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7/20/2004 FCST: ND, SD, MN, NE

Wow is this freaky how much the satellite looks like it did last Mon morning. A weak boundary in ne NE going nw-se with stronger ese winds along it going nw back to an approaching cold front with around 30ktnts at 500mb over and strong to extreme instability developing south of this area. With enhanced convergence in sc SD noted on satellite and on sfc. I think the show very well cloud be out in the same location it was last Monday n and s of Spencer NE. North of Spencer into SD if we buy the ruc. I just woke up and quickly glanced at this so I could be WAY off here but that is where I am looking right now.

MIke
 
It's about time someone corrected my inexperience. And I say that with the upmost respect. Thanks for the reply and yes, after the post, I did notice that I put it in at 48 hours. Because if inexperience, I base my targets on the look of the SPC outlooks and go from there. And from experience, the SE SD has always been more productive than my position however things tend to flare up just east of I-29. Sioux Falls didn't look so bad either (I didn't look at it until now - and I only use it as an indicator - not as God's guide to chasing). I'll still put up a Bermuda triangle of Sioux Falls to Pipestone to Worthington (cause storms could disappear in there). Hehe, should I put a disclaimer of an inexperienced chaser? I'll always welcome the feedback, even if I do dig myself a hole :P
 
My target: Luverne, MN...

Both the RUC and ETA develop signficant instability (4500-5000 SBCAPE off the ETA and ~3000 SBCAPE if you believe the RUC) in a corridor generally from Pipestone, MN, south-southeastward into western IA. The RUC drops sfc Tds into the mid-upper 60s for the most part, while the ETA increases sfc Tds into the mid-upper 70s -- thus the CAPE forecast discrepancy. Whatever the case, current showers and clouds in the sw MN, se SD, and nw IA area will likely inhibit the development of strong surface-based instability for several hours. While mid-levels remain relatively weak, strong directional shear yields ETA-forecast 0-6km deep layer shear of ~35kts by afternoon from southwestern MN into western IA. Additionally, s-se SFC winds beneath s-sw 850mb winds yields respectable 0-3km helicity in the 200-300 range. Both the RUC and the ETA show a weakness in the cap over sw MN and adjacent portions of far se SD and nw IA by afternoon. While the ETA QPF output seems to develop an MCS west of Pipestone (moving east-southeast) while keeping the 'warm sector' capped, the RUC does develop precip from near Watertown, SD, to FSD to south of Denver, along the front trailing from the low in se SD.

With decent low-level shear and potentially-strong instability, I think, assuming initiation, we could end up with a couple of tornadic supercells from southwestern MN into far northwestern IA (the cap increases to the south, so....). Weak midlevel SR flow will likely tend to put any supercells in the HP range, but, as we've seen many times this year with relatively-weak mid-level flow, we can still end up with photogenic tornado-producers.

I haven't looked much as the southern SD or NE forecast, since I'm partly doing this to aid a friend (Gabe Garfield) who's up there chasing today...
 
I think that area of nc NE is screaming chase me. The area north of Sioux Falls is about the same distance as the O'Neill NE area for me but I think I'm going to go out towards O'Neill-Spencer line or just east of there. The best convergence looks to be out there.

http://www.rap.ucar.edu/weather/surface/sfc_pir.gif

Something should go on that boundary regardless of the 27-28c at 850 out there and 13-14c at 700....and only 20knts at 500mb. Not exactly screaming most times of the year but it seems like in July you are best to chase a boundary that seems like something could ride it south and increase it's storm relative shear. And with such weak 500mb flow it just seems like it'd have to ride that boundary south as it's forward flank precip builds and guides it's inflow. Crazy things happen with NE's July ssw moving supercells. I'll play the chance it can happen again. Just need to get a storm up out there and judging by the temps already and the sfc convergence I would bet it's fairly likely. Good luck to any heading out today.

