04/07/08 FCST: KS/OK/TX

[Mikey Gribble]

Of all the days to have a tornado outbreak in 7 years of chasing tomorrow is the worst. I can watch KU win the national championship or I can go chasing. Chasing has the edge due to the probability of strong tornadoes, but this is by far the biggest conflict of interests I've ever had in chasing.

I am pretty much in the same boat as Jeff. Everything looks quite good for strong tornadoes IF we get adequate moisture return and IF storms fire along the dryline with a couple hours of daylight to work with. There is no point in covering all the good things about this setup since it's already been covered, but if you're interested I repeated it for tenth time on my blog. The negatives are what's important at this point IMO.

I'm going to set capping issues aside due to the fact that the NAM hasn't handled that well so far this year and I'm not good at figuring out whether or not the cap will break. This one of those days where you ignore the capping issues and hope for the best IMO. Moisture return is the biggest concern on my radar. As Jeff mentioned, 60 degree dewpoints make a quick return to the NW and central Oklahoma area. 60 degree dewpoints are on shore now, but as Jeff mentioned it is fairly shallow at CRP and a little deeper at BRO. My biggest problem is that trajectories aren't favorable for a good fetch of moisture until 12Z Monday. 850mb isn't favorable until mid day. 925 does start to get a good fetch off the gulf early tomorrow morning, but getting low 60's all the way past the I40 corridor is pushing it. I agree with Jeff that 61 degrees or so is more reasonable. I do think that will be sufficient to maintain a higher end moderate tornado threat, so if this verifies I think we're in business. We just need the cap to break early enough.

My target is still Clinton. I considered the triple point (I would target Woodward), but I just think the storms firing South of the triple point along the dryline will have better tornado potential. On setups like this where you have better low-level shear along the front and better instability further South, I like to find a compromise of the two. My fall back target of Woodward will be well within range from Clinton, so if a decent CU field isn't developing along the dryline by late afternoon I will move there.

I would go 15% hatched on the tornado prob and I think this is an upper end moderate risk due to the likelyhood of strong tornadoes. The highest tornado threat tomorrow will be in a rectangle from Clinton to Woodward to Alva to Watonga IMO. I posted a forecast here for those that are interested http://loadedgunchasing.com/blog.html

 

[Chris Wilburn]

I pretty much agree with what has already been said so I will not be too long with my forecast. I did notice the mid 50 dews that David mentioned already close to the red river. This has me feeling much better but with that being said I still have some concerns over moisture return and more specifically how deep will the moisture be? I think a really good target is where Mikey mentioned in Clinton with a good north south road in Highway 183. This will allow quick access towards the north along the triple point if things look not so good along the dryline. I think it will be important as always to monitor vis. sat. to monitor the two areas. Everything you would hope to be in place is. Shear looks really nice along with CAPE and moisture. Forecast sounding for Watonga looks very nice. I know you can take these with a grain of salt sometimes, but the sounding is showing the following: LI -8, EHI -6, near perfect horseshoe hodograph, no cap, 100% supercell potential, CAPE 3,200 and very low LCL and LFC heights. To summarize things my only concerns are moisture return and how deep will it be. I think everything else appears to be in place for tornadoes with some capable of being strong. I do like the forecasted 40kt 500mb winds yielding 24kt storm motions. This day sort of reminds me of June 12, 2005 near Jarell, TX where the 500mb winds were not particularly strong but it turned out to be a very nice tornado day. I promised to keep it short but it didn't happen that way lol I would target near Clinton with an eye on moisture return and the triple point. I too am ingnoring the cap since the NAM hasn't handled it well lately and hope for the best.

 

[Eddie Natenberg]

Im still stickin by my guns on this one and saying this looks like a major late afternoon and evening significant tornado outbreak. As new obs are coming in I feel the depth of the boundary layer moisture is going to be deeper with trajectories tomorrow afternoon and night originating from a region that has had some decent rainfall the last two weeks. Therefore deep moisture return is not going to be the question in this case, it just might happen later in the day/evening.

As for the cap I expect it to be stronger than predicted with daytime heating today and tomorrow along the caprock region and west where the capping inversion layer originates. That makes this event an all or bust event completely dependent only on upper level divergence and differential vorticity advection.

My last concern of cold air advection in the PAC NW behind the trough is now not an issue with agreement between all models the the trough should continue to dig between 12z and 21z tomorrow keeping differential vorticity advection downstream to a minimum and allowing for pressure falls in NW oklahoma. I am guessing the upper air forcing is being underestimated by the models and that shortwaves (emanating from a region of increased baroclinicity at the trough axis) are not resolvable yet will help break the increased magnitude of the capping inversion.

