6/7/08 FCST: NE/IA/MN/IL/WI/MI

[Mark Sefried]

Things appear coming together for what appears to be a half way decent chase day especially over northern/north central Iowa per the latest 12z models today. Per the GFS model low lcl's, good lfc's, adequate cape to 4000 j/kg, 0-1 km EHI near 5-6, and sr helicity near 200 m/s definitely has my attention. If the GFS model verifies, I would not be surprised to see the SPC slap a moderate over a good chunk of Iowa for tomorrow. Per parameters the tornado potential is there especially when the storms first develop. The NAM is not nearly as bullish for potential though. It's definitely worth keeping an eye on to see what tonights models show across the area. Perhaps it may be a good day to introduce my gf to chasing.

 

[Mark Blue]

Perhaps it may be a good day to introduce my gf to chasing.

That is a good idea as my wife Jane and I now chase together and I couldn't think of any other chase partner I'd rather be with. We are planning to chase Nebraska again tomorrow and are currently in Norfolk eyeing things with a possibility of chasing Iowa for the first time. The airmass here feels "fallish" today, being post frontal and all. The dewpoints in Oklahoma are pretty juicy and it appears the LLJ will be strengthening again over the next few hours. With the CAPE predicted to be pretty substantial ~ 3000 J and the lack of any cap tomorrow, I'm am keeping my finger crossed that we'll finally have some luck.

 

[John Thurston]

Wonder if I am missing something here with lack of chatter for tomorrow.
However, models do show above parameters, mid 80's for temp and with approaching front, and current SPC 30% slight.............
At any rate camped for the night in Waterloo near 4 way road junction.

 

[Bill Schintler]

Chase Target for Saturday, June 7

Chase target:
Stuart, IA (30 miles west of Des Moines).

Timing and storm mode:
Elevated storms will fire over north central Iowa by late morning, and then build southwest towards the target area while becoming increasingly surface-based through 4 PM CDT. Primary storm mode will be multicell clusters, however embedded supercells will also be possible given the magnitude of instability and shear.

Synopsis:
Today, IA was between a departing storm system and a developing system over the CNTRL high plains. A somewhat drier air mass had worked into the area on NWRLY LLVL flow, however things will soon change as strong moisture advection commences overnight. The flow aloft will amplify slightly over the next 36hrs as the WRN CONUS trough digs and places the upper Midwest in increasingly SWRLY flow, with IA along the SRN fringe of the strongest WRLYS. At the SFC, all MDSs (WRF, GFS, SREF) agree to increase SFC dewpoints to nearly 75F along a narrow axis parallel to I-80 by mid-afternoon Saturday. The WFR had been an outlier to the north concerning location of LLVL features, however it comes into agreement with the latest run.

Discussion:
At the SFC, low pressure will strengthen over SERN CO with a baroclinic zone extending to the E through IA. A mesoscale low should form between OMA and DSM, resulting in locally backed SFC flow near I-80 in WRN IA. Rapid LLVL moisture recovery will commence after 06Z, with ST overspreading much of IA from SW to NE during the morning as a 50kt LLJ transports H85 dewpoints AOA 18C into the region. MLCAPEs will rise to 3000-4000J/kg as SFC dewpoints rise well into the 70’s with a deep mixed-layer beneath moderate H7-H5 lapse rates of 7C/km.

Elevated convection will initiate first in NRN and CNTRL IA N of US-30, and then build to the S and W while becoming SFC-based through 21Z. H7 omegas will increase slightly to -3ub/s in the right-entrance area of strongest H5 flow, while mid-level temperatures cool several degrees. Hodographs will become large during the evening as the LLJ increases to 65 kts and overspreads SRLY SFC flow. Overnight, storms should merge into an MCS and remain largely stationary. Corfidi vectors suggest a slow SWRD motion however establishment of a cold pool may cause acceleration of the storm complex to the E. Very heavy rainfall will be likely in CNTRL IA.

- bill
10:00 PM CDT, 06/06/08

 

[Brandon Sullivan]

Targets For 6/7/08:IA

Looking over 00z Models I do indeed like the setup for tommorow. I sadly will not be able to chase due to a friends wedding..

