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3/18/TX/LA Severe prospects


Indystorm

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It must be March Madness.  Surprised no one is following what might occur later today from DFW eastward.  Although SPC has conditional caveats there is a slight risk with 5% tor and 15% hatched hail possible eastward from the metro.  Refinements expected by 2000Z update.  Elevated t storms now ongoing in sw OK.

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  Mesoscale Discussion 0133
   NWS Storm Prediction Center Norman OK
   0233 PM CDT Sun Mar 18 2018

   Areas affected...Western north Texas and far southwest/south-central
   Oklahoma

   Concerning...Severe potential...Watch possible 

   Valid 181933Z - 182130Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Isolated thunderstorms may develop across portions of
   western north Texas and far southwest Oklahoma over the next several
   hours. Any thunderstorm that develops should move generally east
   toward the I-35 corridor, posing a risk for large hail and strong
   winds, although a tornado or two will be possible with any sustained
   thunderstorms.

   DISCUSSION...Visible satellite imagery indicates thinning/clearing
   clouds across western north Texas in the wake of morning
   clouds/precipitation. Strong heating in the wake of the clouds has
   allowed for cumulus development on the dryline near its intersection
   with a weak surface front that extends northeast into southern
   Oklahoma. Additional cumulus development is noted along the
   aforementioned surface front as far northeast as far southwest
   Oklahoma.

   Current indications are that afternoon insolation will combine with
   continued low-level moistening to allow for isolated thunderstorms
   to develop out of these increasingly agitated cumulus fields over
   the next several hours. Steep/steepening midlevel-lapse rates will
   support most-unstable CAPE ranging from 1000-2500 J/kg at the same
   time a strong mid-level jet moves across the region supporting
   effective-layer shear on the order of 50-70 knots. This environment
   will support a supercell threat with any thunderstorm that can
   develop and become sustained. Large hail and strong winds will be
   the primary threats initially. The tornado threat will slowly
   increase this evening as the low-level jet increases and storms move
   east into the better low-level moisture.

   ..Marsh/Guyer.. 03/18/2018
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I'm wondering if there might be the potential for storm formation to the northwest of the current cells located around Lake Whitney.  Nothing seems to indicate so at this time, but the ingredients (EHI, supercell composites, along with somewhat higher helicity, though helicity is still marginal) are in place just behind where the current storms are.

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9 minutes ago, Chicago Storm said:

SPC with another terrible performance in progress.

12z guidance suggested a threat extending much further south. They did expand the risk earlier, but not nearly enough. And oh look, earlier guidance was right and they’re out of the loop once again.

Agreed.  Plus there is even a severe thunderstorm ongoing even south of the general thunder area in South Texas.

I'm still not ruling out the northern part of the slight risk until I see evidence that there won't be storm initiation, though.  HRRR doesn't say storms will initiate, but you never know with that dryline and what appears to be a triple point west of DFW, plus the main area of low pressure is still off to the (north)west.

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11 minutes ago, Indystorm said:

But as Chicago Storm points out our present storms are a far cry from the Red River/TX/OK border.

Exactly.  Bad call on SPC's part, but sometimes the cap breaks where you don't expect it to.  It just doesn't want to break over the outlined area I guess (that's good news for DFW though).

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SEVERE THUNDERSTORM WARNING  
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX  
629 PM CDT SUN MAR 18 2018  
  
THE NATIONAL WEATHER SERVICE IN LEAGUE CITY HAS ISSUED A  
  
* SEVERE THUNDERSTORM WARNING FOR...  
  SOUTHWESTERN TRINITY COUNTY IN SOUTHEASTERN TEXAS...  
  NORTHWESTERN SAN JACINTO COUNTY IN SOUTHEASTERN TEXAS...  
  SOUTH CENTRAL HOUSTON COUNTY IN SOUTHEASTERN TEXAS...  
  SOUTHEASTERN MADISON COUNTY IN SOUTHEASTERN TEXAS...  
  WEST CENTRAL POLK COUNTY IN SOUTHEASTERN TEXAS...  
  WALKER COUNTY IN SOUTHEASTERN TEXAS...  
  
* UNTIL 715 PM CDT.  
  
* AT 626 PM CDT, A SEVERE THUNDERSTORM WAS LOCATED NEAR HUNTSVILLE,   
  MOVING EAST AT 45 MPH. THESE STORMS HAVE HAD A HISTORY OF   
  PRODUCING BASEBALL TO SOFTBALL SIZE HAIL. RADAR INDICATES THAT   
  STRONG INFLOW INTO THE STORM COULD EASILY EXCEED 70 MPH IN GUST.   
  PERSONS IN AND AROUND THE SAM HOUSTON NATIONAL FOREST AND   
  INTERSTATE 45 CORRIDOR THROUGH WALKER COUNTY NEED TO TAKE   
  IMMEDIATE SHELTER!  
  
  THIS IS A VERY DANGEROUS STORM.  
  
  HAZARD...80 MPH WIND GUSTS AND BASEBALL SIZE HAIL.  
  
  SOURCE...RADAR INDICATED.  
  
  IMPACT...FLYING DEBRIS WILL BE DANGEROUS TO THOSE CAUGHT WITHOUT   
           SHELTER. MOBILE HOMES WILL BE HEAVILY DAMAGED. EXPECT   
           CONSIDERABLE DAMAGE TO ROOFS, WINDOWS, AND VEHICLES.   
           EXTENSIVE TREE DAMAGE AND POWER OUTAGES ARE LIKELY.  
  
* LOCATIONS IMPACTED INCLUDE...  
  HUNTSVILLE, TRINITY, POINT BLANK, RIVERSIDE, SEBASTOPOL, CRABBS  
  PRAIRIE AND OAKHURST.  

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