06/17/10 FCST: SD/ND/MN/IA/MO

[Greg Blumberg]

Seems both ABR and MPX have done a special 18z sounding to get a firmer grasp on the event. Only trouble is I think the MPX balloon got shot down by someone and so it only goes up to ~500 mb. Either way, the ABR sounding looks impressive for severe weather, but I'm concerned about the unidirectional shear from the south up to 500 mb. Splitting supercells in the area...possible, but it looks like a linear setup.

The MPX sounding seems to suggest what Mikey said. The 0-1 km shear in that sounding (however short it was) is very impressive for tornadoes. Lower level lapse rates look good too. My guess is that the ABR sounding is tainted by it's position near the cold front. Further east, our MPX sounding has a much more valid look at the lower portion of the atmosphere.

http://w1.spc.woc.noaa.gov/exper/soundings/10061718_OBS/ABR.gif

http://w1.spc.woc.noaa.gov/exper/soundings/10061718_OBS/MPX.gif

As I type this, SPC has put out a tornado watch for Iowa and Minnesota. Let the show begin and let all stay safe.

EDIT: The full soundings are out.

 

[Mikey Gribble]

I really don't like the poor 850-500 crossover over the Iowa portion of the threat area. I would adjust the best tornado threat area farther north to account for that, but I'd keep my Brookings target.
The 850-500 crossover is great farther north over the North Dakota area, but unfortunately I think linear forcing will greatly mitigate the tornado potential so the better shear doesn't really matter. The best spot is in the overlap in between over southwest and west central Minnesota where 850-500 crossover is decent and convective modes will tend to be more favorable for tornadic storms. Here is the updated map that I threw together...

 

[Greg Blumberg]

It seems that four sites released 18z soundings instead of the two I mentioned. One looks very impressive:

http://w1.spc.woc.noaa.gov/exper/soundings/10061718_OBS/OAX.gif

OAX has very nice lapse rates, very strong CAPE, and very strong shear. That is a very dangerous environment near OAX. I still think Iowa has potential for tornadoes, especially if the 850 mb winds back a bit more. The storms down there also might be more discrete.

I mentioned above that the MPX sounding was incomplete, but apparently SPC has updated it. This area has some real potential as well.

http://w1.spc.woc.noaa.gov/exper/soundings/10061718_OBS/MPX.gif

 

[Mikey Gribble]

just a copy and paste from my blog...

So far storms have initially fired as a line of broken cells over North Dakota. They will still pose a tornado threat as they become more established downstream given the very strong SRH available. I’d stay out ahead of the line a ways to keep my options open in case a supercell in the broken line becomes a little more discrete or dominant and move in then.
Farther south near my virtual target of Brookings convergence is happening over a wide area so I’d go ahead and move downstream to Marshall. Updrafts that are trying to get started have been flying, so cheating downstream of your target is a smart idea. Storms should be a little more discrete than whats firing to the north. Good 850-500mb crossover is in place over the southwest quadrant of Minnesota. This area has the best tornado threat today. I think they’ll see a few tornadic supercells capable of producing multiple tornadoes.

 

[J Trueblood]

Judging by the pretty good low level shear, being on the nose of the jet, high dewpoints, a bullseye of EHI, and a good amount of instability, I'd say the tornado probability needs to be pushed further north. I'd look in a general area around Fargo. Also, given the high cape values, if anything goes up and can stay discrete, I'd look in the sanborne/worthington maybe a little east more areas of the Iowa/MN border for something. But who knows, I'm new at this so we'll see.

13 counties near fargo went tornado warned with 8 reports so far.
Also, cells are starting to pop up in north central Iowa.