8/4/07 FCST: MN / IA / WI / IL / MI

[Brian Stertz]

The 12z ETA was showing a fairly strong wave will move across C/S Minnesota and N. Iowa into Wisconsin by Sat. night. Looks like the directional shear will be excellent with some good instability/helicity parameters forecasted to be in place near the IA/MN stateline. May have to keep an eye on this one....even though the 500mb temps are questionable to put it mildly. Outside of the possible tornado threat, there may be an organized squall line by evening moving into Wisconsin that could cause some trouble.

 

[MatthewCarman]

I am watching this closely as I am heading to NY Sturday afternoon. Looks like the system will also push into the northeast with a chance for severe storms. Where do you expect this system or severe weather to be after Saturday? Was hoping to have a easy drive up there but now I dont know.

Saturday looks like it could be stormy across the midwest although nothing points towards a big or realy severe outbreak at the moment. Have to wait and see.

 

[Michael O'Keeffe]

I've been watching this as well and may head out since it's a Saturday and I havent chased since June 16. I'm liking the S MN area...moderate instability, good SE winds, temps only in the 80-85F range, helicity is looking great as well. I'd target close to the surface low from Blue Earth to maybe Mankato. I agree the 500mb temps are a bit concerning. Also tds will be in upwards of 75F to 80F! So we could quite possibly see a few good supercells with a tornado or two before becoming a major squall.

 

[Brandon Sullivan]

I as well have been watching this. Todays 12z WRF showed a nice little bullseye over me in W Central IL. With -5 LI's and 4000 CAPE. GFS I note is somewhat weaker with the amount of destabilization. I think the warm front will be my focus, I will be interested to see SWODY 2 Tommorow. Looking at a Central IA target as of now. But still lots of refining to do.

 

[Derek Weston]

Yup, N. Central Iowa, S central Minnesota on Saturday, from the looks of it.

We certainly have the directional shear going.

Worries: The cap. Weak 500 flow.

The pluses: Juicy cape, good winds up high and down low to get things spinning. (really, about as good as I've seen this summer strength wise)

Intersting... interesting...

edits: Note, this is for the NAM forecast. GFS puts the best shear out ahead of the instability, which is more confined and further west than the NAM run. This thing is pretty dicey.

 

[Josh Richardson]

Well I dont have much else to add, so far we're looking at Southern MN/Northern IA. Problems will be cap/warm air aloft. Still aways out yet, will update later.

 

[Mike Hollingshead]

500mb temps via 18z nam

OUCH. Looks like a mushball-fest to me. I just hope I can avoid chasing it.

Looks like on the forecast soundings the cap is gone pretty early in nw IA/sw MN. Cape is big early, it's just hard to get excited when I can't come up with anything worth a darn in those kind of mid-level temps(or even cooler than that). Hmmm, will hate to see that come to be from home though lol. Thinking more about chasing the day now, and being stupid seeing what I've seen so often in warm mid-level days(course the lower, 700-850mb temps, may have been the bigger cause to mushballs those days). The shear certainly looks friendly.

 

[scott r currens]

500mb temps via 18z nam

OUCH. Looks like a mushball-fest to me. I just hope I can avoid chasing it.

Looks like on the forecast soundings the cap is gone pretty early in nw IA/sw MN. Cape is big early, it's just hard to get excited when I can't come up with anything worth a darn in those kind of mid-level temps(or even cooler than that). Hmmm, will hate to see that come to be from home though lol. Thinking more about chasing the day now, and being stupid seeing what I've seen so often in warm mid-level days(course the lower, 700-850mb temps, may have been the bigger cause to mushballs those days). The shear certainly looks friendly.

My thoughts exactly. This setup reminds me of every chase I have had in Iowa. Losts of potential + plus lots of questions = Me busting with out AC in an overheating truck because it is 89/79. Unfortunatly it is on a Saturday so I'll probably go out and waist time and money.

 

[Craig Maire II]

I'm pretty sure there will be at the very least some isolated hailers on Saturday and since I live in the target area and don't have to work on Saturday I'll definitely be ready to chase!

