6/18/09 FCST: IA/MN/NE/WI/IL

[Jeremy Den Hartog]

Its looking like thursday will be the first significant widespread severe weather outbreak of the season for the northern plains as a strong cold front moves into the area...to early to tell how much of a tornado threat there will be at this point though but hopefully all the key ingredients can come together for a nice show

 

[Randall Cooper]

Ive had my eye on this setup on Thursday and/or Friday for a few days now, since I cant chase before Thursday due to work, Ive been watching it very closely! If the GFS verifies, I think we have got a fairly decent chance at some severe weather, possibly even a couple tornadoes on Thursday in parts of N IA and MN, at this point I am definitely thinking about chasing Thursday unless something drastic changes.

 

[Jim Zandonai]

Better add IL to the thread..a Strong warm front will be moving in from the south..Activity will be most active along and north of the warm front..I plan on chasing Thursday and Friday. To early to pin down a target of course but it looks like a good day for strong straight line winds and perhaps a supercell early on along the warm front..finally this area looks good probably the best so far this year.

 

[Jim Zandonai]

Thursday looking better n better for severe storms up here.. looks like a case of rapid developing cells in N. IA area then moving east and SE developing into a bow echo with damaging winds. For once instabilty looks decent...NAM showing 3000-4000j/kg cape over IA into NW IL..Warm front moving in from south too..There is expected to be a cap south of the warm front however but north of it looks decent as storms may ride ESE along and north of it.
I expect a moderate risk on monday mostly for wind damage from NW IA-NW IL perhaps.. If anything can develop early I'll be in N-IA..could be supercellular then go to linear/bow..by then the expected Mcs toinght/am should be out of area..
I dont see much interest in this potentially good set up here..but I'll be ready to go in A.m

 

[Bill Schintler]

Chasing Target for Thursday, June 18

Chase target:
Cherokee, IA

Timing and storm mode:
Storms will arrive in the area at 4 PM CDT, with severe wind the primary threat. During the evening hours into the overnight hours, storms will evolve into a derecho and race southeast across MN and IA.

Synopsis:
Little change in the large-scale pattern as the central US ULVL ridge slowly slides EWD. Warm mid-level temperatures will hold convection at bay S of the ridge, while storm complexes move E along the ring of fire. The upper-Midwest MCS currently underway will exit to the Ohio valley by early Thursday, and attention then turns to SD for renewed development.

Discussion:
Tricky FCST, with boundaries all over the place from tonight’s convection, and a worked-over air mass from widespread earlier activity. The air mass should quickly recover, however, with strong insolation while an ULVL jet streak currently over AZ/NM approaches the area. MLCAPEs will approach 5000J/kg as dewpoints climb into the mid-70’s owing to evapotranspiration. Storms should initiate by late afternoon along the retreating WF/OFB in SERN SD into NWRN IA.

Elevated convection will be ongoing during the first part of the day over north central SD, N of the WF. These storms will track SE and become surface-based, and should then rapidly become severe given the degree of instability and shear. SFC-6km shear should increase to 50kts with the approach of the aforementioned wave. Furthermore, hodograph curvatures along and north of the boundary will become extremely large as the BL begins to decouple and the LLJ strengthens and veers over backed SFC flow. During the evening hours and overnight, convergence at the nose of a 40kt – 50kt LLJ will aid in the maintenance of a large storm complex that will track E through IA and MN. An expanding cold pool and extreme instability will lead to the formation of a bowing MCS resulting in widespread wind damage across IA and SRN MN.
- Bill

9:45 PM CDT, 06/17/09

 

[Derek Weston]

might try to luck out in E. Iowa with any boundry interactions that may take place. According to the 0z NAM this area is more favorably sheared for tornadic supercells. (though I worry our main forcing will be back NW a ways -- a gamble)

 

[Andrew Pritchard]

Waterloo, IA area looks fantastic tomorrow. Early storms will likely congeal into an MCS overnight and spread into Illinois early in the day. Most of Iowa should be in the clear allowing for rapid destabilization along the warm front and outflow boundary from early storms. Extreme instability atop very good turning with height along the boundary will have NE and E Iowa primed for tornadic supercells tomorrow evening. I'll be heading to Waterloo, IA early tomorrow watching the corridor from Waterloo to Iowa City for a couple big time supercells. That low level jet really kicks in during the evening, under a nice 55-60 knot H5 streak. That coupled with mid-June instability should be potent. Supercells will likely trend towards a powerful bow echo that will follow the instability gradient into northern Illinois overnight. Supercells may be possible further southwest along the warm front, but it looks like most of Illinois will remain capped and plagued by subsidence from the early storms.

