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

[Mike Hollingshead]

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=033&STATIONID=kspw

70 knots at 200mb should be good vent for whatever can happen.

I'd say warmfront or bust tomorrow...and just hope something can ride more along it. Cape gets very skinny north of it. I think it is reasonable something can stay very close to it with the flow aloft, and it lifting eastward.

 

[Jim Bishop]

The 12z WRF and GFS are at odds with each other in terms of convection across Minnesota/Iowa/Nebraska. Basically the GFS again develops a massive MCS over Eastern South Dakota late tonight, and has it moving through much of Minnesota, Eastern Nebraska and Iowa. That outflow boundary would likely play havoc on the warm front and boundary layer recovery. In fact the GFS suggests the surface low would develop over Northeastern Nebraska, keeping the warm front much further south than the WRF implies. I'm not saying the GFS is correct, but it adds a great deal of uncertainty to tomorrow's setup.

The WRF continues to suggest the potential for tornadic supercells developing late in the afternoon across Southwestern Minnesota. It will be interesting to see what the models show tonight.

 

[Derek Weston]

ETA is rather stingy with its CAPE in Minnesota, really, only a narrow strip of it. Besides the cap, I'm concerned about the actual placement of the low in relation to our CAPE, I'm concerned the much of the CAPE will be sitting back too far SW to make use of some of our tornado inducing ingredients.

But, I do like that shear, and, if a *good* scenario plays out with these ingredients, we've got the potential, I'd like to think. (ok -- so we could say that about almost any setup, but, hey... not so much to work with during the dog days of Summer)

 

[Mike Hollingshead]

Hmmm, well that tornado warned supercell in western NE right now doesn't seem to care about the -3c to -4c present at 500mb, as it's been showing some high reflectivities. Surface temptures ahead of that aren't even as high and juicy as they should be tomorrow. Tomorrow should have a similar or better thermodynamic setup than today...likely no worse...and the 850-500 cross over should be similar as well, though tilted. Anvil/upper level flow should be better than today as well. So it might prove interesting to see how well isolated storms do today.

 

[Mike Hollingshead]

Fun little forecast hodo from the 18z nam run for Jackson MN at 0z.

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=META&fcsthr=030&STATIONID=kmjq

EHI of 11 there. I'd say the target tomorrow should be rather confined to a small area near the triple point. I hope the mid-levels don't weaken any further and that the overnight stuff doesn't ruin a possible decent, if localized, day. Looks like a Sioux Falls to Jackson line might be the spot. No idea why I bother now.

Storm in NE right now took a fast crap, but was probably more due to the essentially 0 storm relative winds at anvil level there today...more than the warm mid-levels. Until it turns right and drops south I guess.

 

[Jim Bishop]

Mike - I think if the WRF is correct there will be tornadoes in Southwest Minnesota tomorrow afternoon. I guess I'm just being picky here in looking at the GFS and seeing a major difference between it and the WRF. The GFS solution just worries me.

I wanted to leave this afternoon and head up there to chase, but unfortunately my car is having some major problems. So no go for me.

 

[Jim Bishop]

I looked over the European (ECMWF) solution. It's very interesting that it also shows an MCS moving through Eastern South Dakota/Minnesota tonight. BUT, it also fires a large area of convection over Western and Central Minnesota, and northern Iowa by 00Z, suggesting the WRF solution is correct.

What I'm thinking is there will be a large MCS tonight, but the atmosphere will have time to destabalize, and what the WRF is forecasting is probably correct. The GFS may be on another planet.

Maybe all this analysis really means things are rather conditional at this point? I'd really like to see the 00z models to shed some light on the details!

 

[Derek Weston]

Mike - I think if the WRF is correct there will be tornadoes in Southwest Minnesota tomorrow afternoon. I guess I'm just being picky here in looking at the GFS and seeing a major difference between it and the WRF. The GFS solution just worries me.

I wanted to leave this afternoon and head up there to chase, but unfortunately my car is having some major problems. So no go for me.

Big fat difference between the two... thought the GFS looked like junk.

And let me say, I have to admire somebody willing to drive up from Texas for something like this. Here I sit in E. Iowa, and I'm on the fence. (although I suppose it's mostly the gas money I'd have to part with -- though nothing compared to your costs)

edits (maybe you're not in Texas anymore... from Houston?)

 

[Jim Bishop]

Big fat difference between the two... thought the GFS looked like junk.

And let me say, I have to admire somebody willing to drive up from Texas for something like this. Here I sit in E. Iowa, and I'm on the fence. (although I suppose it's mostly the gas money I'd have to part with -- though nothing compared to your costs)

edits (maybe you're not in Texas anymore... from Houston?)

Yes, I currently live in Houston. I was planning on meeting up with Simon Brewer in Oklahoma, who I believe is still going with another guy, but alas my car. But it would be worth it, in my opinion, to risk the long drive. I do believe tomorrow has big tornado potential. It's just hard looking at the GFS and having high confidence in the tornado forecast.

But as you said, the GFS is junk. Yes it probably is. BUT, I'd have much more confidence in that statement tonight once the new GFS & WRF come out. For anyone making a long haul chase like I was planning, waiting that long to make a decision is simply not an option.

Good luck if you decide to go!

