5/22/07 FCST: TX / OK / KS / NE / SD

[Skip Talbot]

GFS has been showing a trough entering the plains on Tuesday, and now that the WRF is in range, it seems to agree. The models differ on the position of the triple point, with the GFS placing it up by the NE border near Goodland and WRF to the southeast by Dodge City.

Looking off of the WRF:

Although the upper level winds are not as strong as we have seen in the big setups earlier this year, the 0-6km shear is still forecast to be between 30 and 50 knots over west central KS, which is definitely sufficient for supercells. A 998 surface low over the panhandles will back the surface winds with nice veerying up through the levels to mainly westerly at 500 mb. SRH values between 150-300 and a decent LLJ.

The dryline is forecast to tighten as moisture advects in from the south. With dewpoints near 65, there is a forecasted SBCAPE of 2500 in west central KS. The WRF also shows a stout cap in the morning, but it erodes across South Dakota, Nebraska, and finally Kansas in the early evening. Precip is forcasted by 0z, and the cap gone. This situation would make for a nice chase setup with the early crap being suppressed and supercells going up when the upper level winds have had more time to enter the area, and with a few hours of daylight left.

I'd say west central Kansas looks like a good spot for supercells on Tuesday evening with a tornado threat as well given the LLJ and adequate moisture. I'll narrow my target down as the models settle on the location of the triple point.

 

[Michael O'Keeffe]

I agree with Skip 100%. The WRF is showing precip erupt along the dryline mainly north of US50 in C Kansas. I would expect storms to fire along the dryline around 6-7pm and quickly go severe warned. I think the conditions are suffient for tornadic development. My way far out target is Great Bend-Russell.

 

[Chris Hayes]

I have to concur with the 2 previous posts. If things were to stay the same as they are now, according to the WRF model, I'd be targetting DDC. Situation for tuesday deffinately looks a lot better than it had for isolated supercells along the dryline, with the attendant threat of tornados. As skip said, it doesnt have outbreak written all over it, but I would expect a moderate risk for tuesday across western Kansas.

 

[Joshua Jones]

I have been watching this for the last 4 or five days... I think we could see a few tornados. My target for monday is going to most likely be down near Amarillo, then For Tuesday I am thinking Hadley, OK.

Hope to see you all out on the road.

Josh

 

[Chris Wilburn]

I agree that Tuesday has the potential to be a decent chase day. I will not go into much detail now being it is still 4 days out, but it is nice to see the GFS and NAM somewhat agree with the position of the triple point. We just need to see where it will actually set up. Nice CAPE and moisture should be in place as well as some decent helicity values. Low level shear is nice, but like mentioned the 500mb winds are on the weak side, but at least we will not have to chase with our rocket boosters. Anyway, it could be a really decent day and probably a moderate like Chris mentioned. Only time will tell and still many model runs to fine tune until then. General target would be near the triple point. Going off the NAM at this point I would say a general area from Dodge City and just play things from there. This will change of course as we have several model runs to go.

 

[Ray Walker]

As of the latest GFS model run I am really likeing the SC Nebraska area for Tuesday. The GFS paints a pretty picture for this area with 3000j/kg of cape, dews in the low to mid 60s, and nice wind feilds all coming together. The model is showing the triple point setting up in this area as well, however it is still a few days out and things can change but as of right now I am leaving tonight for southern Kansas or the Dodge city area for monday and that way I will be in possition for Tuesdays event. If things come together as the GFS is showing, A deeper, stronger trough, better instability in conjunction with good wind feilds then I do see a localized tornado event in the central plains area on tuesday. The trend for the GFS has been for a deeper trough and a slower solution for the frontal boundary, which is a good thing.

 

[Andrew Stoller]

I like how there is a huge cap around Dodge City with upwards of 3,000 j/kg cape and the cap erodes all day to nothing by about 6 pm. Maybe that will help things stay very supercellular and explosive in development. Sup 1000 mb surface low to the south west should make for nicely backed winds in south central Kansas. Dodge AFD mentions Monday may be decent, but the real show on Tue with a few tornadoes possible.

