2016-10-04 EVENT: TX, OK, KS.

[adlyons]

SPC SWOD48 has highlight a 15% risk area for day 6 across portions of the southern plains for a potential severe weather day. This has been something myself and a few friends have been watching on the long range guidance for a few days now. It has remained remarkably consistent over the last few runs with some minimal changes in timing and structure of the ejecting wave.

General Synopsis:

Current upper level flow is dominated by enhanced ridge across the central us associated with a west coast rex block as well as a remnant cutoff low over the ohio valley and eastern us. Medium range guidance indicates little change over the next 3 days with high latitude zonal flow developing around the periphery of the central US ridge. Cut off low is expected to meander around the east coast eventually weakening. Beginning day 3 western US ridging begins to break down in advance of developing west coast trough moving on shore by Day 4 Sunday. Trough continues to dig and move into the great basin 4 corners region by Day 5 Monday with the development of a strong lee cyclone along the front range. There is some uncertainty regarding the placement and strength of this low. 500 mb trough should continue to deepen before ejecting out across the central US and southern plains by day 6 Tuesday. Strong flow aloft and the development of a strong lee low suggest potential for strong low level jet development. In terms of moisture the gulf has generally been unaffected by several weak cold fronts along the gulf coast and has retained seasonably strong moisture with PWATS over 2 inches pooled along the mexican coast. However TS Matthew is inducing offshore flow along the eastern half of the gulf shore which could potentially impact moisture return. Regardless, Models show the development of a nice sharp dryline through much of the southern plains with adequate moisture (dewpoints in the upper 50's and low 60's)

Things to like:

• Large 500 mb trough with strong jet streak and several smaller embedded shortwaves in the flow.
  
• Quite a strong low level jet with 850mb flow southerly in the 40-50kt range. GFS for comparison.
  
• Ensemble GFS is hinting at the development of a strong LEE cyclone along the front range that helps to back low level flow.
  
• Kinematics look excellent with strong shear favorable for supercells and tornadoes.

Things not to like:

• Timing differences between GFS and ECMWF have been noticeable at times. GFS has been showing the main wave ejection earlier and more neutrally which drags the whole system to the east and north wile messing with the shear profiles. AKA Veer Back Veer.
• Moisture return has been iffy on several runs. Offshore flow from TS Matthew could impact the quality of moisture return. The GFS has been mostly consistent in keeping low 60's (62-63) into southern kansas.
  
• Mid and low level lapse rates have also been less than ideal. Cloud cover ahead of the dryline in some of the models appears to be limiting the surface temperature impacting instability. Would like to see the development of a wider instability corridor and some higher surface temps.

Summary:
Looks like the fall season could get rolling here soon with an active pattern. This setup may be worth watching. Looks like some of the major ingredients are in play. Fall events can be quite large like last years November 16th Outbreak. Always good to pay attention and see what happens.

 

[Jacob Punch]

I agree entirely on what you have said. The main problem so far (and I know that the available energy is the hardest to predict) is that we don't know how much energy will be in the atmosphere. Also, where do you receive forecast accurate hodographs? I cannot ever seem to find any, especially on Pivotal Weather.

 

[adlyons]

I agree entirely on what you have said. The main problem so far (and I know that the available energy is the hardest to predict) is that we don't know how much energy will be in the atmosphere. Also, where do you receive forecast accurate hodographs? I cannot ever seem to find any, especially on Pivotal Weather.

Not sure what you mean by forecast accurate hodograph.

 

[Jacob Punch]

I was meaning that some of the hodographs were completely different than the SPC, which I have fixed the problem on my own, forgetting that there were numerous forecast models! Thanks anyway though.

 

[Robert Forry]

Good stuff! 12Z GFS today got my attention. Agree with your "Reasons For" and have the same concerns. Moisture always worries me with fall set ups, but like you stated the GFS has been consistent at progging low 60 dews. Be nice of that sun was out in advance of the DL to really drive up CAPE and lapse rates. It's a long drive out so here's to things improving over the next few days.


Sent from my iPhone using Stormtrack mobile app

 

[Ethan Schisler]

The event has came into the range of the 12km NAM as of this morning. One thing I've noticed is that both the GFS and NAM have shown a secondary surface low forming in SW KS/NW OK during the day on Tuesday, however there isn't agreement on how well organized/long lasting it will be. As of right now based on the NAM/GFS I've been favoring the area in South Central Kansas/Oklahoma border region. Instability on the latest NAM is quite higher than the GFS (however that is usually the case with that model), likely overdone somewhat. Storm mode will be the biggest question if the NAM solution comes into fruition in my eyes. I'm not a fan of the NE/SW oriented dry line, nor the strung out surface lows.

