6/20/06 FCST: MN / IA / NE / WI / IL / KS

[nickgrillo]

Pretty cool setup the latest 12z NAM run paints across southeast IA (and into much of Illinois) with strong 500mb flow on Tuesday. Strongly backed low-level flow along the warm front combined with strong flow aloft to yield highly favorable deep-layer shear profiles for supercells will exist near the front -- attached to the sfc low in northcentral MO and curving east-southeast into IL. Given the nice +30kt southwesterly 850mb flow atop backed sfc flow, hodographs should be large with favorable low-level curvature... For that matter, the NAM currently proggs >300m2/s2 0-3km across much of the region (strongest near the front) given the magnitude and spin of the flow in the inflow layer. With the moist boundary layer also in place (with relatively-handleable t-td deficits) the NAM also shows widespread 2500-4000 j/kg of CAPE (with very strong to extreme instability by lifting both surface and mean-layer parcels) and localized pockets of eroded CINH (so boundary layer air may freely rise to LFC and initiate DMC). I do, however, wish the timing of that shortwave would slow down a bit (to help induce ascent further west into the warm sector during peak heating).

Basically, the ambient environment is pretty supportive for organized severe weather (and there could be 2-3 day period of organized convective days across this region) including strong supercells. I'd so would love to at least get a Derecho day around here... :huh:

EDIT: Corrected for headline date...

 

[sebenste]

Well there are three scenarios that I see potentially playing out...and two of them seem good for tornadic activity across the NE 1/2 of IA.

(Personally I'm still going with option 1 because I haven't seen anything to change my mind from several days ago. LLJ pivoting in with e-w boundary roughly parallel to upper flow. It doesn't get much more classic than that for a long lived complex of storms. I think that as it establishes a cold pool Monday Night it should become pretty progressive so overall the WRF situation seems reasonable. Then redevelopment back in Iowa is to be watched for supercellular characteristics. We shall see...I am still mulling whether or not I want to chase. It would be nice if there was more of a tornado threat in NW IL...I'd be all over that.
[/b]

I'd like to go with a 4th option. Several things bug me about the model scenario. #1, first and foremost, is that at 12Z, the main energy for the system this week was still partially offshore and poorly sampled by upper air data. Next, the GFS has a propensity to push said systems way too fast across the country, partially because it doesn't initialize and/or deepen troughs out there well.
Per the 12Z NCEP discussion:

NAM RUNS BACK TO 00Z SHOW A SIMILAR EVOLUTION SFC AND ALOFT.
COMPARED TO YDAYS 12Z NAM... LATEST RUNS ARE SLOWER WITH HGT FALLS
PROGRESSING ACROSS THE NRN PLAINS/UPR MS VLY AND A TAD MORE
AMPLIFIED WITH THE TROF EXTENDING SWD FROM THE CLOSED LOW ALONG
THE US-CANADIAN BORDER. THIS TREND YIELDS SLOWER TIMING WITH
PLAINS LOW PRESSURE BY DAY 2.

THE GFS HAS BEEN TRENDING MORE AMPLIFIED WITH CNTRL CANADA FLOW BY
DAY 3... WHICH RESULTS IN A SLIGHTLY FASTER TREND WITH MID LVL HGT
FALLS/SFC LOW PRESSURE OVER THE UPR MS VLY/GRTLKS.

So...this means that the main event could be even as far west as Nebraska and South Dakota, with a second, less dramatic perhaps show on Wednesday. We'll see, but I'm not hopeful for a close chase
at this time. I hope that changes.

 

[Ryan Pfannkuch]

Well, this one has my full attention given things could go down right in my backyard...

18z NAM maintains very interesting setup for IA with 50-60kt westerly mid-level speed max moving across the MN/IA border area by 0z on top of 20-30kt SW 850mb flow punching across central-northeast IA. At the surface, both 18z NAM and especially 12z WRF depict a surface low taking shape over WC IA with backed winds along a warm front running from NC into EC parts of the state providing very impressive low-level shear profiles. With deep layer shear from 40-50kts over the north 1/2 of IA things could get interesting for a few hours.

