4/22/2007 FCST: IA/IL/MO/NE/KS/TX/OK

[Brandon Sullivan]

Forecast models continue to advertise a negatively tilted upper level low to eject north northeastward across the upper midwest. While models obviously vary with the timing and track, the general model consensus would support a severe weather scenario. While this mornings 6z GFS is less favorable on atmospheric destabilization, morning DGEX appears appears more favorable. Forecast Hodographs and Kinematic Fields only appear semi favorable for a tornado setup, with helicity values around 250 and bulk shear values around 40 kts. Directional Shear A.O.A. 80 Degrees. Storm motion is 263 at 29. So a good chasing speed... Instability has been somewhat weaker as in past runs, most likely due to the slower timing of the system, and thus loss of strongest insolation. The system is advertised to be in North East North Dakota by 0z Monday.. Dont see moisture as a problem, as I am seeing 55+ degree dp's across the entire region. Partially saturated mid levels supportive of large hail. UVV's and MPL's are slightly lacking.. Plenty of time for change with this one

[Adam Atkins]

Thought I might stir up some discussion about Sunday again...since the NAM has slowed down this trough so much before it's ejected across the plains. From our meteorological knowledge, lifting troughs tend not to lead to widespread synoptic scale vertical lift. However, higher Td's and in the boundary layer will exist leading to possibly some moderate instability behind the nocturnal convection, which might also leave some nice outflow boundaries behind. The dryline seems to have a SSW to NNE orientation through C Oklahoma with a cold front intersection somewhere in SC Kansas. The lack of strong ageostrophic flow in the boundary layer may be compensated by more westerly flow at the mid-levels still leading to 45-55 kts of deep layer shear across C/E Oklahoma...

Provided there's sufficient boundary layer destabilization behind the morning convection, things could be interesting around the I-35 corridor on Sunday.

[matt patterson]

The NAM/WRF is advertising a very good setup for the second run in a row for the Southern Plains. This is still 72 hours out, but with saturday becoming more and more of a cross country chase for me, this looks pretty good.. Westerly 500s forecast around 45-50 knts and 60+ Tds with a stout SSW to NNE oriented DL. Too far out to pick a target, but this is really impressive model consistancy showing the best area between SC KS and Far N TX. My guess is that the DL will not mix as far East as progged by the models so we may end up (if at all) west of I-35 before all said and done.... the next 5 days look like a lot of FUN....

[Brandon Sullivan]

Timing combined with Dynamics and Instability appear that they could come together rather nicely on sunday afternoonm across central IA, northern MO, into western IL.

Afternoon destabilization, combined with strong shear, and semi impressive CAPE, will support strong to severe convection. Storms will probably be organized into a nice squall line, however a few supercells could be possible early in the period. With the amount of shear, wouldnt be surprised to see a few tornado reports too.. Severity should wane rapidly after sunset.

[Bob Hartig]

What kind of shear are you talking about, Brandon? Directional or speed? I glanced at the models earlier today and did a double-take because the system actually did look pretty good at first glance with a good negative tilt and 1,000+ CAPE. However, the winds at all levels appeared to be southerly. I know the SPC is talking about the possibility of isolated tornadoes, but I didn't see much in the way of helicity, so I'm guessing that any occurrences would be brief spin-ups.

But I've got plenty to learn about using models. I'd love to believe you're right, because Sunday is my only opportunity for a chase and I've been yo-yoing up and down about heading for Iowa. Am I missing something here?

[Brandon Sullivan]

Well, with the new 18Z WRF, speed shear is really nice.. Effective Helicty Values now around 315.. Incorporate the now found low level moisture, and already present shear, it could be a nice setup! Cant wait till tommorows outlook.

I put in some SKEW T soundings below.. As you can see by the Hodographs in the top right, especially in ottumwa's sounding, the profiles are more linear, indicating a speed change rather than a directional one.. I should have pulled up an image from a IA MO border area that is further to the west.. But these should suffice..

http://www.met.utah.edu/jhorel/images/models/nam/NAMSKEWT_OTM07042018F054.gifhttp://www.met.utah.edu/jhorel/images/models/nam/NAMSKEWT_DBQ07042018F054.gif

[Jesse Risley]

I'm going to set an initial chase target of somewhere between Des Moines and Dubuque, assuming I have time to chase after a meeting on Sunday, after looking at the latest models. I think the key issues will be timing in eastern Iowa, but shear profiles do appear to be favorable.

