April 24-30th Severe Potential

[OUGrad05]

Not sure what to make of the larger cell just south of Ponca.  Only having a couple of possible options on the 4KM makes me concerned that we may only have one cell in OK...if any...

[ZackH]

Regarding the 12z NAM... I generally like what I see. The 850s have definitely improved over KS and parts of OK ahead of the dryline. Southeast 850s near the triple point... backed surface winds all along the triple point and dryline. However... the H5 flow is still really meridional which is really messing up the upper levels on soundings. Haven't been able to find a decent sounding without at least some VBV structure. However, most of the VBV is above 700mb which may mitigate the effects of supercell/meso strength. But it still may make the storm modes messy as has been mentioned. If the 4km NAM is to be believed at all, the messy convective mode definitely looks possible. While some nice cells get going around 22z in northern KS, it looks pretty messy shortly after. 

[OUGrad05]

Regarding the 12z NAM... I generally like what I see. The 850s have definitely improved over KS and parts of OK ahead of the dryline. Southeast 850s near the triple point... backed surface winds all along the triple point and dryline. However... the H5 flow is still really meridional which is really messing up the upper levels on soundings. Haven't been able to find a decent sounding without at least some VBV structure. However, most of the VBV is above 700mb which may mitigate the effects of supercell/meso strength. But it still may make the storm modes messy as has been mentioned. If the 4km NAM is to be believed at all, the messy convective mode definitely looks possible. While some nice cells get going around 22z in northern KS, it looks pretty messy shortly after. 

By 03Z it starts to get messy in N TX and SE OK.

[wildwestpb]

If I had to guess, from living here for around 12 years of my life I bet it'll be bad for around 7-10 o clock then die down like it has almost every single time.

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Possibly. OUN has said that around 5 PM is the time they expect storms to start firing along the I-35 corridor, isolated to scattered at that time. If they form over the I-35 corridor at that time, and move NE at around 45 mph, would make sense that they would start effecting the Tulsa Metro around the 7PM time frame. However, if they are only moving at around 25mph, it will be closer to the 9-10PM time frame.

[Smokey_mountain_vols]

Possibly. OUN has said that around 5 PM is the time they expect storms to start firing along the I-35 corridor, isolated to scattered at that time. If they form over the I-35 corridor at that time, and move NE at around 45 mph, would make sense that they would start effecting the Tulsa Metro around the 7PM time frame. However, if they are only moving at around 25mph, it will be closer to the 9-10PM time frame.

If it's 9-10 then they won't be as bad. They will still be pretty bad but at night they usually weaken up quite a bit.

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[weatherextreme]

Looks like Forbes main tornado threat location is for central and east KS with a Torcon of 7

[jpeters3]

Think this is the same article,your link didn't work

 

https://ams.confex.com/ams/16Meso/webprogram/Paper274591.html

 

Thanks guys

[jpeters3]

After looking at the 12Z NAM, I've got my eyes on the KS/NE boarder somewhere between Belleville and Phillipsburg KS.  While the NAM goes crazy with sigtor in southern Nebraska, soundings from this area all show a shallow and very moist inversion, suggesting to me that they are north of the effective surface front and that surface parcels in this area will be somewhat convectively inhibited.  I like the profiles I see in northern KS around 00Z.

 

[bdgwx]

A TORCON of 7 downscales to a ~26% probability of a tornado within 25 miles so it's not quite at the SPC threshold for a high risk outlook, but honestly, that's kind of splitting hairs.

 

The 12Z NAM does look a touch better. But, another mitigating factor I noticed is that a big chunk of that moderate risk area has BRN values > 50. Normally we see a better balance between instability and shear during high risk style outbreaks. Like others have mentioned the northern part of the risk area near the triple point still looks pretty hot.

[brettjrob]

Forget a cap bust. Something like this is more what I'm worried about.

