6/6/07 FCST: ND/SD/NE/KS/MN/IA/MO

[Scott Lincoln]

This setup is very conditional, and I hope that with all of the people traveling such far distances for this storm system that the conditions are met.

Moisture is the big one. Winds from the Gulf dont seem to become favorable for really good moisture return until just a few hours before dark. The 18z NAM in particular somehow magically brings the 70F dewpoint contour north from near the Gulf all the way to almost to Nebraska in 6 hours. I really feel that the moisture is overdone. Less moisture, less CAPE, and also a significanly lower chance that there will even be storm initiation to realize the shear present with the system.
Complicating matters, the system keeps slowing down from run to run, as has been a usual occurance this year. That makes the distance even farther for the moisture to travel.

Looking at the BUFKIT profiles for Chamblerain, SD, it is apparent that looking at just the 700mb temperatures for the cap strength is insufficient. The main part of the cap appears to be just below that. The whole environment at that location appears to be pretty warm, meaning that any CAPE that gets realized looks to be narrow.

We may have a really strong system forming with a decent dryline and triple point, but that doesn't mean anything if we cant get storms to form... and we for sure cant have a decent shot at long-track, strong tornadoes if any storms that form are elevated.

Not trying to depress everyone, but we just have to see better moisture return from the Gulf if this is to be the big outbreak its hyped up to be.

 

[Darren Addy]

I would love it if the target area would shift as far south as Kearney. The location of the surface low seems to be coming south (and west). However, currently LBF expects the triple-point on Wed. to be near Mullen at 21Z with the dryline from west-of-Valentine to west-of-North Platte at that time. NAM has the leading shortwave arriving 18-21Z. LBF says that triple-point location corresponds to the location of weakest convective inhibition. If true, that sounds like an initiation trifecta at about 4 PM CDT.

If the show starts around 21Z there should be plenty of daylight as the motherships (hope-hope) move into even juicier air to the east (and north). Other good news for this scenario would be no Missouri River crossings to worry about, although you might not be able to say the same for the North Loup and Niobrara rivers.

The good news (from the standpoint of personal property/human life threat) is that this part of Nebraska is really sparsely populated. The bad news is that the road network is pretty poor for chasing. I'd make Thedford (down Hwy 2 east of Mullen) my target area. Storms moving NE would be on a line to pass near Ainsworth and Bassett (about 70 miles from Thedford as the crow flies).

 

[Chris Hayes]

My two main concerns are dewpoints, and forward storm speed. I did a loop of the 18z ETA and it showsa plume of 70+ dewpoints advection northward into the target area, so hopefully that will verify. Second concern is the forward storm speed. Correct me if I'm wrong, but arent the storms going to be movint at 30-40kts? The lower end of that isnt too bad, but not as slow as I'd like to see, like on May 29, 2004.

 

[Glenn Rivers]

Magical 70+ dewpoint problem

Several people have mentioned the magical 70 + dewpoint problem that appears on the NAM between 18Z and 0Z. Besides the low level convergence and "pinching", could excessive ET be occurring over a large area of the warm sector due to the high soil moisture combining with sun and strong winds during the 6th? Such a day can extract up to 10 mm of soil moisture on a regional basis if soil moisture is high enough to begin with. Many arears in the warm sector of this system are close to waterlogged from weeks of heavy rain. Any thoughts on this?

 

[Mike Hollingshead]

My two main concerns are dewpoints, and forward storm speed. I did a loop of the 18z ETA and it showsa plume of 70+ dewpoints advection northward into the target area, so hopefully that will verify. Second concern is the forward storm speed. Correct me if I'm wrong, but arent the storms going to be movint at 30-40kts? The lower end of that isnt too bad, but not as slow as I'd like to see, like on May 29, 2004.

http://www.wxcaster2.com/CENTRAL_ETA_ATMOS_STORM-MOTION_60HR.gif

For now.

Or you can click on the hour you like on this link:
http://www.wxcaster2.com/central_models.htm

Towards the top("Storm Motion").

