5/31/09 FCST: MN/SD/NE/IA/MO/IL

[jshields]

After looking at that Nebraska City sounding, and SW IA in the models..I completely agree with you guys (again)..why wouldn't the SPC notice this?

i'm thinking i'm going to stick to my guns and stay in se nebraksa/sw iowa, although i suppose i could head north a little too. it just seems that the ingredients are way better further south. i can't believe the spc is moving the risk further north too. i guess they're planning on the cap holding all day. the 12Z run of the nam today makes for very nice hodos in se nebraska and sw iowa. i pulled this one for 03Z 6/1(39 hours) for just north of omaha. the llj really kicks in at 40 kts and lengthens the hodograph considerably. the winds are backed at the surface too. the warm level is very low, looks like about 900mb, so hopefully something can bust through that!

0Z 6/1 just north of omaha:
http://twisterdata.com/index.php?sounding.x=493&sounding.y=305&sndclick=y&prog=forecast&model=NAM&grid=221&model_yyyy=2009&model_mm=05&model_dd=30&model_init_hh=12&fhour=36&parameter=CAPE&level=SURFACE&unit=none&maximize=n&mode=singlemap&sounding=y&output=image&archive=false(note: time sensitive)

03Z 6/1 just north of omaha: (earl's weather shows 0-1 km srh is almost 350 at this time!!)
http://twisterdata.com/index.php?sounding.x=493&sounding.y=305&prog=forecast&model=NAM&grid=221&model_yyyy=2009&model_mm=05&model_dd=30&model_init_hh=12&fhour=39&parameter=CAPE&level=SURFACE&unit=none&maximize=n&mode=singlemap&sounding=n&output=image&archive=false&sounding=y&sndclick=y (note: time sensitive)

 

[J Trueblood]

What about the cold front? Sure the thermodynamics look great, but if the cold front reaches SW IA too late, then nothing will initiate, right? How's the timing on that looking?

 

[Derrick Herndon]

What about the cold front? Sure the thermodynamics look great, but if the cold front reaches SW IA too late, then nothing will initiate, right? How's the timing on that looking?

I will also be sticking to my target of SE Neb then follow storms into SW IA. I am not sure why SPC is hesitating to extend the outlook into this area given the thermodynamics. NAM dews will be a few degrees too high but should still be enough to break the cap. The question is trigger. Cold front is too far away so I think we are looking at surface heating to be enuf to initiate convection.

 

[J Trueblood]

One more thing..while the NAM shows great stuff for SW IA, the GFS shows a huge hole and virtually to instability..I guess it comes down to which model you trust more.

 

[jshields]

yeah i noticed that too about the gfs too. it seems a little odd, don't know the reasoning for that.... as far as a trigger, i think it was mike o'keefe that noticed something coming through that atmosphere that could set off something ahead of the cold front, otherwise yeah the front will prob be too far away to initiate anything. temps are forecast to be in the upper 80's tomorrow which is right around the convective temp, so i'll be keeping my fingers crossed. i guess if it doesn't look too good tomorrow, i could always shoot north. the iowa/south dakota border in southeast sd, is only about 1 hr 45 min from here

 

[Mark Blue]

I also think SE NE/SW IA could be a play if the NAM tells us anything, there is a small piece of energy coming into that area if you look at the 500mb winds which are fairly strong compared to what we have seen the last few weeks and I have more confidence in better moisture and instability.

I noticed that too after looking at the 500 mb charts. There is a little ripple in the 500 mb heights or a chunk of vorticity (X marks the spot) in the proximity of SE NE and SW IA:

http://www.rap.ucar.edu/weather/model/eta36hr_500_vrt.gif

The winds are also slightly elevated in this region as depicted by the 500 mb winds graphic:

http://www.rap.ucar.edu/weather/model/eta36hr_500_wnd.gif

The Skew Ts on Earl Barker's site are looking very nice in the triangle bounded by these towns: Falls City NE, Nebraska City, and Clarinda IA. Very nice hodographs at each location and as Fabian mentioned the LCLs appear to indicate surface based storms. Very high lifted indexes and EHI numbers here as well. The two concerns I have are the timing and cap. It appears it could be between 0Z and 3Z to me and I'd much rather chase during the daylight hours. I'm planning to study this forecast closer tomorrow morning and will refine the target as necessary, but right now I'm in the triangle mentioned above.

