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

[afischer]

The GFS and NAM have trended a lot weaker with their 700 mb cooling signal over northern targets (from when I looked at the models a couple days ago, anyway). What is shown by the 12Z runs may be more a function of the localized convective explosion they forecast, than true CAA. The forecast EML remains just nasty... in my experience you're hard pressed to get a significant tornado (co-location of sufficiently weak CINH/low LCL) in this type of set-up unless you're talking July in the corn belt with mean BL dewpoints of 20+C. Storms may well initiate along the cold front and dryline... but whether they can tornado will be a delicate situation. CINH will likely become a problem away from the deeply mixed low-level thermal ridge, especially as diurnal cooling sets in. I think a narrow window for tornadoes may exist 00-03Z... again, probably up north where LFCs may be lower.

 

[Ken Johnson]

I really like Jeff Synders forecast discussion. He always seems to be right on the money. I agree with Jeff about td's. Looking at 4casted soundings, the moisture depth is not deep at all. We have to take into account that mixing could occur, given from dry/warm air aloft. However, strength of 850 winds could keep that from occuring. Also, evapotranspiration could play a role and off set mixing. As far as capping. The soundings make it look like a tough day for chasers. The further east you go, the stronger it gets. However, along the dryline itself, there appears to at least be a slightly weaker cap. Weakest cap I saw on sounds that I looked at was PIR and Winner SD. In Nebraska, the cap was between 3 and 6 in most spots. A little futher south, in Kansas and especially OK, along the dryline, it was between 2 and 4, which was weaker, suprisingly, that the places that I looked at in Nebraska. It's a tough call. Southern chasers, don't look past the dryline to the west. Helicty's are 4casted to huge, if storms can go, they could be quick large tornado producers. It's likely a safer bet in S.Dakota, but if you chose to gamble futher south, it could payoff. The cap per WRF 4casted sounding at WWR was 3.3, still large, but not quite as strong as say OMA, where the cap was near 6. Convergence/Daytime heating and one or two BIG ones could go and that could be the best show of the whole day.

 

[Brian Stertz]

Concerns about moisture are certainly valid...cannot disagree with that for now. The main thing with this system is that we are dealing with a surface low that is way deeper than anything the Plains ever sees this time of the year...in fact this may be one of the deepest surface lows in June to my recollection. In this situation, all bets are off as to what will happen as this surface low bombs out...occludes...and then the new triple pt. low forms in C. South Dakota by evening. By looks of the soundings and hodographs at/after sunset...there is a strong signature favorable for strong and violent tornadoes. Many violent tornado events happen when strong moisture advection occurs as things phase in quickly by the triple point/warm front. I think tomorrow represents that type of situation, particularly after 8pm. The outbreak scenario probably will NOT apply but the supercells that do develop will pack quite a whallop. Best of luck to those heading out.

 

[Ryan Pfannkuch]

Adjusting target northward?

As much as I've been hoping for the pre-dark show to make an appearance south of I-90 and even into northern NE...the 12z data is starting to give me a bit of a reality check to start looking harder at areas farther north that may be more of a "sure thing" (cynical side of me is wondering if the sure thing with this system will wait until Thursday in eastern IA and WI )

Per the 12z NAM/GFS and 9z SREF guidance...I'm looking harder at the area just E-NE of the primary surface low effectively along the warm front near the SD/ND border. SREF guidance is certainly more willing to convect this region...

http://www.spc.noaa.gov/exper/sref/gifs/2007060509/SREF_prob_combined_supercell__f042.gif

which is right in the crosshairs of the upper level jet exit region. Along these lines...I welcome thoughts on an alternative 4-county target between the MO River and Aberdeen in north-central SD that may be more appealing to some than gambling farther south:

SD Counties: Campbell, McPherson, Walworth, Edmunds
Including the cities of: Mound City, Eureka, Selby, Ipswich

 

[Andrew Pritchard]

Be careful with targetting so far north. The further north you get into northern SD and upwards into North Dakota things will likely get more and more linear. Up near the SD/ND border you may end up chasing a bow echo that screams into Minnesota before you have time to even complain about the linear mode. I've never liked the SREF, it's just eye candy IMO.