 

[Greg McLaughlin]

00z soundings from CRP, BRO, and DLT show much improved low-level moisture depth/quality. The pump is primed.

 

[Ben Holcomb]

To continue with what Greg said, there seems to have been a notable increase in moisture on all of the aforementioned soundings from 00Z to 12Z. Surface dewpoints have made it to the 60s in Southern Oklahoma per the mesonet at this hour. The real question in my mind is lapse rates - They seem to be mediocre at best both in forecast and in real soundings to the west right now. I would like to see mid levels be >7C right now, but they aren't.

Water Vapor shows a vigerous trough in the western US, just now starting to eject over the rockies. I'm still concerned about timing, as the NAM hasn't had completely optimal timing, but with a system this strong it may not be a problem.

Bottom line, I feel like I'll be pulling the trigger and chasing in Oklahoma somewhere along the dryline tomorrow afternoon.

 

[James Gustina]

The biggest unknown right now for me is when the first jet maxima will eject over the High Plains. We already have pretty meh lapse rates to the west (thanks to the source region being nice and wet along with a Pacific airmass sitting over northern NM/western CO) which would definitely not benefit from a lead impulse shooting off convection over the target region. That said, 6.5C/Km definitely isn't a death knell and it looks like we might get modest height-falls/mid-level cooling in the early afternoon in SW Oklahoma along the dryline to maybe compensate a bit. The shear profiles are also a bit hit or miss just going off what the 12Z NAM has tossed out, but there are definitely some profiles that look favorable enough around the 40 corridor down to the Wichitas.

I don't have any real expectations for this one, but I'd be surprised if we don't see a storm squeak out at least one tornado somewhere on the dryline tomorrow, barring the profiles going full VBV.

 

[David Reimer]

I know most local folks in the Southern Plains will be chasing tomorrow. Not every October you get a decent southern Plains setup. Overnight and morning model data has continued to trend the Kansas target downward in terms of chaseable tornadic potential. It appears probable a cool pool will develop with early afternoon convection. That cool pool/OFB will move east and shrink the warm sector through early evening. It'll also tend to undercut convection and diminish tornado potential. There will likely be a few brief tornadoes along with plenty of large hail and damaging wind gusts. I wouldn't be too surprised to see a small MDT in KS for hail/wind potential if everything were to come together.





My focus on a chaseable target will be in West-Central to Northwest Oklahoma. My preferred model of choice is the 0Z/06Z TTU WRF. This typically conservative model shows the Kansas play well along with a few discrete cells south into Central Oklahoma. 12Z 4KM & 12KM NAM indicate any dominant supercells would have the potential to become tornadic. Storm motions will be a tad more favorable and with more discrete storm mode compared to Kansas. Potential caveats that could diminish potential tomorrow would be convection tonight that results in more cloud cover tomorrow. Another factor would be if moisture return is less impressive or more shallow than models show. If some of this morning's model runs do come to pass I wouldn't be surprised if one or two supercells produced a couple tornadoes tomorrow in Oklahoma - possibly infringing on the OKC metro by 7 PM. We'll see how trends evolve tonight.

 

[Jeff Duda]

Been delighted to see the moisture forecasts improve as this event has neared. It seems increasingly likely we will see mid to even isolated upper 60s dews throughout OK and into S/C KS (not upper 60s in KS, but mid 60s still seems plausible). Cloud cover is also trending downward, leading to warmer surface temps forecast in the 80s rather than the 70s as the GFS had been suggesting for days coming in. Despite the adequate low-level thermodynamics for early October, the comparably poor lapse rates result in unexpectedly lower instability compared to what you'd typically expect from something like 82/68 in April or May. Widespread 2000 MLCAPE during the afternoon appears unlikely, but there will likely be isolated spots where such instability exists, albeit briefly. Such CAPE is still plenty to get tornadoes when considering the impressive deep layer shear and adequate low level shear.

My remaining concerns are the following:
-Will cloud cover verify as more widespread than forecast, thus seriously limiting instability and storm coverage?
-Will storms go too early and overturn the atmosphere, thus wiping out large swaths of the warm sector before prime time?

