04/09/11 FCST: OK, KS, NE, MO, IA, MN

[Jeff Duda]

Ah, at nearly the 0-hour, the models decide to partition the threat area into two separate and generally discrete areas with a large enough gap in the middle that sitting in the middle would likely leave you SOL for both areas.

Such a great choice to make...north or south?

The 00Z NAM has continued to make the warm front look much better in all respects, and aligns it more with the GFS forecast. It also stopped moving the entire system west and actually pushed it east a tad so that the I-235 corridor is now along the back end of the dryline (it was along the forward gradient of it before).

Regarding the north target: sufficient SBCAPE (generally AOA 2000 J/kg) with low CIN (<25 J/kg over a large area of the Missouri River along both sides in E NE/SE SD/W and NW IA); great backed winds at the surface and at 850 mb and continued turning and acceleration with height for great deep layer and low-level shear. 0-3 km CAPE also appears to be pretty decent, especially in WC/NW IA. The backed winds should give a little better forcing when nudging up against the triple point/cold front. The 00Z NAM suggests that perhaps the cold front may begin surging to the north in SE SD towards 00Z, but just to the south in NE NE, a decent triple point appears to exist.

Regarding the southern target: if you get south of I-70, and especially towards the Wichita latitude, both deep layer, and low level shear improve as both the NAM and GFS have SSE winds in SC KS and into OK. The models also show decreasing CIN (although not as little as to the north, which is to be expected), decent 0-3 km CAPE, and is somewhat closer to the mid-level wave, so there may be a tad more upper level forcing there than to the north.

This is tough for me. I've been watching this since Monday and have been targeting the dryline along I-70 in KS the whole time except for starting last night. Within the last 24 hours, the warm front/triple point are now looking more appealing as far as probabilities for initiation go. But shear and CAPE seem to be just as good in the north as in the south. I have a location bias and one area is closer than the other, but I'm still torn between the two target areas. Hopefully the morning runs will help me make a decision.

 

[Mike Smith]

One subtle advantage of the southern area is there may be leftover boundaries from the extensive severe thunderstorms tonight in southern Kansas and northern Oklahoma.

 

[Joel Wright]

The 00z NAM shows a nice bulge in the dryline over far eastern NE late Saturday. The area south of Sioux City looks pretty interesting. 3000j/kg of cape nosing into that area, along with nicely backed winds from 850mb on down to the surface. All of this is occurring on the nose of an approaching mid-level jet. This should be enough to get things going over far eastern NE late afternoon/early evening. The 00z NAM also shows CIN weakening pretty substantially after 00z in this area as well.

 

[Michael Riedl]

I agree Mike, it has thrown something extra in the situation to watch for tomorrow.

I was surprised to say the least when the SPC took the slight rist area out of the Dryline tomorrow.

Right Now I am going to just stay at home, until 1 or so, then head out somewhere along the Dryline, may end up staying put. We'll see.

 

[Mike Smith]

Michael,

I've had a little time to look over the 00Z NAM and I'm very impressed at the potential in south central Kansas if convection can get going. In fact, I'll go so far as to say that (assuming the NAM is a "perfect prog") if supercells can get going along any leftover boundaries, then significant tornadoes (i.e., ≥F-2) may occur.

Mike

 

[Jeff Snyder]

One interesting possibility is for something to come up near ICT. The 00z NAM shows the ICT area to be in the sliver of near-0 CINH by 00z, and it actually keeps CINH locally low around the ICT even at 03z. The 00z GFS doesn't show this weakness in the cap at 03z, but it does show a breakable cap at 00z. Fcst soundings and hodographs near there look pretty good at 00z, and particularly after the LLJ kicks in (e.g. 03z -- http://bit.ly/eLgPJV). Of course, that has the nocturnally-cooled stable layer at the sfc, but I imagine there'd be the usual sweetspot between LLJ intensification (and resultant low-level shear intensification) and near-surface stabilization that typically occurs in the 0-2z time.

EDIT: I see Mike beat me to the south-central KS punch by a few mins. Blasted!

 

[Mike Smith]

Jeff,

You what they say about "great minds..." Over the years, I have grown to respect your forecasting talent.

There is one other thing I want to bring up. The NAM doesn't know how much rain fell over the area this evening. HPC puts out an hourly product that attempts to estimate rainfall and remove hail contamination. It (below) is showing widespread ≥0.75" with isolated areas of ≥2.0". That will not evaporate by tomorrow evening (wind 11kt at KAAO right now with a 3°C T/Td spread). That could help increase the helicity (i.e., temperature differential or leftover boundary) and/or locally lower the LCL.
Mike

 

[Chip Redmond]

Jeff, I hope to not be in the middle come the 0 hour! You are right though, its a big haul and will probably have to chose one or the other. However the southern dryline option will put quite a hinderance on getting north for Sunday's chase. Btw, may be spending the night in Ames.

