3/21/11 FCST: NE, KS, OK, TX

[samuel stone]

the 12z nam is now in range for monday and it progs a 999mb surface low over the co,ks boarder with atendant wf east right along I-70 and a dryline southward along aprox a hays to ddc to perryton line. the leading edge of stronger 500MB s.westerly finally cranks into sw kansas by 0z per and upper 50s lower 60s dp along and east of the dl per 12 nam. descent southerly surface winds in front of the dryline (more backing towards the wf) and descent windfields in the mid and upper levels by 0z should be sufficient for sups If storms initiate but therein lies the problem. 700mb temps still look pretty warm as the main upper forcing and 500mb vort max remains a little further west even by 0z. combine with only marginal istability progged by the nam ahead of the dl leaves alot to be desired. back to wind shear: deep layer shear appears to be OK and the nam progs 150-200m2/s2 helicity values from 0-3km but at 0-1km it still isnt showing much in the way of helicity. stronger more backed surface winds would probably help this.

overall still looks like descent setup for sups and maybe tornadoes if initiation can occur.

i thought somebody should start a thread for monday and nobody was so i decided to but id like to see what more experienced forcasters have to say about the posible scenario.

as of right now i would target the wf-dl intersect as theres lower 700mb temps and more backed surface winds in that area. i do also like how the 500mb winds will be more westerly than southerly so any storm that develops in this target may be able to hang right around the wf rather than more quickly north of it. not to mention those wsw 500mb winds will yeild better directional shear.

anyways..... thought?????

 

[Jonathan Whitehead]

SPC Day 3 has gone with a SLT risk for C KS for surface based storms in the afternoon. Its a classic springtime setup with warm sector/dryline/triple point combination. The 12z NAM just came in and has shifted the dryline a bit further E than yesterdays run (what a surprise right). Still waiting on the GFS to come in. At this time it appears front currently drapped across SP today will rapidly retreat NWRD Sunday to about the NE border in response to pressure falls across the lee of the Rockies in response to next big system crashing ashore per 12z upper air analysis. This will allow a slug of Gulf moisture to surge NWRD in its wake. BIG QUESTION right now is the depth of the moisture on Monday. Right now I think 2 nights and 2.5 days should be anough time for moisture up to 800mb or so to reach the warm sector across C/ERN KS. Of course we wont really know the true answer to this till Sunday night when we can see soundings from OUN/FWD/CRP. Also, it comes as no surprise that there will be a sig cap in place across KS during the day but with temps expected to soar into the 70s and low 80s and SIGNIFICANT mid level cooling with the approach of upper wave, I do expect cap to weaken enough to allow for a handful of towers to make it through. Any tower that is able to break the cap will quickly go severe due to strong directional shear and CAPE. Again, look at upper air analysis this morning and you will see some very cold temps at H50 across CA/OR coast. Those temps hold true, then cap breach will not be a problem. Now lets see what GFS says...

 

[Greg McLaughlin]

IF we do get convection to break through the cap on Monday, it looks like the warm front is the only real play. Moisture return is a real issue. I see two reasons for the lack of better moisture return despite the persistent southerly flow across the Plains the last few days. First, the trajectories across the Gulf have been more from the east due to a surface high over the eastern Gulf. This has resulted in air from the east coast being recycled over the Gulf and then being lifted north into the Plains. Since we don't have a true southerly trajectory from the Caribbean, we aren't getting a true tropical airmass to advect into the southern Plains. Despite that, there have been pretty nice dewpoints in the western Gulf the last several days, however this air hasn't made a surge inland despite the good southerly flow over the southern Plains. Looking at the US Drought Monitor graphic, its clear the moderate to extreme drought conditions over the southern Plains are really sapping the moisture out of the air as it tries to advect north over the bone dry terrain.

Despite this, the NAM is showing a decent surge of moisture on Monday to lift north and pool along the warm front. IF this occurs and good insolation takes place early in the day before 850mb RH increases, then we might actually end up with a fairly large warm sector immediately south of the warm front. I am not seeing a true triple point setting up as the actual surface low is progged to be further west along the lee of the Rockies, not in Kansas. And even by Monday evening it has yet to really deepen. Obviously this is because the main vort lobe and LFQ of the main upper jet is still further back over the inter-mountain west. Interestingly enough, the NAM is showing a ripple in the flow overspreading the warm front during the afternoon and evening of Monday. These details are hard to make out at this point and timing and strength of this wave is still uncertain. Assuming this is a well-timed wave, then the potential for diurnal convection may exist. The best low-level shear will be right on the warm front, and if a storm is able to develop and anchor on the warm front, then I would suspect a localized tornado threat may materialize. This is quite an assumption at this point, and a rather optimistic one at that. The odds say that Monday will be a minimal to non-event, however sometimes things work out just right. Its a setup you don't want to write off just yet, but for the chasers who do get their hopes up, Monday has real "let down" potential. Hey, its only March!

 

[Andrew Stoller]

Monday is looking a bit better now based on the 12 z NAM. 55+ degree dewpoints are giving way to 2,000+ J CAPE/LI -7 near the intersection of the dryline and warm front near Hill City, KS. The overall deep layer shear is moderate; the upper trough is still a bit to the west, but it's decent. The NAM does break out convection/precip finally and moves it into south central NE after 00z. If a sustained supercell can stay on the warm side of the front as it lifts north and ride along it, I think there's a decent shot at a tornado.

 

[TimothyCarroll]

I'll just throw this in as a real quick assessment;

Has anyone taken a look at NW/W Texas? I'm seeing a nice pocket of 1000 j/kg of CAPE, -3 to -4 LI's, CINH is only AOR -50 in these areas, nice directional shear with decently backed winds in the mid and upper levels, it could be a nice dryline play, temps in the 65-70f range with Sfc TD's AOR 60f ... The only problem I see is the dryline doesn't advance East out of the central panhandle, and into this pocket of convergence until around 00Z or later, so it MIGHT, if things DO initiate, and the system doesn't slow the pattern, turn out to be a nocturnal event.

chances for this whole setup look very marginal to me, I'm not very excited right now, but we will see with later runs. . .

any suggestions... ?

 

[Derek Weston]

Definitely seems to be a worthy chase for those in the region. 0z NAM depicts an eroded cap across far N/C KS into S/C and SE NEB. Widespread area of CAPE > 1,200 j/kg across this area as well. Hodographs show nice turning with height. Any discrete cell -- in particular, near the WF, where low level shear ought to be maximized -- should have a chance at producing a tornado.

Biggest question mark is the cap. Trough is a bit west yet, so WF will likely be the focal point where forcing is concerned. My play would be to get out a bit ahead of the triple point early on and then track NE with warm front.

 

[Chris Carter]

Read the new SPC discussion for tomorrow. I was going to stay in Omaha and wait for initiation, but I think Beatrice will be my starting point and watch for storms to fire along the dryline before they become elevated.

 

[Darren Addy]

Surprising to me to see this good of a set-up this far north, this early - but I think the odds are still pretty long. Biggest negatives are the combination of the cap and cloud cover not allowing insolation in the area. The RUC sees a much bigger bullseye of EHI than does the NAM. Hastings FD says that models all point to cap winning until later and east of their CWA, where OMA says "tornado cannot be ruled out". However, I think if you want to "swing for the fence" we need to hope that the NAM is right with the placement of the warm front by 0z.

If I were chasing, I would make my initial target Red Cloud, NE and hope that something can beat the cap SW of there (say south of Alma, NE in KS). Nice slow-ish storm motion and the possibility of a right-mover hugging the boundary, rather than crossing over it, are within the realm of possibility - though I think the probabilities are pretty low at this time. Another worrisome development would be a massive bunch of convective crap south of that area in Kansas, which the HRRR is currently indicating by 0z (and indicating no severe storms anywhere by 0z).

If an isolated storm can fire, and it can become a right-mover, you've a nice chasable storm moving ENE at 15-20 kts. I put the best chances for a tornado before sundown in the Alma - Red Cloud - Hastings, NE triangle. But as mentioned above, you could see a whole lot of nothing until later and farther east.

 

[Ryan Pfannkuch]

Ah, the first forecast post of 2011: Sitting here at home in Hastings right now, and I'm putting my money on a "whole lot of nothing" in this immediate area to quote the previous post. Been looking at a variety of short term models this morning, and the message of a stout cap holding on until at least 00z seems to be rather clear. That being said, the latest RUC is starting to catch my eye a little bit with its attempt at initiating something just north of the sfc warm front in the 21-00z time frame near the IA/NE/MO border area. Whether it's real or not, it is depicting a weakness in CIN in that region, possibly due to the fact that 700mb temps in that area should stay more so in the 4-6C range versus the slightly more "cappy" 6-8C range farther west into southern NE/northern KS. Then again, the RUC/NAM as is often the case this time of year are likely overdoing CAPE as well, given sfc dewpoints progged in the 60s near the warm front, which in reality should top out more so in the upper 50s. I'd certainly be more confident in seeing something surface/near-sfc based if the 00z WRF-NMM gave any hint of it, but it, along with the model consensus is really downplaying any legitimate daytime play.

If you are desperate to see anything this evening, even it's only lightning (and yes I'm starting to get that desperate), my advice would be to set up somewhere in a WNW-ESE corridor rougly 60 miles or so either side of a line from Yankton SD - Carroll IA -- Des Moines IA and wait for rapidly moving elevated convection, possibly supercellular, to develop along the nose of the H85 low level jet.

 

[Brandon Sullivan]

Latest RUC trends show the CINH eroding gradually from around 4pm to 7pm from MO back west through northeast Kansas... There is some insane low level lapse rates about 10c/km across northeast KS, with HRRR showing 3000+ CAPE in some locales across KS/NE/MO area.. RUC also starting to show some precip breaking out in that area. Already pulled the trigger and we are on the road. Even if cap holds, could be some nice night supercell shots, and another chase tomorrow.. Good luck everyone!

 

[Mike Johnston]

Interesting area over the next few hours might be the Kansas City metro and surrounding locales. Lifted Indexes showing -5 now, and the 3-hour RUC forecast has CAPE getting up over 2,500 j/kg with CIN eroding. Observations tend to support some developing instability with 79t/61td reported at Kansas City International airport the last hour and visible satellite has been showing nice clearing area just south of the warm front. Initiation is still an issue, but the LFC levels are down to around 2,000 meters now, and the LCL-to-LFC relative humidity ~ 80% over this area. RUC is also showing some hints of precip around 20z. I don't know, it's not strictly in SPC's risk area, just some conditions I've noticed this afternoon that seem to be developing.