5/23/08 FCST: NE, KS

[Chris Hayes]

Thought I would go ahead and start a forecast thread for Friday. Still 5 days out, but it would be good for some discussion. My thoughts are based on the 12z GFS at 138hours (00z Saturday). Feel free to correct me on anything I get wrong. At 00z saturday the trough will be centered over Idaho, extending into Nebraska and western Kansas. 25kt flow over the target area. 850mb winds will be at 35kts. CINH at this time wont be extremely strong so the cap might be able to break in a couple areas. CINH values of less than 100 across much of my target area. The dryline at this time will be bowing out at the central Kansas/Nebraska border with >50 degree dewpoints behind it, and DPs well over 60 ahead of it. At this time I would target an area from Russell KS to Kearney Nebraska.

 

[Mike Umscheid]

this has the potential to be a very fruitful, high-production several days. The thing to watch out for with slow moving huge gyres like this is model tendency to focus things too far east. Unfortunately, there is no high-res ECMWF data on the web, but we have access to some ECMWF fields in the NWS that many cannot see. There is growing run-run consistency of meridional flow from 700 to 300mb, the eastern edge of which not get much farther east then say Broken Bow-Hays-Canadian TX longitude.... all the way through Sunday. There could very well be multiple fantastic days in the same areas of Western Nebraska, Kansas, TX Panhandle...with the threat slowly expanding south each day as H5-7 temps cool down a little bit each day. I think Friday could be fantastic from the Nebraska Panhandle south to along the CO-KS border region...perhaps as far south as West TX depending on the strength of the cap. The dryline should be pretty far west. We'll see how it plays out... but think High Plains in a pattern like this... this is shaping up to be a great pattern for successive High Plains chases. For those who have centered their chase trips around May 22-25, you should collect some nice stock

 

[Mikey Gribble]

A fairly potent combination of directional shear and instability seems to be coming together for Friday. Given the breakable cap that should be in place, my confidence is increasing that we may have a tornado outbreak, with several tornadic storms coming off the dryline. The setup is very similiar to Thursday, but we should have more mid level cooling, better moisture, and a weaker cap. It's not very often that we get really good directional shear, good moisture, and a breakable cap all on the same day. Thursday looks good too if the cap can break, but Friday is shaping up to be the bigger day of the too IMO for the reasons stated above.

 

[Mike Peregrine]

Thursday may be looking sweeter than apple pie right now, but for those of us who actually still have to work for a living, I wanted to resurrect or at least keep an eye on the Friday thread. Some of it may be contingent on what finally happens Thursday, but Friday holds potential. Close to the same target area as Thursday too.

Forecast L.I.s remain in the -6 range, in western Kansas, with 80/70 spread still forecast by the GFS. I wonder how the winds will finally end up by then. Currently GFS predicts surface winds at 15 kts, 700mb is turning south at 25, and then 500 and 250 are both out of the south/southwest at 30-40 kts. ECMWF shows low pressure at 997mb, basically in the same location as Thursday. Hoping the cap will also be weaker this day. Still have plenty of time and a couple dozen model runs between now and then. If things continue trending this way, I'd hope for something around Hill City to Norton maybe.

Could end up being a good old fashioned Memorial Day chase weekend if things hold up -

 

[Mikey Gribble]

Honestly Mike I think Friday is going to be the more wide spread outbreak. I would bet we'll get more tornado reports on Friday than we will on Thursday. If I had to pick a day to chase I would go with Thursday, but Friday is a close second IMO. All you can go off of obviously is the ECMWF and GFS (left ensembles out because they were a mess before) and if you compare the two days each has its advantages, but there are a few things I like with Friday. I focused in on NW Kansas for both of these days, so what I am about to say primarily applies to the NW quadrant of Kansas. For one on Friday 850mb winds aren't backing quite as much, which will give us more turning in the 0-1km layer. Mid level winds are slightly stronger and are veering a little more. Another 24 hours of moisture advection means dewpoints will be a little higher too. I don't think it will actually happen, but if you look at the GFS the moisture gradient is pretty wide on Thursday, but on Friday the dryline is much tighter. And finally mid level cooling means we will have less of a cap to deal with on Friday so storms should fire earlier in the day.
I'm not a huge fan of composite indices, but the GFS has the sig tornado and EHI higher on Friday than it is on Thursday. LCL's will also likely be lower thanks to better moisture and slightly cooler surface temps from overnight convection/cloud cover. There could very well be some outlow boundaries intersecting the dryline as well.
I would be bummed too if I couldn't chase Thursday, but Friday may just be the better of the two. I don't know why there hasn't been much talk on this forecast thread, but I bet you after the NAM picks up on this tomorrow the thread will grow rapidly.

