5/28/07 FCST: SD/MN/IA/NE/ND/WI

[Brian Stertz]

The setup for supercells looks like it will be quite good on Monday (Memorial Day) across mainly SE North Dakota , E. South Dakota into WC/SW/C Minnesota. This threat area may include sections of extreme NE Nebraska and NW Iowa as well depending on the progress of the WF lifting north. The SB CAPEs look favorable 2000-3500 j/kg...deep layer shear ranging from 50-60 kts. and strong LL shear/vorticity on the boundary. The only limiting factor would be some capping (particularly across SD) and timing of the inbound wave. Tornadic supercells should be on the menu from late Monday afternoon into the mid-evening hours. Looks like things may organize into a large MCS cluster by late evening and the tornado threat will be on the wane then.

 

[Darren Addy]

I propose a couple of new acronyms: LOMRTG (Lots of model runs to go) and WASALWO (We are still a long ways out). With those out of the way. . .

I'm looking at the same ingredients that Brian is seeing and have just a couple of things to add. This must be a LLJ sort of an event, but (if I'm reading it right) the 96HR GFS is only showing tds of 59 in the area. With a forecast of upper-70's low 80's temps in the area that would make for quite a dewpoint spread (indicating high-bases and probably lowering tornado chances). I'm guessing hailers will be the biggest threat of the day.

The other interesting feature of the 96 hr GFS is where it shows no cap at 00z, which is right in the same area as the highest predicted CAPE values. If the inbound wave times it right, (and the model continues to verify) it could be very interesting in extreme northern Nebraska and extreme southern South Dakota. If I had to draw a box right now, I'd say the four corners would be:
Chamberlain to Mitchell, SD, down to O'Neill and Ainsworth, NE

 

[Skip Talbot]

This setup sure looked promising when it popped up on the GFS with dewpoints in the upper 60's across Nebraska. Now that the WRF is in range, both models are showing dewpoints in the low 60's over a target that has shifted north into South Dakota. One thing that worried me was the lack of 500mb winds as the 50 knot streak was still in Montana at 0z Tuesday. However, the WRF is plotting 50 knots 0-6km shear, which is ample for supercells. The WRF fires precip on the dryline in SD near the MT/WY border. With temperatures in the 80's and our drop in moisture, the LCLs are forecasted at around 2000m. That's pretty high. With 3000 Cape and 300 esrh we could definitely see some elevated supercells though. I just wish the LLJ was pumping in more moisture for this one.

 

[Jonathan Behle]

hey all,

This is my first post, I will be more of a reader then a poster, but for this scenario, we must keep in mind how it seems like most guidance advances everything too quickly to the east. But I do agree this setup for Monday looks interesting, right now I would target South Central South Dakota.

 

[Scott Weberpal]

I'll be heading out with a small group, at this point I'm keen on the area just NE of Pierre. Given the forecast position of the upper jet, this should be in an area of strong UVVs, and will also 45-55 kts of 0-6km shear. Mid-60 Td's are now into S. KS with Td's in the lower 60's as far north as the KS/NE border. Shouldn't be a major issue getting that moisture into (at very least) C/N SD by initiation time Monday. Given the prospects beyond Monday, I'll take advantage of what chasing I can do now.

 

[Michael O'Keeffe]

I agree with Scott. I will target Pierre tomorrow and most likely move north. I think with 4000j/kg of CAPE in place in N SD I think the cap won't be an issue. Moisture will be abundent too. Supercells are a sure bet with a pretty high tornado threat. This may be the last chase for awhile so I'm going to take advantage as well.

 

[Bill Schintler]

Chase target for Monday, May 28

Chase target:
30 miles west of Aberdeen, SD.

Timing:
Storms will move into the target area from the west at 5 PM CDT.

Storm mode:
A few supercells will be possible early in storm evolution however storms should quickly transition into a multicellular complex. From the evening into the overnight hours, this complex will evolve into an MCS that will track to the east.

Synopsis:
Progressive pattern is in place over the NRN CONUS with the primary features being a closed upper-low north of the Great Lakes, a deepening trough in the Pacific PAC NW, and a larger wave off-shore in the Pacific. South of the main ULVL flow, convection has fired over NERN CO into SWRN NEB in response to a compact H5 mid-level vort max and attendant up-sloping SFC flow.