The biggest indicator of tomorrows potential will be the 850 mb winds which will keep the boundary layer coupled through the evening and even with higher LCLs durring the day, decending LCL during the evening will lead to an impressive 0-1 km layer of strong low level cape, enhanced moisture convergence near the diffuse warm front, and near perfect half to 3/4 circle hodos. This is an impressive sub cloud layer. Storms will be isolated with the greatest time for sig tors around 01-04z until the 850 mb winds veer helping to evolve storms into a small MCS that will propagate downstream into MO by 12z.

And thats my 2cents. Now to be productive and try to ignore weather maps/data for a few hours.

 

[Brandon Lawson]

I'm starting to get a little concerned about the moisture return. Looking at the latest surface maps, you don't see anything higher than 55 degree dewpoints until Austin, TX. The higher dewpoints are only in the low 60's and they're sitting on the gulf coast. There is still 24 hours for moisture transport, but I would say I'm slightly worried. Perhaps the dewpoints will pool by the surface low, but then the depth of moisture may end up being pretty shallow.

It's tough having everything look so good, but for one thing: no moisture. Anybody that knows more about this than me (which is probably everyone), feel free to spread some light on our chances of seeing adequate moisture return. Otherwise, the setup is looking phenomenal.

EDIT: Jeff, you kind of answered my question with your post. I briefly skimmed over it without fully reading it the first time. Thanks.

 

[David Drummond]

What surface map are you using Brandon? I just looked when you said that (on GRLevel3 station plots). I am seeing mid to upper 50s all around the DFW metroplex. KDFW has 56 dewpoints for instance. 61 dewpoint in Gainseville at the Red River. There is a dryline and cold front intersecting the state in half...the better moisture to the east of I35 right now slowly creeping north.

 

[Chris C Sanner]

I think the models are onto something as far as surface TDs are concerned. ADM is reporting 72/61 right now. I'm not so sure the depth of the moisture is all that great though, after a quick glance at some 0z soundings. The depth and quality isn't really all that great all the way down to the Gulf Coast. Continuing to be negative, I'm kinda worried about subsistence in the warm sector tomorrow afternoon if we get a wave in the morning that touches off convection. Plenty to look for tonight in analyzing things for sure..

 

[Mikey Gribble]

IMO you can't really stake much on one station reporting a 60 degree dewpoint when it's surrounded by low 50's. COD has a nice smoothed plot with contours. http://weather.cod.edu/analysis/analysis.sfccon.html
The good moisture that we need is on shore, but not very far on shore. CRP and BRO 00Z soundings both show good moisture depth, which is certainly a good sign. Now the question is will it get up here in time. The 00Z RUC has backed off on overnight moisture advection compared to the 21Z run. I don't put much trust in the RUC though. Looking at profilers over Texas right now confirm that there isn't much wind pumping that moisture northward at the time. If the NAM is to be believed there won't a good fetch of moisture until early tomorrow morning when 925mb winds kick in, so moisture return is largely a question that will have to be answered tomorrow. I am fairly confident we'll get 60 degrees up to the I40 corridor, which will be sufficient to maintain the tornado threat. Anyways, I just wanted to throw in my two cents on moisture questions. Now it's time to start looking at 00Z data.

edit - Basically all the surface features have shifted South with the 00Z. I have just started looking at data though. This actually could be a good thing since it will cut down the travel distance for the good moisture along the coast.

 

[Shane Adams]

A glance at the current OK mesonet doesn't inspire much confidence. And I'm pretty sure that Gainseville mesonet reading is whacked out most of the time, showing to be 4-5 degrees higher than reality. Surface flow isn't great at all for overnight transport of moisture, but stranger things have happened. We'll chase this because it's close and the rest of the setup is just too potent to ignore. But what a waste of shear and instability this would be. Arrgggh

Good thing is with the excellent shear, if we can get something going in that environment, 70/55 would work. Hell 70/50 might even work. In either case, I think everyone's question about why SPC went slight has been answered.

 

[Mikey Gribble]

I think SPC will go moderate with the Day 1 outlook. Especially with the surface features getting shoved South a bit with the 00Z NAM (assuming it verifies), storms coming off the triple point and dryline should realize dewpoints of 60. If we hit 60 that is adequate for strong tornadoes with this setup.
The main thing that changed with the 00Z NAM is that surface features got pushed South. The triple point is closer to the I40 corridor now as opposed to being near Gage in the 12Z run. Aside from that not much else has changed. The NAM is once again hinting at breaking out convection near the triple point/warm front and Hobart and Clinton soundings show the cap eroding in the 21-00Z time frame. This in addition to the fact that the NAM has tended to be a bit bullish with the cap this year has me all but convinced that we will get a few storms off the triple point and dryline tomorrow.
All the parameters are about the same. The Clinton hodograph at 00Z is extremely favorable for tornadoes. Anyways, my confidence is increasing that the two big question marks (moisture return and capping) won't be a problem tomorrow. The bulk of the moisture advection will happen during the day tomorrow, so by noon or so it should be evident whether or not this is going to happen, but like I said, I'm fairly confident we'll see 60 degree dewpoints over the warm sector by 5PM. I am still targeting Clinton, but Hobart is pretty appealing too. If this verifies there should be a localized tornado outbreak along and South of the I40 corridor, with a few strong tornadoes likely. I posted a forecast here if you're interested http://loadedgunchasing.com/blog.html

