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andyhb

April 13th-14th Severe Threat

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Been lurking reading everyone's thoughts, great job guys, but man, this doesn't look good at all... Getting that feeling on the back of my neck like I do before big tornado days. I'll be around all weekend nowcasting.

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Good lord at that Experimental HRRR run, from start to end. Maybe too many storms scrunched up together, but that is a very intimidating simulated reflectivity.

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0Z HREF/SREF-blended tornado probability guidance. It is more difficult to get higher probabilities, so the large 10% is actually pretty significant. As for my coverage area (Texas) it does seem we'll be dealing with a higher tornado risk compared to what I thought 24 hours ago. 

guidance_tor_spchazcal_024h.conus_.f0360 

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26 minutes ago, SmokeEater said:

Been lurking reading everyone's thoughts, great job guys, but man, this doesn't look good at all... Getting that feeling on the back of my neck like I do before big tornado days. I'll be around all weekend nowcasting.

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I appreciate that greatly.  I only have access to NWS radars and your radar pictures are quite helpful.  Will be monitoring this situation closely Saturday.

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In my mind, storm mergers/interaction are the only thing that lead me to be a bit hesitant to put this in 4/28/14 territory. 

Good discussion with Lyza on Twitter. Low level shear is a bit more impressive tomorrow, but I’d counter that with somewhat less impressive lapse rates/instability and similar to slightly less deep layer shear. Profiles are also rather saturated this go around. High res guidance show a lot of convection, possibly early in the event, which may be a limiting factor.

Numerous tornadoes appear likely, along with at least a few EF-2+. If storms are not too cluttered or in close proximity along the prefrontal trough, then you’ll get several long-track, tornadic supercells. Don’t overlook the warm sector east into Mississippi as well before 00z. Deep layer wind profiles are even more impressive there, suggesting you may see long residence time if you manage to pop a sustained supercell or two. Wind profiles become more meridional farther west into East Texas, but a QLCS tornado threat may still evolve. Fortunately the tornado threat seems limited north of the AR/LA border due to a mass of convection and weak buoyancy. 

Each event is different. A great parameter space isn’t always a slam-dunk outbreak, but odds favor an outbreak tomorrow for a variety of reasons. 

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Via Twitter, New Orleans and Fort Worth are doing special soundings at 6 and 18Z in support of VORTEX-SE.

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6 minutes ago, Superstorm93 said:

Just for the sake of posterity, here's an observed hodo derived from the VWP @ SHV from 4/2/17 

7d04c6b9d03c46d0a6de96a29e65fe25.png

SRH was more impressive (than forecast for tomorrow) over a large chunk of Louisiana on 4/2/17. That being said, each outbreak is different. mcd0405.gif

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Just now, Quincy said:

SRH was more impressive (than forecast for tomorrow) over a large chunk of Louisiana on 4/2/17. That being said, each outbreak is different. mcd0405.gif

The region of best instability that day was much further south, and predominantly south of the crazy hodographs in central and northern LA, so i don't think the comparison is entirely fair.  Somewhat better overlap between great low-level profiles and instability projected for tomorrow tomorrow.

 


 

snapshot2.png

snapshot.png

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I'll agree with Quincy that the prevalent low-level saturation that has shown up in most convection allowing models makes me every so slightly concerned.   On the other hand, there isn't extremely strong WAA/synoptic ascent through the warm sector.  Also agree that low-level lapse rates could be a tad steeper.  

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41 minutes ago, Quincy said:

In my mind, storm mergers/interaction are the only thing that lead me to be a bit hesitant to put this in 4/28/14 territory. 

Good discussion with Lyza on Twitter. Low level shear is a bit more impressive tomorrow, but I’d counter that with somewhat less impressive lapse rates/instability and similar to slightly less deep layer shear. Profiles are also rather saturated this go around. High res guidance show a lot of convection, possibly early in the event, which may be a limiting factor.

Numerous tornadoes appear likely, along with at least a few EF-2+. If storms are not too cluttered or in close proximity along the prefrontal trough, then you’ll get several long-track, tornadic supercells. Don’t overlook the warm sector east into Mississippi as well before 00z. Deep layer wind profiles are even more impressive there, suggesting you may see long residence time if you manage to pop a sustained supercell or two. Wind profiles become more meridional farther west into East Texas, but a QLCS tornado threat may still evolve. Fortunately the tornado threat seems limited north of the AR/LA border due to a mass of convection and weak buoyancy. 

Each event is different. A great parameter space isn’t always a slam-dunk outbreak, but odds favor an outbreak tomorrow for a variety of reasons. 

Great summary! 

I have a feeling if something goes in the eastern target, it’s going to put down the most significant tornado of the day.  If I was chasing, I’d seriously consider taking a gamble on that target.

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And Saturday begins as expected....

 

Mesoscale Discussion 0311
   NWS Storm Prediction Center Norman OK
   1140 PM CDT Fri Apr 12 2019

   Areas affected...Southwest TX

   Concerning...Severe potential...Watch possible 

   Valid 130440Z - 130645Z

   Probability of Watch Issuance...60 percent

   SUMMARY...Thunderstorm coverage is expected to increase across
   southwest TX over the next few hours. Some severe hail is possible
   with these storms.

