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April 1-3 Severe Threat

1900hurricane

By 1900hurricane,
in Central/Western States

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CGChaser

CGChaser

Posted
Posted
13 minutes ago, Chinook said:

I am wondering if the most impacted area will be on the north side of the moderate outlook, away from Houston and Dallas metro areas. Some of the convection-allowing models show quite a bit of activity in this area which could be supercells, or a rather complex scenario of and MCS with embedded tornadoes.

SHGGO1y.png

Emulates my thinking as well, at least per models at this time. Environment may be extremely volatile in the moderate risk area, but if no storms tap the environment, most impacted may likely be farther north along warm front. 

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bjc0303

bjc0303

Posted
Posted
4 hours ago, jojo762 said:

Not related to today or sunday, but Tuesday is looking potentially interesting **IF** we can get DPs at or near 60 and storms to fire along the DL. Lots of caveats, but wind fields look pretty solid.

if half the troughs that traverse this area had this or that, they'd be interesting. And yet it's still wishcasting. I'm as hopeful as the next guy but I'm not seeing it yet 

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CGChaser

CGChaser

Posted
Posted
Just now, bjc0303 said:

if half the troughs that traverse this area had this or that, they'd be interesting. And yet it's still wishcasting. I'm as hopeful as the next guy but I'm not seeing it yet 

Think chasers too often look for perfect setup. Granted moisture still likely an issue w/ this setup on the heels of Sunday's system. VWP decent, especially with curvature at low-levels. Just something to watch, but even 3/26 pulled off a tor with moisture lacking. 

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janetjanet998

janetjanet998

Posted
Posted

KSAT

STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP JUST OVER THE  
BORDER IN MEXICO WEST OF DEL RIO AROUND MIDNIGHT AS A LEAD SHORTWAVE  
ROTATES AHEAD OF THE BROADER POSITIVELY-TILTED TROUGH WEST OF BIG   
BEND AND THE SYNOPTIC COLD FRONT MOVES INTO THE REGION. THE INITIAL  
STORM MODE SHOULD BE SUPERCELLULAR GIVEN SHEAR VALUES IN EXCESS OF  
40-50 KNOTS, SO THE DAMAGING WINDS AND HAIL WILL BE THE MAIN THREATS  
OVERNIGHT, BUT A TORNADO CANNOT BE RULED OUT WITH SRH VALUES AROUND  
100 M^2/S^2 THAT COULD BE LOCALLY ENHANCED DEPENDING ON HOW THE STORM  
INTERACTS WITH THE ENVIRONMENT. A STEADY FEED OF LOW-LEVEL MOISTURE  
SUPPLIED BY A 20-30 KNOT SOUTHEASTERLY LLJ WILL SUPPORT LOW LCLS THAT  
COULD ALSO INCREASE THIS THREAT. THIS LLJ WILL ALSO HELP PROVIDE A  
BRIEF WINDOW FOR LOCALLY HEAVY RAINFALL AFTER MIDNIGHT IN THE EDWARDS  
PLATEAU AND RIO GRANDE PLAINS UNTIL THE COLD FRONT APPROACHES AND THE  
SYSTEM BEGINS TO BECOME COLD POOL DOMINATED BY 7 AM. A FEW INSTANCES  
OF FLASH FLOODING MAY BE POSSIBLE DUE TO TERRAIN AND RAINFALL TOTALS  
UP TO 3 INCHES IN ISOLATED AREAS, BUT NOT WIDESPREAD ENOUGH OR LONG  
ENOUGH TO ISSUE A WATCH AT THE CURRENT MOMENT. THESE CELLS SHOULD  
TRANSITION TO A MORE LINEAR SYSTEM MOVING FROM WEST TO EAST ALONG THE  
FRONT BY SUNRISE.   
  
