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May 7th-10th Severe Outbreaks


andyhb

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Well, tomorrow looks increasingly like a letdown--not because the UL trough is more negatively tilted, but because the GFS and the NAM have now trended toward a slower solution, leaving a notorious back-veer-back profile in the upper levels due to shortwave ridging. The unfavorable wind profile now extends well south into western OK on both runs, including along/just east of the dry line on Saturday evening. Given the lack of a stout EML early in the day, widespread convection breaks out all over the warm sector on the 18Z runs (including the NAM), and the day thus increasingly looks like a wash. Back-veer-back + insufficient instability for early May (due to early convection) is not a promising combination, even with somewhat stronger mid-level winds over OK. Given today's HP supercell profiles and everyone's earlier expectations for today and tomorrow, coupled with the lack of significant disturbances ejecting after Saturday (at least through the medium term), the overall trends aren't what I hoped they would be. And these are after I switched to a much more bullish outlook on tomorrow. Oh, well...

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Well, computer off for the night for me.. Almost 2am UK time. I have stayed 2 hours longer than I normally do...can't help but feel that today has been quite the let down. Wednesday, which was barely mentioned has/is going to turn out to be the best chase day. The prognosis is certainly not as strong for tommorrow as it was...but we will see how things go. I suspect Sunday may turn out to be the best chase further north. 

 

We will see. 

 

Goodnight from the UK.

 

:drunk:

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Well, tomorrow looks increasingly like a letdown--not because the UL trough is more negatively tilted, but because the GFS and the NAM have now trended toward a slower solution, leaving a notorious back-veer-back profile in the upper levels due to shortwave ridging. The unfavorable wind profile now extends well south into western OK on both runs, including along/just east of the dry line on Saturday evening. Given the lack of a stout EML early in the day, widespread convection breaks out all over the warm sector on the 18Z runs (including the NAM), and the day thus increasingly looks like a wash. Back-veer-back + insufficient instability for early May (due to early convection) is not a promising combination, even with somewhat stronger mid-level winds over OK. Given today's HP supercell profiles and everyone's earlier expectations for today and tomorrow, coupled with the lack of significant disturbances ejecting after Saturday (at least through the medium term), the overall trends aren't what I hoped they would be. And these are after I switched to a much more bullish outlook on tomorrow. Oh, well...

I am not seeing much if any veer-back-veer on the NAM. The GFS is notoriously going to be low on instability so much so that it should be tossed with respect to instability. It grossly underdid the instability for the last 3 days. Also Tony has explained why the GFS is showing the veer-back-veer and why it should be discounted as being suspcious.

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I am not seeing much if any veer-back-veer on the NAM. The GFS is notoriously going to be low on instability so much so that it should be tossed with respect to instability. It grossly underdid the instability for the last 3 days. Also Tony has explained why the GFS is showing the veer-back-veer and why it should be discounted as being suspcious.

Agreed... Plus if you look at the mesoscale/ High-Res models still show a very favorable environment developing over much of southwestern KS/Western OK. Am still concerned by the trends that the NAM/GFS have shown.
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I am not seeing much if any veer-back-veer on the NAM. The GFS is notoriously going to be low on instability so much so that it should be tossed with respect to instability. It grossly underdid the instability for the last 3 days. Also Tony has explained why the GFS is showing the veer-back-veer and why it should be discounted as being suspcious.

The NAM shows back-veer-back extending well south and west of Enid, though not as far southwest as areas west of Gould and Vinson. The overall trend throughout the day has been to extended back-veer-back farther SW into OK. The 18Z run shows considerable stabilization of the warm sector through 18Z due to cold pools in the wake of early convection. Destabilization along the dry line thus only picks up considerably by and after peak heating (~21Z). A narrow sliver of 3000-j/kg MLCAPE along the TX Panhandle/OK border by 00Z tomorrow evening is really rather meager for the time of year, and the air mass, while of high quality and deep moisture, will be largely saturated prior to 21Z. The NAM shows storms firing along the dry line by 00Z, but then quickly dying off thereafter. I think that the main threat tomorrow will be large hail and a few isolated tornadoes, but nothing more. I see more of a hail threat than a tornado threat. I'd say 10% TOR and 45% hail probabilities.

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The NAM shows back-veer-back extending well south and west of Enid, though not as far southwest as areas west of Gould and Vinson. The overall trend throughout the day has been to extended back-veer-back farther SW into OK. The 18Z run shows considerable stabilization of the warm sector through 18Z due to cold pools in the wake of early convection. Destabilization along the dry line thus only picks up considerably by and after peak heating (~21Z). A narrow sliver of 3000-j/kg MLCAPE along the TX Panhandle/OK border by 00Z tomorrow evening is really rather meager for the time of year, and the air mass, while of high quality and deep moisture, will be largely saturated prior to 21Z. The NAM shows storms firing along the dry line by 00Z, but then quickly dying off thereafter. I think that the main threat tomorrow will be large hail and a few isolated tornadoes, but nothing more. I see more of a hail threat than a tornado threat. I'd say 10% TOR and 45% hail probabilities.