 

[Van DeWald]

00Z Nam still looks favorable for initiation between I40/I44 between 21/00z. Nam still progs lower 60s dewpoints, resulting in LCLs ~850m near/south of Watonga which is very promising. 1km shear around 00z is only 15kts or so, but increases to 25-35kts by 03z. 3km CAPE about 175 J/kg is respectable. Sig Tor parameter approaching 2-4 and 0-3km lapse rates approaching 7.75. I've always thought that strong dynamics could overcome marginal moisture. Looks like a moderate risk to me, I'm guessing we'll see an upgrade on the new Day1 Outlook.

Van

 

[Bill Schintler]

Chase Target for Monday, April 7

Chase target:
Cordell, OK (12 miles south of Clinton).

Timing and storm mode:
Surface-based storm initiation: 5:30 PM CDT. Medium- to high-based supercell storms with large hail will be likely during the few hours following initiation, and a tornado threat will increase during the evening hours.

Synopsis:
A slow moving S/WV in the upper-Midwest is the primary ULVL feature while a 110kt H3 streak is coming on shore over CA accompanied by H5 height falls concentrated over NV. Ahead and S of the main flow, a couple of lower amplitude H7-H6 waves are moving through NM and WRN AZ. Steep mid-level lapse rates are noted on upstream soundings (EPZ, ABQ, MAF, and AMA). LLVL moisture is lacking, as evidenced by SFC dewpoints AOB 40F over most of OK. Soundings in TX S of I-20 also indicate lack of moisture depth and quality.

Discussion:
Strong assent from a 110kt H3 streak ejecting from the trough base along with a coupled jet structure with a SRN branch will overspread the area during the day Monday. SRLY flow and moisture advection will increase E of cyclogenesis centered over the TX panhandle. Models continue to agree to bring a surge of moisture N into the area. Cloud cover during the day will affect insolation and attendant instability. Thick SC, associated with the WF, will blanket areas N of I-40 between OKC and AMA and this will result in differential heating and tightening of the baroclinic zone. Additionally, a couple areas of CI in association with larger scale assent will move through the region. To the N, mid- and upper level cloudiness will persist over much of KS during the day; while further S a second area of broken CI will overspread areas S of LBB to CDS during the afternoon. This cloud cover along with warmer mid-level temperatures with H7 temperatures AOA 7C should inhibit convection along the DL S of the Red River.

Elevated convection will develop N of the WF in NRN OK/KS by early afternoon. SFC-based convection should initiate first near the WF/DL triple point and then one or more discrete cells should fire further S along the DL, with the SRN extent of the convection near I-40. Following initiation, cloud bases will be relatively high with LCLs in the 1000-1200m AGL range with SFC temperatures AOA 80F. During the early evening hours, the environment will become increasingly favorable for tornadogenesis as storms move into increasing SFC moisture and LLVL hodograph curvatures with SFC-3km SRHs AOA 300m2/s2 under a strengthening LLJ. Instability will increase during the afternoon hours with differential advection of the aforementioned mid-level lapse rates/EML and LLVL moisture, and MLCAPEs should increase to 2000-3000J/kg over a narrow N/S axis ahead of the DL. During the overnight hours, the LLJ will increase to 40-50kts while aiding in the maintenance of a large convective complex which will track E through OK.

- bill
9:45 PM CDT, 04/06/08

 

[Jeff Snyder]

Man, if some of these forecast soundings and hogographs verify, I think tomorrow could be quite a day for some across central and southern Oklahoma and possibly into western north Texas. As others have noted, the 00z NAM forecasts the warm front to be a little more south than previous forecasts, and the forecast Tds are in a little more in line with what's likely (they're about 3-5F lower than the 12z NAM in some locations). In addition, the 00z NAM shows convective precip ahead of the triple point and along the warm front near I40 W of I35. With all that said, check out this hodograph (valid along the warm front) --> CSM forecast sounding valid 3z . Now, let's suppose the immediate near-sfc layer (<400-500m) doesn't cool off quite as much as shown... That's 700 m2/s2 0-3km SRH on a hodograph that is beyond ridiculous. Even if the storm is slightly elevated, as the thermo profile may suggest, with a parcel origination level as low as 500m AGL, the hodograph would still indicate >500 m2/s2 500m-3km SRH. Other hodographs
from around the area are similar. Even if Tds are held in the upper 50s (which I don't think it unreasonable looking at sfc obs and the very poor low-level flow in southeastern TX), the thermo profile should still work out such that surface-based convection can initiate by late afternoon. This setup looks better than any other I've seen so far this year for the Plains, at least now that we're <24 hours from initiation. I agree that a MDT looks likely, and I can only imagine what might be if we were to have 64-69F Tds along the warm front (not gonna happen this time, though).

