`s honestly about it for major cons, but it`s a pretty big
    one as it could keep convection slightly elevated (doesn`t
    limit the hail threat but would limit tornado threat).

* Threats: The most likely threats will be the potential for very
  large hail and potentially destructive wind gusts but the most
  concerning threat will be the possibility for strong and
  potentially long-tracked tornadoes. Strong and violent tornadoes
  tend to happen in the presence of MLCAPE, MLLCL, and shear
  numbers similar to what was discussed above.

* Timing & Location: The worst of it should be 6 PM - 2 AM tonight
  east of a roughly Guymon to Panhandle to Claude line. Storms
  will be moving at very high rates of speeds, likely over 50 MPH
  and in the dark so that will increase the danger.

* Summary: This event has the potential to be a top 3 Panhandles
  severe event in 2021.

Simpson

 

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URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 522
   NWS Storm Prediction Center Norman OK
   345 PM CDT Tue Oct 12 2021

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Far Eastern Colorado
     Western Kansas
     Far Southwest Nebraska

   * Effective this Tuesday afternoon and evening from 345 PM until
     1100 PM CDT.

   * Primary threats include...
     Several tornadoes likely with a couple intense tornadoes
       possible
     Scattered large hail and isolated very large hail events to 3
       inches in diameter likely
     Scattered damaging winds likely with isolated significant gusts
       to 80 mph possible

   SUMMARY...Several supercells are expected to develop near the
   Colorado/Kansas border, before then moving east-northeast this
   evening. All severe hazards are likely, some of which may be
   significant. Greatest tornado potential appears to be across
   southwest Kansas.

   The tornado watch area is approximately along and 60 statute miles
   east and west of a line from 30 miles west of Liberal KS to 40 miles
   north of Imperial NE. For a complete depiction of the watch see the
   associated watch outline update (WOUS64 KWNS WOU2).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A Tornado Watch means conditions are favorable for
   tornadoes and severe thunderstorms in and close to the watch
   area. Persons in these areas should be on the lookout for
   threatening weather conditions and listen for later statements
   and possible warnings.
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URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 523
   NWS Storm Prediction Center Norman OK
   530 PM CDT Tue Oct 12 2021

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Western Oklahoma
     Northwest Texas

   * Effective this Tuesday afternoon and evening from 530 PM until
     1100 PM CDT.

   * Primary threats include...
     A few tornadoes likely with a couple intense tornadoes possible
     Scattered large hail and isolated very large hail events to 3
       inches in diameter likely
     Scattered damaging winds and isolated significant gusts to 80
       mph possible

   SUMMARY...At least isolated intense supercells are expected to
   develop this evening across western Oklahoma and the eastern Texas
   Panhandle/western North Texas near a northward-shifting warm front
   and a dryline. The environment will be very supportive of intense
   supercells capable of large hail and a tornado risk, potentially
   including a couple of strong tornadoes given seasonally rare
   low-level moisture and strengthening low-level shear/helicity.

   The tornado watch area is approximately along and 75 statute miles
   east and west of a line from 55 miles east northeast of Guymon OK to
   50 miles southwest of Wichita Falls TX. For a complete depiction of
   the watch see the associated watch outline update (WOUS64 KWNS
   WOU3).
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Absolutely wild day for October.  This looks like it could be one of the more serious situations this year.  Ample CAPE and some really noteworthy shear -- these would be great parameters in early April to say nothing of mid-autumn.

Definitely going to be a long night across the plains.

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Surprised no reports/TORR-type warnings with the way that couplet looked earlier, has to be a horde of chasers on it so if anything happened it would have been seen.

*TOR warning dropped, there's another one in far NE CO but the storm is linear.

Going to go right over Clinton, where I sat for a few hours on the afternoon of 5/27 (a miserable bust).

*Edit: New TOR warning near Sharon Springs, KS. Also linear but looks like it has potential.

*Edit 2: Ninja'd by @OhioWX

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