 

[Sam Hall]

OK, I am SO glad everyone else here is stumped by why SPC are putting a 30 % risk so far north. Could it be left-overs from tonight or something ??

To me, the best place to situate ourselves so far is anywhere near the borders of KS, NE, MO and IA. CAPE is best round here, LIs are all positive above here, but up to -4 in E KS, winds are greater and better directional shearing there... CIN is a slight concern but nothing major, nice temps and dews...

The ONLY thing I can think of is perhaps that SPC are taking into account a triple point, moving from ND into C/MN by 6pm ish (according to some front charts), but I just don't see anything else of much significance up there ATTM... not like in MO and other parts anyway :/// I wonder if they can see something we can't? I am not as experienced at all as many of you guys, so it's easily something I have missed, but what?

Edit: Just wanted to say I completely agree with Mark B in your post before mine... I too will study this again first thing, and hoping that SPC may revise their target or at least something become clearer... but will make a firm decision on where to go tomorrow and I am hoping too that it all works out at a decent time :.

 

[Fabian Guerra]

After looking at the new nam I wouldn't change my target much from this afternoon. I still think the far southwest corner of IA holds some supercell possibilities. This new run actually has the 500mb winds slightly stronger with a 0-3km helicity bullseye (500+ m2s-2!) in that far sw corner of Iowa where the best CAPE and moisture is. The cap strength might be a factor tomorrow but I noticed that the nam composite reflectivity actually had slight precip breaking out by 21Z then dissapearing by 0Z. I wouldn't agree with that output. I think that if storms do go up tomorrow in that area then they'll be supercellular right from the get-go and the CAP could help them stay more discreet. It's not going to be a little rainshower or popcorn storm...IMO it's going to be all or nothing tomorrow in sw Iowa/se Nebraska. It's not an easy call for those of us who would have to travel a great distance and be back home on Monday but for local chasers and chasecationers I would think its the best play.

BTW, here is a a forecast sounding for Red Oak, IA with some sexy inidicies and a nice hodo (click on 24 hour):
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&STATIONID=krdk

 

[Craig McPeck]

Im with all you guys, going with a group starting in Nebraska City or so, then traveling to Southwest Iowa. As always, will take a look at morning parameters.

It seems that SPC is not getting the full jist of things. Time will tell at the 1:30 AM update.

 

[Derek Weston]

Agree that the SW IA area looks like the best shot for nice discrete supercells. Nice to see the latest runs paint an even better picture shear wise...

Per latest NAM... seems like a window around 0z where they want to break the CAP off to the west of this area, but well capped by 03z. Also want to break precip out further west into east central Neb, where no cap exists...

Still not sure we'll have significant forcing mechanism in place in SW IA...

There is a reason the SPC hasn't given this area too much attention... seems to be a pretty conditional threat.

 

[Dick McGowan]

Huh? Cap breaking at 21z in SW IA? Looks like CINH City to me: http://www.twisterdata.com/index.ph...nglemap&sounding=n&output=image&archive=false

That Red Oak Skew-T shows -116 CINH, extremely high LFC's @2800 m and a whopping 16 j/kg for 0-3 km CAPE. IMO best chance for any convection is along the cold front way further NW into S. SD and NC/NW Nebraska.

 

[Bill Schintler]

Chase Target for Sunday, May 31

Chase target (north):
22 miles east of Huron, SD.

