4/26/09 FCST: KS,OK,TX,MO,NE

[Jason McKittrick]

I have a feeling the day two maybe a little overdone. I am still concerned about the lack of a capping inversion across the warm sector as well as moisture quality given a significant MCS occurs across Oklahoma tonight. This mornings WRF model shows the overnight convection pushing an outflow boundary all the way south to the I 20 corridor. Considering I was not able to chase today and am planning to go tomorrow I sure hope Broyles is on to something. My target area has not changed since Wednesday looking at somewhere between Arnett and Medicine Lodge.

 

[Chad Cowan]

I've been wondering why they've waited so long for this type of wording when a sig-severe event on Sunday has been synoptically evident for a few days. I figured they were waiting to see verification of precip clearing out early to throw the "O" word out there. Even with little recovery time, a widespread area of mid-60's dps beneath a powerful jet like this is going to be trouble, especially given the climatology of late April.

The NAM has been consistent for a few runs now in firing storms off the boundaries well into the warm sector in a Enid to Wichita to KC line. There is definitely a risk/reward in targeting this area as these supercells would likely have potential for long(er)-track tornadoes but, IMO, there will be tornadoes up and down the warm-sector.

Seeing as though it's the weekend and will likely be a zoo out there, it's nice to see more than a 100 sq mile target area like today.

 

[Derek Weston]

Like everything but the possible instability "problems"... at least if the NAM is to be believed -- that's not great instability. (day 2 seems really optimistic too... do we really get that large an area of 2000j/kg + CAPE? -- if that does verify, I agree... big outbreak)

 

[Jim Tang]

I have a feeling the day two maybe a little overdone. I am still concerned about the lack of a capping inversion across the warm sector as well as moisture quality given a significant MCS occurs across Oklahoma tonight. This mornings WRF model shows the overnight convection pushing an outflow boundary all the way south to the I 20 corridor. Considering I was not able to chase today and am planning to go tomorrow I sure hope Broyles is on to something. My target area has not changed since Wednesday looking at somewhere between Arnett and Medicine Lodge.

Definitely agree with you there. Widespread convection develops in the free warm sector by 18Z, possibly due to an ill-timed impulse and a complete lack of a cap. I just don't see how we will end up with a tornado outbreak up and down the Plains. We might see a couple of isolated tornadic supercells, but this event will likely end up being another 4-24-07 vs. another 4-26-91.

If I were chasing, my target would be somewhere in the TX Panhandle. That area will be a little more removed from the influence of junk convection.

 

[Mike Smith]

I am still concerned about the lack of a capping inversion across the warm sector as well as moisture quality given a significant MCS occurs across Oklahoma tonight. This mornings WRF model shows the overnight convection pushing an outflow boundary all the way south to the I 20 corridor.

If you'll allow a 57-year old meteorologist to comment who worked the day of the Andover tornado (in ICT) and has looked at a lot of model runs over the years.

From my very first post regarding Sunday, I have commented that the key is the airmass recharging on Sunday. Yes, precipitation output of the NAM keeps showers and thundershowers across KS a good part of the day. If that is the case, then there will be severe thunderstorms and possibly isolated small tornadoes.

However, if one considers the climatology (the Andover analog) and look into the model internals one sees potential for an outbreak tomorrow.

First, Andover analog. Yes, there is a boundary pushed to I-20 on one of the models. But, is that bad? Take a look at a map of the SPC reports from April 26, 1991: http://en.wikipedia.org/wiki/File:4_26_1991_storm_reports.png
See the tornadoes near I-20?

Second, there was major overnight convection on 4/26/91, including at least one tornado warning. The 12Z NAM and WRF-convective both have tonight's convection in virtually the same area.

Now, the models. Both the convective and NAM show dry 700mb air over most of tomorrow's threat area at 18Z, including in spots where it shows precipitation on the QPF. Not very likely. Remember, according to Miller's classic work, you want dry air to come in from the SW at 700mb, which is the case tomorrow according to both models.

Here is the 12Z NAM and HR 700mb forecast for 18Z tomorrow: www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/12/images/nam_700_030m.gif

www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/hiresw/12/images/hiresw_700_030l.gif


Look at the forecast soundings at ICT, PTT and WWD early tomorrow afternoon. http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&STATIONID=PTT , for example. These are Miller Type 1 soundings, the type associated with outbreaks. Compare to the soundings for 4/26/91 posted by Tim at: http://stormtrack.org/forum/showthread.php?t=20137

I tend to skeptical of model details, especially when I see precipitation in an area with dry 700mb winds.