AHEAD OF THIS LINE, SCATTERED SHOWERS SHOULD BE ONGOING ACROSS THE   
REST OF THE REGION BENEATH A WEAK CAP WITH ISENTROPIC ASCENT AND AN   
INCREASING LLJ OUT OF THE S-SE. DEEPER CELLS SHOULD BEGIN TO DEVELOP   
BY SUNRISE AS THE CAP ERODES MUCH EARLIER THAN NORMAL NEAR THE I-35   
CORRIDOR NORTH OF SAN ANTONIO AS THE LARGER-SCALE FORCING AND HEIGHT   
FALLS ASSOCIATED WITH AN UPPER LEVEL TROUGH EJECTING OUT OF MEXICO   
APPROACHES THE RIO GRANDE PLAINS. THIS TROUGH WILL BE TRANSITIONING   
FROM A POSITIVE TO MORE NEGATIVE TILT THAT WILL INCREASE DIFFLUENCE   
ALOFT FOR AREAS MAINLY ALONG AND EAST OF I-35 FOR THE MORNING AND   
AFTERNOON HOURS ON SUNDAY. SHEAR VALUES IN EXCESS OF 50 KNOTS WITH  
ABUNDANT CAPE INCREASING FROM ~1500 J/KG TOWARDS POSSIBLY 4000 J/KG   
BY NOON WITH STEEPENING LAPSE RATES ALOFT WILL SUPPORT STRONG   
SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WINDS. VERY   
LOW LCLS AND SRH VALUES INCREASING TOWARDS 250-300 M^2/S^2 PROVIDE   
STRONG SUPPORT FOR TORNADIC SUPERCELLS (POSSIBLY STRONG TORNADOES)   
TOMORROW MORNING INTO THE AFTERNOON HOURS FOR OUR EASTERN COUNTIES.   
IF THE LINE MERGES WITH THESE CELLS, WE COULD SEE SOME INSTANCES OF   
QLCS MERGERS, BUT SOME HI-RES MODELS ARE TRENDING TOWARDS WEAKENING   
THIS LINE WITH FEWER, BUT MORE SIGNIFICANT SUPERCELLS MOST LIKELY   
CAUSED BY SIGNIFICANT DRY AIR MOVING IN AT MIDLEVELS. IT IS HARD TO   
TELL WHICH SCENARIO WILL PLAY OUT AT THIS POINT, BUT THE GENERAL   
THREATS WOULD REMAIN THE SAME AND MOST MODELS SHOW THAT THE TORNADO   
AND SIGNIFICANT SEVERE THREAT SHOULD END BY EARLY OR MID-AFTERNOON   
FOR THE I-35 CORRIDOR AND BY 6 PM FOR OUR EASTERN COUNTIES. 

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Msalgado

Msalgado

Posted
Posted
19 minutes ago, bjc0303 said:

if half the troughs that traverse this area had this or that, they'd be interesting. And yet it's still wishcasting. I'm as hopeful as the next guy but I'm not seeing it yet 

How is that wishcasting when thats exactly what some of the models show?

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weunice

weunice

Posted
Posted

NWS LIX short term forecast is interesting ... 

Area Forecast Discussion
National Weather Service New Orleans LA
402 PM CDT Sat Apr 1 2017

.SHORT TERM...

(removed text regarding rain threat)

Regarding severe weather potential, it does appear all modes will
be possible given the degree of low level speed and some
directional shear to develop for tornado potential along with
steep lapse rates and storm top divergence for adequate hail
generation. The CHAP output on both the NAM and GFS does ping on a
high risk situation, showing a Ricks Index at or above 200, which
is typically a Particularly Dangerous Situation range. If model
soundings are correct, these values show potential of EF-4
tornadoes with rotational velocities close to 200 kt, 95 kt gust
potential and golf ball to baseball sized hail potential. Be
mindful these are just potentials at this point, but does shed
light on the Moderate Risk area currently depicted by SPC over SE
Texas and SW Louisiana on the Day 2 outlook. One degree of
uncertainty will be how much precipitation loading takes place to
diminish the severity threat? It does appear in the CHAP guidance
that the severe weather threat is greatest at onset and
transitions to heavy rain as the event unfolds.
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bjc0303

bjc0303

Posted
Posted
7 minutes ago, andyhb said:

Would like to see more background on this referenced parameter.

yeah that's really interesting. Lots of NWS offices have forecaster-developed tools they use in their CWA. TSA has a few but mostly fire wx products... 

But this is interesting sounding...

6 minutes ago, CGChaser said:

Still not a fan of rating possible tornado strength before event..

They're not rating anything. It's no different than the conditional sig tornado probabilities. They're just measures of potential given some constraints. 

 

44 minutes ago, Msalgado said:

How is that wishcasting when thats exactly what some of the models show?

What makes you believe moisture return will be anything above marginal? "some" of the models might show good moisture return (good in the loosest sense) but most of what I've seen was incredibly marginal moisture return. Sure you could squeeze out a weak tornado near 00z or 01z with upper 50s dewpoints... but for a more realistic and probable/substantial tornado threat gonna need a lot more. 

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Msalgado

Msalgado

Posted
Posted

Both the GFS and NAM keep 60+ dewpoints in East Texas after this low passes on Monday.  Both the GFS and NAM show dewpoints in excess of 60 north of the Red River on Tuesday.  Not sure why anyone is acting like moisture return on Tuesday is some kind of a miracle if it happens.  We have an incredibly warm Gulf Ready to send moisture north right now and there is plenty of ET to add to that from all the green plants throughout East Texas right now.  Not to mention the possible flooding rains tomorrow that will keep this area quite moist.  

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jojo762

jojo762

Posted
Posted
6 minutes ago, Msalgado said:

Both the GFS and NAM keep 60+ dewpoints in East Texas after this low passes on Monday.  Both the GFS and NAM show dewpoints in excess of 60 north of the Red River on Tuesday.  Not sure why anyone is acting like moisture return on Tuesday is some kind of a miracle if it happens.  We have an incredibly warm Gulf Ready to send moisture north right now and there is plenty of ET to add to that from all the green plants throughout East Texas right now.  Not to mention the possible flooding rains tomorrow that will keep this area quite moist.  

