4/18/06 FCST: IA/MO/IL/AR/TX

[Chris Foltz]

Wanted to go ahead and kick off a thread for the potential setup on Tuesday. Won't go into too much detail as it would be pointless this far out. Though currently several hundred miles apart, both the GFS and the NAM depict a negatively-tilted closed circulation at 500mb. Broad area of >60 to near 70 Td's are forecasted to push up across the western half of Missouri into southeastern NE based on the 00Z 4/16 runs. Obviously the models have been overdoing the moisture so far this spring as they are prone to do. However, if mid-60 Td's can be realized with surface temps in the mid to upper 70's, LCL's would be low enough to support the possibility of tornadoes. NAM showing srongly backed surface winds with 850-mb winds out of the south and 500-mb winds out of the southwest which would provide nicely curved hodographs. Will obviously have to see what the future holds but it bears watching.

 

[Bob Schafer]

12z NAM from this morning has tons of instability in W MO @ 00z 4-19 (e.g. CAPE>4k), as well as big-time UVV's @ H85,700, & 500. Hodo's will reflect that some storms will rotate, but there are some "oddities". For one, because the sfc low is depicted as centered invof SGF, and isn't deep (~1000mb), sfc winds will be light up and down W MO. And look at the H85 winds W of the CAPE...

My thinking attm is that lack of sfc winds will result in storms quickly going to hell and creating an awful MCS scenario right away. Successfully witnessing a tornado may be a total crapshoot where you have to depend on OFB's kicking up secondary convection and enhancing SRH. Either that, or you have to wait for high-based storms to get rooted as they progress eastward and get over the moisture, as NAM shows a disconnect between helicities/theta-e ridge (@00z).

This post probably doesn't even make much sense, LOL. I guess I'm confused.

On the other hand, let's just wait for the models to evolve over the next 48 hours......

Bob

Oh, I also want to ask: What's the terrain like in W MO? I've never chased there.

 

[Mike Smith]

The westernmost counties in Missouri aren't bad. From Platte County (north Kansas City) to Jasper Co. (Joplin) it is low rolling terrain. Highway 71 is the main north-south highway.

Far northwest Missouri (north of KCI) has somewhat higher hills and would be a little more difficult.

Similar conditions in the far eastern counties of Kansas. Highway 69 is main north-south highway.

 

[Mikey Gribble]

I am also worried about 850mb winds being so weak. If this verifies, we could be in trouble. I can also be optimistic and say I don't see this being much of a problem with storm motions strengthening throughout the evening, (NAM showing AOA 30kts by 00Z) SR inflow level winds should still be strong enough for long-lived storms. That is based on the shortwave being open, giving us better directional shear and more easterly storm motions. I am a little worried about new convection going up along outflow boundaries, but as long as one storm gets out ahead of the convection going up on it's flank, it shouldn't be a show stopper.
One of the things I like is that there is a 700mb dry slot that moves in during the afternoon. The shear vector ought to be normal enough to the boundary for discrete storms and with >40kts of deep layer shear supercells will be the favored mode of convection.
I am a little bit worried about the timing of the shortwave. Hopefully storms will go early enough to give us a couple hours of daylight to work with. My biggest concern with this setup is weak inflow level winds. IMO that is the one thing that needs to change for us to have a good chase day.
NW Missouri isn't a fun place to chase, but it's doable. The farther East you get, the worse the terrain gets so let's hope this slows down a little bit.

 

[Mikey Gribble]

Now the problem is the cap. This just goes to show you that there is no reason to worry over little details when you are several days out. Bottom line is that it's almost May and we have a trough coming in with good moisture ahead of it, so we should be in business.

 

[Jason McKittrick]

Although Saturday resulted in some pretty awesome structure and several tornadoes, moisture was still mediocre. I posted in a previous forecast thread that I was not going to get too excited until near 70 DP's made it to Dallas. Well tonight I see there is a 70 DP being reported along I 20 near Tyler, TX, and widespread low 70 DP's across south Texas for the first time in quite a while. It now looks like the moisture is available for some blockbuster storms. however as far as Tuesday is concerned I am not a big fan of cold front storms. IMO, cold fronts seem to produce squallines more often than anything else, but who knows looks like storms will be in this years favored location; Missouri. If I were willing to travel that far I think the triple point would be the best location for anything interesting. Looks as if the GFS, which did very well in forecasting Saturdays event, is forecasting the triple point near Joplin at 18z and moves it to near Quincy,IL by 00Z.

 

[Matthew Crowther]

Tomorrow is an interesting forecast problem- the SRH and CAPE look good at first glance for tornadic supercells in Missouri- but there quite a few question marks. The 500mb flow is quite anemic at only 25-30 kts, there is a nasty cap in place so CI is in doubt before dark (the NAM and WRF break out precip in the warm sector right at 00Z) and it is a cold front with weakening low pressure (as mentioned above). So my gut says a squall line will develop at 00Z- there could be a few weak tornadoes, but it does not really look like a good chaseable scenario.

Matt

 

[Mike Johnston]

Kind of surprised there hasn't been more forecast interest in tomorrow's setup. Plenty of surface moisture advecting nww'd...even now the 60td gradient across the south nosing into SE OK (check out the 65td Mcalester OK last hour), and broad area of surface wind field out of the SE overnight and into tomorrow should carry >65 td's up to N MO by tomorrow afternoon. Closed lows at both 850mb and 700mb over Wyoming, with strong dig behind; 500mb temp at -32 over northern Nevada, pretty low for this time of year. Already, very steep lapse rates across the southern plains. As an indicator of potential for instability, find it interesting to see a -6 lifted index over NE TX even this evening. Models show lee surface cyclogenesis to develop in a negatively-tilted fashion. CIN should hold across the warm sector until just the peak of heating. If CAPE comes anywhere close to the 4,500 j/kg over NW MO as NAM model shows, potential for severe tomorrow over central plains, especially MO Valley, could be notable.