Discussion:
SFC low pressure will become established in NWRN NEB along the CF of Pacific origin during the afternoon hours. Storms should initiate first in ERN WY/WRN NEB in the drier SFC air mass in response to strong insolation, before moving E into the deeper LLVL moisture E of a developing DL in WRN NEB. The strongest H5 flow will remain well to the W and N of the key SFC features and attendant moisture axis, which will limit deep layer (SFC-6km) shear to AOB 30 kts. However, a strengthening and veering LLJ above backed SFC flow should result in moderate hodograph curvature with (SFC-3km) SRH’s to 200m2/s2. Further N in SD where more favorable shear and instability parameters will exist, SFC-based convection should remain capped until late afternoon.

A couple of lead impulses ahead of the main trough should provide lift to overcome strong capping as H7 temperatures cool several degrees. Overnight, a 40kt SRLY LLJ will aid in the maintenance of an MCS which will track SEWRD in the late evening hours.

[FONT=&quot]- bill[/FONT]

 

[Paul Knightley]

We're overnighting in Pierre tonight - I like the area just NE of here, although I'm a little concerned that the upper flow seems to be a bit slower coming in on some of the models...looks like it could be an evening show.

 

[Johnathan Brouwer]

INCHASE will be in Fargo for the early target. We think the set-up will be a bit farther north. Once daylight breaks will probably adjust west...

we are on spotternetwork as KC9INJ

 

[Ben McMillan]

I am in Alliance, NE with chase partner Ryan Pfannkuch. I am surprised no one has commented on the 996 surface-low that is becoming more defined on tonight's NAM run in northwest Nebraska...Thinking the arrival of the upper-level dynamics may be a little late further north. The GFS and experimental RUC also show this feature. Noticing better surface convergence and somewhat backed winds in this area at 00z...

http://weather.cod.edu/forecast/ETA/GL/etaGL_2_temp_24.gif

Also noticing a small area of enhanced 500mb winds north of this feature...

http://weather.cod.edu/forecast/ETA/GL/etaGL_500_spd_24.gif

Any thoughts on this region?

 

[Johnathan Brouwer]

Ok, here is our update. We are staged in Jamestown,ND...waiting for update. Obviously, plans will change if parameters change dramatically... our thoughts are that this action late today will be a bit north (where we are) and a bit more east...but...no big weather words until update


Ok, update out, we are thinking the triple point will be just south of jametown, ND....but we could be wrong seriously...this depends on the heating today, if we can see the clouds clear and some serious heating going on then we'll have some fun.

 

[Jason Persoff]

Just got done looking at the 12z runs. I think the setup is very encouraging for the S ND, N SD border.
At the sfc, best winds will be southerly in C/N SD with a small area of brisk winds extending into eastern ND. A very poorly-defined but nevertheless present drypunch will overrun SW SD by 00z, however this will be in an area of very warm winds at H7 which will likely cap the atmosphere along that feature. As one approaches southern ND, however, the cap weakens. There are some decent winds at H5-H3 today, but a big of a negative is that they are along the right front exit region of the jet with some convergence of the wind fields over ND which may favor subsidence to some extent.

That said, CAPE is thus far almost surreal this far north with some areas expected to exceed 4500 J/kg (?!). Early initiation should be awesome. My initial target will be Mound City, SD (along US 83). I've got some driving to do to get there, so time to pack it in here in Chadron, NE.

 

[Stuart Robinson]

Agree with Jason on particulars. Targeting Mobridge, SD to Bismarck, ND along Rt. 83. Expect quick transition to squall line. Don't like the strongest winds aloft hanging back over the cool air. Do like the easterly surface winds in ND enhanced by morning MCV there. TM

 

[Tim Jones]

With the best upper flow well to the North, I think the best chances for tornadoes will be along the ND/SD border - or close to it. Probably no chasing today, but I would be west of Hwy 281 between Aberdeen and Jamestown - perhaps in the Wishek, ND to Eureka, SD area.

If things hold off for a bit down here in my DMA, I might sneak over to the Panhandle and see if we can get another brief landspout/tornado. Good luck to everyone out today.

 

[Jeff Piotrowski]

ND today target Jamestown

Based on 0Z 4KF & 12Z ETA, RUC i expect storms to fire around 21Z north & south of Jamestown ND. With 4000 Cape and 40+ SW flow tornado are likey in that area. This area will also be on the EDGE OF THE & 700 MLB 7C cap. The second area i like is SW/SD with the new 996 surface low forms after 0Z.

Then a squall line forms after 3Z from SE-ND/SW to SW-SD.

Tuesday Target now is Lamar-CO.