The cap scares me, a lot. But it's there to stay, and you can either suck it up and chase, or chase and watch from home. Either way, half of us are going to be really upset on Wednesday evening.

The best area for discrete supercells and long track tornadoes is likely central and southern Nebraska, but getting convection to go in this area will be harder with the stronger cap. But, should the cap go properly, you could end up with a heck of a show. It's a tough call, but I'm biting the bullet and will be there, crying tears of joy or sorrow with the others.

 

[Scott Weberpal]

Though I believe it'll be difficult for the atmosphere to hold down that much forcing before dark tomorrow, I'm sitting this one out. With the forecast slowing of the surface low, questionable moisture return, and a likely more widespread event closer to home Thursday, I have no reason to get a sunburn tomorrow in SD when I can be enjoying a fun night of softball Good luck to the millions chasing tomorrow!

 

[Dick McGowan]

I guess the moderators didn't take my forecast seriously when I posted last night, since it has been deleted! Guess since I didn't cut and paste from the SPC, that a link from CoD's 500 vort wasn't allowed???

I'm geographically biased tomorrow, and will probably head out west from KC after I wake up late in the morning. I'd say there's a 10 percent chance of the cap breaking in N. KS and SC NE, but I'm a gambling man. Might break out the hibachi and cook some brats, throw the frisbee around and possibly do some fishing at a state park waiting for the cap to break and watch stormtrack go down again (or will it??).

The 12z WRF shows hope in punching some holes through cinh and breaking out a little precip in NC KS. Unless tonight's run show's > 100 j/kg cinh, I'm going to head out and then be home in time to play EC KS for Thursday. Good luck tomorrow to those who chase!

 

[Skip Talbot]

The WRF's positioning of the dryline hasn't changed that much, although the thermodynamic properties have a bit. The cape has been reduced over much of the region, but we are still seeing regions over 4000 J/Kg forecasted in northern NE and SD. The cap is very stout ahead of the dryline, but you see it ebbing away right on the dryline. The CINH is pushed back some in northern NE, and hoping and praying this verifies. The 850 vertical velocities also spike down the dryline in Nebraska between 0z and 3z. So given that... I'm looking at Valentine, NE and arriving late afternoon/early evening so we have time to adjust for a 0z-3z initiation from I-90 south into NE (hopefully).

 

[Jason A.C. Brock]

I'd say there's a 10 percent chance of the cap breaking in N. KS and SC NE, but I'm a gambling man. Might break out the hibachi and cook some brats, throw the frisbee around and possibly do some fishing at a state park waiting for the cap to break and watch stormtrack go down again (or will it??).

If your a gambling man Dick then Im a freakin insane idiot. I will target somewhere around the dryline from Guymon OK to Dodge City KS to Woodward OK. I may very well see a dust storm with 60 mph winds and temps in the 90s but there is that one remote chance I could nail the isolated monster. I also just feel bad sitting this out completely. At least I can say i gave it a shot. I wil also be in position for any tailend activity heading into the weekend along the front. It may not be nearly as volatile those days but I will take a few decent chases over 1 long hard marathon chase which could even burn me then.
Ill be breakin out the shorts tomorrow thats for sure for my white legs.
The atmosphere will be perfect if a storm can form in this area and if it doesnt then its not so far away from home that I would want to murder anyone. I think if I went to Nebraska and didnt see anything I mght be on Americas most wanted next week.

 

[Brandon Goforth]

If your a gambling man Dick then Im a freakin insane idiot. I will target somewhere around the dryline from Guymon OK to Dodge City KS to Woodward OK. I may very well see a dust storm with 60 mph winds and temps in the 90s but there is that one remote chance I could nail the isolated monster. I also just feel bad sitting this out completely. At least I can say i gave it a shot. I wil also be in position for any tailend activity heading into the weekend along the front. It may not be nearly as volatile those days but I will take a few decent chases over 1 long hard marathon chase which could even burn me then.
Ill be breakin out the shorts tomorrow thats for sure for my white legs.
The atmosphere will be perfect if a storm can form in this area and if it doesnt then its not so far away from home that I would want to murder anyone. I think if I went to Nebraska and didnt see anything I mght be on Americas most wanted next week.

