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

[Bob Hartig]

Can more experienced minds than mine help me out here? I just looked at the latest GFS, and it seems worlds apart from the NAM. Still seems like a chaseable scenario for northwest OK/extreme southern KS, but the GFS shifts the action south and, from what I can see, paints a considerably less compelling partnership between thermal energy and kinematics, and shows formidable CINH where the NAM largely disposes of it. Frankly, I kind of want to chuck the GFS--I think the NAM is the more accurate scenario; it just makes better sense to me, and I love what it's showing. But I'm still a forecasting greenhorn, and this seems like a great opportunity to learn how to interpret the disparity between models, which to me seems considerable.

 

[Warren Faidley]

Bob, a lot of the initial forecasting is in favor of regional areas where chasers live, like or want to chase. I always look to see where a chaser resides while reading forecasting posts. You have to keep this in mind with any forecast, as we all like for it to occur in our own back yards this far out, especially with the current gas prices. The models are still apart, but coming together. I'm guessing by late tomorrow most models will begin to offer some real forecasting guidance.

As noted before, this coming week will likely offer great chases in multiple areas depending on the type of storm you want, the number of chasers you want to encounter and the "risk" factor of playing a more capped region for isolated activity, etc.

W.

 

[Mikey Gribble]

Well the NAM takes it up another notch and moves the stronger mid level flow even farther out into the plains and once again breaks out precip all along the dryline. 500mb winds at 60kts would take care of any hodograph length questions you might have had. All we need now is for it to verify. One thing of note is that with only 90 degrees or so of turning (due to 500mb being almost due south, nothing wrong with only 90 degrees BTW, I'm not complaining) storm motions are awfully fast with Bunkers showing 30-40kts over NW Kansas. I normally take 5-10kts off that though, so 25-30mph seems reasonable for mature storms. Not terrible, but it's not get out and lounge speeds either. Any storm that could deviate to the right in that environment should light up with the backed 0-1km winds.
Wherever the dryline bulge east of the surface low sets up is where I want to be. Get right off the northeast corner of that and wait for the fun to start. The Norton to Hill City area is looking like a winner IMO.

 

[Mikey Gribble]

I'm surprised nobody is talking about this. I just started looking at forecast soundings and LCL's are pretty high until you get along the warm front. For example Hill City MLLCL is around 1800m AGL at 00Z. Go up to Kearney though and it drops down to more like 700m. Here is a rough map of ML LCL's for Thursday at 00Z. http://beta.wxcaster.com/models/eta/central/CENTRAL_ETA212_ML_LCL_72HR.gif
Those should obviously start to drop as surface temps cool in the late evening, but still those are pretty high over the warm sector. Hopefully storms will fire early enough and the warm sector will be narrow enough for storms firing off the dryline bulge to interact with the warm front before dark.
BTW this is another reason I think Friday may be the better day. With lower surface temps from overnight convection and cloud cover plus an additional 24 hours of moisture advection, LCL's should be lower on Friday.

 

[Van DeWald]

Still 72 hours out, but am liking southwest Nebraska at this point, bounded by the polygon of OGA, LBF, MCK and IML. Nam progs the nose of the low level moisture into this area with surface dews into the lower 60s, 850 dews into the teens and 700 dews to about 4. 1km shear in this area is almost 40 knots. 0-1km EHI about 7 with 0-1km helicity about 500. While I think storms should go down the dryline as well as cap erodes by late afternoon, think the location to the northeast of the surface low (wherever that ends up) just north of said warm front on the nose of the moisture would have the best tor potential. Target could shift southward toward HLC as conditions warrant.

Van

 

[Jason McKittrick]

I was just going over the NAM bufkit soundings and I like what I am seeing. Capes are forecast to be in the 2000 to 3500 range with little if any cap remaining right along the dryline and warm front. It appears that the dryline will extend from SW Nebraska into W Kansas, possibly near Hays and then south to near Pampa. I agree with Mike U's post in the forecast thread for the 23rdreguarding the eventual position of the dryline. The most recent comparison to this set up that I can recall is March 28 2007. I remember looking at the 00z run from 3-28 and targeting Hays only to continually have to adjust westward through the day, as there was nothing to push the dryline eastward. The models did not resolve that situation until 8 hrs out from the event. I suggest if you are chasing and think you only have to drive to Hays, take it from me leave enough time to make it to Goodland. I almost missed the 3-28 event because I did not get on the road soon enough.
Next thing I liked on the NAM is the highly sheared environment with low LCL's along the warm front in SW & SC Nebraska. Will have to pay close attention to the quality of moisture return that occurs between now and then. Potential problems with this senario are; the moisture may be grossly over forecast or if the moisture ends up being too shallow we may see dewpoints mix out much more than expected.
Overall I am still targeting Hays around 5PM. However if the current trends continue I may have to adjust a little more to the NW toward the lower LCLs and higher helicity being forecast in SW Nebraska. A lot of time between now and then for things to change.

 

[Dustin Wilcox]

we may see dewpoints mix out much more than expected.

Can't imagine that being too much of a problem provided the crazy backing occurring a long way up the profile, as has been mentioned I like the WF where moisture and instability gets wedged back west more than the DL, and not due to locational bias, though for the sake of room to chase I hope some opt for the DL further South.

