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

[Jesse Risley]

The severe weather parameters certainly look decent across SW IA, but I think the SPC is aware of the significant CINH present, and based on current model runs, there looks to be little hope of erosion prior to loss of diurnal heating. I did notice that both the GFS and the NAM had areas of CINH eroding very near the target area around 00z, but that seems conditional to me. The threat in this area relies solely on diurnal heating overcoming a rather modestly capped environment.

Based on the parameters, and looking at some of the forecast rawinsondes, if supercells are able to intiate in this environment, it certainly should be a rewarding chase. It's also obvious that the best forcing remains well north and west of this area in the vicinity of the approaching frontal boundary, so that makes for an additional factor that does make this very much a high bust potential for the NE/IA target area.

 

[Brandon Sullivan]

It's also obvious that the best forcing remains well north and west of this area in the vicinity of the approaching frontal boundary, so that makes for an additional factor that does make this very much a high bust potential for the NE/IA target area.

One possible boosting factor is the weak shortwave that is seen over eastern Colorado right now.. Models try to hang onto it and move it into the IA/NE area tommorow afternoon/evening.. This may provide enough lift to set stuff off, in Southeast NE and Southwest IA. IMO I think that area may have the best shot at a decent show tommorow, but also holds a greater bust potential...

On the other side of things, dp's are pretty weak right now in NE at least, they are slightly better in central and western SD however.. But most places AOB 45 with most NE locations AOB 35. Southwest flow at low levels will not help this any, so we shall see what happens. I have read before though, that in NW flow events such as this, that WAA can often help compensate for such things.

If I did not have to work, I would chase just to be in position for Monday..

 

[Bob Hartig]

Am I the only one who's bothered by the weak mid/upper-level winds in SW Iowa? Yes, I've looked at the hodographs. Nice, very sweetly curved. But I also see 500 mb winds around 25 kts, and no improvement with height. That has been my issue with this setup--where there's CAPE, there's weak shear; where there's shear, CAPE is lacking. Maybe I'm missing something her--my forecasting skills still have plenty of blanks to fill in. But I tend to look for H5s at around 35-40 kts minimum. And bulk shear in this area is what? Around 30 kts? Right on the threshold, it seems to me.

My buddies and I almost took the bait on this one, but it's a long drive from Michigan for what looks to me like a pretty marginal setup. Probably tomorrow we'll lament not having made the drive, just as today I could have kicked myself for missing the play down around Indianapolis, which is a lot closer. In all sincerity, good luck to those of you who do head out.

 

[Brian Stertz]

Just taking a look at the NAM forecast sounding/hodos....it looks like there is a small window of sfc based hope in the corridor from Columbus/Fremont NE area and northeast maybe into extreme WC Iowa. The South Dakota area is still a bit intriguing to me ...but have kind of looked with wide eyes at the Nebraska target zone a little closer with EHI's over 7. The CINH is high in afternoon...lowers around 00z and is back way high again at 03z. If something should blow the cap, it could be pretty vigorous for a few hrs. before withering away after dark as a high based t-storm as it moves towards/into Iowa. I certainly think this is worthy of a look see tomorrow morning on the RUC and 12z NAM forecast. Still plan on a chase tomorrow up north either 3.5 hrs. or 6.5 hrs. from KC up I-29.

 

[John Wetter]

I think if this mesolow can happen, SD will be the place to be. I like Bill's forecast basically and would agree with him except maybe slightly more South and East... I'll say Roswell, SD... Though that's just semantics from Bill's target...

 

[Craig McPeck]

It appears that SPC doesnt want to budge and move a little bit further south. It just doesnt seem like the highest instability will not be met in the slight risk area, and where that highest is, to strong of a cap.

 

[jshields]

well the new spc day 1 is out for tomorrow(later today), and it basically shows the same slight risk area, but even there they've lowered the percentages down to 15% with only a 2% tornado chance. if they keep it at 15% further north i'll feel even better about staying down south i don't have far to go so i'll be looking closely at the ruc and even the 18Z runs of the other models before i have to worry about heading out. i think i'll even try to use the short fuse composite!

 

[Chris Carter]

my target area before the spc day 1 update was Sioux Falls, SD, after looking at the new one, i see no reason to change that. It should be an interesting day tomorrow, given the convection can break the cape.

 

[Jesse Risley]

I am worried about today after seeing this morning's things. Though I agree with you three above. I am going to stick to my play of IA/NE/KS/MO border. We are going to head a bit NW and see if anything fires. Perhaps to SE part of NE...

PLEASE DO something...

If the RUC analysis has a good handle on today's events, the southern target doesn't appear nearly as favorable. The best instability doesn't arrive until after 2200Z, which appears to coincide with the return of better moisture. This is also supported by the latest SREF.

The cap doesn't erode right along that immediate border area until around 00Z, and the only area of higher QPF in that region appears to remain in SE Nebraska until at least 01Z, where the cap should erode a bit earlier.

 

[Michael O'Keeffe]

If the RUC analysis has a good handle on today's events, the southern target doesn't appear nearly as favorable. The best instability doesn't arrive until after 2200Z, which appears to coincide with the return of better moisture. This is also supported by the latest SREF.

The cap doesn't erode right along that immediate border area until around 00Z, and the only area of higher QPF in that region appears to remain in SE Nebraska until at least 01Z, where the cap should erode a bit earlier.

Well if the RUC is right nowhere will be good north or south, with moisture being extremely bad right now which I was a bit concerned about however there are upper 50s and low 60 tds just south of I70 now, it is strange because along and north of I70 the dews are in the upper 40s but near along I35 in Kansas the dews 58-62F which means there is some sort of boundary I'm guessing with such as sharp moisture gradient. I still think though that if this moisture can make it to at least NW MO by 0z we may be able to see something decent. Time will tell, and the 12z NAM is looking pretty good as well but is likely overdoing moisture.

