06/16/05 FCST: Central US

Jul 23, 2004
Iowa City, IA
Chase target:
30 miles E of Limon, CO.

Storm initiation 4PM CDT (3PM MDT).

Storm type:
Isolated supercells early in storm evolution, with storms evolving into a large MCS during the evening hours with very heavy rains the primary hazard.

Complicated FCST with MCS underway in KS/NE/WY/NERN CO… Models hint at an outflow-enhanced backdoor front stalling out near the Palmer divide by 21Z, with ERLY flow to the east of this feature and a high theta-E ridge wedged against the Front Range. Given broad ridging coupled with a lack of forcing mechanisms aloft, upslope flow and forcing along the boundary should serve as the primary storm initiation focuses. MLCAPE’s to 2500J/kg and (0-3km) SRH’s locally to 200m^2/s^2 near the boundary will support supercells shortly after initiation in the front range and Palmer Divide areas as a Denver cyclone develops. Given slow storm motion, very weak mid-level winds, and lack of upper-level support, storms will evolve into a large convective cluster and track slowly to the SE.

- bill

Upslope will for sure be going tomorrow on the front range of the CO/KS border. There seems to be a pseudo dryline tomorrow all the way through the TX panhandle and further south which could provide enough surface convergence along with an outflow boundary for surface based storms tomorrow afternoon. The OK/N TX panhandles look ok along with SW KS for an isolated storm. Directional shear is adequate for supercells and the backed low level flow is great for 0-1 km helicity and tornadoes.

I don't like several things about this setup. There really isn't a strong area of surface convergence in the shape of a surface low, (1008 mb doesn't get me excited) or a dryline bulge due to the lack of any mid or upper-level support. There will be large scale subsidence on the west side of a ridge which means the atmosphere wants to come down and we like it to go up for convection. Also the mid-level winds are really lacking (maximum 35 kts per models) and it seems that if storms fire they will be short-lived or extremely HP. Storm motion is crucial for longevity because it increases storm relative helicity and also prevents the cold pools from gusting out ahead of the inflow leading to mass chaos and storm clusters.

Lastly, breaking a nearly 30 degree cap at 850 mb will be close to impossible without STRONG synoptic forcing. Eh, stranger things have happened...right? I may venture out because summer starts in less than a week and I really have the storm fever.
Tomorrow looks to be a decent chase day. Deep layer shear at 40-50kts throughout the target area along with CAPE around 3000J/KG will be sufficient for supercells. Dewpoints should be in the mid to upper 60's which will mean LCL's higher than I would like, but probably low enough to get the job done. The NAM is showing dewpoints at 70, but I don't think that is going to happen after looking at surface charts. Some of the positives I see are great directional shear and the dry intrusion at 700mb across WNW Kansas. The forecast hodograph for DDC at 00Z was looking pretty good too. One of the concerns I have is weak flow at 700mb. The NAM is showing slightly better 700mb winds along the Oklahoma border. I do think a couple of tornadoes are a decent possibility. I am just not sure where lol. I have not decided on my target for tomorrow. I will be heading to DDC around noon and will get data and figure it out from there. Good luck to everyone who heads out.
The NAM hasn't updated, but the RUC is showing much better mid level winds. If this were to verify, I would be much more confident about a few tornadoes. It also looks like dewpoints in the upper 60's can be expected throughout western Kansas. I haven't looked at much yet, but what I have looked at has me more optimistic. I have to go run errands now so I can get out of town.
The NAM hasn't updated, but the RUC is showing much better mid level winds. If this were to verify, I would be much more confident about a few tornadoes. It also looks like dewpoints in the upper 60's can be expected throughout western Kansas. I haven't looked at much yet, but what I have looked at has me more optimistic. I have to go run errands now so I can get out of town.

Yes RUC is showing much better mid level winds and also a nice veering in the low levels. The only thing I don't like so much is the lack of a significative low level jet, even if it's not bad (10-15knots from SW).Besides I see dew point on 70 East of Ok city.
All in all I guess east of Ok city is the better place like target at the moment (by this run). Another good target could be Wichita with a good dry intrusion at 700hpa.Let's see the next runs.
About W Kansas is enigmatic: I don't like these 850 hpa temperatures, they smells of bad cap...

Seems there is some reasonable potential for supercell storms later today - though some issues need to be resolved for additional tornadic potential. Morning obs shows an upper level impulse riding up the west side of upper ridge immediately east of Rockies, evident in water vapor imagery. While a modest speed max, persistent upper level divergence is forecast to center near the panhandles later today leading to weak surface cyclogenesis around EHA, and offering at least one potential focal for storm initiation. Deep moisture is available - but northward transport is blocked this morning by 850 trough-ridge pattern leading to westerlies across southern KS region. Model forecasts suggests this breaks down somewhat by later today though - allowing rapid deep moisture transport toward nw KS by this evening. Strengthening 700 mb thermal ridge could offer a challenge for storm initiation - and cloud bases look rather high, particularly further south. If storms intiate early in CO and cells can emerge out over NW KS by evening, this area will be favored for tornadic potential owing to reasonable wind profiles and lower cloud bases, but lack of a focal for intiation could leave this area void of storms alltogether during daylight hours. Better wind profiles will be in place further south according to the model forecasts, and always possible slightly better low-level moisture makes it into the region than forecast as RUC appears to be overmixing the moisture out in that region.

Good luck to those who decide to venture out today.

Looking at the setup around mid-day, see the RUC now has the surface lee low at 998mb by 00z, deeper than maybe we would have expected. Yesterday, similar but not identical setup resulted in some tornadic activity in Trego Co KS area (although I see no damage mentioned on SPC prelim storm reports of this tornado, I understand second-hand there was mention of some damage on Wichita TV yesterday.) I kind of favor the same general area, but perhaps a little further south, today: say Hayes down to Dodge City. Far enough east to be in the NW/SE oriented axis of instability, but far enough west for convection to still be in supercell stage before evolving into another evening MCS. Decent surface moisture convergence and very steep lapse rates in this area forecast on the 12z NAM run.

Another interesting possibility would be further SE around Wichita, where wind crossover w/ height looks more ideal, stronger SRH possible, and LCL's are lower. Question mark here will be initiation -- although forecast lid strength index is certainly not insurmountable, surface lifting mechanism may still be too far west at diurnal peak.