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Chase Case #7

Pat Lawrence

Feel free to state the date and/or location -- first person to give the correct date wins :)

Tornadoes did occur..

Here are the 12Z maps and soundings:






All upper charts use temperature, dewpoint depression, and heights in the station plots. The 300mb map has wind shading at ~ 50, 70 and 90 kts, and includes divergence.


Midland TX
Shreveport LA
Norman OK
N Little Rock AR
Topeka KS
Salem-Lecrone IL
Peoria IL
St Cloud MN
Green Bay WI

I'll add 15Z and 18Z surface analyses later.


All maps were generated by Digital Atmosphere
At first I thought this might be April 7, 2002 (Throckmorton), just because of the surface data out of Texas, but this looks too warm to the north to be that day, since it stayed cool and murky north of the warm front. My eyes are still drawn to Texas, though ... the sounding out of Midland is looking good, showing instability and good curvature, so I'm going to go with somewhere in central Texas for this. Probably another Throckmorton day other than 04/07/02, since tornadoes seem to love that town.
I will start at Duncan, Oklahoma and wait for the next set of data. I will definitely be prepared to move further south depending on what the 18Z data shows, but for now I am going to stay at Duncan.
I'll go for the southern setup as well, I just can't ignore how dry a lot of the northern soundings are. Im also not a big fan of the wind profiles for these areas. However, If I did chase the northern target I would chase Stevens Point, moisture is not ridiclously shallow and should increase, winds should back more and increase in speed and would create quite a good amount of low level wind shear. Most important the OFB from Madison should find its way there for some interaction and may further create enough rotation to ignore other factors.

I prefer the southern target for outbreak potiental. The low isn't very deep but the directional shear looks more classic, wish there was more speed shear but that could change. It looks as though the northern cyclone could deepen more with some help from the left exit region. The fog is okay with me, keeping the LCL's low and creating some differential heating boundaries.

Im not overly sure but I'll goto Dallas and wait for my data...:)
Boy -19c at 500mb with morning obs of of 60/54 and a nice sfc boundary pushing east under strong sw flow aloft. Give me the lfq of that upper jet and the deeper sfc low with those dews. A 996 in the north or a 1011 in the south. I'll take the north target, but a bit south on the sfc trough up there. I'm going to the quad cities in se IA.
Hint Peoria IL, Salem IL and St Cloud MN, no longer have soundings


Yes, but when did they stop launching balloons...that is the key...kinda, sorta :)

Stop giving hints, Mike :D

wow - interesting ... it's not May 4, 1977 is it -

Cool that you used Digital Atmospheres for this, by the way ... this makes me want to get it again -
Okay before more data I will go with more northern Target listed in previous post, I like the moisture/instability/shear of the southern setup more. But I got a *feeling about the deeper northern cyclone, OFB, and backed surface winds...
wow - interesting ... it's not May 4, 1977 is it -

Cool that you used Digital Atmospheres for this, by the way ... this makes me want to get it again -

I don't know the date on this one... but looks like a west TX or western-Central TX day to me. My early aftn data stop is ABI.. H7 cold front coming out of NM and mid-teens 850mb dews at MAF, can't beat that..
I like Central / Eastern TX... Good moisture, nice backed SFC flow, 700MB thermal axis should be pushing east of the region late afternoon (allowing for a weakening CAP), and the shortwave over the SW... Decent shear is present too, so I could imagine this being a day that produces a strong tornadoes.
On a day like this where there isn't a good juxtaposition of shear/instability on the large scale, it's a good idea to target where there is large CAPE and sufficient shear. With this in mind, west Texas looks to be a very good target based on the Midland sounding. I think the surface low or any outflow boundaries were likely the biggest players in the events of this day. Since the flow isn't that strong at 500 mb, it is likely that the surface low near Abilene didn't move too much later in the day.

Target: Aspermont, TX

15Z SFC Maps:



This is really fun! A couple of people are REALLY close to the answer. Just remember I want to know the exact date :) Just to give a small hint, a person narrowed down the area of most concern fairly early on...they were a bit off on the area they chose to focus on, sort of, but they basically pinpointed the main chase area :)

Thanks for taking the time to consider the question I posed to the Stormtrack members!

18Z sfc charts will be posted tomorrow.

