5/22/08 FCST: NE, KS, TX, MO, OK

[Jason McKittrick]

1730 Swody 2 outlook has upgraded area to a moderate, with mention of discrete supercells being the dominant storm mode and potential for strong long track tornadoes. After looking over models this morning I am a little concerned about the degree of forcing. Models indicating strong linear forcing with winds only at about a 30 degree angle to the dryline. this is leading me to start thinking about a tail end charlie. Moisture looks great 70 degree isodrosotherm has reached Dallas and 60's are approaching Turkey. Speed and directional shear look good. I am a little concerned about LCL heights the farther south you go, with models showing 3500ft from Hays south to Pratt at 00z. Retreating dryline tomorrow night, hope Day 2 doesn't washout Day 3.

Drive careful everyone I expect tomorrow will be a circus. And for all of you from across the pond keep it on the right side. Just kidding.

 

[Adam Penney]

Will be heading out the door for Hays here in a few hours. I will be chasing this multi-day event through atleast Saturday. You have to love the SPC's mention of possible strong-long track tornadoes, however, there are some obvious concerns. I think the warm front(while Helicity values should be greater up there)is not the "best" target choice. Storms should rapidly move northward into more stable air. A plus for the warm front target is lower surface temps should aid in lower LCL heights, which could be a much bigger problem for targets further south towards DDC. All in all, not going to get too down about tomorrow, as it seems even the best of setups have their question marks. Lets hope for a good tornado day tomorrow, and hope they all stay out of residential areas. We've all seen enough destruction this season already.

 

[Mikey Gribble]

I am actually really pumped about tomorrow. I don't see much to be down on. I think the shear vector not being normal enough to the boundary is certainly a valid concern, but when you add in a NW to SE arcing dryline I'm not too worried about it. I am cheating south a bit farther than I was planning before just to make sure I get a discrete storm though. I really like the potential for any storms firing in a Scott City to Ness City to Dodge City to Garden City square (where depends on the location of the dryline, but it should be in that general area).
As far as LCL heights go, ML LCL at 1000m or so over central Kansas doesn't scare me at all. I would be more worried about LCL's if moisture return looked questionable, but I think we will get mid 60 dewpoints up to at least central Kansas by 3PM tomorrow.
I pulled forecast soundings for ahead of the central Kansas section of the dryline (GBD for the NAM and KHUT for the GFS) and both hodographs are exceptional. Both models are also showing 1km SR winds 35-40kts and 5km SR winds of 25kts. 0-1km SRH clears 300 as you approach the central portion of Kansas. And finally the GFS is peaking the sig tornado in this area as >20 now. That is pretty insane.
I guess I'm an optimist on this setup, but when I go down the list of things I look for in a good tornado threat the vast majority of those paramaters are very good for tomorrow. Yeah there are a couple that could be better, like LCL's and the shear vector being oriented more normal to the boundary, but you are never going to have everything just perfect. As the posts before me mentioned as well, convective mode and LCL's are my biggest worries too, but they don't bother me much.
Just my two cents, but I think a tornado outbreak is highly likely and I would expect several strong tornadoes over parts of Kansas.

 

[Mike Hollingshead]

I'm noticing something on the 18z nam to think about, it's on the 12z some degree too. At 18z the 500mb flow is very backed to south, which is fine if your low levels are strongly backed like the warm front area(if crap wouldn't cross it into not so great air so fast). Along the dryline though, there's not much turning at all at 18z. Only by 0z the mid-levels are prog'd to veer some. I figure if things go too early, they may start off with issues.

Probably not details worth worrying about too much, since things could really go all at once, leaving you no way of avoiding anything anyway. I just hope things hold off as long as they can till that directional shear improves.

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=META&fcsthr=024&STATIONID=kddc

Cap being gone at Dodge City by 1pm with that shear scares me a little I guess.

Improved a bit by 4pm.

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=META&fcsthr=027&STATIONID=kddc

I'm going no matter what obviously, but praying things don't get going too early. After 4 at least would be great.

Edit: Perhaps the southerly 700mb flow will help things hold off for a while too. Would think it'd take longer to cool any capping that way than if it was being directly advected east.

SFC convergence along the dryline does not look that intense early either. Also should help I'd think.

Early target out of boredom: Beeler KS.

"Interesting" precip tracks on the 5km WRF 7-10pm.

http://charlie.wxcaster.com/wrfcentralnojava.php?fcsthour=39&type=1000-500_SLPTHKPRP&region=S-PLAINS
http://charlie.wxcaster.com/wrfcentralnojava.php?fcsthour=39&type=1000-500_SLPTHKPRP&region=CENTRAL

http://www.grib2.com/wrf/NW1_WRF_0-1KM_EHI_36HR.gif A 0-1km EHI of 10 would be a little absurd, lol.

