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

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Three consecutive ETA runs depict a potent 700 mb shortwave intersecting an area of extreme instability from northeast NE through eastern South Dakota, eastern North Dakota and west central Minnesota. What catches my eye about this setup is a stout LLJ through the evolution of the system and a strong dry punch at the surface.

Too early for targets, but somewhere east of that surface trough might be interesting. Midlevel winds are modest, (and there's some upper level ridging) but my high plains and northern plains friends are helping me overcome my south plains bias regarding H5 and early summer winds aloft in general up there. 8)

Should be interesting to see this early summer system evolve.
 
Amos since you live in IN, did you also check out the 72H-84H 12Z ETA? I believe this run may be suffering from conv. feedback, but these are the parameters for the IWX through DTX areas:

CAPE: 3500J/KG
0-3KM HELICITY: 400M2/S2
TDs: 70-75F

Anyway, if this trend continues, I will start a thread for 7/21 for the Great Lakes region...
 
Looks interesting

I saw the 1200 UTC run of the ETA today. The 0-6 km shear looks lincredible, as well as the 0-3 km shear, which looks to be supportive of tornadoes. CAPE looks incredbile, and the moisture availability does as well. There's going to be a strong cap, but initiation shouldn't be a problem along the warm front where the 850 mb winds are backed with cooler temps.

My only real concern is the lack of strong upper level winds (300-200 mb). With this type of scenario, it seems supercells will form and produce low-level mesocyclones "briefly", or for say 10 or 20 minutes, and then become undercut by outflow. Not to mention the massive HP monsters they will very likely be! Of course, it's still a couple days out....

Jim
http://stormgasm.com
 
I hope tonights 0z doesn't follow the path of what the 18z spit out.
 
Didn't look at the 18Z, but the 00Z is certainly trending in an unfavorable direction. Much weaker wave, subsequent hemorrhaging to lower level shear, and a stronger cap to add insult to injury.

Glen
 
06Z run unimpressive, but the 12Z ETA run looks interesting again. Gotta love that run-to-run consistency.... This is kind of an interesting forecast, as you can clearly make out the upper disturbance in current water vapor imagery, but the handling of this wave as it shears out over the top of the ridge axis has been very consistent by the ETA with regards to timing, just disagreement over the intensity of subsequent waves. Overall setup isn't that bad, aside from weak storm-relative flow aloft. Still worth watching I guess.

Glen
 
I have backed off chasing plans because of other committments, but I still like Tuesday's setup and agree with Jim Bishop and other that there will probably be a monster isolated storm alone under the cap and tornadic.
 
18z run is interesting, to say the least...Back to extreme instability (on the order of 4000 j/kg) and juxtaposed with strong 0-3 km shear (>300 m2/s2) over a broad area from SW Iowa to WC Minnesota. I think that any outflow boundaries from tonight's convection will greatly influence tomorrow's probabilities. If convective debris can clear out in time, watch out. Right now, I like SW MN because it appears that an OFB will set up in this region.

Gabe
 
06Z run unimpressive, but the 12Z ETA run looks interesting again. Gotta love that run-to-run consistency....

12Z run looking like the outlier again - deep layer shear really falling apart without the strongly backed winds at the surface. Unless there is a huge MCS marching into nw IA in the morning.....


Glen
 
I'm impressed with how consistent the ETA has been with the timing and strength of the shortwave. I think a feature this strong with moderate to extreme sfc instability means the surface features might be better than advertised, though the setup has a storng cap and upper level ridging to contend with. I expect one or two supercells in eastern South Dakota with a modest tornado chance if a surface trough sharpens and pushes east as a boundary on which the storms can propogate. Guess I'd pick Watertown if I could go.
 
This is one of the few times I hope the pattern stays well to my north. I've got two important (as in job critical) practicums I need to take Tuesday and possibly Wednesday.

It can all go to Hell on Thursday and Friday for all I care. I'll need something to do.
 
Re: FCST

Who's headed to MN/SD today? :wink:


ummmmmmm I'm already here lol........But we'll probably go west towards worthington then once storms develop follow them back to mankato or plan B just wait here in Mankato...but thats only if my dad is off late :roll:
 
Re: Pipestone, MN

I'm going to have to say Pipestone, MN. Things look pretty good from this:

http://www.wxcaster.com/modelskewt.php3?mo...&STATIONID=KPQN

But, I could be wrong. Anyone got an ETA for all of this? Spotter activation is possible after 400 pm for me in Brookings. I'm going to try to time it right so I can get out of softball as soon as things start heating up.

Anyways, that's my two cents.

Ed, can I call you Ed? Anyway, the forecast sounding you provided a link to is valid Wednesday night, not tonight - so it wouldn't be applicable to this thread. Further, it is actually not a very favorable sounding. Note how shallow the moisture is in the boundary layer, mix this moisture out and you have very little CAPE. Also, the dry boundary layer air would favor very high based convection, if any, and the 0-3 SREH of 75 is also pretty low. Maybe you provided an accidental link?

The 12hr forecast sounding from this morning's run for the same location does look better, but has high relative humidity through the depth of the sounding - which could mean extensive cloudiness, and this also limits the mid-level lapse rates, though the low-level lapse rates (just above the surface inversion) are decent, with 0-3 km CAPE of ~ 350 J/Kg. 0-6 km shear of ~35 knots is not so great - but is probably ok for the degree of instability (MLCAPE 3700), and 0-3 helicity of just over 200 is ok, but you'll probably need a boundary as well to get a tornado. Surface winds of 5 knts will rarely get it done.

Following that extended blurb, I'd never recommend using a forecast sounding to pick a target. While they are cool to look at - I don't think they verify very well - and can be very misleading. Will Pipestone be a good target for later today? IMO, it's a bit too far north, but it's too early to pinpoint. Right now I'd lean more towards Vermillion for initiation, but subject to change. Seem you are already in the general vicinity - so I'd worry about a target when things are clearer - say early afternoon.

Glen
 
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
 
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