Obviously the effect of any late night/morning convection won't be known until the potential event nears, but at this point, I am focusing my attention on the north-central IA region in an area roughly bounded by Fort Dodge-Mason City-Waterloo. If the 12+ degree 700mb temps surge farther into western IA, as suggested by the 12z WRF, the show could be a little later and closer to the IA/MN border east of I-35.

Although the overall setups differ, the SFC features could generally resemble some significant past IA events such as 5-11-00 or 6-11-04 depending on how well-defined any warm front can become. Now we'll see how well the mere mention of those days jinxes this whole thing!

 

[David Draun]

It could definitely be an interesting day tomorrow to my west, and here during the evening and overnight. Chicago news/weathercasts are downplaying the threat as usual. I do believe a violent bow-echo may be located in E IA/NW IL/SE WI around this time tomorrow night. Dewpoints should shoot well into the upper 60's and low 70's as that warm front starts to roll northward. Shear looks good for supercells and tornadoes, mainly west of I-35. One negative I see: Very strong heating may completely remove the cap early, so storms will become numerous quickly. The convective mode at initiation will be supercell though. I think SPC will go for a MDT risk tomorrow, especially over IA. I'm too busy to chase tomorrow, otherwise I would be sitting near Des Moines right now for a quick jaunt to a target tomorrow. But I will definitely enjoy the onslaught of the squall line tomorrow night!

 

[Kurt Silvey]

Well, this one has my full attention given things could go down right in my backyard...

Obviously the effect of any late night/morning convection won't be known until the potential event nears, but at this point, I am focusing my attention on the north-central IA region in an area roughly bounded by Fort Dodge-Mason City-Waterloo. If the 12+ degree 700mb temps surge farther into western IA, as suggested by the 12z WRF, the show could be a little later and closer to the IA/MN border east of I-35...
[/b]

My thoughts exactly . . . Unfortunately I can not get out of Omaha until about 21z. I can make Ames in about 2 1/2 hours from here, but I would like to get slightly north and east of there, so I could be playing catch up. Let’s hope the AM showers clear out early, but as this is “06â€￾ I’m sure something will be around to screw this up.

 

[nickgrillo]

It's late and I'm tired, so I don't feel like writing much of anything... At any rate, I've decided to sit this one out (considering my target would be Mason City, IA along I-35 in northcentral IA and that's a solid 8.5hrs from here). Nonetheless, the strong instability and low-level shear profiles during the afternoon along the effective warm front could yield promising results, including the potential for a few (surface-based) supercells (with the large-scale ambient conditions charactorized by very favorable low-level kinematic and thermodynamic profiles -- with 35-50kts of 0-6km shear) with NAM forecasting large and cyclonically curved hodographs along around I35 (and eastward) in northcentral and northeast IA with 2000-2500j/kg of MLCAPE quite possible north of I-80 by 00z. Like previously mentioned, tomorrow will be a VERY complex situation (and the models shed little light on it), and the WRF certainly doesn't make tomorrow look tempting (with nothing initiating along the warm front during the day -- with a small-scale complex initiating south of the warm front in southwest IA around 03z and a powerful bow echo racing through northern IL around the same timeframe) and I don't feel like driving a solid 500-600 miles tonight to get to the TA in this kind of situation.

I'm pretty confident in SPC's decision to issue a MDT for the SWODY2, given the strong deep-tropospheric jet digging into the southern Great Lakes and a deep, moist boundary layer below fast midlevel flow (but that's another thread...) with the potential for numerous small-scale and large-scale damaging convective bands to occur throughout the day on Wednesday (from northern MI southward into northern/central IL and IN).

 

[Jason McIntosh]

EDIT A: Well SPC went Moderate on SWODY2 apparently they think there will be a continuation of the MCS from tonight and also another one developing in E IA/S WI/N IL and then moving east again. Several large swaths of wind damage. Cannot wait for the day one now!

EDIT B: Well Slight Risk on first SWODY1 and I don't blame them either. Basically echoed my concerns on complex forecast. Really shocked by hatched 30% hail and 10% tornado over SW WI, was not expecting afternoon development this far east but I suppose it is possible. Great, now I have a whole new set of concerns and I have to consider a chase now. Time to watch a movie...
[/b]

Wow it's been a while since i've been on here chating about the next days possibilities. I will say this; regardless of what happens or doesn't happen today, the last few weeks of sporadic tornadoes(in WI) when everything wasn't there should show us all that there is much to learn about the evolution of a tornadic supercell.

