4/24/08 FCST: NE/KS

[Jason Boggs]

I'm also going to play the southern target today. Obviously, strong daytime heating along with very rich moisture will create very high instability in southern KS and northern OK. I'm tired of dealing with lots of convection on previous chases, so I'm going to play south along the dryline and hope to get some isolated convection when the cap breaks in late afternoon. I think the main threat will be very large hail until 3-6Z. At this time, the LLJ will get cranking and it is feasible to have 850 winds of 50 knots or more in southern KS. If this pans out, I think a strong tornado is definitely not out of the question.

TARGET: HUTCHINSON, KS
Not only for the location, but the road network out of town is really good.

 

[Alex Lamers]

Boy...I'm not exactly encouraged by the southwesterly flow at ~850mb observed on the Vici, Lamont and Purcell profilers this morning. In fact the 12z RUC keeps the winds sw-ssw through 00z. The NAM is the only model that really backs them to more southerly over OK and far S KS. The 12Z OUN profile looks decent...not much of an EML observed there, but go west to Amarillo and it's quite obvious. I think we'll be in trouble this far south if we advect that atop the boundary layer through the late morning and afternoon.

Latest SPC mesoanalysis shows the edge of the much drier 850mb air is along the TX Panhandle and OK border, with pretty nice 850 dewpoints over W OK (15-16C!) to the east of the dryline.

It really depends on how that cap evolves and monitoring exactly where that dryline bulge winds up.

AJL

EDIT: Although, if you look north into N KS...progged effective SRH by the NAM is actually quite low, as opposed to 200-300 m-2/s-2 along the dryline from S KS into OK. Better surface dewpoints in this area too. I just don't know...this just seems like one of those cases where all the best ingredients are scattered in different places.

 

[Ryan Pfannkuch]

4-county target area in southwest NE: Hayes, Frontier, Hitchcock and Red Willow

Including the cities of: Hayes Center, Stockville, Trenton and McCook.

Very torn this morning on the whole north vs. south issue. Given the uncertainties with initiation farther south...think I will play up toward the northwest edge of the primary instability axis being wrapped westward north of the sfc low, where SBCAPE is still progged to reach 2000 j/kg. (per 12z RUC). This area definitely seems like more of a "sure thing" for storms per the various RUC and high-res reflectivity progs. In fact, I am gonna be very curious to see what transpires even farther northwest....with initial activity expected up along a line from Scottsbluff to Ogallala. Wonder if that area could see some surprises (or should they even be considered surprises?). At any rate, by targeting the Mccook area I feel that is a workable middle ground, where I can shoot north or south on Hwy 83 if need be as the situation unfolds. Don't get me wrong, that DL bulge and instability max depicted over south central KS looks awfully tempting, but given the late-day arrival of the main mid level wave, at this point I think I'd like to stay north given the higher likelihood of initiation. Not sure what to make of TOR potential however, given the rather anemic 0-1km shear in this area before dark...hmm.

 

[Fritz Kruse]

Agree with Alex,

First blush looking at the upper air charts, I really don't like all the veered out 850mb winds and the 700mb temps are warm. Then looking at the WRF it shows the 850mb winds backing as a warm front develops, probably in response to cyclogenesis in the lee ahead of the mid level shortwave trough. The best mid level winds of around 40 to 50kts look to be around I70 in the Hill City and north region and this is where a nice theta-e axis slices in underneath. CAPES however are much less in the north but great in the Pratt area but the h5 winds are around 30kts compared to near 50kts in the north.

It would be nice to have a sounding by 21z in the Hill City and Pratt areas to see how the winds are responding and is the WRF correct. Maybe the best thing is to watch the RUC and make SFC charts every few hours. Initiation should be along a dry line near Dodge then moving into the higher CAPE areas east.

So do you chase north with the best shear or more south with best CAPE, or maybe split it down the middle to someplace between McCook and Pratt like Great Bend or Russell KS?

 

[Scott Olson]

In a perfect world I'd been heading to North Platte right now. I like the overall consensus of storm intiation there that has been present between the models (which seems to be 21z for intial intiation off extreme W NE Panhandle and giving way to further development near North Platte and south at around 23z-0z). Intial soundings aren't something to call home about but the real window certainly appears to be 01z-04z where soundings do show a good oppurtunity for rather robust storms as they move east into central SC Nebraska and ultimately eastern Nebraska. Both the high res WRF-ARW and WRF-NMM depict this scenario and seems in line with what I'm seeing from the NAM/GFS. With all that said, my challenge today is trying to get something off the eastern ends of the frontal boundary. My current focus is on more Western or more likely NW Iowa. Forecast soundings from the NAM show modest CAPE (around 500 j/kg MLCAPE though higher per the RUC). So this somewhat hinges on the RUC being right and instability being somewhat higher. I should note that low level cape is particularly high on most of the soundings sampled (though cloud cover right now is tricky with some subsidence behind the intial wave causing clearing but another compact impulse firing off more storms to the west).