Timing and storm mode:
Storms will fire between 4 and 6 PM, with a few supercells likely before dark. Storms will later evolve into a large complex and track from southwest MN though IA.

Chase target (south):
55 miles east of Midland, TX.

Timing and storm mode:
Isolated storms will develop along the dryline after 3 PM CDT, with supercells likely early in storm evolution.

Synopsis:
The persistent Hudson Bay trough and attendant NWRLY ULVL flow will finally break down, with a transition to an increasingly zonal pattern over the next 48 hours. An upstream system will track E along the US/CAN border, spreading stronger ULVL flow over the Dakotas and NRN MN. At the SFC, a retreating WF will intersect a SEWD-moving CF and associated low over ERN SD, with the CF trailing SW through SD and WRN NE.

Discussion (Upper Midwest):
Moderate instability will develop from SD into MN and IA despite limited moisture. SFC dewpoints will increase to nearly 60F, contributing towards MLCAPE’s AOB 1500J/kg beneath steep mid-level lapse rates of 8-8.5 C/km. Frontal convergence will be maximized near the CF/WF intersection at the nose of a 35kt LLJ, and lift will increase as an H7 shortwave approaches. Large hodograph curvatures should exist along and immediately N of the WF and CF, and supercells will be likely early in storm evolution. Current indications also suggest the development of a mesoscale low in east-central SD, with attendant backing of LLVL wind fields and enhanced directional shear E of this feature. During the evening and into the overnight hours, a strengthening LLJ will aid in the growth of an MCS which will track SE through WRN MN and IA. Tornado probabilities will be greatest between 01Z and 04Z, as helicities increase when the BL decouples and LCL levels fall with the loss of daytime heating.

Discussion (Southern high plains):
Isolated storms will develop along a DL as strong SFC heating takes place. Shear will be weaker in this area then further N, however rotating updrafts are likely with initial storm development given the degree of instability.

- Bill
KD0DJG
www.twistertoursusa.com
10:52 PM CDT, 05/30/09

 

[Adam Penney]

I have to agree with Dick. CINH looks to hold tight over SW IA. Its a hop-skip and jump for me so I have tomorrow morning to look things over.

As of now, Im 60/40 on chasing.

Certainly will be interested to see the new Day 1 outlook late this evening to see if the SPC changes things up a bit.

 

[Andrew Pritchard]

Also not sure where you're seeing something even showing at 21Z.

http://wxcaster2.com/CENTRAL_ETA212_1000-500_SLPPRPTHK_21HR.gif

I wouldn't be so convinced on the "all or nothing" motto, either. Even though I'm siding more with "nothing", I've seen the middle ground countless times. Little piddly rain showers will form as towers struggle against the cap, and occasionally a storm will even pierce the cap, get severe warned only to be swallowed back into nothing but an anvil.

I'm not incredibly impressed with the northern target either, but I'd probably try for Sioux Falls, SD.

I bet the southern target doesn't even get outlooked by the 5% hail/wind, for those staying up til 1 am tonight.

 

[Fabian Guerra]

Dick, you bring up a couple very valid points. I actaully don't agree with the nam having slight precip breaking out at 21Z but I do think that there is a chance for rotating storms aoa 0Z when the cap does erode. Yeah, the LFC's are high but there have also been many cases where supercells were able to generate tornadoes in larger CIN/higher LFC environments when supported by large EHI resulting from large amounts of low-level SRH. If its convection we're looking for then yeah there will probably be planety of it in SD/NE/MN but, as conditional as it may be, IMO the best shot at tornadoes tomorrow is in far sw IA/se NE.

Edit: Andrew, slight precip shows on Twister Data's nam composite reflectivity - hour 21 (21Z). I don't have an all or nothing motto but I do think that will be the case tomorrow in that target area. You may be right about SPC's prob's about tomorrow but I don't let their probablilites sway me either way. Countless times we've all seen tornadoes happen in no risk areas and vice-a-versa.