2009-05-12 FCST: KS,NE,MO,IA,IL

[Jeff Duda]

Pretty sad how we're saying that mid-upper 50s dewpoints are now becoming sufficient to get people excited about severe weather! Up here in Iowa, we have struggled significantly to see dewpoints exceed 60, let alone hit it. It's causing instability to suffer (even when shear is good) and causes storms to be high based. It's frustrating me because I haven't had a real good chase day up here yet. Kinda wondering when something will happen.

 

[Brian Stertz]

I am kind of liking the High Plains target more and more across EC/NE Colorado and WC/NW Kansas for Tue. Although the ascent is lacking....there is a good upslope component with increasing moisture with a northward poke of the theta ridge. Should be good enough for supercells, but will it be for tornadoes? Looks like there is that slight possibility by Tue. evening. Plenty of time to monitor things....

 

[Andrew Stoller]

Strange things happen between Denver and Burlington, CO because of the Palmer divide. There's been days where the setup looked fairly close to Tue., with 55 degree dewpoints, a strong cap, good directional shear, but marginal speed sheer. The oragraphic lift provided by the rise in elevation from southeast CO to the I-70 corridor is sometimes enough to initiate isolated strong convection. May 10, 2004 was a prime example.

If the dryline backed up even more into CO, I'd be a happy camper.

Yes, you can call me out for local bias!

 

[Skip Talbot]

Pretty sad how we're saying that mid-upper 50s dewpoints are now becoming sufficient to get people excited about severe weather!

That's enough for stunning supercell structure and even tornadoes in eastern Colorado due to the higher elevations. But yeah, out in Iowa and Illinois mid 50's is pretty paltry.

Oklahoma looks intriguing, as a warm front is pushing through during the day. Instability is much higher as well as helicity as there is a strong 850 jet plotted on the WRF. I'm not seeing any convection firing on the WRF though so the cap must be suppressing it even though the CINH erodes from SE OK up through central OK by 0z.

 

[Jeff Duda]

For Colorado, yeah, 50s dews are fine, but I was referring more to the lower elevations of the midwest and central plains

 

[Michael O'Keeffe]

While the NAM doesn't look very good, the GFS is looking pretty good for W KS down into the E TX Pan/W OK. While 500mb winds may be a bit weak, we will have nice 850s and GREAT directional shear, with fairly large hodographs anywhere along the dryline. If the moisture that the GFS is showing DOES verify then Tuesday could be a pretty good chase day from I70 to I40 however the cap will be fairly strong so it will be isolated but any cell that can develop will likely pose a tornado risk, only if the GFS verifies.

 

[Michael O'Keeffe]

I'm kind of surprised to see no one talking about this day as it is slowly trending towards a better setup especially on the NAM. It is started to agree more with the GFS showing 60f+ tds making it to W KS, however it is still only in the low 60s and with temps 80f+ it could lead to some high temp/dew depressions, regardless we will see some great directional shear, making some large forecast hodographs. The cap also looks pretty stout but it is actually rare when it does hold. Every chase this year it has broken one way or another, maybe not till late but it has. The dryline bulge extending from the KS/CO border through Garden City down through Dodge City and SE towards Coldwater would be my initial target area. I am on the fence about this setup but if it improves slightly then it would be a pretty chaseable day with a good bet for some tornadoes.

Edit: There also appears to be a warm front draped across S KS as well which could enhance the shear.

 

[Fabian Guerra]

More and more I am liking the area n/nw of OKC, around Guthrie or Watonga. My main concern for now is the CAP but if it breaks, and it is a breakable cap, then we could be in for a good show. Of course we could end up sitting in the sunshine all day and see another nocturnal event or no event at all. That being said, some of the indicies on the nam forecast soundings for that general area are downright sweet:
LI: -7.8
SRH (1KM): 280.9
0-3km Helicity: 555.3
CAPE: 3809 j/kg
LCL: 680
EHI: 12.9
VGP: .80
STP: 7.6

Here is a link to the Guthrie, OK nam forecacast sounding for Tuesday (click on 60 hours):
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&STATIONID=kgok

As of now we are planning to leave Chicago tomorrow morning.

Best,
Fabian

 

[Eric Flescher]

is there a guide

is there a guide for reading that forecast information of yours?



:::

More and more I am liking the area n/nw of OKC, around Guthrie or Watonga. My main concern for now is the CAP but if it breaks, and it is a breakable cap, then we could be in for a good show. Of course we could end up sitting in the sunshine all day and see another nocturnal event or no event at all. That being said, some of the indicies on the nam forecast soundings for that general area are downright sweet:
LI: -7.8
SRH (1KM): 280.9
0-3km Helicity: 555.3
CAPE: 3809 j/kg
LCL: 680
EHI: 12.9
VGP: .80
STP: 7.6

Here is a link to the Guthrie, OK nam forecacast sounding for Tuesday (click on 60 hours):
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&STATIONID=kgok

As of now we are planning to leave Chicago tomorrow morning.