As Jeff pointed out in model resolution for precipitation, the same goes for other parameters. The GFS shows a weak cap over a fairly large area but it is likely a compensation within a grid box for parts having CIN while others are un-capped.

Agreed that the 0z models aren't going to have the boundaries or the data from tonights convection. However, RUC is getting that observation in its initialization and seems to be hinting at some sort of moisture or cloud deck around 16z. I am not sure what the heck its doing because the environment and humidity isn't high enough at any level to support a stratus layer, especially with the instability.

Just a few thoughts.

Chip

 

[cdcollura]

Good day all,

Saturday is a potentially significant severe weather day, especially from SE NE and northeastward onto western and N/C Iowa. SPC has reflected this with a moderate risk upgrade in their 6z outlook. Tornado probs are 10% hatched with hail up to 45% hatched (while wind rather low at 15).

I am not chasing this one (was close to going), but I see the region of W Iowa to be a good starting point (south of Sioux City). This is also above the top of the thermal 700 mb ridge (as shown less than 5c) by 0z on the GFS. Capping should either be eroded and / or overcome by this time. As mentioned earlier, the intersection of the warm front and LLJ / moisture axis (DP approaching 70F) would be the best place for tornadic storms.

The Iowa target also is beneath a highly divergent 250 mb flow aloft, just north of the forecasted southern speed maxima of this exit region of a jet at over 120 knots. The 850 mb flow is over 40 knots from the SSE.

On the other flip side, another region of potential exists farther to the SW in south-central OK and northward to about the OK-KS border just west of I-35. This are is along the dryline bulge and west of the upper 700 mb ridge axis (also a weaker cap, but not as weak as the IA target).

The OK southern target may offer slower storm motions on more favorable chase terrain for folks not wanting to head to Iowa.


Good luck and stay safe for all those who head out!

 

[cstrunk]

The NAM has no CIN over west central Iowa at 00z. It seems to me like a good starting point would be around Avoca, IA with storms firing near there by 6 pm. I'm starting the day in Des Moines. I will look things over again in the morning, but will be heading west on I-80 in the afternoon. Shear and instability look great. I'll adjust from there accordingly.

 

[samuel stone]

06z ruc run progs temps in the 50s across almost all of western IA as late a 18z, not sure thats healthy... any thoughts on that?

 

[Paul Sherman]

Latest GFS Shows the risk area much further South and West than what the SPC Has It for today. Agree with above that the Des Moines to Omaha area looks primed for an Eastward moving Supe below the Warm Front. Also as others have noted the Dryline risk further South in Southern Kansas and Central Oklahoma grabs the attention and kind of reminds me of 24th May 2008, not synoptically but for risk areas and what happened that day when nearly everyone got burned and busted in the Nebraska Mod Risk whereas a Cycling Supercell latched onto an Outflow Boundary from the previous Days Convection and fired off 9 Tornadoes in Kingfisher County.

http://plainschaser.blogspot.com/2011/04/saturday-9th-april-2011-chase-target.html

Have a great Chase everyone!

 

[Logan Karsten]

I would definitely stay with the northern target. Things look much less capped there, nice low LCLs, and very nicely backed surface winds. However, with the newer HRRR runs, the area of interest may have to shift a little further south, as the warm front may not make it as far north as the 00Z NAM had. Either way, I plan on heading straight west from central IA today. I completely agree with SPCs assessment of today.

 

[Tim Jones]

I'm going to adjust my target a bit south as well - depending on position of wf. I-80 west of DSM toward Counciltucky seems like a good place to start today. Will adjust from there.

 

[Jeff Duda]

Fairly encouraged by what the RR and HRRR are showing for both targets today and how they compare with the 00Z 4 km WRF from last night. Both runs show a cluster of supercells developing in far NE/E NE just before 00Z and tracking into W IA with gobs of shear and CAPE to work with. I think the CAPE is being well overdone (some parts of IA/MO are > 5000 J/kg SBCAPE), but I think 3000 in many areas will not be asking too much. The warm front is still pretty far south, but the HR(RR) prog it to move rapidly north throughout the midday hours. Pretty good backing winds near the warm front near Sioux City and aloft at 850 mb in the region. Could be a very good day for the northern target.

The HRRR also breaks out a cluster of supercells in NC OK. Haven't looked much more into it than that.