Waterloo at 7 PM

 

[Jesse Risley]

I think North Central IA along the I-20 corridor north of Des Moines is a good starting play for today. I do think today has the potential to be a very decent play given the highly progged CAPE values in excess of 3500 J/KG, coupled with the presence of OFBs from ongoing MCS and a WF which should move northward today.

Any storms that form and become rooted in the boundary layer would have the potential to become tornadic, given backed winds in the vicinity of the surface boundary.

 

[Josh Richardson]

For the 2nd day in a row Im going to go with the NSSL WRF and play over closer to the Spencer area, I may end up targeting a little east of there but with the current MCS out here I'd rather be further west then east today. Overall, target area is Spencer to Algona along Hwy 18 in Northern IA.

 

[Andrea Griffa]

Another outrageus setup today with insane cape well widespread on Ia,Ne,Mn by both WRF and RUC.
As for low level shear it is not gonna be as directional as yesterday even if it could be sufficient for some nice tornado, given the high cape enviroment.
I'm a little concerned 'cause of the real position of the low: RUC gives it in NE IA while WRF gives a very nice low in central IA; I'm waiting for the next runs of Ruc in order to see if it's gonna align with WRF option.
I see a very strong mid level flow that could complicate the storm chasing today: storm motion will be a little more speedy in comparison with yesterday, and so it will be for tornadoes motion.
I'm liking Sheffield,Ia as initial virtual target.
So you guys stay safe today and watch out for too close monsters.

 

[John Farley]

I'm finally pulling the trigger on the 2-day chase I haven't been able to justify all season. Leaving soon for Iowa City, and will re-evaluate and decide where to go from there. Right now I would guess somewhere west of Cedar Rapids on U.S. 30, but may have to adjust farther north or west. Good thing is, since I am coming from the southeast, the storms will be moving toward me, so hopefully if they initiate farther northwest as some have suggested, I can close fast on them. WRF seems to focus precip in the area bounded by DSM-CID-ALO-FDD.

 

[Jared Farrer]

Jared Farrer, myself (Terrence Cook) and Derek Weston will be targeting the Waterloo, IA area and points West. Hoping to find a nice OFB /WF.

PS: Be careful driving to your targets, we just passed a small pile-up North of Peoria, IL on I-74. Believe we spotted Andrew Pritchard in the line of rear-ended vehicles, hope he is alright and can somehow salvage the chase. Be Safe!

 

[Bob Hartig]

Bill Oosterbaan and I are heading north on I-35 toward Mason City. East-west boundary looks to be poised right about where we are and working its way north. We're in the middle of a CU field, but it looks to be nicely capped at the moment. Nice backing winds.

 

[Dan Robinson]

All latest model runs - the 12z NAM and GFS, plus the recent RUCs, have not been breaking much precip out in IA this evening and later tonight. Seems that the entire moderate risk area is dependent on that happening - if not, the whole swath is going to be a bust.

The trusty 4KM WRF was painting a nice picture, but even it wasn't firing much until 1-2z.

 

[cstrunk]

Suprised to see such little talk about a day with such potential.

New MD out for north central Iowa and south central Minnesota. SPC mentions increasing risk of "significant supercells capable of very large hail... damaging winds and potentially strong tornadoes." There is a boundary visible on the DSM radar oriented NW to SE that runs along a line from Des Moines to Storm Lake. This boundary is lifting north as a warm front. There is a lot of heating contributing to strong instability ranging from 3-5,000 J/kg across most of Iowa into southern Minnesota. Moisture convergence is increasing along and north of the boundary lifting north.

I would expect a tornado watch to be issued shortly and supercells to explode within the next couple of hours somewhere in north central Iowa. I'm waiting for initiation and then I'll likely be heading out the door.

I don't have data available on the road, if anyone is available for nowcasting support, I would appreciate it. Shoot me a PM. Thanks.

http://www.spc.noaa.gov/products/md/md1210.html

*Edit: New tornado watch issued for southern Minnesota.

http://www.spc.noaa.gov/products/watch/ww0467.html