Second, deep layer shear is releatively decent (though only half of North Platte's shear) at 30 to possibly 35kts. Several locations yield upwards of 180 m2/s2 0-3km SRH and around 100 m2/s2 0-1km SRH which is certainly not bad, neither are the releatively 700-900 ML LCL heights. Long shot? Sure. But it's just that much more exciting...

Good luck Gentleman (especially those of you in Kansas!).
-Scott O.

 

[Mark Farnik]

After a hearty breakfast at the Village Inn in Colby, I drove east on US 24 to HIll City but ultimately decided to move a little farther south and am currently sitting in the parking lot of the WaKeeney Super 8, mooching off their Wi-Fi and planning on staying here for a few hours. WaKeeney is a good place to be today, splitting the difference between the two targets. Depending on which target winds up looking more favorable, I can either go north to Hill City and Norton or south to Ness City and Dodge City on US 283 and take any combination of other highways that intersect 283 to wherever I need to get to. So I'm just going to sit here in Wakeeney and watch and wait. If and when I move, its probably not going to be until 1 or 2 p.m. at the earliest.
Its currently 67 degrees here in Wakeeney, with a dewpoint of 59 and a light southerly breeze. The air is heavy and the breeze is warm and moist. Its a nice atmospheric portent of things to come later...

 

[Scott Lincoln]

Boy...I'm not exactly encouraged by the southwesterly flow at ~850mb observed on the Vici, Lamont and Purcell profilers this morning. In fact the 12z RUC keeps the winds sw-ssw through 00z. The NAM is the only model that really backs them to more southerly over OK and far S KS. The 12Z OUN profile looks decent...not much of an EML observed there, but go west to Amarillo and it's quite obvious. I think we'll be in trouble this far south if we advect that atop the boundary layer through the late morning and afternoon..

Am I understanding you correctly that you want the 850mb winds more southerly than southwestly? If the 850mb winds were more southerly in combination with mostly southerly surface winds, wouldn't you have a reduction in 0-1km helicity? I think I'd personally be more excited to see turning in the lowest levels. Based on some recent research presented at some conferences I've attended, it was suggested that the 0-1km helicity or even a smaller layer, perhaps 0-500m helicity are more important to tornado development, particularly significant tornadoes, than something larger like 0-3km.

 

[Alex Lamers]

Am I understanding you correctly that you want the 850mb winds more southerly than southwestly? If the 850mb winds were more southerly in combination with mostly southerly surface winds, wouldn't you have a reduction in 0-1km helicity? I think I'd personally be more excited to see turning in the lowest levels. Based on some recent research presented at some conferences I've attended, it was suggested that the 0-1km helicity or even a smaller layer, perhaps 0-500m helicity are more important to tornado development, particularly significant tornadoes, than something larger like 0-3km.

Veered 850mb winds have also squashed potential on a few other days already this year. I suppose if the cap can be broken and you have southwesterly winds then everything could be just dandy...but I'm primarily concerned about getting initiation at all, and pulling in increasingly warm, dry air from the TX Panhandle wouldn't help.

The 16z SPC mesoanalysis shows that the dry 850mb air that was restricted to the TX Panhandle this morning has since pushed a row of counties into OK.

And point taken about the veering of the winds with height...but I suppose how the rest of the wind field is oriented (in the vertical) would also make a difference. Winds that get closer to westerly at 850mb would produce an increasingly linear hodograph if the winds aloft are southwesterly or west-southwesterly, which would then favor splitting supercells and more of a hail threat.

AJL

 

[Shane Adams]

Am I understanding you correctly that you want the 850mb winds more southerly than southwestly? If the 850mb winds were more southerly in combination with mostly southerly surface winds, wouldn't you have a reduction in 0-1km helicity? I think I'd personally be more excited to see turning in the lowest levels. Based on some recent research presented at some conferences I've attended, it was suggested that the 0-1km helicity or even a smaller layer, perhaps 0-500m helicity are more important to tornado development, particularly significant tornadoes, than something larger like 0-3km.

The main desire for more southerly 850 winds is more to do with moisture than helicity; a strong southerly h85 jet would further enhance moisture return into the target area, where a more SWerly flow tends to bring drier air into the area. With good SWerly h7 winds above them, due south h85 winds are just fine for producing great helicity. As for southerly surface winds underneath southerly 850s, many times a supercell worth its salt will create its own localized airflow, and back surface winds in its environment SErly or even due east.

