2013-10-04 FCST: IA/MN/WI/MO/KS/OK

[Brian McKibben]

I have been watching the GFS since last week. It keeps wanting to bring a system into the southern plains later this week. The past few runs have slowed it down a bit to make Friday look like the day.

500 hPa flow of 60-70kts overspreads most of KS and NW OK by 00z Sat. NC KS looks to be in the left exit region too. 850 hPa winds are cranking from 35-50 kts, strongest in NE KS. Tds are in the upper 60s.

This is still 5 days out and there seems to be some disagreement among the models, but this looks like the only show for a while.

12z NAM tomorrow should help shed some light on the set up.

 

[Jeff House]

12Z Euro just in slows down the system more in-line with recent GFS runs. New Euro shows a slower, deeper, farther south system over the Central Plains Friday. Sfc low is Iowa at 00Z, vs GFS Nebraska, but that's a whole lot closer than the previous Euro in Wisc. However Euro still shows a little CF surge on Friday, behind the Thursday lead wave. GFS shows a better DL Friday, but I'm skeptical.

On either model one needs to watch that CF behind the lead system. If the back wave can become clearly dominant, a warm and humid airmass will be available coming out of Texas. Dews could become better than last week, iff the back Friday system clearly dominates. Jet stream energy appears stout. Not much else at this early time.

 

[Zach]

Looking interesting. The dprog/dt keeps pushing it back on the GFS. Hopefully that will lead some time to become more unstable. It would seem the surface low might go more south according to the models. It's really early. Should include MO, IA, and maybe WI in this one if models keep surface low to the north.

 

[Skip Talbot]

The models are hundreds of miles apart on the position of the surface low, with the 12z GFS keeping it down in western Iowa and the 12z NAM ejecting it much earlier and placing it up by Minneapolis by Friday evening. You're going to want to hug that surface low. Winds look pretty veered down the cold front and I'd expect mainly a linear show from SW IA down into KS. There are great shear profiles up by the surface low, but the cap is also wide open the entire day. Cloud cover and early crapvection could kill the instability there.

This setup has chase potential if the warm sector stays clear near the low. Hopefully the timing issues are worked out, but I could see the position of the cold front Friday evening still being in question Friday morning (it's happened a few times this year already). I also hope there is some sort of compromise on the location of the surface features. Eastern MN/western WI where the the NAM has the low is not chaseable. It doesn't have to slow down much, as Albert Lea, MN would make a great target.

 

[cdcollura]

Good day all,

Probably not dropping the big $$$ to chase this one but here's some of my thoughts...

1). The GFS is a bit slow bringing the low east. I would focus anywhere from NW Iowa and south of the I-90 corridor into about Central Iowa / Southern MN. This is the only real place I see backed winds (S to SSW at surface south of the warm-front).

2). The surface winds turn ESE ahead (N) of the warm front pretty much near the IA / MN border. Wherever the low-level jet intersects that warm front will be the play late in the day (5 PM or so). This is dependant on how earlier precipitation shapes up.

3). There will be little or no capping. So convection can start early the day. Staying near the warm front and ahead (E) of the surface low should be the reminder of the day. Storm mode should be HP if supercells do get organized, with a linear mode trailing SW along the cold front to the SW.

4). Storm motions also will be high (40+ knots) since 850 winds are SW and remain so all the way up to 250 MB (with an increase from 30-40 Kts up to 120 Kts). Most of the veering with height will be in the lower 1 km of atmosphere (surface / 925 MB to 850).

Good luck and stay safe to all who chase this one...

 

[Clarence Bennett]

I will spare you the details, but virtually, I plan on busting today north of Concordia near the state line. Tomorrow I will be in the Sioux City area playing around the warm front/area of low pressure.

 

[Logan Karsten]

Given the close proximity of the pay tomorrow, I will be probably heading out to play the warm front in either IA or southern MN, depending on exactly where it sets up. I like the 12Z NAM putting very backed flow in the warm sector near the warm front. Terrain and road networks in the region are pretty nice as well, so it's a no-brainer for me.

 

[James Gustina]

I'm more interested to see which model solution ends up being right, because if the GFS is right and the cold front doesn't come sweeping down the plains like the NAM/SREF have it then western Oklahoma might be fun for the initial few storms before it turns into a hot linear mess. Both models at least have decent instability and ok vertical shear profiles out there, it really just depends on low/front placement tomorrow morning.

 

[Rocky Rascovich]

One of the more classic set ups for severe weather unfolding for this day. Without regurgitating much what SPC and other more professional folk's input regarding this day, it's pretty evident that if all the parameters come together, this will be one of the more notable days for this season, especially for the northern end of my aforementioned areas.

