5/25/08 FCST: WI/IA/MN/IL/KS

[Andy Wehrle]

Sunday looks like the Upper Midwest's first shot at severe storms in about a month. We'll finally be free of the influence of this eastern trough/central ridge pattern.

Instability parameters appear favorable across most of Iowa into southwestern Wisconsin per SPC Day 3 30% prob zone. Given clearing from overnight crapvection (when is that not a concern around here?) I think that area could see some decent supercells with a few tornadoes, if not an epic wedgefest like the past two days in Kansas.

Both NAM and GFS show very strong 500MB and 850MB winds over the area for 0z Monday, although the 850s are badly veered to the SW, the 500s are straight out of the west so there is at least some turning there.

Surface features appear somewhat ill-defined at the moment, but all it takes is a cold front to light off some storms...

I'm considering heading out for my first real chase since June 2006. My target for right now would be SW Wisconsin, Platteville-La Crosse region. I really don't want to venture any farther from home due to gas costs, plus the possibility of having to chase across the Mississippi. Plus, it looks as good as anywhere else for the moment. Areas further east probably won't see anything until later in the evening, when everything has re-congealed into MCS mode.

I've noticed quite a few more Wisconsinites joining the forum lately. If anyone is heading out and interested in possibly parterning up, shoot me a PM.

 

[MatthewCarman]

According to the SPC and NWS temps will be in the low to mid 80's across IA with dewpoints in the 60's to low 70's. Also MLCAPES looks to be 2000-4000 J/KG along the primary instability axis. 40-50 KT of deep layer speed shear will help to. We should have MOD-STRONG instability. With dynamics like that I would not be suprised to see a few tornado reports tommorow. IA looks to be the most active state tommorow but SW WI/NW IL could be active to.

 

[Scott Weberpal]

I may actually be keying in on Northeast KS for Sunday evening. Looks like an area of backed surface flow within 3000-4000 j/kg CAPE. Helicity is enhanced in the area due to the backed surface flow and the NAM breaks out precip there. Staying the night in Iowa City just in case I decide I like Northeast KS in the morning.

 

[Dean Baron]

I am going to try to be out tomorrow in southern Minnesota or northern Iowa, i dont feel like dealing with the forests in Wisconsin. Like you guys have mentioned, temps in these areas will be around 80 with dewpoints climbing well in to the 60's. Good instability with MLCAPES up to about 4000 j/kg. However, the thing i am worried about is no where in this area is there a large area of backed winds, most of the area looks like it will have surface winds out of the south or SSW, and upper level winds coming out of the SW, doesnt seem like real great shear, but nevertheless helicity values near the MN/IA are decent so maybe it the winds wont matter as much as i think they will. Prelim target would be Albert Lea, MN to Mason City, IA.

 

[Josh Richardson]

Yeah veered winds are certainly a problem, oh well will see what happens. Of course still need to see tonights and mornings runs and will nail down a final target. Right now, Im leaning between Central IA and NE IA. Probably just gonna set up just west of Waterloo and move from there. If your out there Dean and want to meet give me a call if you still have my cell number, if not just grab it off Spotter Network.

 

[Bill Schintler]

Chase Targets for Sunday, May 25

Chase target - north:
Colfax, WI (60 miles east of St. Paul).

Timing and storm mode - north:
Convection will fire at 10 AM west of the Twin Cities, and then develop east into an environment of favorable instability and shear through 3 PM CDT. Supercells with a few tornadoes will be likely.

Chase target - south:
Great Bend, KS.

Timing and storm mode - south:
Convection will initiate in western KS in the morning, with eastward development of storms along I-70 by early afternoon. Storm mode will be primarily multicell, with embedded supercells.