 

[Matthew Crowther]

Thursday may be looking sweeter than apple pie right now, but for those of us who actually still have to work for a living, I wanted to resurrect or at least keep an eye on the Friday thread. Some of it may be contingent on what finally happens Thursday, but Friday holds potential. Close to the same target area as Thursday too.

Mike, I feel your pain, I was unable to get Thursday off, and since I am an East Coaster I have to fly out Friday into Dallas...so if Friday is in Nebraska or northern Kansas, screw job # 2. Luckily there appears to be a threat Friday into the TX Panhandle (maybe the title of this thread should be amended to include OK and TX). Also, Saturday and Sunday look to have some potential as well. But if Thursday is " the day"- it will join a litany of other big tornado days I just missed due to work obligations and the fact I do not live in "chase alley".

 

[Mikey Gribble]

After seeing the 00Z GFS I am even more convinced Friday will be the better of the two days. Right now there is a big tornado bullseye in the I70 area ahead of the dryline in NW Kansas.

Pretty much all the things I mentioned in my previous post are still the reasons why I think Friday is the better day, so I won't go over all of that again, but the main ones that stick out as being especially important when comparing Thursday to Friday IMO is that Friday will have a weaker cap allowings storms to fire ealier in the day (although this becomes a little muttled with the latest runs, but I'm disregarding it) and better moisture and lower surface temps (LCL's as low as 600m in NW Kansas). When you combine SBCAPE AOA 3000, backing 0-1km winds with 850 at 30kts, low LCL's, and decent mid level flow out of the SW, I think you have a pretty good setup for a few tornadic supercells (especially over the NW quadrant of Kansas). The weak spot for this setup is definitely the mediocre mid to upper level winds though, which will keep hodographs a little short (which I haven't seen yet obviously). Other than that there isn't much I can find to complain about. I am really surprised nobody is talking about this.

Some nice paramaters and composite indices over NW Kansas include significant tornado up to 12, 1km EHI at 6, 0-1km SRH >200, 0-3km SRH >320. Not too shabby.

 

[Chris Wilburn]

I agree Mikey that Friday will be the better day. This doesn't mean I don't think Thursday will be good because I am really excited about that as well. I don't expect the CAP to be a problem on Thursday too much, but Friday the CAP should even be weaker which is good and like Mikey mentioned it will give us another day of really good moisture return and lower surface temps to lower LCL heights. The dryline does look very good on the GFS along I-70 in NW KS. The only negative I could possibly see is the lack of turning with the 500mb winds. 500mb winds due south to slightly south/southwest isn't the best, but should suffice given the amount of 0-1 SRH, low LCL heights, moisture and instability. It would be nice to see the 500mb winds "veer" a bit more, but with the very backed surface flow and 850mb flow I am not sure it will matter in the grand scheme of things. This mornings 12z run of the NAM will bring Friday on board on the 84hr so it will be nice to see what it has to say. As of right now I would target the dryline along I70 in NW KS which I am sure will change between now and then.

 

[Mike Peregrine]

The lack of winds veering with height, and the fact that UL winds are not appearing particularly dynamic are both legitimate concerns at this point ... that, and the fact that we still don't have a clue what we're talking about since this is four days away .

I always think about things like UL ventilation and whether the storms will be able to maintain balance in an environment like this, and also the effect that over-abundant convection might have on the scenario. It looks to me that storm motion will be similar to Thursday, in a north-northeast direction. Because of the orientation of the trough, moisture will have to be fed at the surface from the southeast for storms to be discrete and maintain a degree of separation from one another. They will also be moving near parallel to the dryline in the direction of the WF. How fast this happens will be interesting to watch. If steering winds end up getting overblown, that could also present problems as storms in the warm sector might want to cross the boundary quickly. I'm hoping this won't be the case, however. And it could be that I'm not accurately visualizing what the models are currently indicating too ... that happens with me a lot until the day of.