 

[Bill Schintler]

Chase target for Saturday, August 4

Chase target:
Storm Lake, IA (50 mi. E of Sioux City)

Timing and storm mode:
Surface-based convection will take place at 3 PM CDT. All forms of severe weather appears likely, including a few tornadoes.

Synopsis:
The overall UA pattern is deamplifying, with both the Hudson Bay low and the PAC NW trough slowly flattening. This evening, a parade of S/WV’s were moving from W to E through WY, NEB, and SD; S of the strongest flow in SRN CAN. The first wave, over ERN SD, has been associated with an outbreak of storms today in NEB and SD. This MCS is being maintained by a SRLY 35kt LLJ which is transporting 17C H85 dewpoints into ERN NEB ATTM. An upstream H5 wave is noted over ERN WY, and steepening MLVL lapse rates are occurring with this feature. Meanwhile, MLVL warming was advecting towards the NE over NEB in the wake of the MCS. Impressive SFC moisture was in place in ERN NEB, with dewpoints at or near 70F. The WRF-NMM had a good handle on moisture and location of S/WV’s, but it didn’t depict the convection over ERN NEB. The GFS has consistently taken the MCS on a more SRLY track through IA on Saturday. Given current radar trends, mean storm motion, and LLJ speed and direction; it appears that the SRN extent of the MCS will be along US-20 in WRN IA. This represents a compromise between the GFS and WRF solutions.

Discussion:
The primary FCST challenge, of course, is the extent and track of ongoing convection and location of attendant OFBs and with the degree of air mass recovery attained. Per anticipated track and cold pool establishment, an OFB should push S to US-30 in WRN IA before stalling out and then retreating slowly to the NW. Overnight through tomorrow morning, differential advection of the aforementioned steep MLVL lapse rates over WY and warming mid-levels, with increasing LLVL moisture transported on a strengthening LLJ will result in increasingly unstable, but capped soundings. Afternoon Saturday, strong SFC heating should take place in the wake of the morning MCS. S of US-30 in IA and ERN NEB, insolation will be limited by a plum of jet stream CI which will persist throughout the day; and this will serve to limit the SRN extent of convection. The OFB in NWRN IA should provide the focus for SFC-based convection as lift provided by the RRQ of a 35kt H5 max approaches the area. Very strong instability will couple with impressive SFC-3km SRH’s values to 300m2/s2 and LCL levels in the 1km AGL range to support a tornado threat along and just N of the boundary.

- bill
[FONT=&quot]11:17 PM CDT, 08/03/07
[/FONT]

 

[Brian Stertz]

Tonight's ETA is kind of a bit down when you look at the subsidence behind that first wave that is heading out of the target zone. Surface feature wise things look decent and certainly favorable shear and CAPE is there. The million dollar question is will there be enough support in the wake of the departing wave. This scenario says bust to me...not that won't be a few TOR warnings possible, but anything that does try to spin up would have a extremely short life cycle. The temps above are pretty warmish and with subsidence being prevalent, the chances of any cooling to support longer lived supercells looks to be slim and none. I will call this one a no go at this point. Best of luck to those who are heading out. Just too many variables not in place to make this worth a 5 hr drive up there from KC.

 

[Brandon Sullivan]

Well just looking at some 6z models and SPC forecasts. Kinda confused as the RUC now shows the best thermodynamic environment, well south of the area, into MO.. With the favorable Theta E environment, and LI's as well down there. Also appears as though it possibly has slown the system down.I am unable to get ahold of WRF this morning so far, but a check of the 03z SREF shows a pretty small area of severe threat... For target ideas I would say Sioux City. I see some nice parameters nearby to the E and W, and that makes a nice sit and wait point. Good luck all.


Edit: Finally got the 6z WRF, it however has a CAPE bullseye of 4985.7 right over Sioux City, and shows ample destabilization over the entire area, including the southern fringe of the warm front, along and north of the front. Which wasnt looking that promising at 00z last night. Thus, my target stays the same, given the proximity to the low, and CAPE progs. Good luck all again. May update at 12z.

 

[Dustin Wilcox]

Definitely not an ideal tornado setup as has been noted, however as much as I have been trying to talk myself into staying away as I hate chasing the area of NW IA and SW MN, after returning home tonight I am going against my better judgment and setting the alarm to take a more serious look at things in the morning as when its this close I just cant completely blow it off, the 4km WRF sparked some interest as it has a decent storm trekking across NW IA with pretty significant convection also forming farther West into NE where super cells appear less likely, appears as though the SPC day 1 very much resembles the 4km output. My pre-preliminary target Sheldon IA.

 

[Brian Stertz]

Looking at the latest RUC...there is some hope for supercells in NW Iowa and possibly extreme SW Minnesota. The Spencer IA area looks the most primed with a decent theta ridge poke into the boundary there. This would be my target for early this evening. Best of luck to those going out today.

 

[Derek Weston]

It's too bad we won't have better instability near the low. The trick today will be getting as close to the low as possible while maintaining decent instability, I do believe. (and since the low is pulling away from our area of favorable instability.... probably a narrow window of time and area to work with... that said, if things slow down a bit, maybe we get lucky)

For guess sake: Lets try Spirit Lake area around 4PM
(and I guess this is just basically saying what Brian just did)