Best,
Fabian

 

[Brian Stertz]

My attention has turned from the High Plains down to the SC Kansas and NC Oklahoma area after 00z...

The parameters for significant severe wx look to be stacking up nicely Tue. evening/night...particularly across SC Kansas and NC Oklahoma on the slowly lifting warm front. 12z NAM fcst soundings past 00z show an inceasing bulk shear and helicity instability combo (EHI's 9+). Evening NAM fcst shows strong veering wind profiles...very enlarged hodographs in the 0-3km zone...and strong moisture pooling on the WF. MLLCL's are very favorable across SC Kansas for a decent tornado environment should the 12z NAM verify.

The only thing holding things back may be the fairly strong 700-800mb cap. Looking for a triggering wave downstream on the 12z NAM, there is a weak mid-level wave that will move east from SW Kansas and the NE TX Panhandle that may be able to pop a few significant tornadic supercells. Something to cast a watchful eye on the next few model runs. Think it may be time to prepare for a half day off Tue. from the interesting looks of things.


Twister Data 0-3km EHI ...valid 03z

Twister Data MLLCL ...valid 03z

 

[Jeff House]

Believe moisture return will be adequate for all chase targets; mid-50s on the High Plains and perhaps upper 60s just off the Caprock in the Southern Plains. I am not just being optimistic b/c I probably cannot chase Tuesday anyway. Central/South Texas still very humid today (Sunday) and moisture return should be rapid once winds turn this time of year. While it depends on how the cold pool behaves over the High Plains Monday, pattern recognition leads me to favor good moisture return regardless of model forecasts either way. When the front does not get into South Texas, in mid-May, moisture can be back in the Central Plains in 12 hours.

Regarding the cap, remember the High Plains is at 850 mb so that hot 850 prog is not as big a concern as it would be in the Central Plains. In fact some good heat behind the dryline would be a plus. Now we still need to make sure the 700 mb heat plume from the Southwest is not out of control. Overall agree cap will break.

Biggest question IMO, is not moisture but upper levels winds. No wind means it will just be high plains drifters of little consequence. Believe upper level winds should be strong enough given the trend for just enough in the southern stream. Water vapor shows subtle southern stream energy hanging off the Baja Coast. Models strengthen it slightly over the Southern Plains, which makes sense as it approaches a baraclinic zone (boundary in Plains). OK, no more dynamics. How about a target?

If I could go my own target might be a start in Liberal, KS, Canadian, TX or Woodward, OK. Target subject to change until game day. Agree with Front Range chasers that a Denver cyclone could enhance storms if they need to stay local, but I am personally forecasting for the DL bulge and warm front intersection. Good luck to all!

 

[Jim Tang]

GFS has been trending stronger on both winds aloft and low level moisture. Believe there is a small area in southern KS and northern OK where tornadic potential may be maximized by a differential heating boundary that sets up... I'd say in a box bounded by Dodge City, KS, Lipscomb, TX, Enid, OK, and Pratt, KS just to the northeast of the steeper low level lapse rates.

The question really is initiation, and it's a big one at that as the core of the EML actually advects in around sunset. But given initiation, this may be one of the better setups in the Plains this month.

 

[jamesmseitz]

The set up is for a few storms west KS around the Dodge City area. The last few runs have been better. Not has impressive when I started this but chase non the less. I figure if you wait for the perfect chase day you will be out only 2 or 3 times a year. As for now I'm in.

 

[Matthew Crowther]

I am not sure at all the cap is breakable as it is strengthening through the evening, a sunburn bust seems like a very good bet based on what I am seeing.

 

[Jeff Passner]

I'm with Matt in this one.... How in the world are we going to break this cap?? Yes, it can be broken with strong dryline mixing or strong PVA but this will be tough. I'd go up to Nebraska and hope for the best. Up there the moisture depth might be a problem. I'm not convinced that a +13C temp at 700-mb can broken.... I won't say "no" right now, but futute model runs must show some mechanism for breaking that cap in Kansas-Tex Panhandle or I'd bring some sunscreen lotion, although a high-based junky storm can still occur on the dryline. It's still two days away, but I think if anything happens it will happen at sunset or later. If you're looking for a thunderstorm go up to North Dakota, eastern Kansas in the low-level jet, or the Big Bend where heating will break the cap. Right now, I see NO lift on the dryline or anything that can make a severe thunderstorm. In chasing, the CAPE, winds, and surface dew point are all wonderful, but first you must make a thunderstorm. That's the hard part about Tuesday. Hope it trends better but right now the thing I'm struggling with is --- making a severe thunderstorm on the dryline Tuesday.