 

[Mikey Gribble]

I just got back in town from a trip to the lake, where I had no internet access, so I have been in the dark on this setup since Friday morning. Since I just got back this afternoon I haven't had a chance to pick over the forecast, but from my initial glance at things I am very impressed. I am scared to death the cap isn't going to break though. If the cap does break across Nebraska, it is going to be huge. I remember seeing somebody else post this already, but I will echo it because it is the exact same thing I thought when I started looking at the models. I don't remember seeing this good of a combination of shear and instability in a very long time. Extreme instability combined with deep layer shear of 50kts over Nebraska is ideal for supercells. Stong wind fields, especially in the low levels and good directional shear is going to create an extremely favorable environment for strong long-track tornadoes. As far as the best environment for tornadic supercells and violent tornadoes goes, I like southern Nebraska. That option may not be open though if the cap is an issue. Realistically I will probably be targetting farther North near Valentine if it is looking like the cap won't break farther South. I would hate to see the kind of setup there is going to be over southern Nebraska go to waste because the cap doesn't break. I honestly can not remember seeing such a wide spread area so favorable for strong and violent tornadoes since May 4, 2003. Once again, the HUGE IF out there right now is the cap. If it breaks down the dryline through Nebraska I think there is going to be a major tornado outbreak.

 

[Ken Johnson]

The sfc low is radily deepening and there will be very strong convergence due to such sharp pressure falls. That is one thing that will help. There's also a very nice shortwave moving through Nebraska into the Dakotas. The cap is going to be intense, but with the strength of forcing it should break. Not so certain about Kansas, but Nebraska, especially northern Nebraska and southern South Dakota look deadly at this point. Another place could be the warm front. Models seem to have convection along the warm front near Kansas City. LLVL jet is insane across MO and Iowa. Minn. looks good for a late night event.

 

[Charles Kuster]

We will also be chasing on Wednesday. I basically echo what everyone else is saying. Extreme instability, very favorable shear for tornadoes, but also a very strong cap that will be tough to break. I do think moisture will be sufficient for the day. As of now I would target the Springfield, NE, to Winner, SD, to Chamberlain, SD area. Good luck to all who are chasing and stay safe!

 

[Kurt Silvey]

Well with spring sports over with for the kids and things quieting down on the home front, Wednesday appears to be my first decent chase opportunity and close to home to boot. Looking a current forecast models it looks like there will be insane amounts of CAPE (> 5000 j/kg) across most of central NE and s central SD and the swly jet could coincide with maximum heating around 00Z Thursday. The jet streak may be enough to break the proj thermal nuclear cap. In any case we will need as much gulf moisture as we can get as LCL’s are only modest at 1100 – 1500m. As a preliminary target I’ll look at n central NE and s cental SD, Norfolk to O'Neil to Yankton. A second target could be Sioux City as the cap weakens a little and LCL’s drop below 1000m. More tomorrow.

 

[Bob Hartig]

Okay, after several years of watching from the poolside, I'm finally holding my nose and taking the plunge by setting my own target and reasoning out on the table.

After looking at the NAM/WRF, here is why I'm eyeing Fairfax, South Dakota, as a good place to hang out and wait for storm initiation.

• CAPE: 4,500+ SB; 4,000+ ML; 4,500+ MU. (!!!!!!!!!!!!!!!)
• Nicely capped at 18z; erodes in a narrow pocket by 00z (7 p.m.) to the west. Should put us a little ways east of storm initiation.
• Nicely situated on front left quadrant of advancing 500 mb. jet streak; 50-55 kt. to start, with 70 kt. speed max arriving after initiation. This might be an argument to play a bit south, perhaps just across the border in Butte, Nebraska.
• In the sweet zone of Theta-e ridge, with low-70s dewpoints. With steep drop in dewpoints to the west, dryline appears to be situated around the center of the state by 7 p.m.
• Good 3k SRH. Better helicities actually lie just to the east and the south. Again, maybe Butte. Wouldn’t suggest moving east because the cap strengthens considerably.
• Best vertical velocities. These advect to the east and strengthen later on toward tri-state border.
• Looks like decent N-S, E-W road options.

Those of you more knowledgeable than I, please feel free to lean in and offer your critique.

 

[Brian Stertz]

00z GFS looks very interesting and very much outbreak-ish, with supercells from C/E South Dakota into NC/NE Nebraska. 00z ETA looks very focused across C/NE South Dakota during the evening and then late night cap buster supercells over SE South Dakota after sundown. It seemingly keeps the main action on the triple point which will be racing northeast out of SC South Dakota near Winner SD towards the Aberdeen SD area. Still more data to chew through and plan to be setting sail for Sioux City tomorrow evening no matter what. Time for shut-eye for now and then a 1:30am wake up call to check the Day 2 ...and then head back to bed. I'll have my Vortex Times forecast updated late tomorrow morning for those interested.

 

[Derek Weston]

New SPC forecast is out. Seems to think our cape/shear combo will be ample... no big concerns from them over moisture.