 

[jojo762]

FWIW, despite that most of them over-convect, by a lot,  the WRF-NMMB, WRF-ARW, and WRF-NSSL all show impressive UH-tracks basically with any storm that develops from SE/SC NE southward into the C OK. Like I said yesterday, there will be a certain amount of time, probably from 22/23Z to roughly 03Z where the wind-profile will be sufficient, and not wacky enough, combined with the strong/extreme instability where any storm will be capable of producing high-end tornadoes. 4 or 5 hours of potentially numerous intense discrete supercells across the dryline and warm-front is enough for me. 

[thewxmann]

Forget a cap bust. Something like this is more what I'm worried about.

 

 

Euro, among others, has been hinting at this. And with shear vectors being as meridional as they are, you betcha any early-initiating storms will line up quickly. 

 

I would be completely shocked if any high risk is issued, and would be even moreso if one verifies.

[jpeters3]

FWIW, despite that most of them over-convect, by a lot,  the WRF-NMMB, WRF-ARW, and WRF-NSSL all show impressive UH-tracks basically with any storm that develops from SE/SC NE southward into the C OK. Like I said yesterday, there will be a certain amount of time, probably from 22/23Z to roughly 03Z where the wind-profile will be sufficient, and not wacky enough, combined with the strong/extreme instability where any storm will be capable of producing high-end tornadoes. 4 or 5 hours of potentially numerous intense discrete supercells across the dryline and warm-front is enough for me. 

 

I am still convinced that most of the profiles in southern NE are actually slightly north of the surface front, and any supercells that develop there will end up being elevated.  Take a look at some profiles out of the high sigtor regions in S nebraska.  They all look like this:

 

http://climate.cod.edu/hanis/model/fsound/index.php?type=12|NAM|US|con|stp|36|*129,113*|ml|severe

 

Shallow saturated stable layer.

[JoMo]

That would be more of what I'd expect in my area. We typically get an intense squall line with embedded tornadoes with storms that initiate in central KS/OK. The GFS positioning of the dryline being farther east into SE KS was worrying me a bit, but it looks like it's moved back west. 

 

The UH for (almost) the entire run sure is a mess though.

 

[jojo762]

I am still convinced that most of the profiles in southern NE are actually slightly north of the surface front, and any supercells that develop there will end up being elevated.  Take a look at some profiles out of the high sigtor regions in S nebraska.  They all look like this:

 

http://climate.cod.edu/hanis/model/fsound/index.php?type=12|NAM|US|con|stp|36|*129,113*|ml|severe

 

Shallow saturated stable layer.

Using both DP's and ThetaE as markers for where the surface WF could be, i'd say the warm front will end up about 10-20 miles or so north into Nebraska from the border by 00Z. So on that basis, yes many of the best parameters are north of the warm front, but any supercell along and slightly north/south of the WF will pose a significant tornado risk, no matter where exactly it ends up.

[brettjrob]

I am still convinced that most of the profiles in southern NE are actually slightly north of the surface front, and any supercells that develop there will end up being elevated.  Take a look at some profiles out of the high sigtor regions in S nebraska.  They all look like this:

 

http://climate.cod.edu/hanis/model/fsound/index.php?type=12|NAM|US|con|stp|36|*129,113*|ml|severe

 

Shallow saturated stable layer.

 

To me, that just looks like a sounding where shallow convection is occurring in the model. There's also no inversion nor any real SBCINH. I don't think it's north of the WF, although it's basically right on it. The temperatures on the north side of the boundary don't become chilly too quickly, so I can see storms having strong tornado potential right as they cross it.

[snowlover2]

SPC sure taking their time putting out the new day 2. Maybe thinking about pulling the trigger on a high risk area?

[bdgwx]

The 1.3km fire weather NAM nest doesn't look very interesting for southern KS and northern OK by 0Z. Maybe it would have been better to have that domain shifted north towards the triple point?

[jojo762]

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF SOUTHEAST  
NEB...CENTRAL/EASTERN KS INTO S-CENTRAL OK...  
 
...THERE IS AN ENH RISK OF SVR TSTMS ACROSS PORTIONS OF THE CENTRAL  
AND SOUTHERN PLAINS...  
 