 

[Andrew Stoller]

Based on the newest RUC, I'm heading for north of Goodland, just over the border in Nebraska towards North Platte. The RUC breaks out what looks to possibly be one or two nice Supercells by 9 pm.

FWIW, the RUC also shows a big nice lone cell right on the OK/KS border south of Wichita, along with other convection right through the middle of OK. However, that convection quickly dissipates by 9 pm. Goodland to North Platte looks to the the best area for my liking.

Best of luck to you guys and gals!

:edit: the lone cell I talked about looks to initiate right on the tip of the dryline bulge in the 65 + degree dewpoint air. Darn, that is tempting cause it has major tornado potential, but it's too far for me.

 

[Mikey Gribble]

Scott said...
"Based on some recent research presented at some conferences I've attended, it was suggested that the 0-1km helicity or even a smaller layer, perhaps 0-500m helicity are more important to tornado development, particularly significant tornadoes, than something larger like 0-3km. "

SPC has a paper on this too about how the lowest 1km is a better indicator of tornado potential thatn 0-3km. I am divided on the subject though. In some cases I don't think veering 850mb winds are such a bad thing, but in others they are horrible. Just depends on the setup. For today if they veer a little that doesn't bother me, but I don't want them veering worse than SSW.
With the uncertainty on the dryline location I am thinking DDC again. It may be a bit west of the dryline, but I can check data from there and there are good road networks leading in every direction out of there. This plan is very fluid at the moment though. I will get out of town in an hour or so and I plan on stopping in Pratt for data. I will figure out how far West I need to go from there. I'm still a little undecided on exactly what area I want to play. I think being in line (east-west) with DDC is a pretty safe bet today. You keep the southern Kansas option open and you still have the capability of moving north a bit if you need to. That will likely be my play, but I definitely favor the southern area. We just need the damn cap to break.

 

[Darrin Rasberry]

Looking at the Ames, Iowa situation, the RUC models from 0z-3z look like they have some promise. 0-1 and 0-3 are in the 200's, CAPE values are between 1500 and 2000, Td's are high, winds from 850 are nearly straight south, CINH isn't a problem ... I'm guessing the only thing that could interfere here in Central Iowa is the current cloud cover that's just hanging out here for some dumb reason. Other than that, I think that there could be a tornado potential here this evening, too.

 

[Gabe Garfield]

Regarding helicity in the lowest 1 km:

Actually, you don't want much veering in the lowest km; this actually reduces the helicity. I wish I had to time to draw the hodograph, but the area that you sweep out with SW winds just off the deck is less than it would be if the 850 mb winds are more backed (to the S or SE). The latter profile would lead to the infamous hodograph "kink" that has been noted in conjunction with significant tornado events. So, not only are backed 850 winds great for moisture advection, they're also great for enhancing helicity.

A really good paper by Edwards & Thompson that mentions hodograph kinks:
http://www.spc.noaa.gov/publications/thompson/3may99/waf.htm

 

[Dave Winslow]

Northern Target-SW Nebraska option

I spent a lot of this morning looking at data and comparing models, was just about to leave NW Iowa for North Platte but called it off. The cons I see are as others have stated: 1). main dynamics coming at or after 00Z 2.)lack of good 700 mb flow <20 kts, lackluster 850 mb winds < 30 kts. I have a feeling there may be a more multicell or cluster storm mode because of these things.
That being said, IF I had left for the North Platte area, it has some things going for it. A stalled out boundary will form in the area with good easterly winds at 10-15 mph, below easterly 850 mb winds, and nice 500 mb winds of 35-50 kts and 200 mb winds over 70 kts. This combination does suggest some potential for supercells early in the life cycle of storms, and storms could be riding that nearly stationary front east into better moisture. I live in Northwest Iowa so it's just not worth the 6 hour drive at this point. Good luck to those of you who are in position!

 

[Donald Giuliano]

Regarding helicity in the lowest 1 km:

Actually, you don't want much veering in the lowest km; this actually reduces the helicity. I wish I had to time to draw the hodograph, but the area that you sweep out with SW winds just off the deck is less than it would be if the 850 mb winds are more backed (to the S or SE). The latter profile would lead to the infamous hodograph "kink" that has been noted in conjunction with significant tornado events. So, not only are backed 850 winds great for moisture advection, they're also great for enhancing helicity.

Excellent point, Gabe, and one I was thinking of making myself until you did. I would like to point out, though, that it is possible to substantially increase low-level helicity with a veered 850mb wind, but only when there is little speed shear below that level.