Everything right now -- based upon everything I've ingested -- seems to be pointing towards central SD being our best bet for supercell development before dark. (where the cap ought to be less of a concern) edits: though, the latest gfs seems to paint more favorable conditions into central nebraska...

Going south, and into Eastern Nebraska (possibly W. Iowa, SW Minnesota and NE Kansas) is more of a wildcard. The cap is the concern, but the area ought to be juicy. If the cap breaks down further south early enough in this area, all hell may break lose and we'll have a potentially large outbreak. (as it stands, according to some of the models, it seems there is a good threat for tornadic activity after dark, particularly in the E. SD, SW. Minn, NW. IA area)

Just my take . . .

 

[Edward Ballou]

Looks like the spike on a lot of the models points right into Winner, SD. It seems as though something will happen on one side or the other. I like the absense of convective inihibition west of Winner. Yet there's something calling from a town named Ideal when you're looking for a chase target. I almost want to go there just to say that I waited for storms in the Ideal location. (ha ha) Anyways, that cap is fairly strong and I'd hate to sit there and wait for things to go for quite some time. Though the benefits are too great if things get going. The cap looked to be below the 10,000 line, so perhaps if we all go to one location and blow real hard...lol. As for timing, I hate chasing after dark, this system's timing and the breakdown of the cap will be very important. I was very impressed with the low level shear and the hodograph profiles look pretty good. Not worried about cape - good grief, it's the best I've seen in quite some time.

 

[Ryan Pfannkuch]

Latest thoughts from the 6z NAM/0z GFS runs:

Little change from my thinking 24 hours ago regarding target area...although the cap strength still has me very sceptical of tornadic supercells occurring any more than 75 miles or so south of the NE/SD border...despite the fact that the current MDT Risk and 45% probs reach all the way down to north-central KS. Anyone else expecting the southern end of the highest probs to be trimmed northward a little in subsequent outlooks?

I still feel the GFS has a more realistic handle on dews/CAPES with mid to MAYBE upper 60s dews and MLCAPE topping out in the 3-3500 j/kg range. I for one will be surprised to see 70 dews up into the SD/NE border area...although the latest SREF does show some hope of maybe getting 70 into the OMA area by 0z...but this is still well east of the boundary.

At any rate...both the NAM/GFS do fully agree that areas along a line from Bassett NE to Huron SD could have some serious issues AFTER dark...but the pre-sunset time frame is looking a little more nebulous to me. As a chaser basing my target on pre-sunset potential...my latest four county target area focusing on 0-3z shows very little change from the one I posted last night...although I shifted it slightly east to account for what I believe will be a later show:

NE: Keya Paha, Brown...including the cities of Ainsworth and Springview
SD: Tripp, Gregory...including the cities of Winner, Gregory

Due to capping concerns south...I would probably favor the northern end of this target area around Winner, which has nearby access to several road options.

 

[Jeff Snyder]

I'd be happier if the troughs speeds up by 6-9 hours to bring the better mid-level cooling and forcing over the warm sector earlier. Regardless, I still have very strong doubts about moisture return, particularly with the well-organized bow echo moving through deep south TX right now. In addition, CRP and BRO soundings from this morning show unimpressive moisture depth. Given this, I just cannot imagine how in the world Tds will exceed 70F tomorrow, save for perhaps a very shallow depth (10mb) near the sfc, which won't matter much for storms. I have not liked the NAM Td forecasts from the past couple of years (despite the fact that an apparent bug was fixed last year), and I have to think that the GFS will verify much better in terms of low-level moisture return. Unfortunately, that plays havoc with LCL height, and maybe even storm mode. I still foresee a squall line and potential derecho situation in SD after dark, given the backed mid-level flow and potential for relatively low boundary layer RH (i.e. strong cold pools). 60-65 F dewpoints seem much more likely, with perhaps 65-68F tds farther east of the dryline. I hope I'm wrong, though!

I'm wondering, however, about the potential a little farther south down the dryline. The past few models runs of GFS and NAM have indicated significant moistening in the 700mb layer (see 700mb RH plots), indicative of shallow convective scheme and strong convergence along the dryline. In fact, several runs have had small areas of QPF along the dryline, either down in western TX or in central KS and northwestern OK. Midlevel temps should be rather homogeneous south of I80 or perhaps even south of the NE/SD border, so I would imagine that it'd come down to convergence and boundary layer theta-e.

If we only had one more day of Gulf moisture return I think we'd be looking at a high-end tornado event. As it is now, I'm not so sure.