4/20/07 FCST: KS/OK/TX

[Michael O'Keeffe]

Well it looks like Friday may be shaping up to be a decent chase across parts of KS/OK/ and the TX Pan. The latest NAM is showing 3500j/kg of CAPE across SW Kansas close to Dodge City and points southward. Shear looks decent and this very well could be a day before the big day event that always seems to be rewarding.

 

[Skip Talbot]

Thanks for bringing this one to my attention, Michael. If I can get two chases in on a marathon run, it makes it all the more worthwhile to go.

According to the 12z WRF: The directional shear looks great on this day. 850's are out of the southeast and and 500's are almost west. Even surface to 850 has quite a bit of veering with height. Saturday's cyclone is still far off, however, so I'm wondering if we will have any focus here for initiation? There isn't a front in sight except the dryline (which is pushing west, not buldging east). The magnitudes of these winds are going to be quite modest, although 850's look pretty good, 500's look fairly weak as do surface winds near the best instability in KS (the lack of the cyclone again). The precip forecast is pretty quiet accept off to the east by the MO border, further from the instability and shear.

This day might spawn a chase if we can get some upper level disturbance from the approaching system to come into play, and if those dewpoints verify. On the other hand it might just be a quiet day building up our moisture return for Saturday. A good day to watch, and let's see if this gets SPC's attention.

 

[Adam Atkins]

Good instability develops during the day in the pocket of progged 60's Tds, probably due to a lot of evapotranspiration and evaporation after today's and previous rainfall...it seems there won't be a lot of mixing in the boundary layer so these Td's are pooling at the low levels...strongly capped IMO. Southeasterly surface winds up the front range and all along the plains means it's going to be hard to get any decent surface convergence for an updraft. The shear is definitely there, but I'd actually look further west maybe for some upslope.

This type of day really is in need of some strong surface forcing because there just isn't a lot of upper level support with the trough way out west. I wouldn't rule out some elevated storms from isentropic lift, especially during the peak moisture return Thursday and Friday.

Just setting the stage for the big weekend, though right?

EDIT: Just checked ensembles and it shows mid-level ridging during the period which would reinforce my notion of a warm air advection (strong capping)..height rises during the day Friday. Might really be a stretch to initiate surface based storms in the S Kansas, N Oklahoma region

 

[Michael O'Keeffe]

Skip,

The SPC's 4-8 day mentioned the possibility this day, that's actually how I found about this setup. Also, I do agree on your points as there is still much that could be better. Hopefully it will pan out so I can get in two days of chasing instead of just one. It will also probably get us into position for Saturday too.

 

[Brian Stertz]

00z ETA pops the DDC area pretty hard well after dark on the warm front, nose of intensifying 850 jet...and north of the 6 degree line at 700mb. Bet those are pretty heavy duty hailers Friday night. Shear and CAPE are also pretty high at that time of night so may possibly get a few nighttime tornadoes in the DDC CWA. Deeper LL moisture looks like it is sneaking northbound through the Ft.Stockton-Del Rio TX route by early Sat. morning...hmmmm...

 

[Skip Talbot]

I love to gawk at severe parameters and Friday is one to gawk at. There is a line extending from McCook, NE to Wichita, KS with very favorable parameters. On the NE end, the WRF is plotting 2500 J/Kg SBCAPE, 400 m2/s2 3km SRH, and 50 knots of 0-6km Shear. That is impressive. On the Kansas end: 3500 J/Kg, 300 m2/s2, and 40 knots. The resulting composite indices are quite high with a sig tor of 5 across the area at 0z, reaching over 7 by 3z, supercell composite approaching 50, and 1km EHI over 3. These are very favorable numbers for tornadic supercells.

The big problems of course are lift and the cap. Our upper level system hasn't quite arrived yet so we don't have much of a focus for initiation. We'll have to rely on an upper level disturbance. SPC also says that the WRF is not properly indicating the strength of the cap. I've noticed that the models are quite bad about accurately predicting the cap as I've been burned on a few chases where holes did not appear.

So watch this one closely. If there is convergence on the dryline in west Kansas, a burp at 500 mb, and sufficient cap erosion, we will have a very nice supercell roaming the plains at sunset.

 

[Dan Robinson]

The current north winds and dewpoints in the 40s on the Gulf coast are tempering my impulse to get on the road tomorrow for Friday.

 

[Matt Hines]

I am only going slight chance pops here on Friday. Cap looks pretty strong and the main dynamics from our low for Saturday look to be a little too far west. I will say NAM has a little vort at 500mb moving through Friday evening. That maybe enough to break 1-2 storms through. If they do manage to bust through the cap...a nice, picture-perfect cell may form.

 

[David Drummond]

The current north winds and dewpoints in the 40s on the Gulf coast are tempering my impulse to get on the road tomorrow for Friday.