[Brandon Sullivan]

Tomorrows continues to look more and more enticing.. Low Level Moisture, with heat, instability, shear, helicity, come together nicely in the afternoon for a possible supercell and associated tornado threat. An upper level wave will pass over the area to act as a trigger for this development.. NWS says between 1-3 is the best tornado threat.. And I cant argue with that.. Also see a 30% over almost all of IA. May stay close on this one, given im about in the nicest area thus far.

[Travis Carlson]

Oh I agree, I'm starting to get excited about the prospects tomorrow after really not liking them most of the week. It would be not long of a drive and in a great area for chasing being central Iowa and all. I also like how after comparing water vapor with the intital model runs that the system may be digging a little farther south then the models depicted during there initialization. This would definately help the cause for a decent severe wx outbreak including some tornadoes. A farther south track would greatly influence the chances of supercells. Shear and moderate instability are definately in place. Morning convection may not be a problem with this one, but we'll have to see what happens in the western-central high plains tonight. I'm thinking that you'll get some development along the cold front early on but discrete supercells would be possible ahead of the line of convection that forms. I'll make my decision late tonight or early tomorrow morning whether I'm chasing this one. We may not have had many of chaseable days so far around IL, but at least the days we do are falling on weekends. You cannot ask for anything more:cool:

[Andy Rice]

Well.. it looks like with the 0Z data.... things have slowed down and moved West a few 100 miles..... Glad I decided to drive from Madison to DSM tonight instead of waiting for the AM.

Target Tomorrow will be down I-35 to St. Joseph.... will try to stay on the south side of the action....

21Z SREF Sig Tor Parameter for 21Z tomorrow

http://www.spc.noaa.gov/exper/sref/gifs/2007042121/SREF_prob_sigtor_1__f024.gif

I am guessing I may have to adjust a little farther west.... and maybe north...... but will play it by ear in the morning.

[Brandon Sullivan]

I'm having a hard time picking a target on this one.. I'm leaning toward South Central IA..New outlook out from SPC, still only slight risk.. But probs moved some.. I still want to try the IA MO border. Maybe sit on I 35

Maybe I am just distracted by the day 3 moderate risk!

[Daniel Christianson]

Right now im looking at playing with Highway 2 from Nebraska City moving East? idk hard telling whats gonna pan out... i need SLEEP ;+

[Josh Richardson]

I agree with Daniel, we are targeting SW IA not all that far from the area he was referring to. Havent pinpointed an exact target yet as I am, obviously, waiting to see what were going to have for clearing in the area and then adjust from there.

[Mike Hollingshead]

May want to think of being west of there. Some aggitated cu are forming around the Hastings area right now. I'd say at least west to Lincoln, maybe further west or sw....and probably pretty darn early. I'm heading to Lincoln now and will go from there. I'm sure it's just another waste of gas! Getting pretty sick of that shorter drive to Lincoln(on way to various chases), this is for sure. But anyway, good luck.

[Josh Richardson]

May want to think of being west of there. Some aggitated cu are forming around the Hastings area right now. I'd say at least west to Lincoln, maybe further west or sw....and probably pretty darn early. I'm heading to Lincoln now and will go from there. I'm sure it's just another waste of gas! Getting pretty sick of that shorter drive to Lincoln(on way to various chases), this is for sure. But anyway, good luck.

Yeah, thats what Im hearing from a buddy of mine who is on his way back from TX right now. CU has been forming in NE KS as well but I am waiting for my one of my chase partners still so I think we will have to go with SW IA. Also hoping things stay a little discrete as it heads towards the MO river as shown on the 4.5 km NMM WRF.

[Skip Talbot]

Based off the RUC, Mesoanalysis, and satellite, here are my thoughts for the day's setup: As SPC has noted we have a stacked low. Although speed shear looks quite good for severe weather over the targeted area, the directional shear is going to be lacking. There is very little veering from 850 to 500 in IA. Storms here will probably not stay supercellular for long. Also working against today's setup is the forecasted instability. I believe the RUC maybe underforecasting the CAPE by only showing pockets of 500 J/Kg over IA and MO. Mesoanalysis already has a pocket of 1000 J/Kg over Kansas, and I expect this dryslot on satellite imagery that SPC has also pointed out, to destabilize the environment more than the models are indicating. With that said, portions of MO and souther IA may see CAPE over 1000 J/Kg. Helicity values are very high in Missouri where the shortwave and LLJ are at their peaks and the veering is improved. I'd target the I-35 corridor in extreme southern IA and northern MO. Crappy chase terrain, the distance, before a work day, and the lack of critical instability are going to make me pass on this one. Good luck to those heading out. I think this has the potential be a great local chase for those in the area.

[Josh Richardson]

On the road right now to pick up Jayson Prentice in Ames. Heading towards I-80 and gonna hope for the redevelopment in SW IA and see what happens from there.