I would also echo Mikey in cautioning against using a single surface obs to say the "60 F tds are here'. Some ASOS obs are notorious for being too high with the Td, and it's expected that Tds will increase near sunset (as part of the diurnal cycle) in a very shallow layer immediately above the sfc. Sure, there are a couple 60-61F tds in S OK and N TX, but they are surrounded by 50-57F tds. The Ardmore ASOS noted previously in this thread is notorious for being too high on the Td observation. Looking at nearby obs from the Oklahoma Mesonet (including the Ardmore mesonet site itself) shows 54-57F Tds in the area.

 

[Chris Wilburn]

After viewing the 00z data from the NAM and the GFS not too much has changed which is good considering the models lately. The GFS does have slightly lower dewpoints, but just by a few degrees. Backed surface winds with southerly or very slightly veered 850mb winds along with 40-50kt 500mb winds creates very nice wind shear with very chaseable storm motions. 0-3 SRH is near 350 and 0-1 SRH 150-200 which should increase towards dark. CAPE will be more than enough. I too agree that SPC will probably go Moderate on the Day 1 outlook. I would say 10% hatched probably from NW OK into NW TX. Looking at the models there appears to be two possible plays. Just north of I40 in western OK and south of I40 in western OK from Clinton to Hobart to Frederick. Forecast soundings look very nice from these three locations. I would say initiation between 21/22z to 00z with the triple point going first then down the dryline. The threat for tornadoes will increase towards dark as the LLJ picks up and storms enter a very friendly environment. There are mid 50 dewpoints showing up from several different observations along the red river and I35. I guess moisture return and depth is the only concern I have at this point with all other parameters look very nice for a potentially awesome chase day in western/SW OK. Right now my plans have not changed. I will head towards OKC then west on I40 towards Clinton keeping an eye on vis. sat. and moisture. Find an area of backed winds roughly 40-50 miles east of the dryline and hope for the best is all I can say. Target is Clinton to Hobart on Highway 183 with a possible drop towards Frederick or up just NW of Clinton north of I40 for the triple point. Good luck to all that go out!

 

[Jonathan Whitehead]

Well Ive been waiting on putting in my 2 cents till I can look at run to run model consistency, which I havent been able to do till today. All 00Z initializations handle the current moisture setup quite well and are consistent in slowly (and might I emphasize slowly) bringing it north beginning around dawn tomorrow. By 18Z, all models have 60dews right along the Red River. Therefore, the question then becomes time of initiation b/c the longer initiation holds off the more time moisture will have to work northward. Therefore, that brings in to question the strength of the cap b/c stronger cap will hold off initiation longer. So A leads to B leads to C, but do not collect $200. Right now I am unsure of cap strength as I have not dissected it in great detail. Although from what I have looked at, Im not seeing initiation anytime before 18Z. I think we ALL will know what is going to happen by sunrise tomorrow with hardcore data from sfc obs, soundings, NM vad wind profilers wrt to shear and TX wrt to moisture transport at sfc etc.....
All in all i think its splitting hairs wether SPC goes MDT or stays SLT. IMO id keep it SLT till hard data and trends come more into focus at 8am outlook.
As far as chase target, right now I havent decided on one as for me it's still too early to pin down exactly how things will play out and where. Again ill know more in the morning.

 

[Donald Giuliano]

Although I agree that Monday looks like the best chase day for Oklahoma so far this year a day in advance, my take is that unfortunately that's not saying much. Having due westerly flow at 500 mb, barely 30 kt at 850 mb, and southeast (and maybe even more easterly than that) boundary layer winds simply does not excite me. On the positive side, like every other event so far this year, as long as the moisture returns as forecast (which I think is a reasonable assumption given model forecast trajectories along the dryline that appear to originate near Brownsville) then initiation should not be a problem and will probably occur around 22Z or so based on persistence.

There's a reasonable chance the situation could improve, so I think a 10% tornado (no hatched area) is warranted with a possible downgrade to 5% after the 12Z models come out. I will almost certainly be chasing tomorrow afternoon due to proximity, great terrain and the high probability of supercells, but I fear this looks all too much like March 30 and will probably have a similar result. Hopefully there will be a few good tubes tomorrow, but I'm not counting on it.