2012-04-12 FCST: KS/OK/TX

[Tim Supinie]

Seth, it's fine. My basic reasoning is that that parcel of air is going to need to have 10-15 F added to the dewpoint between now and ~42 hours from now for the NAM's dewpoint forecast to verify. Where is that moisture going to come from? The processes that govern these sorts of things are usually parameterized in the models, and therefore are handled poorly on occasion. I'll spare you the details for now, but if you're interested, I can send you a private message explaining more.

Also, it's quite possible that my trajectory analysis is off and the true source region of the parcel has a higher dewpoint than 50 F.

As to whether or not I'm chasing, in a world where I have infinite time and money, I would, just to see what I could see. However, I have a meeting on Friday that I need to prepare for, and a trip to central KS or even Shamrock, TX, on Thursday is not a good idea.

 

[Jacob Ferden]

It seems blatantly obvious to me that moisture is going to be at least a factor for Thursday, as is common with these "day before the day" type setups. The NAM has kept pulling the EHI max farther and farther north, and there are excellent forecast hodographs in the vicinity of I-70. However, color me a little skeptical of whether or not moisture will be good enough that far north to allow for sustained, robust convection. The 00z NAM is forecasting relatively high surface LCL heights (> 1000 m) ahead of the dryline except for a small area in northern Kansas adjacent to the dryline bulge.

The GFS is painting a considerably different picture, with better moisture in the warm sector. It also shows some capping issues not extant in the NAM run, but a hole in the forecasted CIN would also suggest a Kansas target, but potentially a bit farther south.

It's all pointless this many hours out still, but if I were to chase this based off current model runs and trends, I probably would target somewhere along the dryline in a Dodge City-Great Bend-Woodward triangle, in the hopes of finding the sweet spot between the excellent hodo's to the north and likely richer moisture a bit farther south.

 

[Jesse Risley]

Just piggybacking off of the 12z/10, 00z/11 and 12z/11 (NAM) MAF suite here, it looks like a good census is that low pressure will be centered over E CO at 12z Thursday, with a dryline extending southward proximal to the TX/NM border region, while a warm front orients itself S/SE from Burlington, CO to near Sherman, TX. It looks like some convection may ongoing across parts of NE down into NC TX ahead of the surface front.

The surface low looks to deepen to around 996 mb and nudge into far E CO near the KS border region along I-70. A nice dryline should setup from somewhere along an axis from just SSW GLD - LBL - AMA - ODO, with a noticeable bulge possibly edging into the HWY 83 corridor from SW KS into the far NE TX panhandle, enhancing low level shear and convergence. The best forcing for ascent remains well off to the west, though the NAM and GFS are hinting at a perturbation approaching from west (GFS is slightly stronger) with 40-50kt H5 flow moving into the area of interest after 21z THUR, though it looks like the GFS depicts a better vorticity lobe than the NAM. Hopefully the timing of better flow aloft will be such that the unstable air to the east can be lofted throug the potentially lingering inversion.

If storms do fire off the dryline, SFC-500 mb bulk shear values of 35-50 kts should be sufficient for supercell maintenance. Still some differences in progged instability parameters, with the NAM far more magnanimous on SBCAPE values, though as Skip noted, there is at least a narrow wedge of instability that, with progged CAPE values AOA 1500 J/KG, would be sufficient to sustain storms till at least after diurnal heating erodes. It should be noted that the GFS is remaining more stalwart on the EML than the NAM, though forcing may still be sufficient to overcome some of the CINH.

Directional shear profiles from forecast Skew-T, Log-P parameters off of the 12z/11 (today's) NAM have greatly improved, and both the NAM and the GFS have been hinting at favorable surface LCLs as well (AOB 1000m), so tornadic supercells appear plausible. Additionally, noted mid-level hydrolapses, WB0 levels around 10k feet and adequate lapse rates suggest large hail and damaging winds are also possible with any supercells that develop ahead of the dryline and move eastward. The models seem to be in some agreement at least where northward return of 60 degree+ dewpoints are concerned, though some differences remain on how much the surface low will actually deepen and where it will lie.

I think areas along the dryline in the aforementioned zones bear watching for a show on Thursday afternoon. If storms do form and take advantage of the instability, then I would expect that this narrow corridor ahead of the dryline could be rewarding.

 

[Andrew Stoller]

The 12z NAM still looks good, but the GFS is still keeping temperatures in the 50s and low 60s immediately ahead of the dryline and that is dramatically limiting the instability it's forecasting. However, looking at forecast highs according to the NWS in areas east of the dryline, they're forecasting temps in the 70s which correlates more with the NAM. I really hope the NAM verifies because, although this won't be a huge outbreak, it has the ingredients for more photogenic/smaller size and slower moving tornadic supercells in west central/south central KS and points to the south into western Oklahoma. Shear isn't going to be a problem. GFS and NAM are still opposing one another regarding CIN though.