Hoping there will be at least a moderate cap in place, to prevent clusters or too much convection at once. Hopefully some sort of balance can be achieved. For towns along the dryline this isn't a particularly fun scenario, because they could get raked with several big storms before it's over. I keep going back to Mike U's post above too, wondering whether the models are pushing too far east. Time will tell - -

EDIT - - also, wonder what effect the leftover OFBs are going to have! Could be interesting!!!

 

[Mike Hollingshead]

FWIW there's no lack of veering with height.

http://www.rap.ucar.edu/weather/model/eta84hr_sfc_mslp.gif
http://www.rap.ucar.edu/weather/model/eta84hr_850_wnd.gif
http://www.rap.ucar.edu/weather/model/eta84hr_500_wnd.gif
http://www.rap.ucar.edu/weather/model/eta84hr_250_wnd.gif

That looks SICK to me. If western NE can estabilish a wider warm sector north of the DL arc by then, it should be crazy. It's probably wide enough as is, but man those easterly SFC winds in the model want to keep it pinched. I'd think by then you'd have some healthy dews into the east winds, but who knows.

GFS loving the dry dry easterlies in NE too. I just wonder how well you can mix down the juice aloft from the llj in that flow. You'd think after a while it would pool on down, but I guess dry sfc would want to counter any of that. Hmmm. Sucks is all I know. Better upper support is going to tend to be nw on Friday I'd guess, so it'd be great to have the dews get up in there with some sort of width.

 

[Mike Peregrine]

989mb for a low is really not too shabby at all ... looks like plenty of energy available. Sort of reminiscent of a little encounter in the town of Hallam, Nebraska once upon a time.

It would be amazing to think of a line of supercells stretching all the way across the middle of western Kansas up into Nebraska, but that is how it is looking right now. Thanks for not poo-poohing the forecast for Friday, H - makes me feel better.

Wonder if anyone has any thoughts (preliminary) about initiation times. If the cap is weak, they could start up early.

 

[Chris Hayes]

I almost wish the cap was a little bit stronger for both thursday and friday to keep stuff isolated for a longer period of time. With so much forcing, we may end up with too many storms. Thats why I'm tempted to stay along the dryline on both days. Just hope them LCLs aren't as high as is being forecast. However, it still appears to be a good (or bad) couple of days.

 

[Mike Hollingshead]

Well, mid-levels actually warm on Friday compared to Thursday, so that could help.

http://www.wxcaster2.com/CENTRAL_ETA_500_GPHTMPWNDVORT_60HR.gif

http://www.wxcaster2.com/CENTRAL_ETA_500_GPHTMPWNDVORT_84HR.gif

Pretty big difference between the two days. Low level juice/instability should be higher and offset that though I'd imagine. Won't shock me if somewhere around Colby KS would work Thursday, Friday and Saturday. That'd be fun.

 

[Mike Peregrine]

GFS loving the dry dry easterlies in NE too. I just wonder how well you can mix down the juice aloft from the llj in that flow. You'd think after a while it would pool on down, but I guess dry sfc would want to counter any of that. Hmmm. Sucks is all I know. Better upper support is going to tend to be nw on Friday I'd guess, so it'd be great to have the dews get up in there with some sort of width.

Theta-E is targeting Kansas nicely, though -

http://www.rap.ucar.edu/weather/model/gfs084hr_sfc_thet.gif

Last weekend when I was out, the vegetation across SE Kansas was abundant (and really beautiful). Everything down there is green and growing fast. I think this might contribute some juice to the cause.

 

[Mikey Gribble]

You really need to keep in mind that the direction of mid level winds and directional shear is relative to lower level winds. 500mb flow may only be out of the SSW, which normally would suck, but with this setup we have ESE surface winds. It's like the whole shear profile was backed 45 degrees. 90 degrees of turning will do just fine. I'm not worried about LCL's either. We may have moisture problems on Thursday, but I seriously doubt we will have any moisture problems on Friday. LCL's should be well below 1000m AGL over the warm sector. All in all I think Friday looks like a good tornado day where we will likely have several tornadic storms from Nebraska down through southern Kansas. Pinning down an exact target is tough right now, but somewhere between I70 and Norton looks pretty good to me.