   DISCUSSION...Strong moisture advection throughout the evening has
   significantly modified the low-level air mass across the region.
   Dewpoints across the area have increased 10 to 15 degrees over the
   last 3 hours with much of the region now characterized by dewpoints
   in the upper 40s and low 50s. At the same time, ascent attendant to
   the shortwave trough moving through northern Mexico continues to
   increase, resulting in both an increase in high-level cloudiness
   over the region and a deepening of the surface low centered near
   FST. Continued moisture advection amidst this ascent, surface
   convergence, and increasing instability is expected to result in
   eventual convective initiation. 

   Current expectation is for most of these storms to be elevated north
   of the warm front, although surface-based development cannot be
   entirely ruled out later tonight across portions of the Edwards
   Plateau. Vertical shear supports updraft rotation, with hail
   possible within the more persistent and robust updrafts.

   ..Mosier/Guyer.. 04/13/2019

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The real question is if they will go high risk at the first day 1 for Saturday. Imho, the risk to life and property should override the what ifs. There's enough there to warrant it. High risk captures the public's attention more than moderate. Again, imho.

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Just now, wotan said:

The real question is if they will go high risk at the first day 1 for Saturday. Imho, the risk to life and property should override the what ifs. There's enough there to warrant it. High risk captures the public's attention more than moderate. Again, imho.

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The same was said on April 2, 2017 - and there was some pretty harsh backlash when that event didn't live up to the 'high risk' expectations. It's a tough line to walk between societal impacts and maintaining scientific/meteorological integrity. 

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The same was said on April 2, 2017 - and there was some pretty harsh backlash when that event didn't live up to the 'high risk' expectations. It's a tough line to walk between societal impacts and maintaining scientific/meteorological integrity. 
I understand. The same holds true for potential tropical cyclones. Ultimately, why does the nws exist?

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7 minutes ago, wotan said:

The real question is if they will go high risk at the first day 1 for Saturday. Imho, the risk to life and property should override the what ifs. There's enough there to warrant it. High risk captures the public's attention more than moderate. Again, imho.

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I'd hold off on the 0600 OTLK and go mod but mention chance for upgrade to high... wait to see how the early morning starts out.  Go for it at 1300 OTLK if everything is coming together... 1300 is 9am so people will be getting up around then and will see and hear about it on the morning news

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I'd hold off on the 0600 OTLK and go mod but mention chance for upgrade to high... wait to see how the early morning starts out.  Go for it at 1300 OTLK if everything is coming together... 1300 is 9am so people will be getting up around then and will see and hear about it on the morning news
That's more than reasonable.

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As I understand it, the svr risk level is scientifically based on the anticipated number of storms within a specified geographical area.  I remember that May 3, 1999 in Oklahoma had an increasing level of risk issued throughout the day as the parameters came into focus.

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37 minutes ago, Superstorm93 said:

Even more bullish for 16z tomorrow...

a7451f99772df2376cd3f2dd6b9b43ea.png 

Greetings from Gregg County - about dead center of this terror map. 

Ill be updating tmrw as much as I can.

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As I understand it, the svr risk level is scientifically based on the anticipated number of storms within a specified geographical area.  I remember that May 3, 1999 in Oklahoma had an increasing level of risk issued throughout the day as the parameters came into focus.
If nws were purely a basic science outfit, that would be valid. But as Sandy showed, that's not really how people work. Nws has a responsibility to the general public that isn't always served by scientific rigidity.

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3 minutes ago, wotan said:

If nws were purely a basic science outfit, that would be valid. But as Sandy showed, that's not really how people work. Nws has a responsibility to the general public that isn't always served by scientific rigidity.

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Yes, and after Sandy the NHC changed the way they issued warnings for hurricanes that had lost the warm core characteristics in a technical sense so the public could better understand the threat.   With severe storms that's why I follow Hazardous weather outlooks which lead to mesoscale discussions, watches, and warnings.    But then I am a wx nerd and the general public might not be that attentive.  I know sociologists have studied and commented on this communication issue...most recently with the EF 4 in Alabama.   We'll see how this plays out today.

 

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12 minutes ago, yoda said:

I'd hold off on the 0600 OTLK and go mod but mention chance for upgrade to high... wait to see how the early morning starts out.  Go for it at 1300 OTLK if everything is coming together... 1300 is 9am so people will be getting up around then and will see and hear about it on the morning news

Everyone here knows about tomorrow - events being cancelled, etc. It’s a high risk without a SPC high risk mark already.

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Yes, and after Sandy the NHC changed the way they issued warnings for hurricanes that had lost the warm core characteristics in a technical sense so the public could better understand the threat.   With severe storms that's why I follow Hazardous weather outlooks which lead to mesoscale discussions, watches, and warnings.    But then I am a wx nerd and the general public might not be that attentive.  I know sociologists have studied and commented on this communication issue...most recently with the EF 4 in Alabama.   We'll see how this plays out today.
 
I'm saying that's basically why I would go high risk Saturday. The general public are really the audience, not those of us who understand nuance.

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5 minutes ago, 1900hurricane said:

06Z is moderate risk.

Looking at the expansion of the Mod area, they left room for a smaller High area if needed in the next outlook.

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