 

[Michael O'Keeffe]

The WRF is showing a monster supercell that is isolated in S Kansas near the Greensburg area. I will be targeting Pratt - Greensburg- Dodge City. I will most likely hang out in Pratt as I will not be able to head out till about 2pm. I agree with Andrew the stout cap will erode and explosive tornadic supercell development. The only thing is that I think it will be one storm that fires and becomes very powerful so it wont be very widespread causing signifcant chaser convergances and especially since Greensburg in the line of fire. I expect a very small localized tornado event Tuesday for SW/SC Kansas. Good luck to everyone.

 

[matt patterson]

The one thing that im not liking about tuesday is the amount of 0-6 km shear... We will be lucky to see 25-30 knts. Granted that 25-30 is sufficent when you have 4000 CAPE, we are probably only going to see 2500 to 3000 CAPE. I think that if we are going to look at the WRF precip signals (3.5 days out) that we might need to consider that in this enviroment, that the Blob of precip may be nothing more than a large cluster of storms that. The positives for tuesday include good moisture, a good foci for development and a stout cap. This may be my last long distance chase of the year unless it falls on a saturday due to summer classes, so i hope some things start to look up....

 

[Chris Wilburn]

Going off this mornings 12z runs both the GFS and the NAM have the surface low in the same general area of the northern TX panhandle/OK panhandle region. Surface winds are backed nicely and the NAM shows a very nice southerly 850mb flow at about 40-50kts. As discussed before the 500mb winds are somewhat lacking which got me thinking of a certain event in the same area that somebody may be willing to chime in on. I didn't chase this day, but while looking through some archived data I noticed that May 12, 2004 had somewhat weak 500mb flow too. This was the day near Attica with several tornado reports in this general area. I am not sure of CAPE and other factors that day so somebody with knowledge of this day and chased feel free to chime in. I have only been chasing for about 3 years so I have not yet had good luck with weak 500mb winds, but I am sure there are several examples of where tornadoes occured in such an environment. Ok back to the forecast. Helicity loooks good in the sw KS/nw OK region at around 300-400 and CAPE values near 2,000 J/kg. Td's are progged to be around mid to low 60's. Everything is there except for maybe a little weak 500mb flow. Plenty of moisture and instability as well as nice directional shear. Would be nice to see the trough and 500mb flow dig a bit further south to get some more speed at the 500mb level. Still a few model runs left so just take it from there I guess. General target area hasn't changed much as I would target near the Coldwater area of just west.

 

[Dan Robinson]

May 12, 2004 had less-than-ideal 500mb flow, but featured strong to extreme instability if I recall, at least 4000 j/kg.

 

[Ray Walker]

I chased the 5/12/04 event also and yes the 500mb flow was very weak, however instability was extreme as I recall it was up towards 5000j/kg. I think that tuesday will be a very good chase day, as long as the instability and creep or exceed the 3000j/kg mark.

 

[Dan Dawson]

May 12, 2004 had at least 35-40 kts of 500 mb flow over the area where the tornadic storms formed. Check out http://www.spc.noaa.gov/exper/archive/events/040512/index.html

and look at the 00Z DDC observed sounding and 500 mb charts. 35 kts at 500 with 40-50 kts at 400. My memory of the model forecasts for that day is a little fuzzy, but I seem to recall that they in fact underforcasted the strength of the 500 mb flow. Regardless, this is not by any stretch "weak flow", and especially when considering the ESE winds at 10-15 kts, that's more than enough shear for supercells. In fact, if you go back and look at many of the bigger tornado events of 2004, you will find that many featured 500 mb flow of 35-45 kts.

 

[Brian Stertz]

Yes...you are correct in that statement about 2004. The 500mb flow for Tue. 5/22 falls below the 50 kt. threshold that seems to be the sweet spot for tornadic supercell forecasts. However, if you look at many of the other things that stack up nicely for Tuesday...according to the 18z MesoEta...namely good diffluent mid-level wind split, a well focused triple point, favored east(possibly even southeast storm motions), and good 0-1km SRH...I think the recipe is certainly in favor of a spicy tornado day across SW Kansas into NW Okalahoma once again Tuesday. I am hoping this does not include Greensburg for the sake of their safety, but at this point it could be close by once again.

 

[Ilya Neyman]

Also gotta realize CAPE has been, in many cases so far this season, consistently underforecasted by the models...even leading right up to the event. As such, it would not be out of the question to meet or exceed 3,000 J/Kg on Tuesday. All other parameters are looking quite impressive as well, especially the directional shear component of the winds and the significant LLJ.