...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE ENH RISK ACROSS  
THE CNTRL AND SRN PLAINS...  
 
...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLIGHT RISK AND  
INCLUDING PORTIONS OF THE OH VALLEY AND NRN MID-ATLANTIC...  
   
..SUMMARY  
 
SIGNIFICANT SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS PARTS OF  
THE SOUTHERN AND CENTRAL GREAT PLAINS TUESDAY AFTERNOON INTO THE  
NIGHTTIME HOURS. TORNADOES...SOME STRONG...WILL BE POSSIBLE...IN  
ADDITION TO VERY LARGE HAIL AND DAMAGING WINDS. ADDITIONAL ISOLATED  
STRONG STORMS ARE POSSIBLE ACROSS PARTS OF THE OHIO VALLEY TO THE  
MIDDLE ATLANTIC COAST REGION.  
   
..SYNOPSIS  
 
DEEP UPPER TROUGH CURRENTLY EXTENDING FROM THE PACIFIC NW INTO THE  
WRN GREAT BASIN WILL CONTINUE EWD THROUGH THE GREAT BASIN TODAY  
BEFORE CONTINUING THROUGH THE FOUR CORNERS AND INTO THE CNTRL PLAINS  
ON TUESDAY. SHORTWAVE TROUGH CURRENTLY ROUNDING THE BASE OF THE  
UPPER TROUGH WILL EJECT NEWD INTO THE CNTRL HIGH PLAINS  
TONIGHT...LEADING TO SURFACE CYCLOGENESIS THIS AFTERNOON AND EVENING  
ACROSS THE HIGH PLAINS. ASSOCIATED STRONG NLY LOW-LEVEL FLOW IS  
EXPECTED TO PERSIST OVERNIGHT...CONTINUING THE POLEWARD TRANSPORT OF  
LOW-LEVEL MOISTURE OVERNIGHT AND INTO TUESDAY. SECOND SHORTWAVE  
TROUGH NOW MOVING THROUGH NRN CA WILL FOLLOW A PATH SIMILAR /BUT  
SLIGHTLY MORE SLY/ TO THE LEAD SHORTWAVE...MOVING THROUGH THE  
SRN/CNTRL HIGH PLAINS TOMORROW AFTERNOON.  
 
SURFACE CYCLOGENESIS RELATED TO THIS SECOND SHORTWAVE TROUGH IS  
EXPECTED TO RESULT IN A SURFACE LOW ACROSS THE CNTRL HIGH PLAINS BY  
EARLY TUESDAY AFTERNOON. SOME UNCERTAINTY EXISTS ON THE EXACT  
LOCATION OF THIS LOW BUT CURRENT THINKING IS THAT AT 18Z IT WILL BE  
CENTERED OVER NE CO WITH A DRYLINE ARCING FROM THE LOW EWD TO CLOSE  
TO HYS AND THEN SWD TO SPS AND A WARM FRONT EXTENDING EWD FROM THE  
LOW N OF THE KS/NEB THROUGH CNTRL IL.  
 
PROGRESSION OF THE PREVIOUSLY MENTIONED SHORTWAVE TROUGHS AND THE  
SURFACE FEATURES WILL LIKELY RESULT IN TWO SEPARATE AREAS OF  
NUMEROUS TSTM WITH THE POTENTIAL FOR A RELATIVE MIN IN COVERAGE /BUT  
NOT INTENSITY/ IN BETWEEN /DISCUSSED IN MORE DETAIL BELOW/.  
   
