4/24/08 FCST: NE/KS

[Jonathan Whitehead]

This forecast is Central and Southern Great Plains.
For this forecast I used the 00Z NAM for basic forecasting, then the SPC SREF for severe wx parameters.

Looking at the 00Z NAM, it has 40-50kt SWLY flow from N TX all up through to NE with 30 Kt flow south of I-20. 850 winds are veered through 15-18Z then back to S-SE through 21Z with flow of 25kts.
At sfc winds are southerly all up southern plains with 30* backed winds on a Hays, KS to Greensburg line. Also worth noting NE winds in NEb and SWLY winds in far W KS (triple pt maybe in extreme NW KS)
Also at sfc, gulf moisture will surge northward overnight leading to 60 dews into NE with pockets of near 70dews in N TX and N-S along main body of OK by 21Z. That may be a bit overdone but wouldnt surprise me.

Taking a look at instability, SPC SREF has thin line of MUCAPE>3000 from Del Rio to SAT up 35 (and widening with northward extent) to include large part of Southern, Central, & Northern OK as well as southern KS. Looking at all three CAPE perameters (SBCAPE, MUCAPE, MLCAPE), SREF paints a bullseye over western N TX and southern OK with CAPE >3000 to 4000.

Severe perameters are as follows (at 21Z):
Craven-Brooks sig severe >6000 is maximized around the ADM-Bowie, TX-Duncan area with 30% prob all along I-35 corridor in OK. Supercell composites (>6) are maximized from Bowie, TX NEWD to OKC then NWWD to Enid to Medicine Lodge to ICT with >50% prob. Prob of sig tornado >3 is actually maxed at 00Z with bullseye over I-35 corridor from OKC to ADM with 30% prob all way up to Newton, KS.

Precip:
Now I dk if the NAM is suffering convective feedback issues but it shows precip in northern OK at 12Z then southern OK at 15Z but squash's it by 18Z with no precip in OK thereafter. In KS, the NAM has precip breaking out at 18Z along I-135 corridor. Worth noting, the GFS doesnt show precip till 00Z and thats in KS but has it gone by 06Z.

Discussion:
Everything ive looked at points to a high end severe weather day in KS. The big mitigator is lack of strong, high amplitude 500mb trough blasting into the plains. Just not there. However vertical deep layer is more then sufficient for tornadoes, I just dk about long track violent tornadoes. Also appears capping will be an issue into OK as models are hit and miss on initiating precip in OK. I just wish SPC had some sort of CINH forecast perameter. Only thing I was able to look at were forecast soundings and it showed an almost non existent cap at 00Z at OUN but im not putting a whole lot of weight into that. Hodos are nicely curved all up and down 35. Def looks to be a nice day for everyone in KS.

Below I have posted a few forecast images for your viewing pleasure.
To view fcst images together in one site, please go here: http://s274.photobucket.com/albums/jj256/ouweatherboi69/04-24-08 FCST/

 

[Ilya Neyman]

Some things people should keep in mind - the NAM is MUCH more favorable at a potential severe wx setup for the southern sector i.e. OK than the GFS, the main reason is the progged 850 flow, due southerly on NAM vs SW on GFS. Another thing to watch is whether or not some sort of a dryline bulge develops as both models indicate, with the NAM being more SW than the GFS.

For this forecast I think I will be going with the NAM, not so much because it has the most significant potential on it, but rather because I believe it is catching onto more mesoscale features than the GFS. In other words the NAM is more believable right now. It also has almost full cap erosion juxtaposed with 3,000+ SB/MLCape over WCNTRL/SW OK by 00z.

The main thing will be to watch soundings and wind profiler info during the afternoon. Should the low level flow be generally southerly like the NAM is showing, that will allow the most quality and substantial moisture along with a more breakable cap into the region.

Another thing to keep in mind is convective outflows and differential heating boundaries possibly setting up from Wednesday's convection across TX, OK and KS.

I'm not 100% sold on the cap actually breaking south of KS just yet, but if it does, watch out.

Edit: I think SPC relied heavily on the 4km wrf output, which shows zero convection south of KS. This same model, however, also shows late morning convection across OK, which doesn't seem very probable at the moment. Also, the 4km's performance this season has been shaky, both with convection/lack thereof and location.

 

[Mike Hollingshead]

One thing going into that low level flow difference between the two models might be what they are thinking as far as precip in the plains in the morning.

http://www.rap.ucar.edu/weather/model/eta12hr_sfc_prcp.gif
http://www.rap.ucar.edu/weather/model/gfs012hr_sfc_prcp.gif

NAM has much less in the way of morning convection in the eastern plains. Seems that might be what is allowing it to have the better low level jet. The old NAM had it with more precip and had the little kink in the 850 flow in eastern OK lifting ne sort of late. I'm sort of thinking the NAM will be closer regarding the morning convection.

http://www.spc.noaa.gov/exper/mesoanalysis/s2/850mb.gif
Gotta love the low level moisture already heading north behind the east TX convection.

