3/31/07 FCST: TX, LA, OK, AR, MS, MO, IA, IL

[Travis Carlson]

Looks like a severe wx threat is taking shape sat afternoon and evening. A strong neg tilted low heads into central Iowa and MN. 00Z GFS and 00Z ECMWF show this very well...Looks like as I thought last night that eastern Iowa, and west central Illinois will be in the warm sector setting the stage for severe wx sat afternoon and evening. Only fly in the ointment seems to be morning convection and whether temps can climb into the 70's with sunshine during the afternoon hours increasing instablity. Shear looks good near the warm front and possibly a triple point setup as well. Dynamics look impressive in Iowa as well. SPC has Day 3 this area in an SWODY mention. Overall, im impressed with everything at the moment. Expect this to get narrowed down later tonight and tomorrow...Definately something to watch

 

[Kevin Crawmer]

Most of the discussion on the 3/30/07 FCST thread has shifted to 3/31, so I will start a thread.

There currently appears to be two areas of focus. One being central and eastern TX into the lower MS valley and the other being the mid to upper MS valley region.

In central/eastern TX and into the lower MS valley it appears that convection will be ongoing at the beginning of the period which will be the focus for continued activity later in the period or a focal point for boundary related convection. Moisture will not be a problem and strong vertical shear would be favorable to the formation of sustained supercells...possibly evolving into bowing segments.

The mid to upper MS valley region is where it gets tricking. LSX has been speaking of the possiblity of a severe weather outbreak in this region on some of their longer range forecasts with the consistent limiting factor being the need for clearing from previous precipitation to increase daytime heating/instability. It appears that there will be certain areas that will get this clearing and instability should increase rapidly. Strong surface winds will be southerly and very strong deep layer shear will be high enough to support rotating supercells and the subsequent risk of large hail and tornadoes.

I agree with Brandon in the fact that a higher risk in the mid to upper MS valley region will evolve from the SPC the next few days. I even believe that a small hatched area or even an upgrade to MDT risk is even possible for a small area in this region by Saturday morning.

 

[Brian Stertz]

I am keeping a watchful eye on S.Iowa for an early afternoon show Saturday. It shows that there will be a pocket of instability near the surface low and eastward along the warm front by early afternoon when some clearing occurs. While not the wild shear/instability that occurred yesterday (Wed. 3/28), there is enough directional shear and moderate instability to sustain a few supercells and a few tornadoes. The window of opportunity does not look to be a very wide one Saturday so would have to be in place upon initiation.

 

[Jesse Risley]

I'm gonna say somewhere between S. Iowa and NW Illinois could very well see a few supercells on Saturday. While models may have a better handle on this by tomorrow, it's appears to remain uncertain as to how much clearing will take place (and where) by Saturday morning. This has the potential to be the first "respectable" outbreak of 2007 for the Eastern MO/Central IA/and Northwest and North Central IL region, but then again it could be marginal at best.

 

[Kevin Crawmer]

I may have overstated the risk possibilities when I said it could go to a MDT by Saturday morning, but I do think there is a good likelihood for isolated supercells and tornadoes given the dynamics in place. A widespread event does not look likely unless significant clearing happens. I know the road network improves about 45 miles into Iowa, so I will keep my fingers crossed for something north of there.

 

[SteveCarter]

Looking at the latest GFS and NAM soundings, I'm thinking more like SUNDAY with this, and from St. Louis to Champaign, IL. Naturally, they disagree somewhat, but are closer than usual...lol After not being able to go to the Plains Wednesday, I'm ready to go ANYWHERE right now!! Anyway, haven't had a chance to really get into the nitty gritty about this weekend, but I may start a Sunday thread for IL/IA/MO. Any thoughts about SUNDAY vs SATURDAY?

 

[Kevin Crawmer]

I sure hope it doesn't slow down enough to put the show on Sunday. I also think the MODS may need to add MN/WI to the list for me. Depending on the position of the low and warm front, they could be in play also. The focus of any convection will be any areas that see clearing ahead of the triple point and along the warm front. There should be some isolated pockets of high CAPE values to kick things up.

The kicker will be what happens tomorrow. Hopefully most of the convection will stay in central/northern MO and clear out through the day. It will be interesting to see if the models line up more as I know the GFS has been the odd guy out at times this week.

 

[Kevin Crawmer]

Here is a collection of maps from the RUC model. It has handled things fairly well with this week's storm.

http://maps.fsl.noaa.gov/disp2.cgi?/w3/rapb/plots_13km_dev/.//+sa+am+69

As you can see it puts the center of the low in the vicinity of western IA at 21:00z on Saturday. Surface temps are in the 60s for the southeastern 1/3 of Iowa at this time. Given the availability of instability, initiation should begin at this time in my opinion.

