5/22/2010 FCST: NE, SD

[Bob Hartig]

I'm not surprised that a forecast thread hasn't been started for Saturday till now. GFS and NAM have been at odds, instability and UA support have been in two separate worlds, and the whole thing has looked to be squelched by a nasty cap.

But when the NAM kicked in it started offering signs of hope, opening up an uncapped corridor through NE into SD with big CAPE. I didn't trust it, but it has been appearing consistently, and last night the GFS finally capitulated and started eroding CINH as well. This morning is painting a similarly hopeful picture, with some nice curved hodographs, plenty of instability, and enough shear to git 'er done.

The SPC is now singing a better song as well in this morning's Day 2, with talk of tornadoes in their forecast.

I doubt this setup will be a wedge fest, but I'm thinking it will turn out something, assuming that the cap erodes as the models suggest. And since I can finally afford to get out and chase, and the models are at last showing some congruency, I figured I'd toss tomorrow out there on the table for discussion.

 

[Josh VandenTop]

I'm not new to chasing but I'm relatively new to the forecasting side of things, so here is what I'm thinking about tomorrow. I've been watching this set up for the past few days now, and I'm also suprised that a forecast thread for this day is just getting started. The last couple of runs have been giving me more hope for a good chase. It looks like there will be alot of instability and good daytime heating, and I know this area has plenty of moisture to play with. The two things that have me slightly concerned are there isn't an incredible amount of shear, but I think there might be just enough, and also breaking the cap. If the cap goes I think the storms will fire fast and it could be a good day. As of now I think my initial target will be somewhere near Yankton, SD, then reposition from there as needed. Hope to see some of you out there tomorrow!!

 

[Logan Karsten]

I would be very concerned about a cap bust tomorrow. Sunday on the other hand may be a different story...

 

[Matthew Piechota]

I wouldn't throw out the idea of a cap bust tomorrow but the models are improving on having storms go in NE/SD tomorrow after and evening near the triple point and possibly down along the dryline.

12z WRF is pooling low 70 dew points....with very impressive amounts of CAPE.

 

[jshields]

this day definitely isn't an easy one. i'm not sure what to think of the potential cap. nam shows it completely eroded in a large area of central neb into southern sd, and the gfs shows minimal cinh remaining at 0Z. 700 temps are 10-12 C across a large part of that area though, however there is an area of <10 C temps near the s central sd/ n central neb border which is near the triple point. winds are also a little more backed in se s dakota. it bothers me that there isn't precip breaking out on the models, but the 0Z NAM last night did have a cell in scentral neb, however it shows nothing today on the 12Z run. the low is forecast to move more north than east so convergence might be the problem along the front. i noticed the shear is better on todays 12Z runs with definitely a larger area of shear >30 kts in the high instability sector. i would be pretty tempted to go up along the neb/sd border as a starting point. i will hopefully be out chasing tomorrow!

 

[Bob Hartig]

This is definitely a gamble with the cap. But the models have lately trended toward peeling away the CINH. And if it goes, there's some pretty muscular CAPE just itching to fulfill its mission. I'm betting that's what's going to happen, and I agree that the triple point is a good bet. Shear? I'm happy with 40 kts at mid-level. Storm motions should be easy to keep up with.

This is obviously not an easy, in-your-face setup, but since I don't see any such scenario in the immediate future, I'll take what's here and see how it pans out.

 

[L.B. LaForce]

Yes, I have also been watching this, and almost started a thread last night, but got sidetracked. Latest runs have been showing the cap eroding, but you never know what will happen. I'm currently headed out that way for tomorrows chase. Lots of CAPE to deal with, H7 temps have kinda been coming down the past few runs, and especially around 0z. SPC has now got a 15% hatched area in NE, and SD as of the 1730z update, and I was eager to get out to chase. Hopefully there will be some supercells, and if not a tornado, at least some nice structure shots.

Also: there shouldn't be as much of a hoard of chasers, but you never know.

 

[Chris Bowman]

I've been watching today for just shy of a week. The cap has been a consistent concern. The GFS has been consistent however decreasing the cap by 00z. The NAM is showing the same thing. While the cap is big concern I think getting high CAPE with perpendicular shear and fairly large and looping hodographs makes it worth the risk. And having gone to school at Nebraska the Sandhills fascinate me. If nothing forms I'll have an opportunity to get some good landscape shots with few signs of humanity. The lure of not a huge day in a pretty remote area is also a strong lure.