 

[samuel stone]

I'd love to be able to chase tommorows setup. directional shear is the best of anyday in this upcoming sequence. im i huge fan of good directional shear. slow storm motions, great chase country, and sufficient instability makes this an eniticing setup to me. yes the instability axis is a little narrow but storms will move through it very slowly and have plenty of time to produce as they do. if dews could jump up a couple degrees id probably call in sick to work haha. but thats unlikely given somewhat poor trajectories. it wouldnt hurt if we could get a little bit colder mid level temps over the area as well and bump up those mid level lapse rates, but to me it looks like all is coming together for a couple good sups and tornadoes 50 miles either side of a woodward to hays line. approx.

 

[Mike Johnston]

Seems like this is another classic case of projecting at what latititude the dominant lee surface low will develop - Nebraksa panhandle, northeast Colorado, southeast Colorado? Whichever one, the best low-level CAPE, the best helicities, and the best moisture pooling looks to be right out in front of it. Based on the latest NAM run, looks like the area around Dodge City might be the target, but that could change considerably with the next run. Often, the latitude of the lee surface lows are notoriously hard to predict. Given that, it seems like a trek up (or down) on U.S. 283 in KS. literally from the OK to NE border, and monitoring throughout, might be the most practical chase strategy.

 

[Seth Edge]

Now looking like dodge city,ks. And Im on the moisture is going to be the hindering factor train now.

 

[Sean Ramsey]

In watching the NAM the last day or so it appears the setup could be further south than first anticipated with increased CAPE from Dodge City to Childress, TX. I really like the 0-1km helicity values showing in southwestern Ks, making Dodge City a logical choice, but at this point I'm thinking of playing it more to the southeast and setting up in Greensburg due to GFS showing a clear break in the cap around 21z. Of course this can change overnight so I'll make my decision in the morning when I can get a look at what RUC has to say about it.

 

[Jeff Snyder]

There are a few complications with the setup, and they're typical of the day-before-the-day (or day-before-the-day-before-the-day) events. Moisture return may be suboptimal, but forecast soundings suggest that 60-63 F Tds may be sufficient for thermodynamic profiles supporting tornado supercells. The new 18z NAM that's just coming in now indicates a batch of precip moving across central OK/KS mid-day, which in turn results in a relatively narrow warm sector with northward extent away from the OK/KS border. The other primary concern that I have is whether the mid- and upper-tropospheric flow will be sufficient to get classic supercells. Dprog/dt had been for a slowing down of the western US trough and associated higher velocity winds, resulting in the better flow aloft staying W of the dryline. Current fcst hodographs show pretty good shear profiles, at least good considering storm motions should be ~20 kts for a mature right-mover. Deep-layer shear will not be particularly strong as a result of the not-particularly-strong flow aloft, though both the NAM and GFS show 5-10 kts stronger flow in KS compared to far W OK, and, since we're on the warm side of the jet, I'd prefer to be farther north if possible.

My current target area is western Kansas. I know, it's really specific. I guess I'd say DDC, but that's partly influenced by logistics regarding time of departure from the OKC area. This looks like it could be a crazy week in the Plains (Monday in NW OK, yesterday saw a supercell or two in the TX PH, there's currently a tornado watch for the TX PH, then we have tomorrow's setup before Friday and Saturday's events).

 

[Andrew Stoller]

Can anyone with more expertise than I analyze the issue of stratus and or low clouds DDC AFD mentions this afternoon which it looks like will be the key factor for initiation and or the strength of convection tomorrow? It seems to me that if we can clear out the low clouds and gunk, even for a brief few hours after noon, everything else, to include shear and possible petributions in the leading edge of the jet nosing into the high plains, will initiate storms. It all rides on whether the grunge will clear out to get enough insolation.

 

[Joe Acord]

I think my target is going to be further south anywhere from Shamrock to Woodward. What I have been liking in all the models the past 2-3 days is the increase in sfc DP level across E-TX panhandle and W-OK. Both the NAM and GFS indicate a large area of +60, including a finger of near 65F extending towards the S KS border north of Woodward. I am also liking the increase the CAPE values along the border as that indicates more available daytime heating when compared to area near DDC and n-ward, so I don't think low cloud cover is going to be as widespread as further north. While not taking away from other target areas, the potential exists for some dryline gems over a very large area extending into the panhandle.

