5/30/09 FCST: MN/SD/NE/KS/IA/MO/IL

[John Wetter]

There appears to finally be some hope on the horizon with more widespread storms on the plains again.

SPC has outlined a good area of the northern plains/upper midwest area. I personally think it looks capped until dark at least. The 500mb winds are starting to drop south of the Canadian border just enough to be of some assistance and the models are showing a baroclinic boundary through NE that could set a few storms off and then race SE as an MCS.

Still, with the 500 flow back in town and a boundary setting up, this looks better than most of what we've seen the last couple weeks on the central/northern plains.

 

[Skip Talbot]

Well, the WRF seems to like Kansas as that's where its putting the bulk of the instability. We might as well add that state to the title. The fact that there are so many states in the thread title probably means we don't have a real good idea yet what is going down with Saturday rather than there actually being a widespread severe risk.

Speed shear from the northwest flow and instability are more than sufficient for supercells in KS if the WRF verifies, however, I'd be eyeing southern IA if the GFS is on. The inconsistencies make me hold off on narrowing down a target further.

Besides the inconsistencies, the low level speed and directional shear looks pretty weak across the warm front which will hurt our tornado chances. My hope is that we can get some locally enhanced shear near the warm front. Also the flow is paralleling the warm front which might lead to training storms and a quick transition to a linear mode. There should still be a window for chaseable supercells at initiation or with any storm that stays discrete, however.

 

[Michael O'Keeffe]

After taking a look at the 12z GFS and NAM both are agreeing that C/E Kansas will likely be the place to be. Skip sums it up the best but I wouldn't be surprised one bit to see a few tornadoes along that warm front where helicity is enhanced, and the directional shear is pretty good for NW flow, although it isn't very strong, that is what makes the warm front such an important factor in this sort of setup.

 

[Derrick Herndon]

After taking a look at the 12z GFS and NAM both are agreeing that C/E Kansas will likely be the place to be. Skip sums it up the best but I wouldn't be surprised one bit to see a few tornadoes along that warm front where helicity is enhanced, and the directional shear is pretty good for NW flow, although it isn't very strong, that is what makes the warm front such an important factor in this sort of setup.

WRT to your last statement I think it may also be good that storm motion could be parallel to the front, allowing the storms to interact with the boundary for a longer time. As opposed to the situation we see in SW flow when storms spin along the warm front and then go elevated.

 

[Brian Stertz]

Looking at 00z NAM....there a few severe wx parameters stacked up across C/E Kansas incl. good directional shear. An important item though and a limiting factor to tornadoes is seemingly weak LL storm relative inflow winds. Forecasted 0-1km shear is down below 10 kts. until well after sunset. The forecasted 900/850 moisture flux looks a bit troubling as well. A weak 700mb ripple/blip could touch something off during daylight hrs....but it may have a tendency pulse then fall back down on itself and gust out. It is quite probable that some elevated storms could also get going overnight Sat. into Sun. morning over E. Kansas and W. Missouri...with some hail possibly. This is if the forecast trends continue on this course that is. Guess something to keep an eye on...

 

[Sam Hall]

Yes, attm I am thinking C/E KS for Sunday. WRF showing decent CAPE of up to 2500 J/kg, >3000 farther east, helicity blob (3 km) and a tiny bit at 1 km too right there, plus showing not much CIN at a just doable time attm. After seeing an amazing structure in TX yesterday and a mediocre one today that struggled to stay alive due to the backing winds aloft (I believe attm) we will begin heading back north in hope this comes to fruition and/or intensifies...

The wind profiles are worrying me slightly. Though nice directional shear is progged, as you say, Brian, marginal DLS is available with poor surface winds. I am concerned about the NW flow anyway. But better southerly profile, but just a very poor strength as stated. Though WRF showing *slight* convergence in the discussed area (C/E KS) for midday-ish. LI showing as about -4 for midday and then -5 for early evening... Better DPs later in the day around there, probably from the day heating and slight southerly flows and nice temps in the 80s. One more concern is the 700 temps but with that much CAPE if true, perhaps there'll be enough energy to get things initiated in a decent chase-time window...

Will monitor this and post a target area if and when...

 

[cdcollura]

Good day all,

SPC day 3 has this as a "see text" with 5% severe probs, quite a drop from the 30% we saw yesterday and before.

Moisture and wind speeds aloft will be a problem, as with 500 MB NW flow between the trough to the east and ridge to the SW (yes, still a ridge there). Sorry, but I hate that word too.

The only potential I see along this warm front will be near N Missouri / SW Iowa in the higher CAPE / limited moisture.

 

[Skip Talbot]

Looks like the cap might bite in Kansas. Cap index on the 12z WRF erodes enough for initation at 0z in eastern KS, but it quickly fills back in again at sundown. There is also a substantial drop in 3km Cape at this time. This tells me that if storms go up in Kansas, it won't be long before they become elevated. The cap scene is a little better in MO near Springfield and up 44, but shear in general is really marginal. This day is looking more and more like an isolated/local event.

