2/23/07 FCST: OK / TX / KS

[Craig Maire II]

2/23/07 FCST: OK / TX Reply to Thread

I have class until noon on Thursday but then plan to take off and be in Wichita Kansas by late Thursday night where I will rest up at a hotel. Friday morning I plan on taking off from Witchita by 10 or 11am and will then head to between Woodward and Clinton Oklahoma. I plan on trying to intercept any isolated supercells that may/should develop along the dryline in western Oklahoma during the late afternoon/evening. Will then follow the storms as they move east towards central Oklahoma (probably as they merge into a severe squalline). If the cap does wait until after dark to break I am hoping very much for large amounts of lightning!

 

[Gabe Garfield]

I guess that I'd argue the timing of the wave is really not that good if we're looking for daylight tornadoes. The sun sets around 615-620pm in the general target area. If the sun set more like at 8 or 9, then I'd consider the timing to be ideal.

If simply looking at the 12Z output, I would agree. I anticipate, though, that the timing of the wave will be a bit more favorable given the d(prog)/dt of the model output. That is, the models are trending toward a faster solution. We shall see...

Gabe

 

[samuel stone]

Its a little late to be posting on the nam 12z run since its 7:50 pm but, I just got off work so this is the first I have seen it. The first thing that jumped out at was that the UPPER WAVE IS WAY FASTER and that is just a massive factor in this particular event. without going into detail since I think every one here can read models for themselves, I just want to say, oh my how the 12z nam absolutely screams Woodward, Ok.

 

[Tim Marshall]

Just glanced at the 00z models (FEB 22) and agree it looks marginal for chasing Friday. Timing of the system coupled with poor quality surface moisture are big problems. But, I have the day off work and I'll probably head to Altus. After busting there, I'll probably drive up to Tulsa and stay there Friday night to play the cold core low in E-SE KS on Saturday. All this could change the next model run. More later. TM

 

[Justin Walker]

Just glanced at the 00z models (FEB 22) and agree it looks marginal for chasing Friday.

I guess I am a little more optimistic about Friday. Maybe it is the time of the year, i dunno. The dynamics arrive b/t 18z and 00z, so I have already conceded to the fact of chasing after dark. Shear vector perpendicular to the dry line, but the questionable moisture might help this to go linear from the start. With the moisture not progged to come in until Friday during the day, coming from Colorado, I can't wait and see what unfolds on the moisture return. I will have to make a decision on thurs night.

Edit: After re-looking at the 00z, midlevel forcing arrives around 18z, so that might give some daylight chasing.

 

[Gabe Garfield]

After looking at the 00Z moisture prog, it is apparent that moisture/instability will indeed be an issue for Friday's severe event. While lower to mid 50s dewpoints will be sufficient for severe storms, the likelihood of tornadoes has diminished somewhat. Be that as it may, both the GFS and the NAM are continuing the trend of a faster solution for the wave speed. This may offset the relatively paltry moisture if mid-level cooling occurs earlier and is coincident with daytime heating. We shall see...

Gabe

 

[Jeff Snyder]

I'm taking a moderately optimistic view of the situation I guess. It's been known that the two primary negatives for the event are the meager moisture availability and the less-than-ideal timing of the arrival of the primary vort max to the west. Regarding the first negative -- it's February, that's all I'll say. I don't recall too many February days in the past 5-6 years that featured >60F dewpoints in Oklahoma. When 500mb temperatures are as cold as they will be, I'm not AS concerned about mid-upper 50 dewpoints as I would be otherwise. Of course, temps in the 70s with Tds in the mid-upper 50s still leave relatively high (or at least not ideal) LCL heights. But hey, we've had a hard enough time getting 60 degree Tds by the end of March the past couple of years, so I'll take it.

The timing of the approach of the vort max is still an issue, obviously. The latest 00z NAM indicates the leading edge of the vort max (or basically the area of DPVA) moving into the central TX panhandle by 00z Sat (Friday evening). With sunset around 0030z, this creates an obvious issue. Without a whole lot of mid-level upward motion, we'll have to depend more strongly on low-level convergence (though we usually need some low-level convergence any) to initiate convection. Wind profiles will be moderately strong by 00z, with 50-60kt 0-6km shear oriented perpendicular to the dryline, a fact that should promote discrete initiation initially. Now, I would be quite happy if this arrived 6+ hours earlier, but I'm not sure that is going to happen. As it stands now, the 00z NAM doesn't initiate precip in the target area until 3z-6z (in southwestern OK). As others have noticed, however, model convective initiation (and convective parameters) can be suspect at times, so I'm still holding out hope. Regardless, the bulk of the forcing won't really approach the dryline until near and after 6z. Looking at the deep-layer shear vector forecasts, a squall line looks very likely after 6-12z, as backing and strengthening 500mb flow acts to back the 0-6km shear vector such that it is nearly parallel to the dryline.

[EDIT: Looking at the 0z NAM, it certainly looks to me like the midlevel trough will move out more slowly onto the plains. This does not bode well for Friday activity... I really should address the GFS more in this thread, since I'm not a big fan of the NAM. The 00z GFS remains quite consistent with the 12z run in the positioning of the cyclone and trough by Friday evening. I've generally been more pleased by the GFS than the NAM in the past 9 months, but that's another topic (and entirely anecdotal).]