 

[Eddie Natenberg]

I think tommorrow looks really good, strong cyclogesnsis with continued pos vorticity advection over the same area is a ovious synoptic scale signal for a tornado outbreak. The other half of the needed ingredients is moisture which should also be in place. I have an extra seat in the car if anyone is interested with going with me and a few friends on a multi-day chase (PM me if your interested). Will probably leave Norman after lunch tommorrow to target the warm front in WC to SC KS. Good luck to everyone. ::Can't wait to see tonights ensemble members ::

Eddie

 

[Jonathan Whitehead]

Not sure where to put this but does anyone have any idea as to what the current and developing scenario across eastern CO and TX panhandle will affect tomorrow. Im a little concerned.
Everything else is playing out as expected with surging moisture overnight.

 

[Michael O'Keeffe]

I wouldn't worry too much about it as the convection in E CO is moving almost due north. And the stuff in the TX Panhandle is struggling to sustain itself.

Anyway the 00z ETA/WRF has been issued and it is showing precip north of I70 with nothing south of I70. As of now the tongue of best CAPE and moisture looks to be Hill City, so I know my target for tomorrow. LOL. Everything looks amazing for a nice tornado event over W KS tomorrow.

 

[Chris Hayes]

Not sure where to put this but does anyone have any idea as to what the current and developing scenario across eastern CO and TX panhandle will affect tomorrow. Im a little concerned.
Everything else is playing out as expected with surging moisture overnight.

I'll have to watch them storms. If they move north, they wont affect it too badly. Worst effect I could see is cloud cover. However, they might not get that far north, as they might get into dry air. I'm not too worried about them. In Reality, if they dont produce too much cloud cover, they might help things by throwing out some outflow boundaries for storms to play with tommorow.

 

[Mikey Gribble]

Just glanced over the 00Z and the NAM has pushed everything back north a little farther. The better low level shear doesn't extend as far out into the warm sector as it did before. As a result you don't get nearly as good of overlap with CAPE/low level shear as we did in the 12Z (just going off SRH). I'm not going to loose sleep over these small details though. The 00Z has a stronger cap too and doesn't break out convection south along the dryline. Not too worried about that either since the models always handle convection poorly. If the best low level shear is going to hug the front tomorrow I will probably set up 40 miles or so south of the warm front (assuming mid 60 dewpoints make it that far). Storms are going to be flying tomorrow, which really sucks. 40kts is damn tough to keep up with and that is what bunkers is showing. Overall I don't think the 00Z is as favorable for tornadoes as the 12Z was, but everything still looks fine for some good tornadoes tomorrow.
I like Hays for an intial target. There is a Super 8 as you come in to town that has wifi. I plan on being there by 1PM to do my forecasting and I will pick a final target from there. I probably won't have far to go to get to my target either. Right now I am thinking the Ness City or Wakeeny area is a good spot to pick up on a storm. I am going to try to stay downstream of where I expect storms to fire given the fast storm motions tomorrow. I may even set up a little North of I70. No reason to get right up on a storm while it matures. You just risk falling behind the storm before it tornadoes IMO. I've gotten my pants pulled down more than once doing that.

 

[Robert Balogh]

Very very novice forecaster here (and maybe I can an award for being furthest OFF target when it's all said and done) but I am thinking south and east - LaCrosse to Great Bend Kansas

I guess a lot will depend on what transpires overnight. Surface winds still screaming out the southeast here in Sterling Colo

Goodnight all and better luck tomorrow. A bust day chasing beats a good day at work

 

[Adam Penney]

Im not sure if im buying the CAP holding down to the south of I-70. Models have been consistently backing off on CAP strength for the past 36 hours. I am wondering if the 00Z NAM is taking a "slight" lunch break. We shall see....

 

[Angie Norris]

Just glanced over the 0Z NAM (or whatever it's name is now). Interestng theta-e ridge spike that coincides with a CAPE spike in the 0Z time frame tomorrow just west of central KS and OK. Dryline punch looks to come through in about the Hill City/Dodge City area. Good vertical shear at 0Z as well. FWIW, my very preliminary target would be the Ness City area (subject to change when I can lay hands on a surface chart in the morning ).

Let's all be careful out there tomorrow!!!!

 

[Jeff Snyder]

The lack of QPF on the 00z NAM 24hr fcst S of I70 isn't too concerning since it convects the entire dryline from CDS northward before 3z. I don't put much faith in convective initiation forecasts (heck, we can't do that reliably 3-6 hours in advance, so looking too closely at a model that parameterizes convection 24 hrs in advance may not be too prudent), so I'm not too worried about that. The backed and strong 850mb flow will help make sure that the deep-layer shear vector has a significant zonal component, which, given the orientation of the dryline, also helps ensure that the shear vector is relatively normal to the dryline. The thread for siggy tors is there tomorrow, particularly N of I70. Unfortunately, storm motions between NE and NNE at 35-45kts may put those storm in the stable air farther north relatively quickly. In that same vein, I'd like to hedge northward since it's easier to step east and south to meet up with a cell coming from the SSW than it is to blast NNEward in hopes of catching up with a cell that's just ahead of ya.