Most of the models, especially the NAM, GFS, SREF, and NCAR ensemble, have been rather aggressive with precipitation coverage throughout the day north of the KS-OK border. While more sparse south of the border, forcing is also weaker, and with the potential for limited convergence near the dryline in OK, a "cap" bust cannot be totally ruled out (note "cap" in quotes because there really isn't going to be much of a cap, but storms could still fail to form due to lack of forcing).

It's also interesting to note that two members of last night's NCAR ensemble progged rotating storms along the Red River, near LAW/SPS. Couldn't really discern the environmental differences between those members and the others that didn't fire much down there. So uncertainty is still an issue with this system. At this point, i could see this being anywhere between a regional severe weather outbreak and a mostly benign, isolated thunderstorm day.

 

[Royce Sheibal]

I haven't had a chance to dive really deep into tomorrow, as I won't be able to chase, but based on SPC SREF it looks like we've got a Goldilocks zone from Beatrice, NE down to Wichita, KS. 1500+ Cape, good SRH, OK ESHR, good forcing, good moisture...It's all coming up just about right for a decent fall event.

Regarding the Northern Target: SREF's bulls-eye is somewhere between Beatrice, NE and Friend, NE. If anyone chases Nebraska a lot they know about the tornado-genesis zone in Jefferson county, which has more tornado's per SQ mi than any other county in the state. If I were a betting man, I'd bet that's a good starting target. I am concerned about early morning crapvection, as the CAMs all predict, but it wouldn't surprise me at all if we get super-cells forming out of their remnants shortly after lunch with continued convection down the line to the SW.

As for the southern target, I really like the Wichita area and chasing tail-end Charley. Anything north of that might get cutoff from the southerly flow too quickly or get cold pooled and anything south looks like will have weak forcing. Good luck tomorrow, gentlemen!

 

[Ben Holcomb]

Looking over 00Z data, the NAM seems to be way overdoing moisture. In fact, after looking at the 00Z LCH sounding, I am quite concerned. Most of our sfc winds are out of the SE and gusting up to 46 mph (Beaver, OK) this hour with dewpoints in the upper 50s to low 60's. With that said, the LCH sounding shows significant drying in the moisture profile, especially below 850mb. Flow in the gulf appears to be mostly East to West, with the best moisture showing up in the CRP/BRO soundings.. and even Del Rio.. but that doesn't seem to be our source region at this hour, so I don't know if we'll realize the upper 60s dewpoints the NAM is showing with 2000+ CAPE. Seems like that might be quite a bit overdone.

That said, if anything fires off the dryline in OK, I will be there.

 

[adlyons]

Looking over 00Z data, the NAM seems to be way overdoing moisture. In fact, after looking at the 00Z LCH sounding, I am quite concerned. Most of our sfc winds are out of the SE and gusting up to 46 mph (Beaver, OK) this hour with dewpoints in the upper 50s to low 60's. With that said, the LCH sounding shows significant drying in the moisture profile, especially below 850mb. Flow in the gulf appears to be mostly East to West, with the best moisture showing up in the CRP/BRO soundings.. and even Del Rio.. but that doesn't seem to be our source region at this hour, so I don't know if we'll realize the upper 60s dewpoints the NAM is showing with 2000+ CAPE. Seems like that might be quite a bit overdone.

That said, if anything fires off the dryline in OK, I will be there.

Need to look to the west. DRT has a 65 degree dewpoint.

 

[adlyons]

I haven't had a chance to dive really deep into tomorrow, as I won't be able to chase, but based on SPC SREF it looks like we've got a Goldilocks zone from Beatrice, NE down to Wichita, KS. 1500+ Cape, good SRH, OK ESHR, good forcing, good moisture...It's all coming up just about right for a decent fall event.

I have to disagree about this area. Upper level flow is parallel to the sfc boundary with strong linear forcing and little cap. It screams nasty squall line almost immediately. You may have some embedded rotating cells but in terms of discrete or even semi discrete I really think you are going to have a hard time in that area.