Now, I don't profess to know which is correct, whether it is the QPF which shows grunge precipitation or the dry 700mb and encouraging soundings.

If the airmass recharges tomorrow, then it will be a big day. But, please note: Even though I am using 4/26/91 as an analog, I am not saying the tornadoes will be in exactly the same place. I am saying that people in the moderate risk tomorrow should pay attention to the weather and that it will be a favorable chase day, given a recharged atmosphere.

 

[Jeff House]

Believe that MCS will push through northern OK into southern KS Saturday night. It should eject away from at least the OK chase target on Sunday, and probably also get away from KS target(s). Agree that Sunday should recover.

Model QPF indicates the MCS in progress early Sunday morning over northern OK or southern KS. However QPF does not show additional widespread junk, stuff that sometimes likes to develop after 3am. Only QPF I see is the MCS that starts Saturday eve. New QPF during the day Sunday should be our supercells.

Any outflow from MCS will serve as a focus where it intersects the dryline. Believe that DL will light up Sunday afternoon earlier than it did Saturday, with less cap. Lifting warm front and/or outflow boundary will be another focus, with the intersection of course my chase target. Coming from Texas, I might compromise down the DL just a bit, but the TP will be my ideal target. Believe that Sunday will offer action well down the DL and not just at the TP.

Good luck and be safe.

 

[CZandbergen]

Still waiting for the 0Z GFS to come in, but have looked at the NAM. Still seems to be a difference between the two on exactly how much energy will be available tomorrow afternoon. I am leaning toward the earlier GFS run and am thinking the NAM is under doing it. At this point I am targeting either Erick OK or Shamrock TX. Plan to be sitting there or near there about 1PM tomorrow. Leaving Tulsa at 9AM and will be watching data all the way out there to adjust. LCLs look great, shear is good and depending on what model you are buying there should be plenty of CAPE. Also like the backed winds and the nice dry air at 700mB.

Of course subsequent model runs may change the target.

 

[Bill Schintler]

Chase Target for Sunday, April 26

Chase target:
Buffalo, OK (22 miles northwest of Woodward).

Timing and storm mode:
Supercell storms should develop after 5 PM, with a full spectrum of severe weather likely, including a few strong tornadoes.

Synopsis:
A 60-70kt H5 streak will eject from the base of the western CONUS trough, resulting in a broad region of strong SFC-6km deep-layer shear. A southwesterly LLJ will strengthen to 60 kt by Sunday evening, enhancing LLVL direction shear. This combination of shear and moderate instability will set the stage for a significant severe weather event from WRN TX and OK; and CNTRL and ERN KS on Sunday afternoon and into the evening.

Elevated convection will be ongoing in ERN TX, CNTRL OK, and ERN KS Sunday morning. This precipitation should move E of the area by early afternoon, while leaving a debris CI shield blanketing much of OK, and KS along and E of a Pratt to Manhattan line through 21Z. West of this cloud cover, strong insolation will take place, with SFC-90mb MLCAPEs increasing to 1500J/kg by mid-afternoon.

Discussion:
At the SFC, low pressure will slowly move EWD through the OK panhandle between 21Z to 03Z. A CF will extend NEWD from this feature. A DL will extend S from a triple point over the ERN OK panhandle, which may be the first location of storm initiation as omegas increase to -9ub/s. Looking at models, the NAM indicates stronger localized forcing and a weaker cap, which may favor larger storm complexes as opposed to the more discrete development favored by the GFS.

Deep-layer shear in excess of 60 kts; along with SFC-1km shear AOA 40 kts within the BL; coupled with LCL levels in the 800m AGL range, may support a few strong tornadoes. Tornado threat will increase after 02Z as H85 flow increases to nearly 60kts from the SW, resulting in very large clockwise-curved hodograph curvatures. An SPC significant tornado parameter of 5 is indicated from 00Z to 03Z in NWRN OK and extending into SRN KS.

- Bill

Feel free to PM me after 1 PM for nowcast support

9:15 PM CDT, 04/25/09

 

[Jason McKittrick]

Targeting Elk City, OK today. I am pretty happy with the limited amount of upscale growth with this evenings convection. Shear parameters for later today look awesome along the Texas Panhandle/ Oklahoma border. Dryline this evening is backed up on the cap-rock hope things don't start too far west or I am afraid I won't have time to reach it. Should see the atmosphere recharge across the Mod risk area. Morning insulation looks like a certainty. Still would like to see 700mb temps warmer by about 4c but I guess no event is perfect. I believe we will see a few tornadic supercells in the moderate risk area. given shear and LCL's would not be surprised to see a sig tor, conditional upon cap holding down convection until at least mid afternoon. I thick the triple point storm in NE TX panhandle may be a cyclic moving along the stationary front. Main concern with that play is lack of roads however I very well my end up there.