Earlier in the week I was thinking Phillipsburg, KS to Kearney, NE. No I am thinking up near the NE/SD state line. For now I'm going to try and be at the US183/US20 intersection around 5-6 pm, maybe earlier depending on when I get up and out the door.

 

[J.B. Dixon]

I think the fly in the ointment for quality Nebraska storms, based on this NAM run is simply that the better ingredients are just to our north into South Dakota. For this NAM run for 00z Sunday, the left exit region for the 500 mb jet is around Valentine & points north and east. CAPE is through the roof, which may compensate nicely for the less-than-ideal 0-1km storm relative helicities, the best of which located in S. Dakota, as well. Main issue looks to be capping. 700 mb temps like this, and the lid may very well be kept on. Given forecast temps and ridonkulous CAPE, that may be overcome, but the NAM doesn’t paint a rosy picture for Nebraska. Based on this NAM run, I would pick Chamberlain, SD as a target for Saturday evening.

 

[Bill Hark]

I am currently in North Platte and am cautiously optimistic for Saturday. There is a forecast trough over the northwest giving good 500 mb flow across the western parts of the Plains. There is 30-40 flow from the SW across Nebraska and Kansas, increased to 50 in the western half of South Dakota and part of western Nebraska. The 850 winds are strong at 30-40 from the south. The low level jet is initially a bit farther east than I would like but still good. I prefer the 850’s more from the south east which is only in South and North Dakota by 00Z according to the NAM. Unfortunately, they tend to veer later in the night. The forecast CAPE is amazing at 3500 from I-80 to central South Dakota. The cap may be an issue farther south but the NAM is showing a precip bulls eye over southcentral South Dakota that extends farther south into Nebraska overnight. The GFS also shows the precip but it is slightly to the east by 00Z. The best southeasterly winds are also in south central South Dakota. The cap is a concern farther south but shouldn’t be an issue in South Dakota and will help isolate storms. Both the GFS and NAM (00 init) show the 10 degree line at 700 mb across the eastern part of South Dakota but leaves lower temps over the area corresponding to the forecast high CAPE. My target at this point is Mission, South Dakota along 83.

Bill Hark

 

[Rob Wadsworth]

Not really strong with forecasts - but here I go.
More like targeting...

CAPE is strongest between W cntrl NE to Chamberlain SD - now @ 4000mj's. The trough will move rapidly in a NE fashion, that is the part that is worrisome. Looks like plenty-o-spin; but how fast will the storm motion be? But I believe that storms shouldn't have much problem getting initiated and rooted between Chamberlain and the NE border.- especially in that area of highest CAPE.

The triple point is the best play, so I will take a position between Yankton and Chamberlain - right at the CAPE bulge between the SD and NE border. Yankton might not be far enough W and N if it starts earlier than 21z. I'm going to bet a couple of tanks of gas on it right now...

 

[Mike Heitz]

I think we are going to play the northern stuff, this cap is going to be a pain but i'm thinking maybe heading around the nd/sd border south of jamestown, i'd go further south but i'm wary any storms will be able to fire south of about middle sd and storm motion should be to the northeast. Its a pretty big hit or miss day but the CAPE and low level helicity make for a day that could reward if we do get a few storms to fire.

 

[Tony Perkins]

I like initiation around the Missouri river, so I'm targeting US 281 from Redfield to Wosley in South Dakota. It could be sketchy with the daylight factor.

 

[Mike Heitz]

nice call tony, i've been trying to tell my group that we should probably base camp around aberdeen as they have the n/s and w/e major roads to position.

 

[Michael O'Keeffe]

Based on the 15z RUC I am really liking SC/SE North Dakota where the strongest shear looks to be setup. This is also where the best upper level support is and where the LLJ backs more to the S than SSW. Not a big deal but can make a difference. Also great convergence where there appears to be a windshift line/dryline where the storms should initiate. Great directional shear as well as deep moisture and CAPE exceeding 3000 j/kg, on top of helicity values over 500 m2/s2 at 0-3km is a recipe for tornadoes as long as you can get storms to fire which looks likely in this area.

Another area for development is the Black Hills where upslope will likely break the cap. It is behind the windshift line so shear is more unidirectional but modest moisture and decent shear along with extreme CAPE might allow a nice supercell to evolve.

Good luck to all chasing today!