 

[Tony Lyza]

Kind of surprised there hasn't been more forecast interest in tomorrow's setup. Plenty of surface moisture advecting nww'd...even now the 60td gradient across the south nosing into SE OK (check out the 65td Mcalester OK last hour), and broad area of surface wind field out of the SE overnight and into tomorrow should carry >65 td's up to N MO by tomorrow afternoon. Closed lows at both 850mb and 700mb over Wyoming, with strong dig behind; 500mb temp at -32 over northern Nevada, pretty low for this time of year. Already, very steep lapse rates across the southern plains. As an indicator of potential for instability, find it interesting to see a -6 lifted index over NE TX even this evening. Models show lee surface cyclogenesis to develop in a negatively-tilted fashion. CIN should hold across the warm sector until just the peak of heating. If CAPE comes anywhere close to the 4,500 j/kg over NW MO as NAM model shows, potential for severe tomorrow over central plains, especially MO Valley, could be notable.
[/b]

One of the latest WRF models is showing a whole host of supercells breaking out in the warm sector tomorrow. I am very concerned that Missouri may face another dangerous situation tomorrow, something those poor people don't need.

 

[Andrea Griffa]

http://weather.admin.niu.edu/chaser/tempgif/3546.GIF

I like so much the zone near Columbia where this sounding shows a very strong helicity with values of nearly 380 m2/s2 plus 3500 J/kg of Cape. Too bad for the mid level flow that remains a bit weak, but it could be sufficient for some slow moving supercells, given the strong instability

 

[Brandon Clement]

http://weather.admin.niu.edu/chaser/tempgif/3546.GIF

I like so much the zone near Columbia where this sounding shows a very strong helicity with values of nearly 380 m2/s2 plus 3500 J/kg of Cape. Too bad for the mid level flow that remains a bit weak, but it could be sufficient for some slow moving supercells, given the strong instability
[/b]

I have to agree with you Andrea. If I were chasing today my target would be Columbia where the winds look to be nicely backed, there is an excess of 3000 j/kg cape, effective shear greater than 40 knots and 0-1 SRH near 200 m2/s2. The current obs show fog/mist with a td of 51. If the forecast holds true there should be plenty of clearing with temps around 80 and upper 60 td's allowing the LCL to stay low. To me there is just something about the areas that start off with fog/mist or light rain with dewpoints around 50 and get the rapid heating and moisture return by early afternoon. Wish I could make the chase today and hope that you all have a good day. The people in Mo have to be tired of seeing these forecasts and I hope we don't hear of any more destruction or loss of life today.

 

[Ben Prusia]

Surface OB's already indicating dewpoint temperatures reaching the lower-mid 60's in SW Missouri at Joplin. The 12Z NAM is forecasting to bring up juicy air to the middle parts of Missouri where a 70 degree isodrosotherm line reaches as far north as Columbia, producing forecasted instability values nearing 3,000/4,000 J/Kg. Both the 12Z NAM and 12Z RUC are in agreement with the strength (998mb) of the surface low and the location of the low (between Kansas City and Columbia along the I-70/US-50 corridors). A warm front progged to be stretching from the TP to points E and NE and then SE. Areas a little ways S of the warm front may have higher LCL's combined with a strong CAP (850mb temps 20+ degrees) to inhibit any surface based thunderstorm development. Best initation chances appear to be at the TP and along the WF. My preliminary target choice appears to be along I-70 or US-50 between Kansas City/Columbia/Jefferson City. 12Z NAM forecasted soundings at a preferred target of Columbia at 0Z shows a modestly low LCL around 750m, and modest helicity values with 0-3km readings above 300m2/s2. Instability looks rather extreme and overdone at over 5,000 J/Kg. EHI looks great for development with 1km values of 5 and 3km values above 10. Forecasted storm motions only appear to be around 15-20kts, looks like a chasable situation in a not so chasable state. Good luck all!

 

[Todd Sprinkmann]

I'm in Columbia this morning and talked some with the fellow at the hotel front desk.

He asserts that the area north of Columbia up to Moberly is mostly flat and open farm fields. I kind of grinned a little skeptically and he said that he really is on the level (pun intended).

He also went on to say that as you get down toward and south of Jefferson City, things get a lot tougher. Hills, twisty roads, all the stuff we love Missouri for. :huh:

Just relaying what he told me. It might help someone so I'm passing it on.

I plan on keeping the box bordered by Sedalia to Carrollton to Moberly to Jefferson City in play, with a preferred target of Marshall to Boonville. I now see the Missouri River runs between Marshall and Boonville, so need to keep that in mind too.

 

[Jim Cross]

I agree with Ben the best place to be is along 70 with a option to go either direction depending on the cap and the position of the low.Right now im getting ready to leave for Concordia and gather data and go from there.Good luck to all that makes it out today.

 

[Joe Zemek]

Forecasted storm motions only appear to be around 15-20kts, looks like a chasable situation in a not so chasable state. Good luck all!
[/b]

IF the WF can move further north the chase terrain improves dramatically over the I-70 area.

http://www.rap.ucar.edu/weather/model/disp...rs=hr06hr09hr12

If 65Tds do make it up to the Chilicothe area around 00z as advertised, that is chaseable terrain. You still have hills and trees but to a lesser extent. Since the cap is also advertised to hold till then this would be a better chase scenario.

This will probably be one of those days to pick a good spot, be patient, and hope things pan out.