But on to the goods of the day. The warm front will be the big questions of the day. It looks like a classic setup with the moisture, instability, wind shear, and low moving right at LSE. I can't sleep when systems like this come because it is complex! All i know is i'm due to see something. May it all come together and we might have Aug 18th real fast again. We will know in 12 hours i expect.

2 things i like though about tomorrow is the 2000-4000 Cape and 40-60 Kt wind shear. Ingrediants for explosive supercells that rotate!

Let's see it!

 

[David Draun]

Well, I must say, what a difference a day makes. It could be an excellent setup this afternoon along that warmfront. But convection will be widespread. Any outflow boundaries from this morning's convection could boost the short lived tornado threat. I'm thinking of heading out to central/western IL this afternoon to see if I can get something. And the air is juicy, folks. Mesoanalysis is already showing the 70+ dewpoints on the move south of the warmfront. Let's get some nice low LCL's I believe there will be a few nasty supercells across N IA by about 3pm.

 

[Andy Hamm]

Complex is certainly the word of the day for today. I am a bit concerned with all of the convection in SE SD and Southern MN this morning, though it is quickly moving east and may break up later this morning. It is nice ot see plenty of shear for a change...I am so sick of the pulse severe that we have had up here in northern WI/MN the past month or so. I am thinking of heading south this afternoon, maybe heading towards Albert Lea or just into northern IA. Maybe finally a good chase day...?

-Andy

 

[Scott Roberts]

I'm making a two-day trip out of it, leaving Wichita at 8am headed for Des Moines, to make a target decision there.

Anyone along my route who is on the fence about going...call me and we can meet up. I'm taking the van, so could chase with a group as big as 4. We can meet somewhere along I-35. Anyone local to the IA/IL/WI area who would like to come along is welcome.

316-617-9178...first two to four people!

 

[Bill Schintler]

Chase target:
I-90 mile marker 64 in MN (21 miles east of Worthington).

Timing:
Storm initiation 6 PM CDT.

Comments:
Supercell storms capable of tornadoes.

Discussion:
Large-scale flow has deamplified over the last 24 hrs, and by 00Z divergence in association with mesoscale coupling between a jetlet on the SRN periphery of the H25 main jet should provide enhanced lift. At the SFC, strong theta-E advection has taken place overnight, assisting in the EWRD translation of the advertised MCS now lifting through IA. Very messy SFC map, with a myriad of SFC boundaries. One such boundary, clearly visible on the visible loop, is along US-34 in SWRN IA/ERN NE, and is diving to the SE at 25mph. Three additional boundaries are noted in NWRN IA as per 14Z SFC and radar analysis. One is analyzed along an Albert Lee (MN) to Algona to Sioux City line, and is nearly stationary. Another is along an Estherville to Spencer line and is lifting to the NW at 10 mph. Finally, the KFSD radar loop ending at 15Z clearly shows an E/W-oriented boundary in Lyon and Osceola counties moving to the N at 10 mph.

Regarding model performance, the last four GFS runs have been very consistent with regard to SFC features and moisture. Less consistent have been the UKMET and GFS, both of which have trended further south with features. Moisture return at 14Z has actually verified better then forecasted by guidance, with the 12Z NAM forecast actually about 5F low in IA and the GFS a few degrees low on 14Z dewpoints. Neither model has a good handle at all on QPF in association with the ongoing MCS. Clearly, airmass recovery will be problematic today so renewed SFC-based convection will be a challenge at best as strong inhibition will remain in most areas today despite insolation in NWRN IA area after 21Z. The NAM does, however, suggest a localized area of strong, uninhibited destabilization between US-18 and I-90, and west of US-169 in IA. This does actually seem plausible given the NAMs handle on current SFC dewpoints and temperatures, plus the fact that insolation will commence in this area from west to east over the next few hours as the CI shield is retreating at a good pace.

