4/30/07 FCST: IA / WI

[Genaro Estrada]

FCST: I just finished looking severe weather parameters. The area of northeast Iowa and SW Wisconsin actually look descent for supercell
development. The SPC also gives SW Texas a 2% chance of tornados, and by the looks of the Del Rio International sounding, nice backed surface winds, and curved hodograph. Surface Cape of 1410 j/kg, and CIN of 0. Other severe parameters also look good for southwest Texas.

 

[David Draun]

The temp/dewpoint spread is pretty large for tornadoes however. Also the 850mb temps are quite warm, making the entire setup very conditional. Shear is nice though, so if anything does develop, it will likely be very isolated and quite photogenic IMO. Some of the NWS offices around the area recognize the threat and have highlighted it in the HWO, but the actual forecasts are for no precip. Actual convective instability will be very limited. I will be prepared to chase anything this evening that comes close to NW IL. Might find a nice storm today.

 

[Fabian Guerra]

I think you might want to add Minnesota to this thread. I am on vacation this coming week and found myself generating forecast soundings for tomorrow and really like what I am seeing on the NAM FS for Albert Lea around 21 Z. A very nicely curved hodo and some impressive numbers:

LI = -6.2
0-3km SRH = 615.7 (uh...ok)
CAPE = 2119
LCL = 672.7
EHI = 7.3
Supercell Potential = 91.3%
STP = 5.1

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

So far tomorrow looks pretty good. Definitely something to keep our eyes on. As of now my target will be somewhere along the the I35 corridor from AEL to MCW along the warm front.

Fabian

 

[Skip Talbot]

FCST: I just finished looking severe weather parameters. The area of northeast Iowa and SW Wisconsin actually look descent for supercell
development. The SPC also gives SW Texas a 2% chance of tornados, and by the looks of the Del Rio International sounding, nice backed surface winds, and curved hodograph. Surface Cape of 1410 j/kg, and CIN of 0. Other severe parameters also look good for southwest Texas.

Are you talking about today or tomorrow? SPC hasn't issued a tornado forecast for 4-30 yet. Today's Day 1 is 4-29.

Anyway, I have been watching 4-30 for its chase potential on the iA/MN border. The cap might kill us on this one:
http://68.226.77.253/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_36HR.gif
http://weather.cod.edu/forecast/ETA/GL/etaGL_0_cinh_36.gif

Still, very favorable parameters if storms can initiate with excellent directional shear on the warm front and good instability just below the front in the warm sector.

 

[Brian Stertz]

S.Minnesota looks good

The chase target for Monday be be right on the boundary across SC/SE Minnesota (east of I-35)...looks like much of Iowa will be capped off except for maybe north of a Mason City to Elkader IA line. It looks like a fairly short window between initiation and before the storms/supercells likely become more elevated across SW Wisconsin. I would not be surprised to see a few tornado reports tomorrow between 5-8pm given the spectacular LL shear on the boundary and sufficient CAPE. The 12z ETA forecasted tornado parameters are rather high on the boundary across SC/SE Minnesota.

 

[Scott Olson]

Just some thoughts on tommorow. A look at a whole lot of forecast soundings last night showed a pretty stout CAP. The NAM shows some negative vorticity advection through the early day while the GFS is a little more favorable with some weak DPVA latter on. Both have nice divergence clipping SE MN by 21z and increasing positive vorticity advection than. As for the question of moisture, I looked a lot more at the NAM which is supposedly to be the more represenative and conservative model. This would indicate some possible ML LCL's of around 1200m for my primary area of interest, which actually isn't so terrible stacked up against other events in this area. The deep shear is certainly great for the entire area and even more so for a warm front rooting storm in extreme SE MN/NE IA. One good part appears to be the 300mb jet setup which should provide some decent lift over the area. Two areas I'm looking at.

SC MN and NC IA- (30 miles north and south of Albert Lea). By 0z the NAM gets going with some DPVA and divergence into this particular area and consistent rising tempatures and moisture pooling (as well as a boundary intersection) appear to provide a short window for intiation. The shear isn't as good but still more than sufficent for supercells and the instability axis seems a bit more generous to a storm not having the ability to move into stable air and to give it time to develop and root along the warm front. This is somewhat tempered by the later intiation time though and decrease in heating that will soon occur. Worth noting that the NAM has shown intiation in this area at least since Friday night and even the GFS has consistently shown that this area has little or no CINH remaining by 0z for several days.