Synopsis:
UA analysis indicated a flattening/elongation of the persistent WRN CONUS low, with the primary circulation slowly retrograding over the NRN CA coast while a second circulation had developed over ERN MT. This has led to the maintenance of SWRLY flow from NM NEWRD into NEB, with disturbances embedded within this flow. At the SFC, a weak CF extended from low pressure in SERN MT SWRD along a RAP, CDR, OGA, GLD, to LAA line. An advancing WF extended SE from the low along a MBG, LRJ, to CSQ line. A DL has remained largely stationary throughout the day, and extended SWRD from a triple point near MHE, to GRI and HYS at 00Z. Despite strong instability with dewpoints in the 65-70F range, convection has largely failed to initiate along the DL S of I-80 for a number of reasons: a worked over AMS from earlier convection; subsidence between S/WVs resulting in weak SFC convergence; a stubborn H7 thermal ridge; and a dry push above 800mb, which served to kill updrafts. The main show today was further S in OK where convection fired in a zone of strong instability with the help of a compact S/WV, where established storms maintained healthy storm relative inflow despite weaker wind fields through modification of the storm-scale environment.

Discussion, MN and WI:
Elevated convection will push through MN and ERN IA mainly N of I-80 between 06-12Z on the nose of a 40kt LLJ bringing a surge of high theta-E air. After AM convection moves E of the area, attention turns to the west where storms will fire in ERN MN by late morning near the intersection of a WF/CF/occluded front. The environment E of the WF will exhibit favorable hodographs in the SFC-3km layer as a SWRLY LLJ strengthens to 35kts and overspreads SRLY SFC flow. Modest instability with MLCAPEs of 1500J/kg should be sufficient for storm organization.

Discussion, KS:
A SFC-trough will extend E of low-pressure over SERN CO through KS along I-70 by 18Z. Convection ongoing in NRN OK will also push an outflow boundary NW to near Pratt by 14Z, with continued slow NWRD movement indicated through 19Z. Despite early initiation, the synoptic environment should be favorable for discrete convection with SRHs AOB 300m2/s2 along with bulk shear to 50kts in a zone of ample instability. Shear may also be locally enhanced where boundary interactions occur.

- bill
www.twistertoursusa.com
9:30 PM CDT, 05/24/08

 

[J West]

I was typing my thoughts, but Bill posted in the meantime...

My cliff notes: I'm not sold on moisture return fast enough or far enough into Wisconsin to feed the potential environment at hand tomorrow afternoon. If there are storms that can sustain themselves, don't chase without a chainsaw up in the WI northwoods or near the Mississippi river...two very tough chase locations. Based on what I've seen so far, I'd opt for the WI/IA/MN border area to be the hot spot tomorrow with better dew's and a decent environment overall.

 

[Andy Wehrle]

Still on the fence about tomorrow. Revised my initial target north to Whitehall, WI. Think this area has the best shot of being within shooting range of a supercell or two. Still liking the forecasted deep layer wind fields and instability, but the low level wind fields are really screwy/veered. We'll need some boundary and/or warm front magic.

 

[Michael Stanga]

Will be out today, but not sold on any locations yet. thinking Rochester, MN for fast positioning in any direction. but waiting for 13z updates and 12z balloons and that may change

 

[Josh Richardson]

New Day 1 looking just like I figured it would putting us right in the middle. Not enough time to get way back in KS and Im not even bothering with WI. Might just stay in the area and chase a NC/NE IA to SC/SE MN type of region. We'll see what happens out there, certainly some decent moisture return already this morning with the S/SE winds out there.

 

[Dean Baron]

the new MOD risk has thrown my original forecast out the window. I have no idea what to do now. I live on the western part of the MOD risk so i could just wait it out for something to fire, but i would rather not do it that way. I could target Wisconsin, but there are so many trees i would rather stay in Minnesota as long as i can. May head west of the cities, i think storms will fire west, then move in to the better sheared instead of firing in the MOD risk, and then moving in to Wisconsin.

 

[Joel Wright]

Finally, a decent chase day that's not 4 states away! (Well, hopefully it's a decent chase day. Hope I didn't just jinx us lol.)

Jeremy and I will be heading into Iowa here shortly. We're thinking about heading up towards the New Hampton/Charles City area to start. This area will be on the nose of the best CAPE/deep moisture, and on the southern edge of the best shear and surface convergence. Really think there could be some strong tornadoes today if the storms can get going and stay discrete.