The 00z NAM 24hr fcst shows essentially no theta-e convergence along the dryline S of I70, which is likely part of the reason why it shows no QPF at that time. By 3z, however, convergence strengthens, though the DL is a bit farther W than earlier progs I think. My personal target is somewhere near DDC, though I'm geographically biased a bit S since we'll be departing from OUN.

 

[Bill Schintler]

Chase Target for Thursday, May 22

Chase target:
Hoxie, KS (20 miles east of Colby).

Timing and storm mode:
Storm initiation in the target area is 5 PM CDT, with upscale development of storms west along the warm front and south along the dryline. All forms of severe weather are likely, including a few tornadoes.

Synopsis:
The overall progression of the synoptic pattern is verifying somewhat slower then FCST 24 hours ago, with the WRN CONUS trough taking on an increasingly negative tilt. Over the next few days, this feature will close off into a stacked low over NV while providing several days of unsettled WX to the Plains with SWRLY flow. Today’s event largely failed to verify, owing to the late arrival of forcing which left WRN TX and KS in subsidence. Unseasonably meager SFC moisture also proved problematic, especially in the TX panhandle where the airmass failed to recover from morning convection. The WRF, GFS, and 21 member SREF were investigated. Previous runs of the GFS were fastest with the EWRD mixing of the DL and with the NWRD motion of the WF, possibly due to poorer resolution of the vertical structure of the moisture layer. The latest WRF, however, has come into better agreement with the GFS and everyone seems to be on the same page.

Discussion:
Storms currently in ERN CO will spread NE into WRN KS, and additional convection will fire between 08Z and 09Z in CNTRL, and NCNTRL KS at the nose of a 65kt LLJ. This precipitation will continue in KS north of the WF through 16Z before exiting the area to the NE during the early afternoon while leaving a modified airmass and outflow with an ERLY SFC flow component in its wake. Attention then turns W to the WF and DL where renewed convection will fire by 22Z. Strong insolation will commence as a ST deck exits CNTRL KS to the E and a thick CI shield, an indicator of the strong large-scale assent in the left-exit region of the 110kt H3 streak, remains just W of KS in ERN CO through 00Z. Meanwhile, a mid-level dry slot will punch in from the SW. Low pressure in NERN CO at 12Z will sink slowly SE into WCNTRL KS by the end of the period with an outflow-enhanced WF extending SE along I-70 at 23Z. A DL will mix E, intersecting the WF E of Colby.

A potential negative is the orientation of the storm motion with respect to SFC boundaries and the mode of convection. Convection should initiate along the WF/DL triple point where the strongest SFC convergence exists. Upscale development should quickly follow to the WNW along the WF, and storm motion vectors take cells directly N at 40-50 kts; where they rapidly move into the cool sector while becoming elevated. Storm growth S along the DL is also expected, and this convection should have a longer time window of moist SFC-based inflow before crossing the WF.

Parameters suggest supercell storms and a few tornadoes. SFC-6km sheer in excess of 60 kts along with SFC-2km SRH AOA 400m2/s2 will be juxtaposed with a narrow axis of strong instability as SFC dewpoints increase to 65-70F beneath steep mid-level lapse rates AOB 8C/km. Further S along the DL, hodograph curvatures and bulk shear will be less impressive then along the WF where SFC flow is backed.

- bill
10:30 PM CDT, 05/21/08

 

[afischer]

The forecast challenge for this set-up reminds me in a way of 05/11/05 (northern targets mostly a bust, with a beauty of a tornado after dark near Ullysses KS)... though I'm sure the set-ups differ on a number of counts, and I'm definitely not assuming the results of each of the systems will be similar.

Storms will probably fire on the northwestern portions of the dryline first, and with strongly backed 500-1000m agl flow forecast north of I-70 there could be a major tornado threat with those. However, storms will be trucking at 40-45kts, so a decent swath of low-level destabilization would seem to be required up to near the NE border in order to realize the tornado threat. The NAM-WRF suggests this might happen, but that will be easier to gauge by tomorrow morning or by watching trends tomorrow afternoon.

I wouldn't be surprised to see supercells develop as early as 6pm farther down the dryline into SW KS and maybe NW OK. Low-level shear here is more marginal for a major tornado threat, but is forecast to improve some by 03Z... and I wouldn't be surprised if the accelerating LLJ improves the low-level shear faster than is forecast, given I've seen that happen a few times in the past. The cap isn't forecast to become hallacious quickly after dark, which looks reasonable given the pattern.

Overall, the positives I see are the 7H thermal ridge cresting over west KS around 18Z, helping build strong potential instability ahead of the dryline (3000-4000 J/kg MLCAPE)... and the well-timed synoptic scale lift/dpva, and subsequent fairly high probability of supercellular initiation given the orientation of the 0-6km shear vector against the dryline. The best area to target for tornadoes isn't quite cut and dry for me yet though... will have to make a decision eventually.