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Severe Weather May 17th 2021

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May 17, 2021 0600 UTC Day 1 Convective Outlook








   Severe thunderstorms are forecast across portions of the southern
   Plains later this afternoon and overnight. Very large hail and a few
   tornadoes will be concentrated across northwest Texas.

   ...Southern Plains...

   Well-defined upper low is currently located over the lower CO River
   Valley. This feature is forecast to eject into the southern Rockies
   by 18/00z as 50kt 500mb flow translates across the northern Baja
   Peninsula into portions of northwestern TX by late evening. In
   response, lee surface low should hold across southeastern NM which
   will ensure moist southeasterly low-level flow is maintained across
   the TX South Plains into far northeastern NM. Additionally, a weak
   MCS has evolved over northwest TX early this morning with
   considerable amount of trailing precipitation extending across the
   TX Panhandle into western KS. The leading edge of this complex
   should propagate slowly southeast through daybreak, likely spreading
   into portions of central TX by sunrise. This rain-cooled air mass
   should contribute to easterly low-level component across the TX
   South Plains and a remnant convective boundary may be evident in its
   wake over northwestern TX. If so, this boundary should serve as a
   primary corridor for focused hail-producing supercells.

   Latest thinking is intense surface heating will be noted across far
   west TX into southeast NM such that convective temperatures will be
   breached by 21z. Forecast sounding at MAF by 22z exhibits a 90F
   surface temperature with negligible CINH. It appears thunderstorms
   should develop along the dryline near the NM border, south across
   west TX, then spread/develop northeast along a potential rain-cooled
   boundary. Very steep lapse rates through a deep layer, extreme
   MLCAPE, and ample shear for slow-moving supercells all favor very
   large hail. As mid-level flow increases during the evening, there is
   reasonable confidence that numerous hail-producing supercells could
   emerge into an MCS that will propagate toward north-central TX.
   Prior to this, some tornado threat will be noted both early in the
   convective cycle, and along the aforementioned rain-cooled boundary
   where shear will be maximized.
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Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0717 AM CDT Mon May 17 2021

   Valid 171300Z - 181200Z


   Severe thunderstorms are forecast across portions of the southern
   Plains later this afternoon and overnight. Very large hail and a few
   tornadoes will be concentrated across northwest Texas.

   ...West TX/Western OK...
   An active period of severe weather is forecast for later today
   across portions of west TX and southwest OK.  The latest surface
   analysis shows an outflow boundary from overnight thunderstorms
   extending from southeast NM to near Midland, TX.  This boundary is
   not expected to move much farther south before weakening and
   retreating northward by late morning.  This will allow ample
   low-level moisture to return northward into parts of west/northwest
   TX by mid afternoon.  Strong heating will eliminate the cap along
   the dryline, resulting in rapid thunderstorm development this
   afternoon from eastern NM into west TX near Lubbock.  These storms
   will move into an environment of very high instability (MLCAPE over
   3000 J/kg), steep mid level lapse rates exceeding 8.0 C/km, and
   effective shear values of 40-50 knots.  Intense supercell structures
   are expected, capable of very large hail.  Low-level shear is not
   forecast to be particularly strong, but given the unusually
   favorable thermodynamic environment, a few tornadoes may result this
   afternoon and evening along the western edge of greatest
   boundary-layer moisture/CAPE - therefore have added a 10% tornado
   area.  Storms will expand in coverage through the evening, spreading
   across the TX Panhandle and western OK with a continued risk of
   large hail and damaging wind gusts.

   ...Southwest TX...
   Strong instability will also be present along the dryline extending
   southward toward the Rio Grande.  While model guidance is less
   confident in coverage/placement/timing of storms, there will be a
   conditional risk of supercells capable of very large hail and
   damaging winds.  Have expanded the ENH risk slightly farther east to
   account for recent HRRR runs that depict greater coverage of
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Mesoscale Discussion 0650
   NWS Storm Prediction Center Norman OK
   0139 PM CDT Mon May 17 2021

   Areas affected...Northeast NM...Southeast CO...Western OK
   Panhandle...Northwest TX Panhandle

   Concerning...Severe potential...Watch likely 

   Valid 171839Z - 172045Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Thunderstorm coverage is expected to increase throughout
   the afternoon across northeast NM and southeast CO. Some severe
   storm are probable, with large hail and damaging wind gusts as the
   primary threats.