 

[Brandon Sullivan]

This is looking more interesting by the run! NAM has really stepped this bad boy up... Shear is looking a little better... And CAPE is pretty much left unchanged... If we get any insolation, we could have our hands full! Well, as for anymore thoughts, I am still pretty blank.. It is definitely going to depend on the amount of sunshine.. Shear and Instability and Moisture are all there..

 

[Travis Carlson]

Really excited about this setup...My eyes will be on the SPC day 2 outlook tomorrow. Parameters are coming together each model run for a decent severe wx outbreak Sat afternoon/evening and now possibly extending into saturday night with a potential squall line. Sunshine will be critical as previously discussed saturday afternoon. At this point is seems that we should get enough sunshine to greatly influence instability and the area will be in the warm sector. Supercells will be possible early on in the convective cycle with storms becoming surface based. Later on... I expect these supercells to form a squall line which will lead to a heavy rain and flooding threat overnight saturday with the slow movement of the storm system. Moisture will be in place, CAPE looks decent, shear looks good as well, strong dynamics in place, and surface heating...storms should have no problem getting rambunctious saturday afternoon...I'll be chasin this one for sure.

 

[V. Gensini]

Here is my two cents...I agree that this looks like a decent setup. There are a few things that I do not like however. These early season setups are almost IMPOSSIBLE to forecast this far out. As most of you would agree, you wont be making a chasing decision until early Sat. morning, and that will highly depend upon the postion of the warm front and surface low...Moisture return will hopefully not be an issue... As stated earlier, morning convection may be a problem, but there are hints that things may clear out for a show in the afternoon. I am throwing out the models at this point for the simple fact that they havent done very well with timing with the past few systems. GFS has also been backing up this sustem and centering it somewhere over council bluffs IA. Either way i hope to be chasing along the warm front in hopes of some good action. Good luck Brandon and to all others that may be chasing on Sat. I do disagree that Illinois has a bad road network by the way.... Looking forward to an SPC update for that area...

 

[Kevin Crawmer]

Well suprise-suprise, the models slowed down a little more putting the best areas further south of the suspected area from yesterday. A more pleasant suprise is the better chances of clearing tomorrow afternoon ahead of the front. I am not incredibly excited about the directional shear, but with everything else in place if some small pockets of heightened instability will pop up then we should have quite the show. I don't think at the moment that there is favorable enough directional shear and instability present to support long-track tornadoes, but several marginal tornadoes could form before the storms move into more stable environments close to the MS River Vally. My target at the moment (without collaberating with my chase partners) somewhere between the area of Kirksville and Macon in NC MO. Given the heightened risk area in this part, I wouldn't be suprised to see a hatched area at 1730z and possible upgrade tomorrow morning like I suggested yesterday. All in all I am pleased with how things are coming together as I was expecting to wake up with a mess this morning.

 

[Brandon Sullivan]

OK..Contrary to DVN's thinking, some of the models this morning do show some SCL shear, mainly of the directional variety.. MLCAPE values have went down, a considerable amount.. A thing to think about is outflow boundaries from morning convection.. Any storm that can move over an existing boundary will really enhance the shear.. I love how the models have really hopped up on the shear.. Especially the boundary layer area.. Whole area should be sitting around 40 Kts... Right now, I really want to hit somewhere between SGF and IRK.. Or about 100 miles SW of Quincy.. I just think this could be a nice spot... Or, maybe stay close to home and ride the front.. Im not sure yet.. It is still conditional on the amount of daytime heating.. But with temps in the 70's and 55+ degree dp's. Convective temps will be hit in the afternoon, for rather rapid development.. Right now, not setting any definite targets, but am collaborating with some locals.. Good luck to everyone..

 

[Brian Stertz]

I am favoring C. Iowa

I'll be taking my chances on low topped supercells up in Iowa in the Fort Dodge area. It stands out that the good fetch of east winds will be across Iowa...north of I-80. It will not take too much radical instability given the strong wave that will lift across C. Iowa by afternoon. This probably is not a strong tornado setup, but the LL shear is quite good as is the upper divergence over N/C Iowa. The chances I will be chasing tomorrow have gone up significantly after quick scanning the 12z ETA data.

 

[John Farley]

I am encouraged about tomorrow's chase prospects looking at this morning's models. I think there will be tornadoes somewhere in northern MO, southeast IA, and/or western IL. Too early to narrow down just where, though. I am pretty confident that the very strong dynamics will overcome the lack of instability - the models agree in projecting storms, despite the lack of CAPE. This makes sense, as the upper flow over the area of interest will be strong and divergent. And if storms fire with this kind of shear, I think some supercells will be likely.

This doesn't mean it will be an easy chase, though - issues will include a LOT of storms (SPI pwat is projected at 1.28 at 0Z by the WRF), so it will be hard to hone in on the best one, and also fast-moving storms, as is often the case with these early-season setups. As is often true in this area, crossing the Mississippi River could be an issue, although the large northward component on storm motion might make this a little less of an issue than on some other days.