 

[Mike Smith]

Can anyone with more expertise than I analyze the issue of stratus and or low clouds DDC AFD mentions this afternoon which it looks like will be the key factor for initiation and or the strength of convection tomorrow?

Based on a climatology of violent tornadoes that I assembled rain in the morning is not a deterrent to violent tornadoes later in the day. Think about April 27, 2011. Some areas had one or even two lines of thunderstorms go through before the supercells with violent tornadoes occurred in the afternoon and evening. The great Woodward tornado of 1947 had low clouds and fog along nearly its entire path until mid-afternoon.

It all depends on the unique characteristics of the day.

 

[Jeff Snyder]

Pattern recognition is telling me to head to near the sfc low, which the 00z NAM has near Tribune, KS tomorrow. The warm sector is progged to be relatively narrow that far north, but storm motion is only progged to be ~25 kts for a right-moving supercell based on the 00z NAM, and the temp. gradient in current forecasts isn't very strong. As such, if the front lifts northward with time, I think a storm may be able to reside near the front for a duration longer than it may appear at this time.

I may have a time constraint that affects time of depart tomorrow. If I leave the OKC area around 12:15, that will probably put the sfc low play out of reach. The warm sector farther south along the dryline doesn't look too shabby, so this may not be that unfavorable. Forcing for ascent aloft is not progged to be very strong, so I'll look for the areas in which initiation looks more likely. The first area that I see is close to the sfc low in W KS. Another "pattern recognition" area is where the warmest post-dryline air abuts against the warm/moist sector. The 00z NAM places the warmest air in W TX, and the thermal ridge "hits" the rich boundary layer moisture near Clarendon. Probably not coincidentally, the 00z NAM also shows a maximum in 700 mb vertical velocity in that area. Storm motion would take that into western OK.

Since we're in the right exit region of the upper-troposphere jet and aren't likely to see much in the way of differential cyclonic vorticity advection, we may have some issues with subsidence tomorrow. I see a few hints of that in the NAM forecast soundings (weaker lapse rates in the 500-600 mb layer), but there's not much I can do about that unless I can get farther northwest. The mid-upper tropospheric flow may also be 5 kts higher in KS than farther south.

One perhaps minor point: Looking at forecast soundings and hodographs now, there is very little vertical wind shear in the 800-200 mb layer across much of the target area S of DDC, with winds at 800 mb of 40 kts from the SW and winds at 200 mb of ~50-55 kts from the WSW. Low-level hodograph length and shape is substantial, which, given sufficient CAPE and given a storm, should support a better-than-your-average-chase-day tornado prob. Hodos get very large after 00z when the LLJ intensifies, but with only 45-50 kts aloft, that just means that there's literally 0-5 kts of shear through much of the cloud-bearing layer. I'm unsure how this will affect a storm that's "ingesting" >400 m/s 0-3 km SRH, though.

 

[Kelly Sugden]

Wondering if the convection going through now will have the same effect on SW Kansas as it did yesterday... evaporatively cooled (and drier) air advection from east with a resultant decrease in instability.

 

[Jesse Risley]

I'd agree that ongoing convection and residual cloud cover will have an impact on today's scenario, though it looks like a concentrated area of dissipating cloud cover is being noted on visible satellite and surface observations across SE CO and SW KS. The 12z RUC and earlier runs of the HRRR seem to be indicated a dry punch working into the risk area later this afternoon, per H7-H85 RH profiles, which is likely coterminous with SBCAPE values AOA 1,000 J/KG continuing to be depicted along a narrow corridor of instability from near the NE/KS southward into the TX panhandle.

By late afternoon, a 50-60 kt H5 speed max is progged to reach western KS, with Td profiles in the upper 50s and lower 60s reaching at least far SW KS by the 21z timeframe. Directional shear looks pretty good all along the dryline in W KS, with SFC-500 bulk shear profiles on the order of 50-60 kts. Granted, traditional patterns would favor the triple point region in NE CO/NW KS/SW NE, though other areas further south into S KS, W OK and NE TX would also be favorable for supercells, given the mid-level perturbation that takes aim on the region late this afternoon, which could be enough to ignite convection further south too. There is notable CINH on the models, though forcing mechanisms may well be enough to overcome any residual EML by late afternoon.

If convection does materialize, ample streamwise vorticity, instability and favorable LCLs would promote the potential for some tornadoes; progged Skew-T, Log-P profiles across the region also depict favorable lapse rates, notable hydrolapses and WB0 level around 700 mb-800 mb, so large hail (some significant) and damaging winds are also probable threats. Given progged 1-2 km shear profiles, along with the presence of notable CINH ahead of the main area of forcing, I would tend to think this would favor the evolution of more discrete storm modes with any daytime convective activity that does come to fruition.