Massive differences in the 18Z GFS and 18Z NAM on where exactly the warmfront sets up though. GFS has it much further north, making it into KS and verbatim the 18Z GFS presents a favorable environment for supercells across far S KS and into OK... NAM is much different and only has the warm front making it just past the Red River. NAM is much less aggressive with moisture return, with ~60-62DPs only pooling along the WF, whereas the GFS shows 59-62 DPs across much of the warm sector... Neither model shows a sharp dryline. Not a perfect setup, but it could produce something, especially given the impressive forecast low-level hodographs. Also important to note that surface temps likely will not make it too much above 70 degrees across a lot of the warm sector, meaning T/Td spreads and LCLs would not be that high.

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Msalgado

Msalgado

Posted
Posted

Tuesday may or may not have severe weather in appreciable amounts, but my point is that its certainly a reasonable possibility right now.  The NAM has overdone moisture in the past, but this season its actually underdone it compared to the GFS.  Its a bit of a role reversal.

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janetjanet998

janetjanet998

Posted
Posted

might need a HIGH risk

I don't have much to add as much as it has been discussed

there seems to be some weakness in the 250mb flow in places which may favor HP Supercells and/or messy modes 

but if 

1) if storms fire along the WF in LA early means trouble

2) if storms form ahead of the main line In the warm sector starting early  means trouble

3) if the main line breaks up into discrete storms means trouble

 

if all of the above happens may be an event to remember

 

 

 

 

 

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Jim Martin

Jim Martin

Posted
Posted

Interesting Mesoscale Discussion from the Storm Prediction Center this evening...


   Mesoscale Discussion 0394
   NWS Storm Prediction Center Norman OK
   0720 PM CDT Sat Apr 01 2017

   Areas affected...Portions of the Edwards Plateau

   Concerning...Severe potential...Watch unlikely 

   Valid 020020Z - 020145Z

   Probability of Watch Issuance...20 percent

   SUMMARY...A localized threat for strong wind gusts and large hail
   may exist with cells crossing the Rio Grande River over the next
   hour. However, the threat should remain too small in spatial extent
   for watch issuance within the next 2-3 hours.

   DISCUSSION...Left and right splits of a cell that organized over the
   Serranias del Burro are approaching the Rio Grande this evening,
   aided by a band of ascent associated with an upper-level southerly
   jet. While deeper moisture remains displaced to the east (evident in
   the 00Z DRT sounding), steep low/mid-level lapse rates and
   relatively straight, elongated hodographs (representing around 50-55
   kt of effective shear) may maintain one or both of these cell splits
   as they enter Texas. Moreover, occasional updraft organization from
   strong southwesterly mid-level flow may yield isolated large hail.
   Strong, gusty winds also remain a possibility considering the deeply
   mixed boundary layer. Nonetheless, a lack of more substantial
   moisture and forcing for ascent should keep this severe threat
   brief/localized, precluding watch issuance.

   By late evening into early tonight, a more substantial threat should
   materialize, as low-level moisture surges west and convection
   re-develops along higher terrain. However, this scenario will be
   addressed in a later mesoscale discussion.

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Jim Martin

Jim Martin

Posted
Posted

Tidbit from the latest Day 1 from the Storm Prediction Center...

   Meanwhile in the low levels, southeasterly flow
   will advect richer moisture into the Hill Country and southern
   portion of the Edwards Plateau.  Forecast soundings show strong
   shear profiles supportive of organized storms.  Early in the
   convective life cycle, supercells will be favored and an
   accompanying risk for large to very large hail and severe gusts. 
   Although a weak inversion will likely persist, enlarging hodographs
   in the warm sector near the boundary may prove favorable for
   low-level mesocyclones and a tornado threat.

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Jim Martin

Jim Martin

Posted
Posted

The National Weather Service in San Angelo has issued a

* Tornado Warning for...
  Southeastern Coleman County in west central Texas...

* Until 845 PM CDT
    
* At 812 PM CDT, a confirmed large and extremely dangerous tornado
  was located near Voss, or 11 miles southwest of Coleman, moving
  east at 20 mph.

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janetjanet998

janetjanet998

Posted
Posted

EVERE WEATHER STATEMENT  
NATIONAL WEATHER SERVICE SAN ANGELO TX  
826 PM CDT SAT APR 1 2017  
  
TXC083-020145-  
/O.CON.KSJT.TO.W.0015.000000T0000Z-170402T0145Z/  
COLEMAN TX-  
826 PM CDT SAT APR 1 2017  
  
...A TORNADO WARNING REMAINS IN EFFECT UNTIL 845 PM CDT FOR  
SOUTHEASTERN COLEMAN COUNTY...  
          
AT 825 PM CDT, A CONFIRMED LARGE AND EXTREMELY DANGEROUS TORNADO WAS  
LOCATED 7 MILES SOUTHWEST OF SANTA ANNA, MOVING EAST AT 20 MPH.  
  
THIS IS A PARTICULARLY DANGEROUS SITUATION. TAKE COVER NOW!  
  
HAZARD...DAMAGING TORNADO.   
  
SOURCE...SPOTTER CONFIRMED TORNADO.   
  

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