 

[Chris Wilburn]

I think the best place to be Thursday will be extreme SW Nebraska or wherever the WF is located just east/northeast of the surface low. The dryline also looks good in western KS and it is nice to see the models break out precip. by 00z all along the dryline from western KS through OK. Low level shear will be very nice just along and north of the WF. 0-1 SRH over 500 and 0-3 SRH over 600. EHI of 9 and CAPE of just over 3,000 J/kg make things look very nice as well. A deep forecasted surface low in eastern CO along with very backed surface flow and 850mb flow will yield excellent low level shear. Just like I posted for Friday I would like to see the 500mb winds "veer" a bit more instead of being southerly/ slightly southerly/southwesterly, but with the amount of moisture, low level shear and instability this shouldn't be too much of a concern. The CAP shouldn't be much along the WF/triple point in SW Nebraska. The CAP also doesn't appear to be much of a problem along the dryline in western KS either so I guess either area will be a good play. Another play may be western/NW OK along the dryline where nice instability, moisture and excellent 0-1/0-3 SRH values will be present. As of now the plan is to head west on I70 from Salina and head to extreme NW KS/ SW NE and play from there with a possible secondary area along the dryline in western/NW OK and possibly SW KS, but these details can be ironed out later. Good thing is everything is in place and the CAP doesn't appear to be an issue like earlier than thought.

 

[Mikey Gribble]

With LCL's being what they are over the warm sector I think staying close to the warm front would be a wise move. I would prefer a dryline bulge storm, but if it isn't going to make the warm front with daylight left then that probably isn't a good idea. I basically plan on sticking myself along the warm front in SW Nebraska and that should keep your options pretty much open. I am anxious to see what the WRF radar product will do with this. That will probably influence my decision a little bit, but with the the high LCL's over the warm sector you need to stay close to the warm front for a better tornado threat IMO.

 

[Donald Giuliano]

Wow, the 12z NAM looks gangbusters over the entire warm sector ahead of the dryline. Personally I'm not too fond of the warm front target, as storm motions look to take any convection initiating near the warm front into the stable air pretty quickly.

LCL heights don't concern me too much as this situation reminds me a lot of May 29, 2004 (late season with deeper boundary layer). Also, I think the convective parameterization in the NAM is artificially lowering the CAPE and raising the LCLs, with generally 3000-4000 uncapped CAPE at 21z everywhere ahead of the dryline and LCLs near 1 km (also at 21z) once you get 2-3 counties east of the dryline just prior to the onset of convection. However, by 00z the amount of low-level moisture present in model forecast soundings has markedly decreased over OK/KS, while TX exhibits little change. Given that the NAM shows moisture-rich air continuing to advect in from the south, I'm inclined to believe the high LCLs/lowered CAPE over OK/KS are a result of feedback from the convective parameterization and have little bearing on reality. Now of course one could argue that the NAM in general has little bearing on reality, but that topic is for another thread.

 

[Chris Hayes]

Well, the new GFS is in. It's nice to see it painting pretty much the same negatively tilted trough as the NAM has been pointing out for several runs now. However, supposing the GFS is right, we might have to shift our target area a bit further south. Highest instabilities through 00z friday arent forecast to go much north of the KS/NE border. It appears the warm front will remain situated over Kansas much of the day, with the triple point around Hill City. Leads to a pretty stout corridor from Dodge City northward to Hill City for supercell development with a dryline bulge across western Kansas. Overall, it still appears to be a pretty good setup.

 

[Jim Bishop]

This setup looks so good it's almost as if there WILL be tornadoes, just a matter of how many and how violent.

The only issue I can find is the upper forcing will be quite podent by the early evening, so convection will be more than widespread by 6/7pm. However given the incredible shear it's hard to imagine storms having trouble remaining discrete, suggesting numerous tornadic supecells from Western Kansas into Southwest Nebraska.

 

[Bob Hartig]

Bob, a lot of the initial forecasting is in favor of regional areas where chasers live, like or want to chase. I always look to see where a chaser resides while reading forecasting posts. You have to keep this in mind with any forecast, as we all like for it to occur in our own back yards this far out, especially with the current gas prices. The models are still apart, but coming together. I'm guessing by late tomorrow most models will begin to offer some real forecasting guidance.

As noted before, this coming week will likely offer great chases in multiple areas depending on the type of storm you want, the number of chasers you want to encounter and the "risk" factor of playing a more capped region for isolated activity, etc.

W.

Warren, thank you for your input. It can be a bit tricky trying to ask questions in a forecast discussion without mongrelizing it into an educational thread, but I think it can be done in a way that is relevant to the discussion. You've addressed part of my concern here, which is how to interpret diverging models.

Right now, this system has come within reach of the 72-hour RUC13, which paints a different picture from NAM. The outlook for 00Z shunts the system more to the east, paints a 2,000+ CAPE for most of Kansas and much of Nebraska, and shows vigorous 250 mb support at 80-100kts across the region. Anyone interested will want to compare the forecast for 18Z with 00Z; H25s are backing at 1800, but veer to the SW over time. CAPE of 3,000 nudges against the dryline in west central KS at 18Z, and simulated reflectivity breaks out precip by that time, beginning with a discrete cell in southern KS and moving in a line well up into central Nebraska. Based purely on RUC13, Hays seems like a reasonable target ATTM.

 

[Jason McKittrick]

NAM is indicating an MCS moving east along the WF Wednesday night. If that occurs I have serious doubts about the northward progress of the WF into Nebraska on Thursday. I am betting that we will see a convectively reinforced WF across northern KS on Thursday afternoon. I am still trying to pick apart this mornings models, however this is probably as far as I will go today. Looks like Hays is still a good starting point for Thursday afternoon. Convective parametrization in the NAM indicates a large area of QPF from Great Bend northward, with a few interesting bulls-eyes to the south, which I would like to be in position to check out if the model does in fact verify. Word to the wise leave some extra time, I have a suspicion that there will be some last minute adjustments to this forecast. I would not be surprised to find myself near Garden City or Scott City before Thursday is over.

 

[Brandon Sullivan]

to me it kind of looks like the NAM and GFS have taken things further south..

Looks like the warm front will make less northward movement as someone above mentioned..