 

[Sam Hall]

I am still thinking of heading to C/E KS for Sat... we are currently in Austin, TX planning on moving farther north again tomorrow. I see what you mean Skip about the CIN for later in the evening... especially for eastern parts. I'm thinking the storms (if they pop) will move easterly as well, seeing the wind profiles at 850, 700, 500 and 250 mb on WRF... not entirely sure of this though, those more expert would probably have a better idea. Though if they do, they should enter better moisture, though less heat, so agree that the bases will probably be high again with hail and winds being main threat maybe IF storms initiate of course.

Though I am hoping they will as CAPE 1500 J/kg or so, with not much CIN for midday up to mid evening. Only thing bothering me as usual of late is the wind profiles. Though are much better than have been recently if the models are correct. Decent LI more S/E KS and up to -8 in Nebraska which *could* also be a possibility, central parts as a nice decent blob of CAPE there too.

Farther south in KS (eastern portion) there is also another blob of 2000 or so CAPE where -4 LI is...

I am going to look again tomorrow of course and then as stated previously find a target.

 

[Sam Hall]

WRF looking better today for region specified in last post for tomorrow... higher CAPE values up to 2500 in C/E and farther E, winds pretty similar in direction as before but better strengths, just worried about the direction of the 500 mb. CIN is looking better now, well not SO great for midday but at least it doesn't drop off in evening hours like it looked yesterday now. Dews looking better too. ATTM I am thinking somewhere near Topeka to begin with. May alter that later as the updated charts come in.

We are travelling to Salina today anyway and then can decide.

 

[Skip Talbot]

The WRF seems to have converged with the GFS for Saturday's solution, and I'm not real impressed with it. I'd consider the Kansas target out of play unless you're already there. Both models have most of the state capped except maybe extreme eastern KS, and then only for a brief window. The 12z 4km WRF did fire something off near Wichita, the inhibition will keep anything over there elevated.

The best shear and instability combo sets up near Evansville, IN in the early evening. The Ohio River and the terrain/roads in this area make this target unchaseable, however. The shear isntability combo does exten NW back into southern IL. Right now I'm eyeing a target somewhere between Effingham and Mt. Vernon, IL for 21z-0z initation. Cape in the vicinity of 2000 J/Kg and 40 knots of bulk shear from the northwest flow should be enough to sustain supercells and the cap looks like its a non issue here. Rather mediocre low level shear will probably keep the tornado threat pretty sparse, however. I also don't see a good focus for initation as there is no well defined boundary forecasted. Perhaps we can get something up in the wake of the MCS that might form overnight tonight and move through that area tomorrow morning. I'm not sold on this setup, but if I think southern IL can initiate I'll probably head down state.

 

[Jesse Risley]

Per the 00Z model runs, both the GFS and the NAM keep the best instability mainly south of I-70 across "Illiana," but the best SRH continues to be depicted closer to the Ohio River valley per the NAM. The latest SREF generally supports this trend, but erring on a more conservative note, especially in regards to both 1KM and 3KM SRH.

However, both the NAM and the RUC prog a MCS to develop over southern IA overnight tonight and move ESE towards the Ohio River valley, clearing the western part of the area of interest by early tomorrow afternoon. The GFS also hints at this feature on the Accumulated Precip. model for 12-18Z. This may also be important in terms of any heavy rainfall and residual moisture in the wake of said MCS.

If enough surface instability can preclude redevelopment Saturday afternoon along any leftover OFBs from the MCS, the enhanced windfield could aid in the creation of an environment conducive to the development of supercells over slightly more favorable chasing terrain between I-70 and I-64 in IL/IN. This will definitely be a day worth watching, but I'm going to consider the morning nowcast to be important in discerning the placement of any OFBs that could pay off for anyone ardent enough to venture out of their SDS.

 

[Sam Hall]

Updated my target as I thought I might from this morning... we WERE as stated heading to Salina today, but as I asked Keith to check the charts on the way, as I was concerned about it being farther east, he agreed so we are now in Blackwell, OK again and going to head E tomorrow to chase MO. We have allowed time to get to several places if things change again, if time in morning will give further FCST and target area.

Best CAPE values being progged for early evening hours according to WRF for C parts of MO, maybe California and around. Failry decent wind strengths but are still concerning me with their directions... CIN slightly worrying too still for the best areas for other parameters until evening hours but just for a short time again and worried about 700 temps, though better than 15 degrees like they have been recently in places!! The blob of CAPE for midday near Marshall and Columbia has FCST CIN to be -80 or so... who knows... I *think* wind directions are SLIGHTLY... marginally... better during midday hours... by the 0Z FCST (for early evening) they are not a continual turn with height but kind unidirectional at 850 and 250 mb.

 

[Andrew Pritchard]

This is late and borderline "NOW" material, but I would not rule out portions of central Illinois this evening. It appears things are moving slightly slower than the models wanted, and that wave may kick off a few severe thunderstorms along the cold front in central Illinois during the late afternoon.

Surface cape values are already reaching 2500 j/kg in the warm sector ahead of the cf. LFC's are already plummeting and a cu field is evident on the last scan which may signify initiation in a couple hours. Bulk shear on the order of 55 knots under that NW flow streak will support severe thunderstorms if initiation can take place. Primarily unidirectional flow will likely be more conducive of quick SE moving wind producers, but some low level shear still remains, and any boundary left from early morning convection could aid in a surprise report or two. Worth watching locally this afternoon.

 

[Scott Olson]

That's right Bryan....