 

[Jesse Risley]

Well if the RUC is right nowhere will be good north or south, with moisture being extremely bad right now which I was a bit concerned about however there are upper 50s and low 60 tds just south of I70 now, it is strange because along and north of I70 the dews are in the upper 40s but near along I35 in Kansas the dews 58-62F which means there is some sort of boundary I'm guessing with such as sharp moisture gradient. I still think though that if this moisture can make it to at least NW MO by 0z we may be able to see something decent. Time will tell, and the 12z NAM is looking pretty good as well but is likely overdoing moisture.

I noticed that the NAM was doing the same thing last night with the overdone moisture.

I would agree that if moisture can advect that far north once the cap erodes, there could be a decent supercell in that vicinity.

Taking a quick glance at several previous RUC runs, it does appear to have handled the forecast moisture return reasonably well thus far. However, there is a possibility that it does not have a good handle on convective initiation in that region around the 0z timeframe, and something could indeed fire in that area once the best instability is in place. Time will tell whether or not later runs pick up on this or not.

 

[jshields]

Well if the RUC is right nowhere will be good north or south, with moisture being extremely bad right now which I was a bit concerned about however there are upper 50s and low 60 tds just south of I70 now, it is strange because along and north of I70 the dews are in the upper 40s but near along I35 in Kansas the dews 58-62F which means there is some sort of boundary I'm guessing with such as sharp moisture gradient. I still think though that if this moisture can make it to at least NW MO by 0z we may be able to see something decent. Time will tell, and the 12z NAM is looking pretty good as well but is likely overdoing moisture.

would that be a warm front dividing the moisture like that? the local wfo talks about a warm front blasting north today so it makes it all the way to western minnesota by tonight. that's gotta be where the moisture is coming from... right now dew is 42 here in omaha.....

 

[Scott Olson]

With the latest NAM run, I feel like Nebraska is that nerdy girl in the room that no one ever noticed how attractive she really is. The NAM/GFS both show a weakend cap in Nebraska tommorow and much more impressive shear conditions then I'm expecting along the cold front in South Dakota. There's some subtle moisture convergence from the warmer drier/air being pulled in from the SW but the big player is the shortwave that is in the middle of Colorado right now. NAM seems much more bullish with this wave and even the GFS SOLN shows it well defined and enhancing lift and wind fields. The one thing I asked myself when looking at the models is if this SWV fired off severe convection in Colorado today that I would stop being so shallow and consider dating Nebraska. If we can penetrate that cap, we are looking at a very nice storm all things considered, with around 160-200 m2/s2 0-3km SRH per the NAM. GFS ain't bad either even though the european models seem to discount this possibility. Seriously though, I don't like europeans because they tend to be smarter than me and I have disregard for those smarter than me. That's why I did a write in vote for televisions Peter Griffin from FOX's Family Guy, in the last presidential election.

South Dakota target:
Intiation: 60%
Tornadic: 30% if intiated
Severe: 95% if intiated
Lake Andes to Plankinton

Nebraska:
Intiation: 35%
Tornadic: 70% if intiated
Severe: 85% if initiated

I don't mean to get down on South Dakota. I just don't like the mid-level winds in the area where the storms are going to intiate. The bulk and low level shear is hardly impressive enough for me. That's not to say local conditions, (differntial heating, local enhancement of baroclinic vorticity, outflow boundaries) couldn't make it more interesting. If we can get something going farther NE, that may be game with bulk shear that to me starts saying 'I just might be sustainable'.

/Whispers to the Wind/
Scott W. Olson

 

[Derrick Herndon]

would that be a warm front dividing the moisture like that? the local wfo talks about a warm front blasting north today so it makes it all the way to western minnesota by tonight. that's gotta be where the moisture is coming from... right now dew is 42 here in omaha.....

Yes this is a returning warm front from the front that went through 2 days ago. The front is more of a moisture boundary now. I had hoped for some clarity from the RUC but no luck. In my experience the RUC tends to be a bit dry while the NAM is too moist, esp in the corn belt. The dews near I-70 are encouraging but if you look just above the surface you can see the pocket of dry that the GFS and now the RUC show advecting into SE Neb this aftn. That mixes down through the day and mixes out some of the sfc moisture. I am still planning to play the low level thermal/moisture intersection from York to Fremont in hopes of something. The RUC, NAM and 4 km WRF all fire convection in this area from 22-00Z. The RUC brings a subtle s/w near the CO/NE border East this aftn with attendant enhanced vertical motion. Perhaps that will be just enough. Soooo conditional today but I am close and still feel that the tornado potential is better in this region than the northern target.

 

[Scott Olson]

I see sooo much potiental in this day but everything is incredibly messy right now. I've got the main wave, a glancing SWV in South Dakota, a nice little wave moving through Nebraska. I got a cold front, warm-front and a pre-frontal trough. 35-50kts of Bulk shear in South Dakota and nice instability across the entire SD/NE area. But it's to subtle to pinpoint where is truly the best spot because this setup has truly gone mesoscale, where finite things will determine convective intiation location. I'm not in the mood to try and milk such details out of the RUC/NAM so I will just stay put and chase using mesoanalysis. As for Nebraska, I'm going with Palmyra. I'm staying in South Dakota, I actually like the bulk shear now even though the directional component takes it from SW to NW. The quality of the moisture return/current convection along I-90 and complex surface/upper-air fields make this a tizy of a forecast. I'm going to go along Miller/Redfield line for South Dakota. I need that bit of moisture pooling that has been showed maximized there to get my LCL's down to at least within the possible range. LCL's are tough today, even into my Nebraska target.

I think I will play the front where it meets the old outflow. Huron to Redfield/Miller.