As for targets, I am looking into two separate targets confined to IA at this time.

Target A: Perry, IA (WSW of Ames IA)
Target A has a lot going for it. At 18z Sig Tor's Climb to 9, 6 KM Deep Layer Shear at 55+ KTS. Surface winds are forecast to back at the surface around 21z. This is key to this target, that is likely where the models are forecasting the higher SRH and Composite Params is due to the forecast backing.. LCL's are also very low in the area.. However, LFC's are at a higher level in that area, leaving a modest LCL-LFC depth, but with the frontogenical forcing, I don't think that should be a huge problem... Hopefully

Target B: Red Oak, IA (ESE of Omaha)
IF the winds do not back as anticipated over target A, then that is when target B comes into play... Target B is sitting in a Soupy 75 DP environment (which more than likely is overdone). However, with winds currently not anticipated to back very much over target B. Multiple directional shear intensive parameters are lacking.. Also, with the forecast high temps/dp's the T/Dd Is only 5-10 Degrees, which may keep things rain wrapped and soupy...

Ultimately, I would play the northern target if
A: The winds do back in the afternoon.
B: If storms can fire downstream and move into and realize the increasingly favorable kinematic environment.

For those of us who need the confidence of the SPC I would say it is in the realm of possibility to see a moderate risk tommorow.. Although, the tornado potential may be more localized to areas that can achieve the backed winds... The 00z WRF shows some backed 925mb winds in N IA... As Bill mentioned, there will be a time period in the evening before an evolution to an MCS when the LLJ strengthens that tornadic potential will increase.. Placement of the LLJ will be critical to this potential, lastest models are showing the strongest 850 and 925 flow confined into Missouri.

Good Luck All!!!

 

[Skip Talbot]

I believe this setup has some potential in it. The last few WRF runs have been rather consistent in pooling 70+ Td's around I-80, and there is decent veering with height and adequate speed shear for supercells. My main concern is how early the precip plot lights up. Storms may once again go up before the best instability can develop and the LLJ can ramp up, and we'll be chasing outflow dominant clusters. It seems like this has bit us the past few days, and I hope that as activity builds south and west over time, that it isn't congealed in a linear mess or behind the outflow of the previous storm. I'm targetting Des Moines and points west along 80 if cells can stay discrete.

 

[Jesse Risley]

Our preliminary target will be Atlantic, IA. It looks as if CAPE will likely exceed 3500 J/KG central and western Iowa, with SRH at DMX around 332 and LI of -3.3 according to GFS.

I would like to see better helicity values, but I agree that the setup has potential provided that everything doesn't line out too early. This one is too close to pass up.

 

[Bill Hark]

I am cautiously optimistic about today’s setup. I like the area of SW 500 mb flow, 50 for most of Nebraska, 40 for points in southeast Nebraska. Dewpoints will be sufficient and there is a hint of forecast drypuch to the south. I already like those 70-72 dewpoints in SE Nebraska.The low that is forecast to move northeastward into northern Kansas should produce a localized area of backing especially late. I also like the forecast CAPE of 2500. By 23Z, the WRF shows supercells erupting in southeast Nebraska. The cap will slow things a bit but 10 degree is definitely breakable. Major minus: veered 850 winds. They look more veered than on some of yesterday’s model outlooks.

Preliminary target: York, Nebraska. Decent chance of tornadic storms though I am also worried about quick transition to HP’s.
Awaiting 12Z data. I wish I was chasing today
Bill Hark
http://www.harkphoto.com

 

[Brandon Sullivan]

Looking through data this morning I am really liking Target A (Perry, IA)

Winds are already locally backed per 12z Surface Obs from surrounding ASOS stations, DP is approaching 65 Degrees. Skies are clear.. Again, IF those winds can stay backed, this will be a good day for a chase in IA.

Latest (11z) RUC is less favorable with Kinematic Profiles by mid afternoon however.. Im no model specialist, but the 11z NAM initialized with a 997 Low in W KS.. Which is deeper than the 11z Surface Analysis, and which is not really apparent any longer at the 12z Surface Analysis.. So the RUC could be overdoing some things..