Actually the extent of 2000-3500 J/kg MLCAPE is actually a bit bigger this run compared to previous runs off the 12km NAM. Also any early convection looks meager at best and might actually help the situation as it could cap things off until later in the afternoon, instead of firing by noon.

 

Also any backing I see off the NAM is above 350mb. That isn't as critical compared to backing around 500-700mb and it is mostly confined to Kansas.

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Actually the extent of 2000-3500 J/kg MLCAPE is actually a bit bigger this run compared to previous runs off the 12km NAM. Also any early convection looks meager at best and might actually help the situation as it could cap things off until later in the afternoon, instead of firing by noon.

 

Also any backing I see off the NAM is above 350mb. That isn't as critical compared to backing around 500-700mb and it is mostly confined to Kansas.

The 18Z NAM shows widespread 3-hr. precipitation of 0.35-0.5"+ over N TX as late as 18-21Z, following an MCS with totals over 1" (up to 4" or more!) passing over southern and eastern OK between 06-15Z. Compared to previous runs, the 18Z run also shows greater coverage of precipitation throughout Saturday until mid afternoon (peak heating). To me, with all that precipitation blocking air mass recovery (as the 700-mb flow will be from the SSW around midday CST Saturday), the destabilization shown by the NAM along the dry line looks overdone.

 

Someone needs to enlighten me about the point in bold, since most of the back-veer-back on the models over the past few days has been at or above 350 mb, and others like CUmet were concerned about this back-veer-back, so I don't know why UL backing is less important than if it were at 500-700 mb, especially since, for tomorrow's event, the strongest wind vectors are at or above 350 mb, meaning greater divergence/ascent over the warm sector as on 05/24/2011 (though admittedly not to such an extreme level).

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The 18Z NAM shows widespread 3-hr. precipitation of 0.35-0.5"+ over N TX as late as 18-21Z, following an MCS with totals over 1" (up to 4" or more!) passing over southern and eastern OK between 06-15Z. Compared to previous runs, the 18Z run also shows greater coverage of precipitation throughout Saturday until mid afternoon (peak heating). To me, with all that precipitation blocking air mass recovery (as the 700-mb flow will be from the SSW around midday CST Saturday), the destabilization shown by the NAM along the dry line looks overdone.

 

What?

 

Eastern OK is not the primary threat area for tomorrow. Also if you're talking about 700 mb flow coming from the SSW, how is the convection/precip to the east of the highest threat area relevant to this (i.e. after 15z)?

 

For the record, I have my own concerns about early convection too tomorrow, but some of these points you are raising are bizarre.

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If the NAM is right, the primary risk area for tomorrow is clear of convection by 18z. After 18z, the environment becomes one that is as high-end as you'll ever see on the Plains.

In your professional opinion, where would you place the primary risk area?

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Main limiter might be a not humongous area of the best overlapping ingredients. Seems today's original mod might be the best primary zone for tor. Maybe a bit bigger. Still looks great at 500 but not as good as I'd expect otherwise.

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Going only off the 00Z NAM the highest risk area looks like extreme southwest KS and then moving northeast into central KS with time. This would be right on the nose of the upper level potential vorticity anomoly where UL divergence would be maximized.The typical ingredients based indices would suggest further south and east along the TX/OK border though, but moisture convergence along the dry line seems pretty anemic and so convective initiation could be more sparse down there. Of course it's hard to deny that any supercells that mature further south could pretty potent. Thoughts?

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Going only off the 00Z NAM the highest risk area looks like extreme southwest KS and then moving northeast into central KS with time. This would be right on the nose of the upper level potential vorticity anomoly where UL divergence would be maximized.The typical ingredients based indices would suggest further south and east along the TX/OK border though, but moisture convergence along the dry line seems pretty anemic and so convective initiation could be more sparse down there. Thoughts?

You want somewhat limited CI so storms don't have to compete for instability.  The area with your best lift is also where you risk have too much convection leading to merging and strengthening of cold pools and upscale growth.  You'll have plenty of low-level convergence for CI in tomorrow's environment, where there won't be a convection-killing cap.

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Interesting that the 0Z NAM and the 0Z GFS don't seem to break out any storms in the impressive environment tomorrow afternoon. They only have the morning round of convection.

I'm tired of repeating myself about this every time there's a major Plains threat, so I'll just post a couple pretty pictures and let everyone interpret.

 

namFLT_700_vvel_024.gif

 

 

gfsFLT_700_vvel_024.gif

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