   DISCUSSION...Recent surface analysis reveals a relatively complex
   pattern across the central and southern High Plains. Of interest for
   northeast NM and southeast CO is the weakening cold front extending
   from south-central CO southeastward through the TX Panhandle.
   Temperatures are relatively cool and dewpoints modest on either side
   of this boundary, but persistent low-level convergence is leading to
   some deeper cu, particularly in south-central CO. Additionally, area
   south of front across northeast NM to warm and destabilize. Recent
   TCC observation reported a temperature of 70 and a dewpoint of 53.
   Mesoanalysis estimates convective inhibition has eroded across this
   area, which is matched by modified forecast soundings. An increase
   in cumulus coverage has been noted over the past hour, with deeper
   cumulus recently observed closer to the high terrain where
   orographic effects and strengthening large-scale lift are promoting
   deeper ascent.

   Expectation is for continued destabilization coupled with
   strengthening ascent to result in eventual convective initiation
   away from the higher terrain. Convergence along the front will also
   likely result in storm development. A predominantly northeastward
   storm motion is expected, eventually taking the storms in the TX
   Panhandle. Some in situ development along the cold front is also
   possible. Overall vertical shear will remain modest, but still
   strong enough for organized storm structures, particularly given the
   steep mid-level lapse rates. Hail will be the primary severe threat,
   with some damaging wind gusts possible as well. Low-level wind
   profiles will be weak, but veering with height could still support a
   brief tornado or two.

   ..Mosier/Guyer.. 05/17/2021

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

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Mesoscale Discussion 0651
   NWS Storm Prediction Center Norman OK
   0211 PM CDT Mon May 17 2021

   Areas affected...Southeast/East-Central NM...TX South Plains...TX
   Permian Basin

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

   Valid 171911Z - 172115Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Thunderstorm initiation is anticipated with the next hour
   or two across far southeast NM/far southwestern TX Panhandle/western
   Permian Basin. Supercells capable of all severe hazards are possible
   and a Tornado Watch will be issued to cover the severe threat.

   DISCUSSION...Recent surface analysis places a low over about 45
   miles northwest of ROW. A dryline extends southeastward from this
   low through much of southeast NM before arcing back more southward
   across the TX Trans Pecos. Northward returning low-level moisture
   also results in an effective warm front, which extends from the
   surface low northeastward through De Baca County NM and then back
   southeastward through the TX South Plains. Deepen cumulus has been
   observed within the area between these two boundaries, with a few
   orphan anvils recently noted. 

   Expectation is for eventual convective initiation along the dryline
   as it continues eastward/northeastward. Air mass across the region
   has become moderately unstable, with mesoanalysis estimating 1000 to
   1500 J/kg of MLCAPE is in place with little to no convective
   inhibition. Effective deep layer shear is currently around 30 to 40
   kt, with a gradual increase anticipated over the next few hours as
   the shortwave trough moves through. 

   Overall environment supports initial supercells capable of all
   severe hazards, including very large hail (i.e. greater than 2" in
   diameter) and tornadoes. Some upscale growth is anticipated over
   time, which will result in a transition to strong wind gusts as the
   primary severe threat.

   ..Mosier/Guyer.. 05/17/2021

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

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And just look at how wrapped up that hook echo is.

Looks great on radar, but I sure wouldn’t want to be in the path.



EDIT: it now has a PDS tornado warning on it. Large and extremely dangerous tornado in progress, fortunately this is happening in an area with very low population.

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1 minute ago, TexMexWx said:

Also a tornado-warned storm approaching the Lubbock metro from the west.

I'm watching a stream of a storm chaser on that who has stated that a tornado is indeed on the ground and that he made a full intercept with that cell.

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6 minutes ago, CryHavoc said:

I'm watching a stream of a storm chaser on that who has stated that a tornado is indeed on the ground and that he made a full intercept with that cell.

Needs to be reported to NWS immediately if true.  Current warning says radar indicated.

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