True enough Dan, but I have been watching this trend today. I note that as of 23z the winds are already starting to veer around in the western part of TX. Not only that, it really hasn't served to push moisture out, while it was from the north, it was weak. In fact, we have a weak dryline in West Texas right now with 38-40 dp west of it and 50s east in the LBB area (it's actually showing up on nexrad and the mesonet)

While that is NOWCASTING info, it DOES bode well for the remainder of the week and particularly for the weekend.

The worm is starting to turn.

 

[Kenny Drake]

Friday looks like an outside chance, maybe a day for those chasers who brave the high probability of a bust and find enough surface convergence to overcome the weaker upper level flow divergence due to the 500mb trough still being well to the west. I will base what I forecast from this point out in this reply on the GFS 12Z run as it is has been quite consistent with the ECMWF which both have been consistent run after run. Wind profiles could be better with a SE surface wind from western NE through the TX panhandle, with only SSE 850 winds. Moving north, surface winds back slightly but is also the case at 850mb. To narrow down a location if I were going out I would choose NW OK/SW KS at this point due to an enhanced Theta-E zone. With progged low to mid 70 temps with upper 50 Tds the LCLs are less than ideal, but doable. 500mb winds in this location are light (40knts'ish) and out of the SW so the veering with height is there, but also not as much as I would be looking for. If something does go up, it will be fun to chase and should be quite photogenic due to its isolation. Of course, that is a big IF in my opinion.

 

[Bob Schafer]

I'd pick a target of Tribune KS to Burlington CO for initiation. Stratus deck E of that line. Closer to sfc low, some DL convergence there. I think the cap may break along that line, though would be high-based at first, but storms would migrate into good instability and shear into NW KS/SW NE. Iffy with weak sfc low and upper subsidence.

 

[Tony Laubach]

I thought I hit tomorrow pretty well with this email to a chaser, so I thought it was valid to post here (edited to make sense). This was mainly to account for a chance for some lightning after dark and perhaps a shot or two of hail in a stronger cell. This is by no means making tomorrow into something more than it is as I am primarily concerned with getting out the day before the event and using storm chances on Friday to warrent sneaking out to get into position for Saturday. We can't depart DEN til after 6pm tomorrow anyway, so unless something is that close, we certainly aren't chasing to chase.

My hunch of a southern target for Saturday makes me want to be out there that morning as models as of late have been late with dragging the system further south (and slower) as was the case last week (you remember the blizzard that never came). Basically I want to avoid a Sept. 16 repeat where our target moved 50 miles north and we missed the action by 30 minutes because we left DEN that morning.

SPC has slapped a large area of 5% which extends from North Dakota south through Texas with a buldge in Colorado. Remember that means 5% severe and not just general thunderstorms (for lightning). Models are showing good severe parameters in place tomorrow minus a strong cap and little forcing. However, storms which can fire early in the day have a decent chance of being severe given those parameters. Those won't be in our range I don't think, but as the night wears on, several smaller MCS events may evolve as the low level jet is expected to increase storm coverage in some areas. As we depart tomorrow evening, we should be seeing storms someplace where we can start to head off. My assumption is arriving right around dark on one of these storms and off we go lightning shooting.

I wouldn't be surprised to see a slight go up tomorrow covering some part of that current 5% due to the parameters in place. They'll throw a see text mentioning severe being too isolated for a slight risk, but there may be a small area that warrents a slight for later in the evening.

My two cents... in any case, I'm pulling to be someplace east and south tomorrow night for Saturday.

 

[Shane Adams]

Man, tomorrow in western KS looks like a 90% chance of a capbust and suntan....and 10% of getting a lone supercell that goes insane. Weak convergence and all that other technical mumbo jumbo aside, the shear alone is worth the risk IMO...plus the fact I'm westbound Saturday regardless.

 

[Mikey Gribble]

I haven't been paying any attention to tomorrow's setup until about 30 minutes ago, but I actually don't think it looks too bad out towards Garden City. Does anybody know why the NAM has convection firing over the warm sector at 18Z? I just started looking and I haven't figured that one out yet. There should be an outflow boundary in that general area from overnight convection, assuming it verifies. SR flow up to 25,000ft. looks quite good for rotating storms. The girlfriend gets home from work here shortly and she is going to bitch all night if I'm on the computer (because I was on the computer last night and she threw a fit) so I am probably going to do my forecasting tomorrow morning and make the call then.
edit - I guess there is a bit of a NE to SW temperature gradient there in NW Kansas where convection goes up at 18Z

 

[Michael O'Keeffe]

I'm thinking of possibly heading out tomorrow towards the DDC area. I like the extremely good parameters over this region, but I'm worried about getting a sunburn. I think I may take the chance only because if something does develop in this area of very good parameters than maybe we could see one hell of a supercell. Will make final chase plans in the morning.