I feel the same way, I can't make a trip all the way to SD right now, but I don't wanna miss out either, so I too will probably target areas into NW OK. Besides, SPC is giving the area north of I-40 in NW OK a 20% chance of the cap breaking.

 

[Chris Karstens]

Hi everyone, long time reader, 1st time posting...

Something I noticed that I thought would be worth pointing out...18Z NAM shows the cap along the dryline could be weaker than previously forecasted...

12Z NAM lid strength valid 00Z Thursday:

http://beta.wxcaster.com/NAMSevereArchive.php?datetime=2007060512Z&fcsthour=36&type=ATMOS_LSI

18Z NAM lid strength valid 00Z Thursday:

http://beta.wxcaster.com/NAMSevereArchive.php?datetime=2007060518Z&fcsthour=30&type=ATMOS_LSI

Anxiously awaiting 00z runs...

Chris Karstens
Graduate Student
ISU Meteorology

 

[Billy Griffin]

Target tomorrow is Wheeler - Allison, TX. Time = 5pm - dark. Convective temps should be reached, possibly breaking this "cap of death." If it does go, any cell will be a prolific hail producer with some of the most beautiful structure (and perhaps an isolated tornado!)

Flight gets me back in to OKC from Seattle by 2, so should have plenty of time to get out west and watch the sunset, or perhaps one heck of a monster cell (crosses fingers.)

Good luck to all - safety first!

 

[Rich Thompson]

I'll admit that I've only read a few of the FCST posts for this upcoming event, so someone else may have already discussed the moisture. I don't know about you folks, but I'm awfully worried when I see Tds mixed into the 50s well down into TX, and in 24 hrs we're supposed to see 67-70 F Tds into SD? The closest Tds of that magnitude are near I-10 (!) and must move almost 1000 miles in 24 hrs. It would be one of the more remarkable moisture recoveries I've seen in the past 20 years. It seems more realistic to expect low-mid 60s Tds, which will lead to stronger CIN and relatively large T-Td spreads for a serious tornado threat.

Besides the obvious EML/cap concerns, I also suspect that much of the NAM/GFS precip signal will be related to strong lift and development of high-based convection over the high terrain W of the dryline/front during the afternoon. The few times I can recall this happening, it's usually led to upscale storm growth and continued cold pool problems, even after the high-based storms encounter the richer moisture to the east.

I was able to swap operational shifts in case I decided to chase, but I think I'll save the $1 million in gas and not make the ~1500 mile round trip to the wrn half of SD from Norman. Thursday will provide a much closer chase opportunity for me at the triple point across nrn OK or srn/sern KS.

Rich T.

 

[Mark Farnik]

I was just about to point the NAM model trend out myself. It's encouraging, if nothing else. The prospect of that thermonuclear cap is quite ugly and I don't think I need to remind anyone that if it holds, it could ruin one of the best tornado outbreak setups in years.
We'll have to see what the 00z runs look like; if this trend of a weaker cap in place along and ahead of the dryline continues in the 00z runs, we may yet get a tornado outbreak out of this system. I still believe that if indeed the cap is weaker than forecast and is breached, the dryline will explode and we will have multiple cyclical supercells with possible strong to violent tornado families tearing across central NE into southeast SD by late afternoon/early evening, with other, much more isolated tornadic supercells firing down the remainder of the dryline through KS and into OK. I guess we'll find out whether this was a glitch or a new and desperately welcome trend when the 00z runs come out... here's hoping and praying that this weakened cap wasn't a glitch.

 

[Jonathan Behle]

Quick question for all of you... We have some impressive heat being put out by forecasts in Western KS/ OK, and Western Texas..

With this heat, I assume the lifting will be alot better, then lets say if its only 82F outside. I've often heard meteorologists talk about a magical temperature the temperature needs to get to for a cap to break, what would this temperature be?

Quick Edit:

I dont believe moisture return will be that big of an issue, often times when we have questionable moisture return in a system like this, we get more scattered activity, and constant redeveloping and refocussing of thunderstorm activity if we can get a tongue of moisture into the system. The cap is the major concern for me.