 

[Greg Blumberg]

What looked like a pretty good setup from my (and Tim Supinie's) point of view (per last night's 00 UTC runs) seems to have vanished. A few points primarily based on our analyses of the NWP solutions:

1.) 00 UTC NAM and GFS forecast soundings around the 21-00 UTC timeframe have southwesterly 850 mb winds just present near the dryline. This is noticeable along the central Oklahoma to Wichita, KS stretch of the dryline and seems to be a consistent issue with a few other model runs I've seen (e.g., the 4 km NAM and the NSSL WRF). I'm a little concerned about the possibility that storms won't initiate and if they do, they struggle with the drier air that is being advected inwards by the 850s. In fact, the dryline may be experiencing synoptic scale subsidence during the 23-02 UTC timeframe, which combined with the poor 850s suggests that parcels lofted upwards by the dryline vertical circulation will be quickly advected westward into an environment possibly experiencing synoptic scale descent. Some of the simulated IR imagery I've seen from the 00 UTC 4 km NAM has updrafts that seem to struggle to get going. The model simulated reflectivity doesn't really have any storms that get solidly going near the dryline.

2.) The lack of good 850s is related to the evolution of the 500 mb vorticity max in the 00 UTC NAM and GFS solutions. These forecasts suggest that this vorticity max will have entered in western KS by 18 UTC, and effectively, you can see that there really aren't any substantial surface pressure falls forecasted in the evening, suggesting that any lift may be primarily driven by surface cold pools or dryline/frontal circulations. Between 21 and 00 UTC these forecasts also suggest 500 mb heights may be rising over the TX/OK Panhandle. Not a favorable situation if you want a deeping surface low.

3.) These issues force a decision between which two potential spots to chase. First, you could go up into KS and get into an environment that may favor more mixed or linear modes of convection given the more unidirectional deep-layer shear parallel to the initiating boundaries. Or, you could take the risk and stick around the Enid, OK area and hope that the synoptic environment permits a good storm to form.

The 00 UTC NSSL WRF is encouraging though. It breaks out two supercells around 22 UTC despite the somewhat southwesterly 850 mb winds. It looks like the least offender of the bunch in this issue, so maybe things will work out. But, it could be similar to the night of April 24th, 2016, when one of the convection-allowing-models teased us with the prospect of supercells. Storms in southern KS/northwest OK really struggled that day.

 

[Max Olson]

Moisture is certainly concerning for tomorrow, I don't like what I see on meso-analysis right now. Low level flow is weak and those 70 dews NAM shows making their way up to OK are still way down in the gulf. With how far north the upper low is I really wonder how high our dews (and CAPE for that matter) will actually get tomorrow. No real target decisions will be made until morning but right now I'm not overly excited. I also agree with Greg, April 24th popped into my head as a similar setup to reference from.

http://www.spc.noaa.gov/exper/mesoanalysis/s15/bigsfc/bigsfc.gif?1475562087813

 

[Royce Sheibal]

I have to disagree about this area. Upper level flow is parallel to the sfc boundary with strong linear forcing and little cap. It screams nasty squall line almost immediately. You may have some embedded rotating cells but in terms of discrete or even semi discrete I really think you are going to have a hard time in that area.

I live in Nebraska. I chase in Nebraska. 90% of the time embedded rotating super-cells is all we get. And despite all of this we still get a decent amount of tor-production on days like today. The actual act of chasing, on the other hand, is a total nightmare in this scenario. But such is chasing in Nebraska.

 

[Brian McKibben]

New 12z and 13z HRRR along with the 12z 4km NAM are showing a new trend of storms in Central and Southern Oklahoma. Tds per Mesonet are already in the mid-60s. It will be interesting to see if any of this morning convection lays down an OFB.

 

[Brian McKibben]

New 12z and 13z HRRR along with the 12z 4km NAM are showing a new trend of storms in Central and Southern Oklahoma. Tds per Mesonet are already in the mid-60s. It will be interesting to see if any of this morning convection lays down an OFB.

View attachment 14848

View attachment 14849

Not taking these runs as gold but it is something to monitor throughout the day.

 

[Ben Holcomb]

Color me surprised by the incredible moisture return - as the NAM predicted- in Southern and Central Oklahoma. Not much firing with the early wave, so attention turns back to the wave that is in New Mexico and looks to eject this afternoon per current WV loop. Starting to really buy these central Oklahoma scenarios, and so is OUN

From OUN Hazardous Weather Outlook

IMPACTS...
THE MAIN IMPACTS WILL HAIL TO THE SIZE OF TENNIS BALLS... DAMAGING
WIND GUSTS TO 70 MPH AND FREQUENT CLOUD TO GROUND LIGHTNING.
A TORNADO OR TWO WILL ALSO BE POSSIBLE... ESPECIALLY ACROSS
PORTIONS OF CENTRAL OKLAHOMA.