Tough call... Any chance we could get some closer-up / zoomed surface map from OK/TX area? I like the rich gulf moisture in the southern plains, along with nicely backed flow in TX east of the low. Deep-layer shear should be supportive of supercells given 500mb flow out of the SW at 45-50kt above southeasterly or southerly surface winds. Farther north (from central OK northward), the surface flow appears a bit more veered (SSW-SW). So, it appears that the best low-level shear is in TX and southern OK, though that may spread northward and northeastward with time. The low in TX doesn't appear to be too strong, but it's movement to the northeast from 12z-15z indicates pressure falls are occurring across northcentral TX and probably into southern OK. Despite this, pressures at SPS and DFW have not changed from 12-15z, and pressure has actually risen at OKC and TSA/TUL...

Thermodynamically, a nice EML has moved over much of the southern plains, with very steep lapse rates evident (e.g. nearly dry adiabatic from 840-575mb on the OUN sounding). These lapse rates, atop rich low-level moisture, have the potential to create very strong instability / CAPE by afternoon. However, this airmass has also created a capping situation, as evidenced by the 12z OUN sounding. Surface obs don't show much in the way of insolation south of the Red River, with partly cloudy skies in OK. Farther north into eastern KS and MO, the cap situation doesn't appear to be AS bad on the 12z soudings, but shallower moisture and the advection of warmer 850-700mb temps may cause trouble later in the afternoon. Given the rich moisture to the south (e.g >67F Tds) and sufficient shear, I'm happy to see that I won't have to drive TOO far (from OUN). I'm a little concerned about initiation in TX given that there doesn't appear to be a very good source for surface convergence... Winds at AMA have turned to the NE at 15z, and winds to the southwest of the "low" at MAF are southeasterly... The more I look at it, I'm not sure how much I believe the position of that "low", not that it really matters THAT much since it's pretty weak. Regardless, it doesn't look like the front is moving too much farther south in west TX given that AMAs winds veered to the NE at 15z. I'd be interested to see what the LUB/LBB observation is...

Target: Waurika, OK.
I'd be interested to see what the LUB/LBB observation is...

Funny, it's on the top map, in the very bottom left corner, but not in the southern map. That makes things a little more clear w.r.t. dryline. Still sitting in ABI awaiting for 18z...
I'd be interested to see what the LUB/LBB observation is...

Funny, it's on the top map, in the very bottom left corner, but not in the southern map. That makes things a little more clear w.r.t. dryline. Still sitting in ABI awaiting for 18z...

AAH, good calll... I didn't look too closely at the 1st / northern map. Sure enough, however, it's there. My bad.
Have debated this, but I think I'm going to try to get ahead of the dryline a bit more ... and I'm going to call Brady, Texas (Brady County) for now. In a normal chase situation we would be zooming in on that dryline right now to see what's going on with it, but since we're eyeballing it I'll just have to settle for this for now.
Hmm. Okay, looks like more cloud cover for my area as my cyclone lifts NE, warm front hasn't moved much. And since tempatures haven't risen all at much im thinking at making a push a little further noth towards the WF and maybe push a tad more east. Hopefully the 18z data brings a little more moisture and some clearing. That airmass looks juicy down in Texas all socked in clouds and such.
I didn't scroll past the 12Z data so I don't know if there's been an update, but based on what I've seen so far I'm driving to DFW, and parking myself east of that surface low.
Ok, scrolled down to 15Z data. I'm staying put in Dallas for now, but a little bird is telling me I may need to drift north before long.

Going back to scroll for more data...

EDIT: Ok, there is no more data :lol:
The upper Midwest action is hard to ignore and will probably produce some surprises around the Quad Cities, but TX and OK are just too good. Mix the Norman and Midland soundings and add some heating and moisture ahead of the dryline -- somethings got to give somewhere. Low level winds aren't as backed as would be nice but the low shaping up over west TX should take care of that.

Based on the 12Z data, I'll be going to Altus, OK.

I guess later data may have come in while I was writing this....

[ed: wish I had a satellite picture. The precip in TX south of me at 15Z is annoying. Guess I'll wander south toward Vernon, TX.]
Sorry this is a little late, I needed to beg forgiveness for yesterday :)

The 18Z maps:



Sorry about not having any satellite pics and the like to go along with this.

Hint: About 3.5 hours after 18Z a deadly F3 tornado was produced.

This is the last post, so it is time to name the date.