Mike
 
I think Mike has some good points made, but would like to note the boundary orientation across NE is not favorable for a SSW cell motion - a SSE-SE would be better. Note the orientation of the thetaE axis - highest on the cool side of the boundary (much higher moisture) and oriented NNW-SSE. The river will be a nuisance, but still think best opportunities may lie just across the border into SD. I see the road options favor the route you mentioned - but I might be inclined to head for any area further NE - but this is splitting hairs at this point. Still not impressed with sw MN - current 850 flow of 5 knots, eash... still early but maybe I try for the intersection of 37 and 46 in SD for initiation.

Glen
 
I agree with Snyder...If I go I'll probably target the MN/IA/SD border, there is a nice convergence there, favorable dew points, vvel skyrocketed, and not to shabby CAPE. Problem that the ETA shows is still a pretty strong cap with this sounding. Good shear though, so if it initiates i'm lookin for a supercell or two.

Of course, the RUC shows activity farther north that ETA, so the question is which do you trust more? Which one is more reliable?

But, as the AFD from KFSD said this morning, temperatures are going to probably be WAY to high for any tornados to drop out of these. They're calling for tennis ball size hail and 70+ mph winds.

If I go, I'm going to the tri-state border.
 
The skew-t for OAX is just awesome. This is about the closest to Sioux Falls for a sounding. Cape is already at 2500 with CIN at only 318. The hodograph is showing a perfect shear profile for now. At least that's how I interpret it. Am I right?
 
The morning Omaha sounding, with a value of 318 for CINH
, the atmosphere is capped bigtime, look at the CAP strength
of 6.8 C, and weak speed shear throughout the sounding.
I notice they did not relase a 18Z sounding either, have not
seen any 18Z soundings for ABR, MPX on the COD site.


Mike
 
The skew-t for OAX is just awesome. This is about the closest to Sioux Falls for a sounding. Cape is already at 2500 with CIN at only 318. The hodograph is showing a perfect shear profile for now. At least that's how I interpret it. Am I right?
Click to expand...

CIN of "only" 318 is quite a strong cap. Check the post above.

Looking over the latest SPC Hourly Meso analysis (http://www.spc.noaa.gov/sfctest/s1/index2.html), I'd say we're looking at another north-central NE event, with initiation somewhere in SC SD. Theta-e and winds look to be progging the cells to be moving in a SE/SSE direction. Hopefully we'll get some good hail out of this one, though the freezing height might be a tad high.
 
So, SPC put out a mesoscale discussion, yawn..., nothing really intriguing about the text. Maybe a watch around the 4 pm time frame.

Glen
 
I figured the storm motion(especially the desired) would be ssw along the boundary, as the boundary is aligned nne-ssw(actually sw-ne).

http://www.spc.ncep.noaa.gov/exper/mesoana...sis/s1/mcon.gif

In Neligh Nebraska probably heading towards O'Neill. I don't think any motion other then at least due south will work today. I like how the sfc trof is aligned out here right now though.
 
I figurded the storm motion(especially the desired) would be ssw along the boundary, as the boundary is aligned nne-ssw(actually sw-ne).

http://www.spc.ncep.noaa.gov/exper/mesoana...sis/s1/mcon.gif

In Neligh Nebraska probably heading towards O'Neill. I don't think any motion other then at least due south will work today. I like how the sfc trof is aligned out here right now though.
Click to expand...

Ah, I see what you are referring to - but that is moisture convergence which is highlighting the dryline in this case - which I don't think you'll want a cell on today. Instead, there is a diffuse warm front - follow the sharp gradient in thetaE here:

http://www.spc.noaa.gov/sfctest/s1/thea.gif

and in sfc vorticity here:

http://www.spc.noaa.gov/sfctest/s1/3cvr.gif

If you look closely at the sfc winds, there is a wind shift associated with the gradient, with higher instability NE of the surface boundary. This is the boundary I would want cells to track along - as such storms will have a lower LCL, higher instability and will benefit from the sfc vorticity associated with the cyclonic wind shift.

Glen
 
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