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January 10-11 Severe Weather Threat


DanLarsen34
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So as far as NE Texas into Dallas this was an absolute bust. Schools cancelled events Friday because the forecast and most the region had run-of-the-mill spring-like storms. 
 
My question for those much smarter than me: Why? Parameters were ideal. 


Storm mode was terrible. Throw in VBV and essentially too much forcing and you have a mess of storms and a huge line.

That line of storms is massive right now, but hard to get anything other than spin ups along it.
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I don't think veer-back was really an issue actually. Low level wind shear was ridiculous with huge to borderline comical hodographs (see special 21Z CLL sounding). I think the real failure mode was due to the boundary layer temperature profile. Using 00Z and 06Z LCH as a comparison, when the low level jet kicked to next level, it advected warmer temperatures into the 850-700 mb layer which killed low level instability. Between the 00Z and 06Z soundings at LCH, 3CAPE dropped from 126 to 28 J/kg despite nearly identical surface temperature and dewpoint at both times. I think this make it hard for storms to root at the surface level. A couple more degrees of surface heating may have made a big difference. Areas I drove yesterday were all in the 70-72ºF range and socked in clouds.

J3Lmctm.png

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4 minutes ago, Chinook said:

Radar-confirmed tornado at Carrollton/Reform Alabama (probably what's in the last post?)

Yeah that's what I was referring to. Looks like there is a small area of buildings right off the highway where it touched down (plus copious trees), so there should be quite a few damage indicators. 

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MESOSCALE DISCUSSION 0038  
NWS STORM PREDICTION CENTER NORMAN OK  
1150 AM CST SAT JAN 11 2020  
  
AREAS AFFECTED...PORTIONS OF AL  
  
CONCERNING...TORNADO WATCH 12...13...  
  
VALID 111750Z - 111915Z  
  
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 12, 13 CONTINUES.  
  
SUMMARY...GREATEST POTENTIAL FOR TORNADOES AND DAMAGING  
STRAIGHT-LINE WINDS WILL SHIFT FROM WESTERN INTO PARTS OF NORTHERN  
AND CENTRAL AL OVER THE NEXT COUPLE OF HOURS. SOME OF THE TORNADOES  
COULD BE STRONG.  
  
DISCUSSION...A SQUALL LINE HAS RECENTLY CONSOLIDATED AND  
STRENGTHENED OVER WESTERN AL AS LARGE-SCALE ASCENT ASSOCIATED WITH A  
NORTHEASTWARD-EJECTING UPPER TROUGH OVERSPREADS THE CENTRAL GULF  
COAST STATES. A COUPLE OF EMBEDDED LOW-LEVEL CIRCULATIONS HAVE ALSO  
RECENTLY OCCURRED WITHIN THE LINE. ONE SUCH ROTATIONAL VELOCITY  
SIGNATURE EARLIER PRODUCED A TDS OVER PICKENS COUNTY AL. VERY STRONG  
LOW-LEVEL SHEAR EXISTS DOWNSTREAM OF THE CONVECTIVE LINE ACROSS  
NORTHERN/CENTRAL AL, WITH THE VWP FROM KBMX SHOWING SOUTHERLY  
LOW-LEVEL WINDS QUICKLY STRENGTHENING TO OVER 60 KT IN THE 0-1 KM  
LAYER. SOME CURVATURE OF THE LOW-LEVEL HODOGRAPH IS SUPPORTING  
EFFECTIVE SRH AROUND 450-650+ M2/S2 GIVEN THE NORTHEASTWARD MOTION  
OF INDIVIDUAL ELEMENTS EMBEDDED WITHIN THE LINE. COUPLED WITH A  
GRADUALLY DESTABILIZING AIRMASS DOWNSTREAM INTO NORTHERN/CENTRAL AL,  
THIS VERY FAVORABLE KINEMATIC ENVIRONMENT WILL BE CONDUCIVE TO  
CONTINUED DAMAGING STRAIGHT-LINE WINDS AND TORNADIC CIRCULATIONS  
EMBEDDED WITHIN THE LINE. EVEN WITH A MAINLY LINEAR MODE, THERE  
REMAINS SOME POTENTIAL FOR A STRONG TORNADO OR TWO IN THE SHORT TERM  
MAINLY ACROSS PARTS OF WEST-CENTRAL AL GIVEN THE EXCEPTIONALLY  
STRONG LOW-LEVEL SHEAR.  
  

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17 minutes ago, Calderon said:

That's a false picture he's showing, and should know better. Those trees are clearly in spring leaf out.

That's pretty funny.

By the way, it looks like Huntsville AL radar is not working, but there's a possible tornado southeast of Huntsville.

Edit: HTX has radar data now.

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On 1/11/2020 at 7:27 AM, canderson said:

So as far as NE Texas into Dallas this was an absolute bust. Schools cancelled events Friday because the forecast and most the region had run-of-the-mill spring-like storms. 
 

My question for those much smarter than me: Why? Parameters were ideal. 

For the Dallas area I think the lack of tornadoes was due to the cap breaking too late, mainly due to overcast conditions and from what I remember the 700 mb trough arrived a little later than modeled which also would've helped break the cap sooner.  Looking at the 18Z FWD sounding the low level wind profile was almost linear in the lowest km which doesn't work so well for spin ups.  There was also some subtle VBV above 1km but I don't think that alone was the reason we didn't see much, but moreso the combination of the two. 

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