Looking at the 12Z data, the NAM continues as the most progressive of the models which would have the highest chances of severe across the I-35 corridor from just south of MSP to DSM..and likely northeast up into SE MN. this would include all modes of SVR including fast moving (45knots+) TORS, 2" diameter+ hail, and extremely damaging downburst wind gusts. The GFS seems a little further back that would put regions like MJQ to SLB in the bullseye zone for SVR wx. Potential negatives will be ongoing convection thats progged by all short term models across parts of S and SC MN. to northeast NE. during the early to mid morning hours. I would think this will prevent adequate destabilization, however I expect this to clear out at least some during the early and mid afternoon. Where the warm front sets up, which I believe will at least make it to the MN/IA border.. as the vortmax moves into NW IA around the SUX area by 22Z, we should see scattered supercells form close to that front. Thanks to some impressive low level shear, capes approaching 2K j/kg, (if progged insolation occurs and good moisture returns) .. some of these will rotate strongly. Movement will be brisk.. (45 kts+) will keep the chasers on the move!

As of now.. my gut feeling, and what forecast experience I have.. I would be anywhere along the I-90 corridor from MJQ to AEL by 20Z and adjust west and south from there.
Overall, I expect up to 10 confirmed TOR's with at least one EF3 if a discrete SUP gets energized enough with some neighbouring uncontaminated atmosphere to work with.

Further south and west, I expect more linear convection but we'll be dealing with a hellacious squall line that may be QLCS in nature initially, with some lewps and bows that may harbour some forward flank spin ups and bookend vortexes. This will be most likely from DSM to EMP. Still, I can see some discrete development ahead of the squall line as it ventures into northeastern and eastern KS. and far NW MO. between 0Z-2Z. Further south into OK. shear won't be as great but again, an outside chance that any discrete cells that form ahead of the propagating squall line into northern and NW OK. and ahead of the dryline may briefly attain supercell characteristics with TVS signature or two possible.

On a humourous note, by wife is in AUM and may actually be in route back to Okla. tomorrow or may stay thru the weekend. How ironic that she has seen more tornadoes without even trying than I have seen in the last 10 years (not counting my epic TX PH chase several years back in March). She may get lucky.

 

[Brian McKibben]

Both the 18z WRF and GFS slowed the system down a little bit. It looks like we might get some dryline magic in SW OK around 00z. 12z 4km SPC WRF shows a couple of discrete cells down there. I will have to wait till tomorrow morning to look at the 00z run because I can't stay up that late. Winds look marginal for the LLJ but the directional shear is ok. I am think a nice mothership tomorrow west of OKC on I-40 with a decent wall cloud.

http://www.emc.ncep.noaa.gov/mmb/mpyle/spcprod/12/refd_1000m_f36.gif

 

[Adam R Davis]

I gotta stay home on this one, but a friend of mine is on his way out. We both agreed on north central Iowa. NAM at 21z has hinted at possible divergence on the 500MB, with some of the best surface backing there. Add the warm front and everything looks pretty good.

But then there's that whole lack of a cap thing....

If we don't get a convective mess early in the afternoon, I don't think we're looking at a large scale outbreak (like I've heard on Facebook). I think we're going to see maybe 2 or 3 supercells, with one being a monster that overwhelms the other(s).
I'll gladly accept any disagreement or corrections though.

 

[Brandon Jenkins]

The northern play looks like a "can't miss" for anyone within decent driving range, unfortunately that is not me so my focus has primarily been on the southern play in Western OK where decent directional shear looks to overspread a very unstable warm sector (cape value in excess of 2000 j/kg depending on which model you put your faith into). At quick glance we have near surface winds out of the SE that quickly turn with ascent and are southwesterly at 850mb and parallel to the orientation of the cold front promoting a very rapid up-growth of convection as the front surges southeast this evening. Bulk shear on the order of 40-50kts will promote some organization within the first hour or so of development but I can't imagine anything will stay discrete long enough to maintain supercellular characteristics before the cold front has it's way. The only possible exception to this may be a semi-discrete "tail end charlie" storm but pinning down the exact location will be rather difficult as models have diverged on just how far south convection will fire.

As of now, if I were to go out today (which isn't likely at this point) I would target areas north of I-40 between Seiling and Alva where convection is more likely and be prepared to quickly drop south as new storms develop. Another issue with today is the late arrival of the front which should hold off initiation until 23-00z leaving little daylight to work with when the show starts. I've seen worse setups unexpectedly produce so I wouldn't be surprised to see a couple of brief spinups this afternoon but the window of opportunity will certainly be narrow. Good luck to anyone going out today and as always be safe.

 

[James Gustina]

Some of the higher res stuff (NMM-4km WRF, HRRR, etc.) have a pretty nice looking thermodynamic and kinematic environment from Seiling to Hollis this evening. The WRF was hinting at some pretty noticeable convergence along the nose of the dryline with the H5 jet streak ejecting around the base of the trough at the same time (21-23Z). The parallel shear vectors worry me some but further south where the dryline maintains more of it's identity, I could see a semi-organized supercell for the first hour of convective initiation followed by a line as the cold front overtakes the dryline.

At this point I'm leaning towards Clinton as a starting point that'll give me a good option to hope either north or south depending on which area lights up first. I honestly think this might be a nice little surprise this evening.