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Severe WX April 22-24th, 2020 Severe Weather Threat

Question: in the images below can you please expand on the significance and/or correlation of the colors/numbers I have highlighted with arrows?
al.png

ga.png

I am trying to better understand the models I see on Pivotal Weather. Thanks everyone.

Justin
 
GTWXAlum said:
Yeah..if its the NAM vs. everyone else, give me everyone else.
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I agree.
However, I remember a few events over the years where the NAM being the odd man out was consistent and got it right, both Forecasted Convective Amplification Deficiency and boom. That's no reason of course to give it credence, but it's not completely garbage. I also don't put much stock in much above 48 hours out on the NAM except to evaluate for consistency and model agreement.
 
JRC said:
Question: in the images below can you please expand on the significance and/or correlation of the colors/numbers I have highlighted with arrows?
View attachment 2991

View attachment 2992

I am trying to better understand the models I see on Pivotal Weather. Thanks everyone.

Justin
Click to expand...

Try this explanation from SPC Justin. The colors correlate to the STP values in which you have the arrow pointing too in the soundings you've posted which are significant if most other parameters come into play. A high STP, usually at 5+ is indicative of possible strong to violent , long track tornadoes.


Significant Tornado Parameter (effective layer)

A multiple ingredient, composite index that includes effective bulk wind difference (EBWD), effective storm-relative helicity (ESRH), 100-mb mean parcel CAPE (mlCAPE), 100-mb mean parcel CIN (mlCIN), and 100-mb mean parcel LCL height (mlLCL).

The index is formulated as follows:

STP = (mlCAPE/1500 J kg-1) * ((2000-mlLCL)/1000 m) * (0-500 m SRH/75 m2 s-2) * (EBWD/20 m s-1) * ((200+mlCIN)/150 J kg-1)

The 0-500 m SRH is limited to within the effective inflow layer, if it exists. The mlLCL term is set to 1.0 when mlLCL < 1000 m, and set to 0.0 when mlLCL > 2000 m; the mlCIN term is set to 1.0 when mlCIN > -50 J kg-1, and set to 0.0 when mlCIN < -200; the EBWD term is capped at a value of 1.5 for EBWD > 30 m s-1, and set to 0.0 when EBWD < 12.5 m s-1. Lastly, the entire index is set to 0.0 when the effective inflow base is above the ground.

A majority of significant tornadoes (F2 or greater damage) have been associated with STP values greater than 1 within an hour of tornado occurrence, while most non-tornadic supercells have been associated with values less than 1 in a large sample of RAP analysis proximity soundings. Replacing effective SRH with 0-500 m SRH improves discrimination between significant tornadoes and non-tornadic supercells, per work by Coffer et al. (2019), October issue of Weather and Forecasting.
 
Timhsv said:
Try this explanation from SPC Justin. The colors correlate to the STP values in which you have the arrow pointing too in the soundings you've posted which are significant if most other parameters come into play. A high STP, usually at 5+ is indicative of possible strong to violent , long track tornadoes.


Significant Tornado Parameter (effective layer)

A multiple ingredient, composite index that includes effective bulk wind difference (EBWD), effective storm-relative helicity (ESRH), 100-mb mean parcel CAPE (mlCAPE), 100-mb mean parcel CIN (mlCIN), and 100-mb mean parcel LCL height (mlLCL).

The index is formulated as follows:

STP = (mlCAPE/1500 J kg-1) * ((2000-mlLCL)/1000 m) * (0-500 m SRH/75 m2 s-2) * (EBWD/20 m s-1) * ((200+mlCIN)/150 J kg-1)

The 0-500 m SRH is limited to within the effective inflow layer, if it exists. The mlLCL term is set to 1.0 when mlLCL < 1000 m, and set to 0.0 when mlLCL > 2000 m; the mlCIN term is set to 1.0 when mlCIN > -50 J kg-1, and set to 0.0 when mlCIN < -200; the EBWD term is capped at a value of 1.5 for EBWD > 30 m s-1, and set to 0.0 when EBWD < 12.5 m s-1. Lastly, the entire index is set to 0.0 when the effective inflow base is above the ground.

A majority of significant tornadoes (F2 or greater damage) have been associated with STP values greater than 1 within an hour of tornado occurrence, while most non-tornadic supercells have been associated with values less than 1 in a large sample of RAP analysis proximity soundings. Replacing effective SRH with 0-500 m SRH improves discrimination between significant tornadoes and non-tornadic supercells, per work by Coffer et al. (2019), October issue of Weather and Forecasting.
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Awesome! Thank you. I have to admit I understood about 10% of that, but hey, it is a start. Again, thank you.

Justin
 
JRC said:
Awesome! Thank you. I have to admit I understood about 10% of that, but hey, it is a start. Again, thank you.

Justin
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Your welcome. Just keep digging and reading you'll start getting the meaning after awhile of the parameters etc.
 
00z HRRR is not lending much confidence in a large severe weather threat with the early morning round Thursday (for AL) and looking at wind fields behind it, they're all wonky. Looks like we have some elevated instability, but not much of a surface-based storm threat.

It does show an ugly batch of storms across East TX and a particularly nasty right turner that rakes South/Central LA tomorrow evening.
 
Well, looks very much like a Sunday morning repeat with vigorous storms racing east out of MS in the early morning. Low-level inversion but some elevated storms producing a damaging wind threat. I don't think hail will be as big a problem in the morning with what appears to be a rain shield moving out ahead of it in AL. I suspect damaging winds may be the most likely mode with a 70kt LLJ on the HRRR...just have to see if any of that can be brought to the surface with a surface inversion.
 
I’m wondering if north AL gets skipped this year. By north AL I mean Morgan, Madison, Lawrence, and Limestone Counties. It has seemed to be eerily quiet here the past few years...
 
Jpgood20 said:
I’m wondering if north AL gets skipped this year. By north AL I mean Morgan, Madison, Lawrence, and Limestone Counties. It has seemed to be eerily quiet here the past few years...
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I’ve had more tornado warned circulations go right over my house In far South Huntsville the past year and a half than in 15 pervious years. Had spin ups cause significant damage in Town Creek, Union Grove, and Boaz. I guess if you haven’t personally had a close call it may feel quiet. Looks like areas South and East of Huntsville May be under the gun Thursday afternoon as possible supercells fire back up and track east.
 
The morning round certainly messes up the low level flow for the afternoon. But like I said earlier, I could see refiring of convection in the afternoon but I don’t think low level flow will recover with backing and convergence along the boundary. In other words, more likely a hail threat in the afternoon than tornado.
 
GTWXAlum said:
0z NAM is much less bullish for Thursday than previous runs
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See, I thought it held serve on a large event. The parameters may not be as sporty, but it’s coming to a more realistic scenario. Several CAMs (most based off the NAM) show supercells redeveloping behind the morning convection. I don’t know what will happen Thursday, and there are numerous failure modes, but I’m slightly more confident in an afternoon severe threat. The tornado threat remains nebulous.
 
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Brad Travis was showing storms starting to form as early as 10:45 on his models around Guntersville. Will be interesting to see the what is depicted when we get to the 18hr mark.
 
I'm more focused on the flooding threat than the iffy severe threat up this way (and very conditional severe threat elsewhere) - just got the basement dried out from the last batch of torrential rains.
 
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