My current plan is head to the Arapahoe NE to Norton KS area. I'm scared of the southern KS dryline play, but also a little scared of the likely good pooling ne of the sfc low. If things really deepen like the NAM is progging, I could see a couple very chaser friendly supercells ahead of the sfc low. I like the more sw flow with the upper jet up there as well. Gets a little more anticyclonic south. GFS differs a little with the NAM on that and keeps sw flow aloft above the whole dl in KS. May not matter, but I just like it more left of the storm motion.

 

[Rob Lightbown]

North or south, that is the question??

I took a look at the 00 and 06Z NAM models, as well as the 00Z GFS model for today's setup.

The 00/06Z NAM differs in where they combine the best helicity and CAPE. The 00Z NAM targets northern Kansas by 03Z, while the 06Z NAM really targets southern Kansas during the 00-06Z timeframe.

As for the 00Z GFS model, it appears that the best CAPE may set up right over central Kansas around 00Z, although the STP index points to southeast Kansas.

So, in my virtual, armchair world of chasing, I'd probably setup on I-135 near McPherson during the early afternoon hours, so that I could target any storms either to the north or potentially to the south. Either way, I agree with everyone else that this is a decent setup for a good chase day.

Good luck to everyone that is out there today!!

 

[Mark Farnik]

Good morning, all!
I am writing this from my motel room at the Motel 6 in Colby, KS, where I got in from yesterday's lackluster eastern CO chase about 10 p.m. CDT and got a solid night's sleep. Fwiw this is a pretty decent motel for $48 a night, nice and clean with free Wi-fi and continental breakfast, which I'm going to go partake of in a minute.
Anyway, on to the day's forecast. At the moment, its a no brainer that I need to go further east, and as such I'm heading to Hays as soon as I get a bite of breakfast here in Colby, but its a much tougher call as to whether to go north or south from there. With the later initiation, there will be plenty of time to adjust the target before convection fires, so I'm not going to make any commitment either direction until later this morning or early this afternoon.
Either way, it looks like a potentially awesome chase day with a good probability of tornadoes, one or two of which may be strong, later this afternoon and into this evening across all of central Kansas into south central Nebraska.

EDIT - 1300 UTC Convective Outlook just issued. The Moderate Risk area has expanded a bit north and west towards McCook and North Platte, otherwise the outlook is pretty much the same. Tornado probs are highest over north central KS and south central NE, roughly between Hays, KS and Lexington, NE. I wouldn't totally discount the possibility of tornadic storms south of I-70, but at this point its looking like the big show today is going to be between I-70 and I-80 east of US 83 and west of US 81.
On second thought, I think I'm going to abort my Hays target and head east on Highway 24 from Colby to Hill City and check data again there.

 

[Kevin Statler2]

SPC moved the tornado probs up a little more north then the 0600 outlook. Im not exactly sure why as the SC part of KS looks to be in just as threat as north.

 

[Doug Mitchell]

Is it just me or is the 12z RUC favoring the KS/OK border now? Most CINH eroded by 0z at Woodward and some precip breaking right on the border.

 

[Tim Marshall]

TARGET: PRATT, KS TIME OF DEPARTURE FROM DALLAS, TX: 9 AM - After a stormy night, it looks like the show now will be in KS. PROS- Tongue of higher dewpoint air is moving northward into KS. I expect clearing to occur in the warm sector. A dryline is progged to mix eastward into SW KS and W OK. CONS - The upper trough is still way out west and it will be closer to 00z before stronger winds and enhanced lifting arrive aloft. The cap is progged to be quite strong south of I-70, but I will be looking for a more isolated storm on the dryline. TM

 

[Gabe Garfield]

Is it just me or is the 12z RUC favoring the KS/OK border now? Most CINH eroded by 0z at Woodward and some precip breaking right on the border.

Yeah, the 12Z RUC looks a lot more favorable for the southern target, and less so for the northern (except for the triple pt). The real juice doesn't make it far enough north in this run, so the cap is a bit more pronounced. At the same time, the cap weakens sufficiently for convection across the dryline in Oklahoma into SC KS. The 850 flow is much stronger than previously forecast (~40 kts), which really increases the SRH. Should the RUC sol'n verify, I find no reason to drive north of I-70 today.

EDIT: I like your target, Tim. The RUC sol'n shows Pratt just north of the dryline bulge w/ >4000 SB CAPE, reasonable SRH, and negligible CINH.