I am intrigued by the potential for tornadic supercells across portions of Texas and Oklahoma overnight Friday and into Saturday morning. Intense cyclogenesis associated with the approach of the strong upper-level trough will result in a substantial ageostrophic response. With an increasing pressure gradient, I suspect that the low-levels will remain relatively well-mixed through the night (at least through 6z), which could allow supercells to become surface-based or remain surface-based through midnight. With the low-level RH being not particularly high, radiational cooling may lead to some decoupling, but, in my experience, setups such as this tend to allow for surface-based convection later into the night than is typically observed.

One of the more unfortunate aspects of this event is the fact that the developing trough won't be well-sampled by the RAOB network until Friday morning (the time at which the trough deepens and moves inland), though the downstream environment (relative to the trough axis) may be sampled by some of the sounding sites along the Pacific coast Thursday evening. Of course, there are still thousands of satellite observations (in addition to aircraft obs, etc) that are being used to initialize the models, but it's almost always good to get sounding data.

Whew. I agree that there are plenty of negatives. But, it's February, and I haven't chased since late November (and haven't had a "good" chase since September). I'd much rather be agonizing over this setup than looking at a huge east coast trough, that's for sure (though, there IS a big trough/low moving off the east coast). I have all plans to chase Friday, but my expectations are low.

 

[Mike Hollingshead]

DDC 0z Sat NAM Fcst Sounding

Looking at that makes me want to drive down early for Saturday chase and see what happens, and if nothing else see after dark whatever and be close for Saturday. I mean, even an after dark adventure sounds good enough this early in the year.

 

[Kevin Polston]

Looking at tonites 00Z NAM and GFS.....I get the impression that we will be lucky to see anything develop before 00Z. My reasons for this are it doesn't seem as if there is very good convergence along the dryline and the upper dynamics are still to the west. However....after dark it appears the winds to the west of the dryline really become strong from the west or west southwest so the low level convergence really increases by 06Z over southwest KS/west OK/ and nw TX. So with the effects of the upper system now in play and the focused low level convergence I would expect supercells to develop probably between 03Z and 06Z in this area. Looking at point forecast soundings....there is actually some potential for night time tornadoes where the LFC lowers as a result of increased low level moisture. I would think based on looking at these soundings that the area between HUT - Pratt - GAG would be the area I would look at. The NAM point soundings were showing at 06Z LI's of -8, CAPE of 1700-1800 j/kg, and SRH of 550-600. It also was a "fat looking" cape. So I think there could be some hope for a tornado in these areas. One area no one has really mentioned but I think could see something would be in the area east of the dryline from DRT -SJT after dark. It seems many times you can get these isolated cells south of the main area everyone is looking at. And there are some parameters to support this.....so it will be interesting to see if something does develop in this area as well. I would certainly expect some very large hail to fall from the supercells Friday night....so that will be fun to watch. Hopefully something will develop before sunset but I think an after dark show is more likely.

 

[Rodney Harper]

After looking at the models I really like the southern Okla for poss severe/tornadoes. Looks like that will change quickly when the cold core sets up in possibly Mo. Very questionable still but I think that will be my target. Possibly even as far south as Wichita Falls, TX and points east of there. Sherman,TX and vicinity.

I did not see or realize the latest SPC day 2 update if you will look at the time. But it is kinda funny. LOL. I guess I am on for now at least.

 

[Jim Bishop]

I'm taking a moderately optimistic view of the situation I guess.

I am intrigued by the potential for tornadic supercells across portions of Texas and Oklahoma overnight Friday and into Saturday morning.

Me too on both points, Jeff! I haven't made a final decision, but I'm probably going after this event. I am very interested in the tornado potential after dark across Southwest Oklahoma. The shear looks so good in fact I'm almost considering chasing based soley on seeing a nighttime tornado - but still with the possibility for storms firing before dark.

The latest 12z NAM fires descrete storms between 00z & 06z. With CAPE 1000-2000 j/kg and strong low level shear/impressive hodographs, I'd say tornadic supercells are quite likely after 6pm. This is unfortunate for residents, especially if these storms remain tornadic well into the night after people go to bed.

One more point about storms firing before dark. The NAM still shows the left exit region of a 250mb jet streak going right over Western Oklahoma between 18z & 00z. This *could* be the support necessary for daylight initiation.

 

[Craig Maire II]

2/23/07 FCST: OK / TX

I've decided to cancel my trip down to southern Kansas and Oklahoma, looks like there will definitely be severe thunderstorms and possible tornados but they will develop well after dark and will not be worth a 12 hour drive and at least 250$. I plan on instead targeting east central Kansas or west central Missouri on Saturday where low topped supercells will be possible during the day time. Good luck and stay safe to those who will be chasing those after dark sups in southwest Kansas, Oklahoma and Texas. If those areas were closer I'd go for it!

 

[Stuart Robinson]

I guess that you all know by now that the SPC has upgraded Friday to a Moderate risk....

 

[Justin E. Reed]

Here we go, this could be a good day. I'll keep in touch with my family in Chickasha. It will be a very intresting set up, considering the time of year and time of day. As we say in the Navy, ****s goin to hit the fan, really quick tomorrow evening.

 

[Jim Bishop]

The SPC update doesn't really boost my confidence any as they articulate quite nicely what I've been thinking for days now. But it does get me a little more excited...which is almost enough for me to take a day's vacation and have a long drive with little sleep.

After mentioning convergence and a sublte upper disturbance may initiate convection prior to 00z, they say "However, confidence in late afternoon initiation is not particularly high at this time." That's a perfect statement for Friday's expectations. And if convection wait's 'till after dark, the moderate risk is still warranted.

I've still got a rather difficult decision to make tonight!