..CENTRAL PLAINS  
 
THERMODYNAMIC ENVIRONMENT AHEAD OF THE DRYLINE OVER THE CNTRL PLAINS  
WILL LIKELY BE CHARACTERIZED BY TEMPERATURES IN THE UPPER 70S/LOW  
80S...DEWPOINTS IN THE MID 60S...MID-LEVEL LAPSE RATES GREATER THAN  
8 DEG C PER KM...AND VERY STRONG INSTABILITY /MLCAPE OVER 3000 J PER  
KG/. AS SUCH...THE THERMODYNAMIC ENVIRONMENT WILL BE MORE THAN  
SUPPORTIVE FOR SEVERE TSTMS. THE KINEMATIC ENVIRONMENT IS EXPECTED  
TO BE CHARACTERIZED BY 0-6 KM BULK SHEAR AROUND 40-50 KT. STRENGTH  
OF THE LOW-LEVEL FLOW WILL NOT BE PARTICULARLY STRONG WITH SURFACE  
WIND SPEEDS GENERALLY ANTICIPATED TO BE AROUND 15-20 KT...WITH  
SLIGHTLY STRONGER 850 MB WINDS. THE STRENGTH OF THE LOW-LEVEL WINDS  
IS THE PRIMARY FACTOR ANTICIPATED TO LIMIT HIGHER-END SEVERE  
POTENTIAL -- I.E. NUMEROUS LONG-TRACK TORNADOES -- PRECLUDING THE  
NEED FOR AN UPGRADE TO HIGH RISK WITH THIS FORECAST. THAT BEING  
SAID...NUMEROUS SEVERE TSTMS ARE STILL ANTICIPATED WITH ALL SEVERE  
THREATS POSSIBLE...INCLUDING VERY LARGE HAIL AND A STRONG TORNADO OR  
TWO.  
 
SOME THREAT EXISTS FOR A CONVECTIVE CLUSTER TO DEVELOP ALONG AND  
NORTH OF THE WARM FRONT DURING THE AFTERNOON AND EVENING AND THEN  
TRACK EWD/SEWD ALONG THE WARM FRONT TOWARDS THE LWR MO RIVER VALLEY  
OVERNIGHT. MARGINAL RISK WAS EXPANDED EWD TO ACCOUNT FOR THIS  
SCENARIO.  
   
..SOUTHERN PLAINS  
 
ANTICIPATED CONVECTIVE COVERAGE IS A BIT MORE UNCERTAIN ACROSS THIS  
REGION THAN AREAS FARTHER N. SECOND SHORTWAVE IS EXPECTED TO EJECT  
OUT OVER THIS REGION DURING THE AFTERNOON. HOWEVER...THE SHORT  
WAVELENGTH BETWEEN THE LEAD SHORTWAVE MOVING THROUGH THE CNTRL  
PLAINS AND THE ONE EJECTING OUT OVER THIS REGION IS LEADING TO MORE  
BACKED -- I.E. SOUTHERLY -- MID-LEVEL FLOW...CREATING WIND PROFILES  
THAT APPEAR MORE FAVORABLE FOR LESS DISCRETE SUPERCELLS AND MORE  
QUICK TRANSITIONS TOWARDS A LINEAR MODE. ADDITIONALLY...LIKE AREAS  
FARTHER N...LOW-LEVEL FLOW IS NOT CURRENTLY ANTICIPATED TO BE  
PARTICULARLY STRONG. AS SUCH...THE POTENTIAL FOR HIGH SIGNIFICANT  
SEVERE COVERAGE IS INSUFFICIENT TO UPGRADE ANY AREAS TO HIGH RISK.  
IN FACT...SOME OF THIS REGION MAY ONLY SEE ISOLATED TO SCATTERED SVR  
COVERAGE. HOWEVER...GIVEN THE OVERALL THERMODYNAMIC AND KINEMATIC  
ENVIRONMENT...SUPERCELLS CAPABLE OF ALL SEVERE HAZARDS INCLUDING  
VERY LARGE HAIL AND STRONG TORNADOES REMAIN POSSIBLE.  
 
THE MODERATE RISK WAS EXTENDED SWD TO THE RED RIVER TO ACCOUNT FOR  
HIGH CONFIDENCE IN WIDESPREAD SEVERE THUNDERSTORM COVERAGE. THIS  
AREA IS EXPECTED TO EXPERIENCE THE GREATEST OVERLAP IN ANTICIPATED  
STORM COVERAGE...INSTABILITY...AND LOW-LEVEL SHEAR...PARTICULARLY  
AROUND 00Z AS THE LOW-LEVEL JET INCREASES. SOME ADDITIONAL SWD  
EXTENSION INTO TX MAY BE NEEDED AS DETAILS BECOME MORE CLEAR IN  
SUBSEQUENT OUTLOOKS.  