 

[Scott Roberts]

Has anyone been tracking the recent performance of the RUC at 12 hrs? It seems like such an outlier from the other models in this instance, though the WRF is showing some bias that direction, too.

 

[Mikey Gribble]

I just got done glancing things over and I think I'll stick with my target from last night and set up along the OK-KS border. Both the NAM and RUC have the dryline farther East by 00Z now, so I'll have to scoot back East a bit to account for that. Right now I like Coldwater, Kansas. I'll probably stay in Pratt for a while too because I know of a good wifi spot there. That will be a good starting point. Once CU starts to form (assuming it does) then I'll move southwest from there to the dryline.
It is nice to see the RUC breaking out precip. I trust the RUC about as far as I can throw it though (I think it's pretty good size). I haven't finished my forecasting yet, but from what I've seen so far I have no reason to change my previous forecast aside from scooting 30 miles back East to account for the placement of the dryline. The models haven't been so hot on dryline placement lately so I wouldn't be surprised to see the dryline further West than what is currently being shown.

 

[Mike Umscheid]

I don't think the convergence at dryline bulge you see in the NAM and RUC will be sufficient enough to generate deep moist convection. The thing I really do not like is the upper jet streak positioning. The dryline bulge along the OK-KS border will actually be in the classic right-exit region of subsidence. The overall environmental forcing suggests suppression along the KS-OK border from Pratt to Woodward. I shall be humbled if a classic supercell develops in this area. If I could chase today, I would be along the KS-NE border from Norton to McCook... and be patient. Clearly the best dynamic forcing for very strong ascent will be up in this area. This reminds me a bit of May 22, 2004... there was nice convergence on a dryline in KS... and towers tried hard...only to fail at "zero-hour" along the dryline. All the action was up along and just north of the KS-NE state border. Southern NE will be lighting up this evening...especially late. For the hearty dryline bulge chasers... you can keep track of the short-fuse composite over this area: http://www.crh.noaa.gov/ddc/?n=shortfuse. Best of luck out there.

 

[Mike Johnston]

Is it just me or is the 12z RUC favoring the KS/OK border now? Most CINH eroded by 0z at Woodward and some precip breaking right on the border.

I agree, and the 12z NAM & RUC look reasonably in synch. Given the opportunity, I would set up late this afternoon just west of Wichita...say near the airport at U.S. 54/400 and I-235. Good, quick road options in all directions from there w/ great chasing terain. As far as the atmospheric factors at points just west and slightly south of this location, instability building during the day right along N/S theta-e axis, looks like surface low evolving in SE CO < 1000mb will provide backed surface winds, and any storms that fire should be moving into region of enhanced low-level helicity.

Agree w/ previous posts that the flow at both 850mb and 500mb doesn't look to be the strongest, but at least the directional crossovers are encouraging. Also note a bit if a streak should have rounded the base of the upper trough by 00z and approaching the region.

Also, keep in mind the climatology factor. April 24th is absolutely prime time for S Central Kansas. Wouldn't be surprised at all to see some Harper County magic this evening.

 

[Shane Adams]

I was willing to try the northern half of today's target when it looked like the better of the two (IMO)...but I'm in agreement with others in thinking the show looks to be along the KS/OK border. My main beef with the latest RUC offerings regarding NC Kansas/SC Nebraska is the total lack of low level winds in the western half of those areas, not to mention substantially less instability.
I too am encouraged by the RUC breaking out precip on this latest run, however it somewhat concerns me that there's little/if any intensification/coverage of the precip from 21-0Z...which suggests to me a possible cap issue through sunset....hopefully the RUC is doing what it's been doing most of 2008...doing reasonably well of showing precip or not, but being totally whacked with placement/coverage. But when you look at the other parameters, it seems likely initiation will occur somewhere in the OK11/KS160 corridor between US81 and US 183.

Attm I'm thinking a nice north jog to ICT, then west on 160. Will play it by ear from there.

EDIT: After reading MikeU's post and looking over some UVV maps, I share his concerns about subsidence over the KS/OK border target (amplifying the concerns I mentioned earlier regarding the lack of precip intensification/coverage 21-0Z per RUC). However, I am even more concerned about the lack of LL winds in the northern target of SC Nebraska. I'd rather risk a clear sky bust with awesome potential than probable initiation with mushball storms.

 

[afischer]

I'm a little dismayed with how crappy my prefered northern target (Beaver City/Norton) looks on the new NAM-WRF. Less rich moisture return/CAPE funneling after 00Z, with 850mb flow revving up to a whopping... 15-20kts. It also looks like the cold front may want to start crashing southward through the area, undercutting convection.

On last night's run it had looked like a pretty classic case for a couple tornadoes 02-06Z... as for now I'm not so sure. Of course, I won't see anything unless I leave KC pretty soon..