7/13/10 FCST: ND/SD/NE

[Skip Talbot]

The GFS and NAM have been quite consistent in plotting a nice dryline setup in the Dakotas extending down into NE on Tuesday the 13th. Dewpoints exceeding 70 are forecast to advect into North Dakota the evening before and morning of the event. The wind fields look very nice with backed surface winds across the northern plains, a 20-30 southerly knot low level jet, and broad westerly flow at 30-40 knots. I'd like to see the upper level flow a little stronger, but it looks like the shortwave forecast to eject around the bottom of that upper level closed low is going to be a little delayed, and might play a bigger role on the 14th. Still with 0-6km bulk shear of 40 knots and 100-200 m2/s2 1km SRH just ahead of the dryline, we should have more than enough speed and directional shear for sustained supercells. Strong to moderate instability should yield some robust updrafts, and capping doesn't look like its going to be a problem. The models have been consistent in eroding the cap by early afternoon and shown some storms firing in South Dakota.

This looks like it could be a great chase op with discrete, isolated supercells firing off the dryline in ND/SD by late afternoon. A few tornadoes could be possible on any sustained supercell. The slower midlevel flow and strong veering with height should give us real slow storms speeds as well. I don't think we'll see much of a chaser convergence either since its a weekday in summer and way up in the northern plains.

 

[Mike Hollingshead]

90% sure I'll end up chasing this one. It has some signals for a classic July nc NE deviant beast. One is things should be more isolated south like often is the case. The other is that sfc trough isn't terribly strong and actually backs west into the night. I'd hope that would keep things very isolated in NE. The main thing is where the boundary is located and it trails it ssw. I can think of plenty of July ssw moving flying eagles in that very location under seemingly similar conditions...or worse conditions. It's kinda tricky business getting on those July beasts that do that out there, with tons of days that don't pan out to get to the ones that do. But when you get on one they can be rather special. Often on those days it looked a hair better further north, but then that darn deviant storm in NE lol.

Chased a tornadic one near Ainsworth July 24, 2000, missed chasing one near Burwell July 17, 2001, saw another tornadic deviant beast July 12, 2004 and the crazy supercell last year July 13 at and south of Valentine. There was another crazy one Dean Cosgrove was on up there maybe in 2002, but not sure if that was August or July...dropping south from near Winner SD into NE...wild on radar. Just this very favorable area for that stuff on boundaries when they are between O'Neill and Valentine and a small area north and south of that line...in July....with often questionable conditions made less questionable by storm motion.

O'Neill NE

Turn a storm right in that and interesting things will happen, especially if it isn't being messed with by too many storms. It's actually a little overdue for a true classic one of these.

 

[Andy Jackson]

This setup reminds me of July 11th 2008. I'd say the 0-1km helicity looks best in the northern part of the Red River Valley with emphasis on the MN side.

 

[Greg Blumberg]

I too am beginning to see the comparison with June 11th, 2008, Andy. Some differences though.

Noticeable in the WV imagery is the vort max associated with this system and the jet streak. Higher dewpoints will be advected by south easterly winds into the ND, SD, MN areas to help provide further instability tomorrow. Heating and the current lapse rates from the sounding along with the moisture advection should help create CAPE values around 2000 J/kg with some areas near 2500 J/kg.

With convection firing in W Montana right now and moving eastward, clouds should help suppress heating early on in the day. With the current trends, the 700 mb map has 10 degree C temps that are currently being advected towards the main area of concern. Having these warm temperatures should work to create a cap. Additionally, the convection from tonight should be monitored for any outflow boundaries to work with tomorrow. If the southeasterly winds persist, upslope flow will also become a source for thunderstorm development.

My only concern is the upper level winds stunting the maturity of the storms by contaminating the storm's inflow with precipitation. My concern however, may be false considering the scenarios where this has not been an issue. Either way, whatever happens should make for a good story for the high school students at the weather camp I'll be at tomorrow!

 

[Derek Heide]

Skies are clearing up in Western North Dakota and Southwestern Manitoba. With full sunshine possible heading towards noon, I could see SPC expanding their 10% tornado contour up to the International Border.

I wouldn't count out chasing Northern ND, especially if the clearing continues..

 

[Justin Turcotte]

Skies are clearing up in Western North Dakota and Southwestern Manitoba. With full sunshine possible heading towards noon, I could see SPC expanding their 10% tornado contour up to the International Border.

I wouldn't count out chasing Northern ND, especially if the clearing continues..

This was actually the consensus at my office yesterday. From my experience the better tornado producers in eastern ND/northwest MN/southern MB tend to be where the shear is maximized while the most unstable environment is further south... making tail end charlie cells primarily a chase option of proximity or for better visibility structure shots. While the boundary currently in northeast SD/southeast ND is interesting, I'll be aiming for a cell to pop off the wave currently in southeast SK late this afternoon in the Devils Lake basin. Since the potential target is only an hour away and I still need to at least briefly report to work at 4pm I'll simply hold tight and wait for signs of initiation. If a storm is already popping at the time then it will be a race west.

 

[AndyGabrielson]

I see issues possibly getting a storm going south of I-90, and I see the chance of linear within a couple hours of initiation in parts of ND/CN/MN (north of I94) so im playing sort of a nuetral but still good target area, little more instability in this area (at least as of last nights models) and it would seem storms could get going as early as 3pm and stay fairly isolated... since most of this stuff is just rehasing earlier posts... my current target is Hecla, SD...

 

[L.B. LaForce]

Not chasing today, but my virtual target would be around Summit, SD. Nicely backed winds, plenty of CAPE, and some nice UVV values in the area.

target polygon: