5/10/10 FCST: TX / OK / KS / CO/ MO

[Rob Lightbown]

Quickly looking at the 12Z NAM and GFS models, I think the GFS may be pulling the low northeast too quickly and the NAM, in the end, may be closer to reality. In my eyes, it seems the tendency is for the GFS to speed the timing up a little too much as of late.

Earlier this morning, I thought an area around Lawton would be a good target spot, but now starting to think a little further west halfway between Altus and Frederick.

 

[afischer]

At this stage (and w/ the evolving trough still offshore) I'm still hanging my hat on the EC/GFS/GEFS... the 12Z NAM seems a good bit slower and farther south in comparison. The 00Z GFS and GEFS mass fields looked pretty similar. The 00Z EC came in slightly more progressive, and the brand new 12Z GFS is pretty closely in line with that (e.g. dryline to near I-35 in south KS-OK by 00Z Tues, and forcing via the s/w trough rotating atop the dryline earlier--by at least 00Z). We'll see how the 12Z GEFS trends. It's a bit depressing how cloudy and cool (i.e., basically almost saturated) the last several runs of the GFS have showed the boundary layer to remain ahead of much of the dryline through peak heating... will be interesting to see how that pans out. With at least modest BL heating and the forecast cooling of the EML from the upper wave, hopefully deep moist convection can initiate and be maintained (at least from the KS-OK border northward, etc.) Hodographs forecast by the new GFS remain outrageous (strongly curved, with 50kt+ from 500m agl up), and show 0-1 km SRH of 400-500 m2/s2 for Bunkers right-movers across the KS and northern OK portions of the warm sector by 00Z.

 

[Mikey Gribble]

The 12Z NAM is much farther west with the placement of surface features, but the overall setup and paramaters are very similiar. I haven't seen the 12Z GFS yet so I'm going off last nights run.
I am extremely impressed with what the 12Z NAM is showing. I just updated my forecast on my blog so I'll just copy and paste that here...


Well the 12Z NAM is out and it looks extremely good for Monday. It actually shows an even slightly better setup than the GFS, which was already amazing. It is hard to exagerate the tornado potential should this verify. This would be right up there with the best setups I’ve ever seen.
There are some pretty significant differences on the placement of surface boundaries between the GFS and NAM. That may be resolved with this mornings GFS, but I haven’t seen it yet. The NAM shows the surface low over the very far SW corner of Kansas with a dryline extending south from there into the Texas panhandle. I made the map above based on the NAM’s placement of surface features in its latest run. The exact location of this setup is very much uncertain still though. I would prefer it was closer to the GFS solution where storms would track across southern Kansas. That is by far my favorite place to chase in the plains. The terrain and road networks are great down there. One thing that sucks really bad is that you don’t get a signal in the NW portion of Oklahoma if you have Verizon, which I do. I hate not having internet when I’m in the field, but I can always show up early to a wifi spot.
The NAM is in line with last nights GFS with moisture return and shows mid 60 dewpoints along the dryline. It is also hinting at convection breaking out in a couple places along the dryline. My only two small concerns with this setup have been the cap and veering 850mb winds earlier in the day, and that aleviates my capping concerns. There is a dryline bulge over the southern portion of the panhandle and some place between there and the Oklahoma panhandle is where the sweet spot for tornadoes would be if the NAM’s placement of surface boundaries verifies.
As mentioned in previous forecasts deep layer shear and CAPE profiles are extremely favorable for supercells. Storm motions are normal to the boundary so discrete supercells will be the mode of convection.
The tornado potential with this setup is nothing short of amazing. CAPE is up to >3500J/kg along the dryline with the 12Z NAM. The shear profiles are pretty much the same as in previous runs of the GFS. Surface winds are out of the SE at 20kts, 850mb winds are out of the south at 45kts and mid level winds are out of the southwest at 55kts. I haven’t seen any forecast soundings for the area, but I’m sure the hodograph is amazing ahead of the dryline. Low level shear is about as good as it gets with this style of setup. The NAM is showing 0-1km SRH >400m2/s2 ahead of the dryline in the southern half of the panhandle and >600m2/s2 over the northern half of the panhandle. That is extremely impressive to say the least. That is also right in line with what the GFS has been showing in previous runs.
Assuming the NAM can verify, this would be a major tornado outbreak. With strong instability, steep lapse rates, good moisture and incredible shear profiles the area ahead of the dryline would be extremely favorable for cyclic tornadic supercells capable of producing violent long-track tornadoes. When you consider the paramaters being forecast and the spatial coverage, this is up there with a May 4th, 2003 style tornado outbreak. This is one of the best, if not the best setup I’ve ever seen in the plains. Just consider some of the paramaters the NAM is showing. 1km EHI at 12.9, 400-600 01km SRH, significant tornado probs approaching 20 (have seen that a few times before). This is about as good as it gets.
I am going to go look at the GFS and a few more things from the NAM and then I’ll post a forecast update.

 

[Darren Wilson]

The upstream shortwave "kicker" trough is going to determine the speed and location of our shortwave. Hopefully once the kicker moves on shore the models will get a better hold of it. I tend to believe the slower NAM solution at this moment, don't ask me why it's just a gut feeling.This is shaping up to be a classic setup on the dryline with good instability, high shear, breakable cap, and manageable LCL's. I only wish it wasn't on finals week!

 

[Mikey Gribble]

The 12Z GFS is trying to pee on our parade with the 500mb trough/jet streak translating faster to the east than it has shown in previous runs. The consequence is veering low level winds, which would be damning to the tornado potential.
The good news is that this is a deviation from previous runs of the GFS and the NAM, ECMWF and former GFS runs have all been much slower. The other thing that is keeping me from worrying too much about this is that I almost always favor the NAM over the GFS, especially on timing and location of boundaries.
I'm not going to sweat this at all, but if it shows it again in tonights run then that will start to concern me.

 

[Jeff Duda]

I've been watching the FIM as well over the last few days. I know it's not an operational model, but it has been very consistent with itself as well as with the GFS and ECMWF in having a faster solution. I will continue to keep an eye on d(prog)/dt.

 

[Chuck Robertson]

There has been much posted about the positives of Monday's setup, but as some others have already pointed out, there are some pretty big negatives as well. Yes, there appears to be a lot of potential, but certainly not a shoe in - at least not yet.

I'm pretty concerned with the increasing spread between the NAM and the GFS for Monday evening. NAM has the sfc low at LBL and the GFS has it near ICT. Huge difference! Also, GFS shows 850mb winds solid from the southwest over most of the area.

I'm also concerned about the cold air to the north of the front and triple point across KS. NAM even shows about half of KS in the 40's! Any storms that fire near the front better find a way to turn right real quickly, or they will face a quick demise. According to the NAM, most of KS may be out of this one.

Also, further south, yes the cap may break, but Im concerned about the large T-Td spreads across SW OK and points further south.

Not yet sure we are looking at an outbreak. Could still be more of a local event for a "sweet spot" somewhere, with plenty of chasers there I'm sure. Yes, lots of potential, but with the new model inconsistencies, I'm not selling the farm just yet for a "widespread outbreak ".

 

[afischer]

I guess I didn't find much to be concerned about regarding either veering low-level winds or LLJ orientation on the 12Z GFS in particular. If low-level veering occurred, perhaps that was in reference to past model runs rather than veering with time? If so... actually, the entire hodograph probably "veered" (turned clockwise) rather than just the low-level flow, due to the faster solution and more veered mid- and high-level flow as well. A comparison of 06Z and 12Z GFS hodos verifies this, with the entire hodos turning ~15 deg between the two runs (didn't see the 00Z ones). The 12Z hodos from the GFS are actually trending toward an analog for the 4-2-06 outbreak in northeastern AR-southeast MO-west TN... a very "veered" set-up (e.g. 1km flow from 220 degrees!!) compared to your classic Great Plains cases , but with optimal hodos. The 12Z GFS hodos aren't quite that veered, but are trending that way (the hodo shapes are very similar between the GFS and 4-2-06 observed).

Via high res 12Z GFS soundings, I see 1km flow in the warm sector uniformly from 205-210 degrees, and given the background pattern (i.e., the more zonal solution; relatively veered deep shear vectors, and Bunkers storm motions from 245-260 degrees) this orientation of the LLJ seems fine (if not optimal?). In fact, the fcst 12Z GFS hodos don't come much more classic than that... 30-35 deg of curvature from sfc to 1km (pretty much typical for warm sector sig tor hodos), relatively intense LLJ, and unusually strong mid-level curvature to help the storm move even farther off the hodo than is necessary for large SRH. I also don't personally see any issues regarding either BL moisture depth ahead of the dryline, or the magnitude of moisture convergence along the dryline, on the 12Z GFS. I think the entire solution just kind of changed slightly, but (moisture return/BL heating/EML cooling issues aside) still looks similarly impressive.

 

[Mike Hollingshead]

Nice to see the 12z ECMWF coming in as a compromise between the slow nam and fast gfs.

GFS 12z Monday has trough axis generally along/east of CO/UT border.
ECMWF 12z Monday has it mostly right on the CO/UT border and a bit more amplified.
NAM 12z Monday has it about on the UT/NV border.

I'd say there's some pretty big signals for an epic day. I for one am praying the NAM isn't realized. Too many starved chasers right now to plop that on I40 in the TX panhandle. Please mother nature spread this out more lol.

Seems that last setup out there this year, the one that paid off that I didn't chase. Goodnight TX, KS tors, and CO tors. Seemed that one had a decent spread in sfc features between GFS and NAM. I think the GFS was the one that won out with a north reality. I know before that with some setups in the sw IA/ne KS/nwMO area GFS nailed the lead sfc low/wave veering flow and drying out that area before the secondary low took over. While NAM showed no such thing till very late runs. fwiw

At the same time, the cold air scares me. As in regardless of the current timing differences, I could see that restricting the chase target south anyway. Course I could see it not being an issue at all just as easily. I just sort of keep seeing a stuck cold air mass that gets full of clouds and drizzle as the juice tries to push north. At least a person only needs and can chase one target anyway and no matter what, seems there will be a great one somewhere out there Monday. Might need a tank to find a parking spot however.

 

[Jeff Passner]

The killer in veered 850 winds is not the directional shear or SRH in many cases; it's the depth of the moisture. In the SE USA it is not as big as issue because veered winds still may come from a moist source. In the Plains, a 220wind comes from New Mexico and the desert. Sure, the hodograph may still be adequate but the 850 dew point might drop to 0C or the depth of the moist layer might be reduced to 50 hPa. I'm not saying this will happen, but it's reason veered winds don't matter as much in the SE USA. It's a typical GFS bias anyway to badly veer the 1200 UTC winds. The importance of Churck Robinson's point is the position of the surface low... A deeper low to the west will act to add moisture to the low-level profile and the moisture depth. An open wave, racing to the NE, will indeed reduce the moisture depth.

Lots can happen, but right now, the WRF and GFS have major differences, which is no surprise this far out. One thing for sure, the GFS's solution would have storm motion at 40-50 mph. The WRF would also move the storms quickly. This is no repeat of April 22.

 

[Brett Roberts]

FWIW, the 12z UKMET is more similar to the NAM in the timing of the shortwave through H+72. The GGEM and ECMWF both appear to be a compromise between the GFS and NAM timing, though the Euro is probably closer to the GFS. I'm not sure exactly what I'd prefer, but it's most certainly not the 12z GFS verbatim.

I don't have much to add at this point other than that I'd echo Jeff's concerns about moisture depth should a faster solution verify with veered 850 mb winds. There is a good paper out there by Rich Thompson and others, I believe a case study of the 1999-05-03 outbreak, in which it's found that optimal hodographs for Great Plains tornado outbreaks involve mainly speed shear in the lowest 1-1.5 km, with directional shear kicking in above that layer. I believe the reason is exactly what Jeff stated: we're located to the W of the Gulf of Mexico, so as soon as we start getting a westerly component to our low-level flow, moisture becomes a major concern.

 

[Mikey Gribble]

Yeah there is a big spread between the NAM and GFS on the placement of the surface boundaries, but what other difference has there been if you disregard this mornings run of the GFS? Both models have been showing the same moisture quality for several runs. Both models have shown virtually identical shear profiles over the warm sector. Both models have shown similiar CAPE values for several runs, etc. The paramaters that influence storm potential have not been very different between the models up until this mornings run of the GFS. I've been archiving charts from different runs over the last several days just so I could go back and compare them to current runs if something like this happened.

I don't like the faster timing with the GFS any more than anybody else. Veering low level winds are damning to tornado potential for several reasons as mentioned before in this thread. This is one run of the GFS though that deviates from previous runs of the same model and deviates from solutions with the ECMWF and NAM. Neither of those models have shown the trough kicking that far east by Monday afternoon and although the GFS has been faster than the NAM and ECMWF with previous runs, it has never been this fast and it has never veered low level winds until now.

I have no idea what solution will verify, but I find it extremely difficult to start pointing out negatives with this setup after one bad run. Let's keep this in perspective.
I don't really care where the models place the surface low as long as it doesn't affect anything else. Whether I chase Texas or Kansas doesn't make a whole lot of difference to me.

 

[Chuck Robertson]

Please don't take me wrong. I still think there will be at least some tornadoes on Monday, especially given the fact that we have a strong system crossing the plains in early to mid May with at least descent moisture in place. I'm just not yet convinced that an outbreak of significant tornadoes is a slam dunk - at least not yet. Way too early to say that. Yes, the latest GFS in only one of its runs. However, it happens to be the most important one since it contains the latest data, and extrapolates the least amount in the temporal domain.

Hmmmm! Do you think we will all be anticipating each new run of models for this system with baited breath?

 

[Mikey Gribble]

I see what you're saying.
It is pretty unusual to get a trough with decent moisture through the plains with no tornadoes in May. Things just always tend to work out this time of year.
I'm not convinced either that this will be a major outbreak. I am convinced that if the NAM verifies it will be a major tornado outbreak, but my confidence isn't that high yet in the models verifying. Tornado setups are very fragile things. One subtle detail can complete ruin a setup. When you are hanging by that thin of a thread I've learned never to expect anything until it happens.
Still the NAM does look extremely promising and the 12Z GFS is definitely the outlier. Just pray to god it doesn't show the same thing in the next run. What a nightmare that will be if later tonight the NAM follows suit.

 

[Mike Hollingshead]

Still the NAM does look extremely promising and the 12Z GFS is definitely the outlier. Just pray to god it doesn't show the same thing in the next run. What a nightmare that will be if later tonight the NAM follows suit.

18z NAM took a fairly fat trend that way, so might not have to wait till tonight lol. At least more progressive and flatter. But even if the 12z GFS came to be still looks like a great chase day to me. I think this one will have a lot more work to do to ruin the day than it does to be a great day. It's not as if anything is over veering the crap out of the 850s. I think a lot of those bad days that had some veered 850s also had other issues, like late and questionable moisture...not to mention flow aloft not being as equally veered. Also many of those days, and others, have nearly westerly 850s for a good chunk of the day/morning. Not seeing that on the GFS either. All the GFS has to be is just a hair fast with that sfc low from 18-0z and you'd still have a huge day. Even if it was that fast with that it's not killing the day imo.

If I had to pick a solution that probably averages it all out the most, probably be close to what is showing on the 18z NAM.