Extreme SE MN:
Appears this location would have the best oppurtunity for tornadoes and intiation. Consistently indicated by both NAM/GFS for several days as well as an area of strong/extreme LL shear. 400+ m2/s2 0-1km SRH on a couple soundings and possible intiation as early as 21z. GFS showing nice divergence associated with right entrance region and equally good divergence on the NAM as well. SREF also leads creedence to intiation between 21z-0z in this area with attendant supporting supercell and tornado probabilities that look pretty good. Main concern would be that the models indicate the storm forming in an area of pretty significant CINH and in an area where the WF begins taking on a much more southerly orientation. This would seem to provide little time for a storm to mature before needing to make a deviant motion or face more stable air. Nonetheless, those hodographs look like a convective party might be taking place. The divergence is strongest over the area right at peak heating so I think the chances of intiation here are actually pretty decent. Afterwards the NAM shows divergence increasing in SC MN & NC IA as well as the aforementioned DPVA stated previously so intiation also appears possible in the SC MN/NC IA but there is less support here between ensemble members and I would regard the chance here much less than further east. Low level deformation axis and associated convergence looks to get pretty strong in the latter afternoon, so at least we are not dealing with a weak boundary.

FULL DISCOLSURE: I have challenged Bill Doms to a CHASE-OFF tommorow.

 

[Skip Talbot]

I should add that SPC mentioned unidirectional shear in the Day 2 forecast. Indeed, the 850-500 levels show very little turning (even slightly backing with height) on the GFS. The WRF differs significantly in this department with southwest 850's and northwest 500's. The 0z run might settle things or else we are waiting for the RUC.

 

[Bill Doms]

I am not all that enthusiastic about tomorrow's tornado potential. That SW H85 flow is giving serious doubts of any decent moisture making it here much less pooling in the vicinity of the warm front. I do believe there will be a narrow axis further east than the I35 corridor where the NSE may harbor a better chance at getting a storm with LCL's <1200m but not a favorable area for initiation. Convective temps along the I35 corridor +/- AEL will not be met. The only area of interest to me would be on a line from Rushford, MN down to Decorah, IA. If you are not familiar with this area, it is bluff country and pretty much unchaseable. Unless it looks like initiation on the I35 corridor tomorrow, I'm likely going to let it go.

Scott and I will get around to our chase-off at some point this year, but it's pretty early to contribute to the Opec IA Bust Fund.

 

[Josh Richardson]

Im planning on making this one but only because its a backyard chase, initial target was Albert Lea after looking at the Skew-T last night but it seemed to me all the parameters were pointing towards the east a bit. Will probably just make the call in the afternoon since its a short drive either way. I just hope we end up with better moisture than what we are seeing right now as we are sitting at 88/43 currently.

 

[Josh Richardson]

Latest NAM and GFS runs are looking even worse for this one now. Albert Lea Skew-T is showing LCL's around 1900 at 00z per NAM. The NAM has a little something breaking out in that area but thats about it. I will be available for this one purely because its only a few minutes away, other than that I wouldnt waste my time.

 

[Genaro Estrada]

Sorry, I meant 4/29/07, dohh!!! I was working the night shift, and my brain was on Zulu time. Sorry about that, I'll be more carefull next time I post. But, SPC storm reports show a couple of tornadoes north of Del Rio and a few hail reports over IA/WI border.

 

[Josh Richardson]

Just a quick update after looking at the Day 1 and a quick glance at the 4.5 km NMM WRF, it appears we could have a sup break out in the Rochester area now. SPC seems to be heading in this direction as well with parameters looking much better over in this area. I will probably head out to that area tomorrow afternoon and just play anything that pops up along the WF. Im usually pretty jinxed when the SPC gives me a 5% TOR threat in IA on a fairly marginal setup but I cant resist a backyard chase.

 

[JF Massicotte]

Right now we are heading to Waterloo, Ia, a littlt bit too far south but N-E Ia doesn't seem to be a good place for chasing. We might be heading up north along I-35 later.

 

[Edward Ballou]

Pretty good mammatus over KBKX right now. Parameters looked okay initially for SE SD until I got to low level shear which wasn't good enough for me and then the cap wasn't strong enough, then the whole forecast seemed to fall apart from there. I'll be sitting this one out and saving my gas money til another day.

 

[Josh Richardson]

Still not liking this threat all that much but maybe I can get decent supercell structure out of these storms. Heading for Spring Valley, MN later on and not wanting to head much further east than that.