I'll be waiting to see what the 19Z OUN Sounding shows. Should be a fun day

 

[Brian McKibben]

Color me surprised by the incredible moisture return - as the NAM predicted- in Southern and Central Oklahoma. Not much firing with the early wave, so attention turns back to the wave that is in New Mexico and looks to eject this afternoon per current WV loop. Starting to really buy these central Oklahoma scenarios, and so is OUN

From OUN Hazardous Weather Outlook

IMPACTS...
THE MAIN IMPACTS WILL HAIL TO THE SIZE OF TENNIS BALLS... DAMAGING
WIND GUSTS TO 70 MPH AND FREQUENT CLOUD TO GROUND LIGHTNING.
A TORNADO OR TWO WILL ALSO BE POSSIBLE... ESPECIALLY ACROSS
PORTIONS OF CENTRAL OKLAHOMA.

I'll be waiting to see what the 19Z OUN Sounding shows. Should be a fun day

Surface winds in C. Oklahoma start to back at 23z. That would help enhance the low level shear. Tds are almost to 70 per Mesonet. HRRR puts Tds in the upper 60s and some possible 70s at showtime. Just went for a walk to get a feel for the air. Some of the wind gust felt a bit cool to me. Once these clouds burn off and we get some more heating the atmos should be primed.

 

[Ethan Schisler]

I'm not chasing today personally as life priorities are taking over once again (blah!). However I like the way things are shaping up across Central/Southern Oklahoma this afternoon/evening. I believe the Kansas play will most likely be a wind/hail event (perhaps a couple isolated tornadoes?), things should go linear up there fairly quickly.

Further south, recent CAMs are showing storm developing late afternoon/early evening around the I-40 corridor from OKC perhaps just eastward. If I were chasing I WOULDN'T hedge my bets in between as we have seen classic scenarios where there is an area over Northern OK where nothing occurs (5/19/13, 5/10/10 etc).

The environment in Central Oklahoma ahead of the dry line is pretty good with moisture coming in on the high side of what I've expected (some upper 60s already being evident). MLCAPE is approaching ~2000 J/KG as well which is respectable for early October at 2pm. Low level shear should increase as the evening wears on and winds back more, increasing the tornado potential. I guess in my eyes is how long these *potential* storms stay surface based further south and how early they get going. Forecast soundings off the HRRR show CIN increasing fairly quickly after 01z, so that will be something to keep in mind. If things time right and they stay surface based for a couple hours, there is certainly the potential for an isolated significant event in my eyes.
Good luck to those chasing and be safe.

 

[Ethan Schisler]

Things appear to be trending downward for convective initiation in Central Oklahoma based on what I'm seeing. The latest mesoanalysis plots are showing convective inhibition filling back in near the dry line as of 22z. It doesn't look like much of a CU field on visible satellite imagery either as of 5:30PM. In addition... The 19z OUN sounding also showed quite a cap with -93MLCIN observed...and now the 21z HRRR doesn't convect anymore across Central Oklahoma with a tail-end charlie near the KS/OK border being the only thing in play. We have another hour and a half of daylight to wait things out, but not looking the best as of right now.

As expected, storms across a majority of Kansas are 1) taking on a linear formation and 2) moving in a direction which is taking them into more "CIN rich" (lol) airmass, which is lessening the tornado potential up there despite 0-1km SRH values more than sufficient for tornadoes.

I think if I were chasing at this point, given I hadn't gone already too far south, I would hold out for something near the KS/OK border on the tail-end of whatever ends up coming out of the stuff forming in SC KS at the moment. Easy to say sitting in my armchair though....

 

[Jeff Duda]

Post-mortem discussion:

Trolled by the HRRR. While the OKC storm did finally materialize, it was at least one hour later than about 8 consecutive runs of the HRRR had progged. However, somewhat in opposition to the 00Z OUN sounding, that storm really seemed to struggle to fully organize. With a hodograph like this (note the critical angle value, especially) ...



...I'm a bit surprised the storm evolved the way it did. There was the slightest warm nose around 750 mb, so maybe that combined with slowly cooling surface temps as the evening wore on were enough to disrupt things. Part of me wants to say that stability is not the only factor explaining the lack of strongly organized rotation on that storm, though.

Anyway, I'm glad it failed to evolve since the tip of the hook basically went directly over my apartment. Phew!