[jojo762]

There ya go, meh low-level flow, and relatively messy wind-fields contributing to no high-risk type threat, but still the threat of significant severe weather.

[wildwestpb]

Edit: Deleted SPC Forecast since it was in the thread already.

[weatherextreme]

THE STRENGTH OF THE LOW-LEVEL WINDS
IS THE PRIMARY FACTOR ANTICIPATED TO LIMIT HIGHER-END SEVERE
POTENTIAL -- I.E. NUMEROUS LONG-TRACK TORNADOES -- PRECLUDING THE
NEED FOR AN UPGRADE TO HIGH RISK WITH THIS FORECAST.

[jpeters3]

To me, that just looks like a sounding where shallow convection is occurring in the model. There's also no inversion nor any real SBCINH. I don't think it's north of the WF, although it's basically right on it. The temperatures on the north side of the boundary don't become chilly too quickly, so I can see storms having strong tornado potential right as they cross it.

 

Shallow convection/clouds or warm front are sort of semantics.  Shallow convection/clouds is common just north of a warm front. Regardless of what is causing the profile to look like this, the shallow statically stable layer shows up in pretty much every profile north of the KS/NE boarder, and has in several rounds of model runs.  What the model shows as SBCIN is not based on the actual surface virtual temperature (you see, the lifted parcel path starts to the right of the surface virtual temperature in the sounding), so the actual SBCIN is probably higher than what is listed on there. You can easily get supercells within an environment like this, but it is very difficult to develop a tornado when surface parcels are convectively inhibited.

[jpeters3]

Using both DP's and ThetaE as markers for where the surface WF could be, i'd say the warm front will end up about 10-20 miles or so north into Nebraska from the border by 00Z. So on that basis, yes many of the best parameters are north of the warm front, but any supercell along and slightly north/south of the WF will pose a significant tornado risk, no matter where exactly it ends up.

 

I generally agree with this - anywhere near, or slightly south of the boundary (and slightly south of the sounding I posted) is going to be prime.  I do expect that some of the convection the model is blowing up north of this region is going to be elevated though.  Might end up being elevated supercells with the very high low-level SRH, but elevated none the less.

[bdgwx]

There ya go, meh low-level flow, and relatively messy wind-fields contributing to no high-risk type threat, but still the threat of significant severe weather.

 

It kind of sounded like they left open the possibility for an upgrade tomorrow if conditions warranted it didn't it? Or did I read in between the lines too much?

[FHSC Sam]

It kind of sounded like they left open the possibility for an upgrade tomorrow if conditions warranted it didn't it? Or did I read in between the lines too much?

I agree, it probably depends on how things align

[hlcater]

I agree, it probably depends on how things align

Me too, it sounded like if wind fields could clean themselves up a bit, then a high risk would be warranted, however, I'm not sure they will. Only time will tell.

[ClicheVortex2014]

It kind of sounded like they left open the possibility for an upgrade tomorrow if conditions warranted it didn't it? Or did I read in between the lines too much?

I didn't get the impression that they've ruled it out. I've underlined the key to that sentence

 

THE STRENGTH OF THE LOW-LEVEL WINDS  

IS THE PRIMARY FACTOR ANTICIPATED TO LIMIT HIGHER-END SEVERE  

POTENTIAL -- I.E. NUMEROUS LONG-TRACK TORNADOES -- PRECLUDING THE  

NEED FOR AN UPGRADE TO HIGH RISK WITH THIS FORECAST.

[FHSC Sam]

Me too, it sounded like if wind fields could clean themselves up a bit, then a high risk would be warranted, however, I'm not sure they will. Only time will tell.

I'm holding out hope that they will, although either way, this is a highly volatile system and regardless will probably produce several tornadoes, just not as widespread as it could be. 

[LocoAko]

I'm holding out hope that they will

 

What difference does it make, really?