Regardless, sticking with my target.. If winds continue to back/stay backed it will be a good day. In the last few weeks I have begun to see the importance in that.. Really..

SPC did go MDT over the target area..

 

[Jarrod Cook]

Mark Sefried, Scott Kampas and I are heading to Iowa. Targeting somewhere around Ames at this time. There are definitely some negatives but it's too close to not go like Jesse said. Expect storm initiation as early as noon. Lack of cap worries me that things will turn into a cluster of muck, but if there are any cells that remain isolated for some time they could spin up tornadoes with the fairly modest helicities, and high CAPE. I am hoping for some S to SE winds at the surface to help the 0-1 KM a bit. One nice thing is there should hopefully be many storms to choose from.

 

[Mark Blue]

Confidence is apparently increasing as the SPC just upgraded the 13Z outlook to Moderate. The dewpoints are already really juicy in and along the area of concern as mentioned by Bill (low 70s). My wife Jane and I will be heading to Omaha and as always will be watching the data closely adjusting our target on the fly. The parameters appear to be shaping up in a decent manner and I am a believer in the climatology theory of "persistence" - meaning weather trends tend to persist over several days. We'll be watching the SE NE and SW IA area very closely this late afternoon, but will probably hang around the interstate corridors so we can jet in any direction if necessary.

Mark & Jane

 

[Donald Giuliano]

Decided to pull the trigger on my first Iowa storm chase after seeing the 00z models last night. I think it looks really good in southwest/central Iowa, and left with a couple friends at 7 am. After chasing (or should I say being chased by) what seems like 100 mph storms all year, I just can't pass up the potential for slower-moving cyclic tornadic storms that today holds. Hopefully this pans out, or it'll go down as one of the farthest busts I've ever experienced! At least it's a Saturday, can't ask for a better day for a long-distance chase than that.

 

[Scott Lincoln]

As some of the best parameters sneak into S WI later this afternoon, I'll give you guys a little warning about the topography. Lots of bluffs in SW WI, and changes in topography as there are also many rivers in the area. Also, there's an interesting geological feature in Sauk County near Baraboo and the Wisconsin Dells. Very pretty (maybe if you bust you can go look at that instead), but may obstruct your views.

After you get out of the near-river terrain, it opens up a bit more to flatter rolling hills or fields with sporadic trees towards Madison, Janesville, and Portage.

Not optimal chase territory here in Wisconsin, but it IS doable, especially in the Dane/Rock County area along I-90.

AJL

From what I'm seeing, the best area for initiation appears to be setting up between Omaha and Des Moines/Ames area. Rapid drop of LFCs, highest shear, mid 70s dewpoints, high CAPE.

The good thing is... Iowa IS optimal chase terrain, especially in the Des Moines glacial lobe. Gets iffy in spots near Dubuque, Council Bluffs, as well as some areas of southern Iowa, but most of Iowa is perfect terrain/road networks, especially for storms that are likely to be moving E or ENE.

 

[Darrin Rasberry]

Current chase launch point: My house.

Box: My home, to IA/MN/WI border point, to Ottumwa, to Red Oak will be the reachable area.

Description: Significant areas of clearing are evident in the boxed area (although not directly over my home). RUC currently backs surface winds from the front down I35. Best area of backing caused by the mesolow feature in NE set for 21Z is INVOF the WI/MN/IA border along with an associated area of vertical motion nearby. Also, vertical motion increases from Des Moines to right over my head, implying another possible area of storm development. Yet another particularly strong area of vertical exists over I-35 on the IA/Missouri border later tonight. Shortwave develops nicely.

Wondering how long that mesolow feature on the 15z RUC's prog for 21Z will hold together. If it does, we're all in for a ride, discrete or not.

Same concern as the last post: how will the CAP hold up? I think the localized areas of forcing might be a good sign for discrete action at first, but if the whole roof caves in we're going to get a repeat of the last few setups and my city may soon become a disaster area, with dangerous flooding along the Skunk River.