Good luck to all who go out!

 

[Tim Marshall]

TARGET: DDC-Oakley TIME OF DEPARTURE: 10 AM How about Tornadofest 4 today? -this time back in KS. Looks like those higher dewpoints will push north and west into W KS as a surface low develops in S CO. A frontal boundary will limit the NW advance of the surface moisture. Our nice SW jet aloft will aid in ventilating the updrafts. I figure storms will fire in W KS then move east-northeastward along the front. Surface winds are progged to back (morning RUC) increasing storm relative helicities along the boundary. Morning WRF has boundary farther north along I-70 by 00z and lower dewpoints. Some negatives are the lack of an upper air disturbance to aid in lifting and morning convection in SE KS which has left a CAPE hole. We'll head out west, then be back in SLN tonight. TM

 

[Jeff Snyder]

Currently in SLN after busting in KS yesterday. Outflow from overnight convection is really muddying the picture right now, as very low theta-e air has developed W of I35 in most of Oklahoma. Meteograms from many Oklahoma Mesonet sites W of I35 show that Tds have fallen 10-15F since midnight (with some areas in central and southern OK see a heatburst event). The effect this will have on afternoon and evening convection later today is unknown, but I can't imagine it'll be good. EMC 4km WRF from 00z does show at least one decent supercell in SW KS this evening, but it also appears to be missing the 54-61F Tds across most of the western 1/2 of OK. In fact, the 12z OUN sounding shows how wiped out the moisture is, and it isn't pretty -- 57F Td at the sfc that decreases to 0C at 850mb. Unfortunately, I also don't see a well-defined southern OFB (and it'd be down near I20 I think anyway).

Given potential moisure issues (both magnitude and depth), we're probably going to stay put in SLN for the time being. We may meander W starting around noon, but moisture scouring is ugly, and I can't see how the low theta-e air won't advect northward into southwestern KS later today. There does appear to be a chance that moisture will squeek around to the W of this western OK theta-e "hole", as the 12z AMA sounding would support decent moisture depth in western KS later today (assuming S 850mb flow). So, perhaps the options will be either stay E of the moisture scouring (SLN area?) or head far west to an area W or SW of DDC. Current flow is veered in SW KS, but it forecast to back by 21z, with a sharpening dryline across extreme southwestern KS. Again, though, I know the RUC has had a tendency to over-moisten the boundary layer at times this year (w/ 9-12 hr Td forecasts 5-10F too high on a consistent basis some days), so I'm not sure if it's depiction of >65F Tds warm sector-wide is terribly realistic given the obs in W OK attm. If it looks like >63F Tds will advect back into southwestern KS, the 12z RUC would certainly scream to head into SW KS.

EDIT: 12z NAM is out to 12 hr (at least), and it shows a slightly less favorable situation for SW KS. The NAM's 500mb flow is 10-20 kts weaker than forecast by the RUC, and the front/boundary is located closer to I70 on the NAM. The ~30 kt 500mb flow results in practically sub-supercell shear (25-30 kt 0-6km shear), though improving closer to the boundary a little farther to the N. I suppose the likely plan now is to look to the west and hope that moisture can return in time. The 12z NAM shows 90/60 sfc conditions farther W, so LCLs may well be very high.

EDIT2: Another possibility, I suppose, is that moisture spreads NWward from eastern and northcentral Oklahoma (east of a NW-SE oriented boundary of some sort that stretches from NW of Woodward to W of OUN). We may not have the good 70+ that was in northern OK yesterday, but 65+ seems possible. Too bad we have this "wedge" of relatively dry air, but at least sfc obs in the TX panhandle show >60F Tds trying to come into the OK panhandle and far SW KS.

 

[Paul Knightley]

We're in York, where many other chasers ended up last night! We'll be leaving within 15-20 mins and heading towards the Hays - Quinter region along I-70, perhaps just south of there around Dighton. The moisture issues are a bit of a concern, but I don't fancy heading NE, especially given the outlook for the next couple of days.