Given SFC-based convective initiation in NWRN IA this afternoon, strong instability with SBCAPE’s to 3000J/kg will be coupled with decent deep layer shear in the 50kt range. Synoptic progs show weak hodographs with veering SFC flow after 21Z, however the aforementioned OFB’s will result in locally enhanced hodograph curvatures as well as providing the SFC convergence to overcome the CIN.

- bill

 

[Jason McIntosh]

It looks as if the MCC that moved into MN and IA this morning is starting to weaken rapidly as it gets closer to the Mississippi River. Rapid clearing is now taking place in SW MN and W IA. I think we still have plenty of time to watch this come together. I believe that will be after 5pm CDT. Right now i'm thinking of heading towards Waterloo, IA area around 3 pm. I would leave earlier, but i need new tires for the rain!

I can't wait until the 1630 comes out.
Lookin' good.

 

[Scott Lincoln]

Well the SWODY1 is out and they continued the Slight Risk. No mention of damaging wind threat evolving with an MCS, just talk about what may happen in Iowa later, including possible tornadoes. That would seem to be the place to go!
[/b]

The best part is that the new Day1 is like the same as the last day 1..... literally just minor tweaks but otherwise its the same.

 

[Jeff Snyder]

18Z update shows pressure drops continue. If you look at 700 mb temps you can see a bubble of warming over NE IA. Basically went from 8C to 12C in an hour. Very cool. Compressional heating. Lots of STRONG wake low signals.

[/b]

Are you sure it's actually a wake low and not just a signal that the cold pool associated with MCS outflow is moving away from the area? In other words, it may not be so much that a low exists there, but that the mesohigh is moving away from the area. Current surface obs still indicate that pressures in se MN and ne IA remain high relative to areas farther west and southwest.

The forecast remains rather complicated, largely owing to the obvious effects of the MCS this morning. Models agree in shunting the strongest low-level flow southeastward away from southern MN and northcentral and northwestern IA by late afternoon. Insolation in the wake of the MCS is allowing for destabilization, but CINH remains very strong across all of the area. I haven't seen any 18z soundings (I know MPX will send one / has sent one), but I'd be nice to see what DMX/DSM shows (if only they had one...). The latest RUC continues to indicate that boundary layer flow will veer rapidly in the next 3-4 hours as mixing increases. This mixing also beings to drop dewpoints at the surface... At least per the RUC, a warm-front may be located from near Austin MN into far northeastern IA, with stiff southwest winds in the warm sector and northwesterly surface flow across the western parts of the SPC 10% tornado prob area. It's worth noting that the NAM is a little less aggressive in veering the sfc flow, which isn't entirely surprising since the RUC seems to often be a little too aggressive in mixing. The NAM didn't have a very good handle on morning precip, unfortunately.

I'm actually interested in seeing what happens near and just southwest of Des Moines. It seems that the models agree that that area will be more likely to see convection by early evening given the longer amount of time (relative to other areas to the N-E) they have seen insolation in that area. With the heart of the 850mb and 700mb jets over that area, low-level shear should become moderate-strong by evening as well. There probably won't be a whole lot of directional shear (assuming the winds veer as the higher-momentum flow from 850mb mixes down, as some models project), but supercells still seem like a pretty good possibility. Models (RUC, NAM, NCEP WRF-ARW) indicate that low-level flow over northern IA and southern MN will become relatively weak by 0z, with 10-20kts at 850mb, so I'm not entirely sold on the tornado threat in that area (assuming they destabilize sufficiently to allow for surface-based convection).

 

[Kiel Ortega]

I'm actually interested in seeing what happens near and just southwest of Des Moines.
[/b]

Me too...those quick winds on the Fairbury NE profiler should be getting into W IA...guesstimating with the Slater IA profiler, might have some very long and curved hodographs in W IA later this afternoon. RUC analysis shows the area is capped pretty well, but with lots of WAA in the area and some sunlight, I don't think it'll be too much of a problem.

The wake low thing, I think if it is fomed/forming, it will veer the winds especially with the best pressure drops in N/NE/ENE IA. That won't help with the hodographs, as the sfc winds would want to veer towards the dropping pressures. Looking at an 8 hour loop of the sfc, looks like this is already occuring. Some gentle SE/ESE winds in W IA would be great for later and some long, curved hodographs