 

[Chris C Sanner]

I feel like we just finished doing this....but I think I may be wrong

I'm not sure I like the fact that CINH will be totally gone very early, but I think instabilities will be sufficient for good stuff even early on. The shear however, gradually improves as the day goes on (18z-0z). Supercells are a good bet through the day, but anything really and truly significant will be later on this afternoon the way it looks. Our plan will be to basically target just E and N of a/the dryline bulge which some of the models have hinted at. However, given early initiation...we might play from north to south along the dryline. Either way, unlike yesterday, looks like we are dealing with *too much* daylight rather than not enough. I 'guess' I'll take that

 

[Fabian Guerra]

Iowa?

Due to my geographical limitations I have chosen a secondary target for today. I like the area just south/southwest of Des Moines, IA along the IA/MO border. There is a strong impulse moving in around 4pm and the wind fields are pretty good, expecially in the low levels. On satellite there is an area of clearing to the w/se of DSM and I am banking that we will have a few hours of reasonably good heating. To me that is the main concern. If CAPE can climb to around 1500 by 3-4 pm then I think the ingredients will be in place for a few tornadic supercells. Leavng from Chicago right now.

Nice RUC forecast sound for Lamoni (south of DSM along ia/mo border):
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=RUC&STATIONID=klwd

Happy Chasing!

 

[John Farley]

There is wild disagreement between the RUC and NAM on the amount of instability late this afternoon. The RUC has CAPE over 2000 (and at times as high as 3000) in northwest MO/northeast KS, while the NAM has it only in the 750-1000 range. And in northwest OK, the RUC has CAPE of 4500 in northwest OK, while the NAM holds it around 2000. This seems like a bigger than usual difference this close to the event. Thoughts anyone?

If I had confidence in the RUC, I would probably head for the northwest MO/KC area, but with such a different message from the NAM, I've really got my doubts about driving that far for an unchaseable gungefest, which is what I fear in that area.

 

[Chris Hayes]

I just looked on the SPC mesoscale analysis page and there is already a large area of 2000+ CAPE across Oklahoma. Doesnt appear instability will be much of a problem, especially if it continues to destabilize. However, what I dont like are all the clouds moving in from the south. That'll probably limit destabilization a bit. However, if it maintains 2000+ it wont be so bad.

 

[Alex Lamers]

Looking at WV/IR loops there appears to be some sort of small disturbance moving up into western N TX right now and approaching central OK. There's a batch of cooler cloud tops associated with what I can only guess must be an area of enhanced vertical motion ahead of the small wave. This will be approaching an "uncapped" area per SPC mesoanalysis of SBCAPE 2000-3000 j/kg. Therefore, I wouldn't be surprised to see storms break out over C OK south of OKC around noon, if not a little before.

The dryline has retreated west, as AMA and LBB are both above 60F dew points. There is a pretty solid area of low stratus south of I-40 and east of I-27. If this mass of mid-high clouds can clear out to the east, some of this stratus might be able to mix out closer to the dryline and perhaps provide a window of heating in the early afternoon. As it's already very unstable, it shouldn't take much heating to get things going.

The 12z DFW and OUN soundings are pretty incredible, the deep moisture extends up to almost 700mb! That's the reason why we're seeing decent instability levels and almost no cap on the RUC analyses already.

It should be pretty messy today with storms all over. I think the dryline threat will develop if the stratus can clear by 12-1PM and another upper level wave comes through in the late afternoon.

AJL

 

[Tim Marshall]

TIMS FCST - April 26, 2009

TARGET: CANADIAN, TX TIME OF DEPARTURE FROM CHILDRESS: NOON. Nice to be in the front row of today's MDT outlook, so I can spend more time looking at data. PROS- Open wave trough with plenty of lift is approaching the area with 500 mb speed max and cold pool. A dryline is located in west Texas and is progged (RUC and NAM) to move out to the TX/OK border by 00z. That old front is still around in central KS, making for a triple point in extreme SW KS, NW OK, NE TX. CONS- I don't like all the high clouds here in CDS this morning. Low-level moisture is still less than I'd like to see but better than yesterday. Also, higher winds aloft will make for more race chasing today. So, Carson and I will make the leisure trek northward up Highway 83 and wait in Canadian for round two.