2011-05-30 FCST: NE/SD/ND/MN

[John Peters]

Looks like a pretty decent setup along cold front south of developing cyclone in the Dakotas, through central SD and NE by 6z. 12Z NAM brings 0-1km EHIs into the 3-4 range along the cold front by 0z, models are pretty consistent with convective initiation by this time. Deep layer shear is fairly impressive through central NE/SD as well. Would be a bit concerned about quick evolution to linear storm mode due to linear forcing and slightly less-than-desired curvature in the low level wind fields; however, wouldn't be surprised if we see a few discrete SUPs and isolated tornadoes between 0z and 6z through this area.

Tentative target = Grand Island?

 

[jshields]

i've been watching this for the last couple of days as well. winds at the surface were forecast to be more backed with earlier runs, but still show pretty decent low level shear. 0-1 km srh on the nam is 150-200 m/s2 and 0-3 km is near 300. 0-6 km shear is 50-70 kts!! i suspect that things will go linear pretty fast with such strong forcing, so the best chance would be near initiation for any tornadoes before it evolves into probably a strong squall line. i think things will definitely fire by late afternoon, definitely before the 0Z-06Z timeframe. hastings wfo mentioned in their forecast discussion from this afternoon that they wouldn't be surprised to see a few 80+ mph wind gusts with the squall line. the other thing with this storm will be the strong non tstorm winds on monday, as there is already a high wind watch issued for monday for southerly winds of 40-55 mph. storm speeds are going to be fast as well, probably 50 mph or faster. nonetheless i will be out chasing as this looks like the last good chance for a while as the big ridge sets in later this week. i was targeting the grand island area also. that area always seems to get tornadoes!!

 

[Jeff Duda]

This day looks to have the potential to be a significant severe weather day, but there are things that could keep that from happening. Fast 500 mb SW flow (although I'd like to see it more veered) and great LLJ with extreme 0-1 km shear. However, hodographs from both the NAM and GFS show that S-shape with a kink around 2-3 km AGL and not a lot of shear above that. Also, I'm not seeing too much turning at any level. Winds are mostly southerly all the way up to about 700 mb. So not only is shear not as good as it could be with more turning, but storm speeds will be quite ridiculous (upper 40s to near 60 kts). Also, there are a number of locations that show some minor warming in a 100 mb thick layer just above the PBL top. This cuts down on 0-3 km CAPE and in some cases, raises LFCs to around 650 mb. Given the amount of forcing I don't think there will be a cap bust, but I think these thermodynamic and kinematic profiles suggest a mixed linear/discrete storm mode. I think some discrete storms may form but they will quickly morph or merge into line segments.

 

[Ken Johnson]

My post usually don't make it so hear we go...
I can't believe that nobody is mentioning a further target across Kansas. 500mb winds look to a be bit more veered than points further north. Shear vectors seem to favor a discrete isolated supercell before going squall in the evening. Forecasted hodo out of Pratt shows very strong curvature with srh between 2 and 400. If a supercell can get rooted in the boundary layer, it could go tornadic and potentially be strong. LCL heights are a big of a concern, however further south, but overall, I like the set up for more discrete stuff here, as supposed to further north where 500mb winds are backed to the south. The cap, while fairly strong, does look breakable with all the forcing coming into play. My target areas for Monday right now are from Pratt Kansas up to Concordia into Hastings NEB.

 

[Justin Turcotte]

Strong WAA Sunday night through Monday morning will likely trigger thunderstorms over the Dakotas and Minnesota. I suspect the storm activity will serve to suppress northward advancement of the effective warm front, perhaps similar to what the 5/28 06z NAM offered roughly along I-94 through MN. Subesquent NAM runs continue this theme to some extent while the GFS and GEM plow the front well into northern MN. The effective front, wherever it ends up, should offer the best backed surface flow. There is ample shear further west along the cold front but it is largely unidirectional. Given strong forcing along the cold front I would expect convection to go linear relatively fast. The WF/OFB area will be strongly capped through much of the afternoon given H7 temps in the +12C range allowing SBCAPE along and south of the boundary to potentially exceed 3000 J/kg. The 5/28 12z ECMWF even spits out 4000 J/kg. The cap should erode quickly late in the afternoon or early evening in the MN/ND/SD border area and this area may provide the best shot at discrete supercells before convection along the cold front plows through. The triple point on the northern end of the developing squall line could be Plan B if the WF is a bust. Biggest downside for the potential event is storm motion potentially exceeding 40 kts. This generally makes the chase is pain the tail pipe.

Preliminary target area Wahpeton, ND. This area offers numerous road options including a river crossing. I should also be able to pull McDonalds wifi there since I chase on the cheap. A stronger cold pool would suppress the target south while a weaker one may push it north.

 

[Bill Hark]

I am currently in York, Nebraska. Today appears to be a very interesting set up though I am very concerned about storms quickly “lining out”. My forecast is biased because I fly out of Wichita around noon on Tuesday and that limits the northern extent of my target and also waiting for very late initiation in Kansas. There is a deep trough approaching from the west with 50 to 60 kt SW 850mb winds across most of Nebraska, central Kansas and the Dakotas. The warm front has shifted northward to South Dakota and Minnesota and is out of my chase range. I really like the predicted strong backing of surface winds in eastern North Dakota but again, too far to reach. Surface moisture is good with dewpoints in the 60s through most of central and Eastern Nebraska. The precip models are a bit confusing. The 12Z NAM doesn’t show anything in my forecast area at 18Z but precip extending south through central Nebraska into northern Kansas by 00Z while the 12Z WRF only shows significant precip south to the Brewster area by 00Z and close to the Kansas border after dark by 3Z. The HRRR is showing some precip by 19Z just northeast of North Platt and surprisingly some precip in northwestern Kansas further down the dryline and both areas expand in intensity. To add to the confusion, the 14Z RUC is showing an isolated area of precip by 20Z from Broken Bow to Burwell. At this point, I will head to Grand Island and depending on new data, will shift northward to Broken Bow. I won’t follow storms to far to the north east and will drop south as additional storms form.

Bill Hark