 

[Brandon Sullivan]

Just got done looking at some 00Z Model Data. I am glad to see we finally have an event with a favorable Kinematic Environment. So many times this year we have had cape, but no shear, forcing, convergence, etc.. but it looks like a nice dynamic system. with a good kinematic and thermodynamic environment.

 

[Brian Stertz]

This setup tomorrow looks like a probable S.Minnesota event along/north of the I-90 corridor...and possibly extreme N. Iowa if there is any outflow boundary inclusion into the mix. The theta ridge poke looks like it is aimed at SW Minnesota tomorrow afternoon...and this coupled with strong 0-3km helicity forecasted could mean some legit supercells with a tornado threat. Awaiting the 12z run details ....

 

[Michael O'Keeffe]

Here is a graphic courtesy of the NWS. It seems the highest tornado threat is north of the warm front from around Montevideo to Mankato. The system has seemed to have slowed itself down which is good for most chasers so we wont have to deal with the terrain of E MN or Wisconsin. Though I think this is no major outbreak, but it may provide us at least one or two good tornadoes if we can see it through the haze. ugh. I like the fact the warm sector has increased a bit, but CAPE is down a bit. I think I'll still make the trip tomorrow.

 

[Jim Bishop]

Saturday looks very interesting. First I had to figure out which model, the GFS vs. the WRF, had a better handle on the track of the shortwave (the two are actually quite different as of 00Z Aug 3). I believe that to be the WRF.

That makes things interesting over the extreme eastern South Dakota to Western Minnesota tomorrow afternoon, but also a little complicated. An initial vort max will be moving across Minnesota during the morning and midday hours, but at the same time another vort max will be approaching Eastern South Dakota/Western Minnesota. Granted this will be over the top of a decent sized ridge, but it seems there will be considerable large scale ascent over this region.

With a low tracking east across Eastern South Dakota, a warm front will lift north over Southern Minnesota, and a cool front will move east across Eastern South Dakota into Western Minnesota.

The WRF forecasts some very joicy air with around 2000-3000 j/kg CAPE. The deep layer shear supports supercells, and the shear vector will be nearly perpendicular to the front, so I wouldn't be concerned about linear convection. Also, I like the strong 250mb flow.

My main concern would be convection firing too early (around noon) along and north of the warm front over Western Minnesota, killing the thermodynamic environment for later in the afternoon. If that doesn't happen and convection holds off until later in the afternoon, I smell torndic supercells. So it's a pretty conditional setup at this stage in the game, but it has potential.

 

[Brian Stertz]

Same results on the 12z ETA...believe that SW and then eventually SC Minnesota will be the place to be late tomorrow afternoon. Looks like things should setup nicely for a 2-3 hr. window for possible tornadic supercells with the ETA forecasted surface low in the Sioux Falls SD area and wf draped southeastward from SW Minnesota into NC Iowa. Should be some real serious moisture pooling on that boundary with very strong SRH forecasted (0-1km helicity at 400 m2/s2 plus at 00z on this morning's 12z ETA). The 500mb temps should be a little on the soft side, but shear and instability combo should be good with just enough deep layer shear for supercell sustainment. This may be one of those days where the low level shear may be the big player and spin up some tornadoes. I am interested for sure. Looks to be a legit summer setup.

 

[Andrew Pritchard]

I don't know that I would call the kinematic environment much better than anything else we've seen. I suppose the low levels are conducive, but I'd think "ideal" would be a little more than the progged 30 knots or so at H5. I don't know, I have no intentions of chasing so maybe I just don't share the same optomism as those who do but when glancing at the models before seeing this thread I never really saw anything that screamed chase day. Like I said, the strong LL shear could be enough to spin off a tornado, but I don't think the upper levels are all there for long lived supercells. More likely multicells that briefly may take on supercell form, then die out and have a new storm form 20 miles away and do the same thing. Very annoying to chase. Who knows, I could be wrong and maybe the directional shear and warm front alone will be enough, but I think I'd rather see that summer time extreme instability in place before I rely on such weak flow above 700 mb, which this setup doesn't seem to have either. It's somewhat pleasing to the eyes after seeing nothing at all for a while, but I'd probably only consider chasing it if I were one of the locals.