6/4/08 FCST: KS/NE/OK/CO/IA

[Matt Grantham]

Wow I can't believe nothing has been said about Wednesday's potential. With an unseasonably deep and large 500mb trough digging into the West the stage looks set for a tornado event on this day. Shear and instability are abundant across the forecast area with a warm front depicted on the NAM draped across northern Kansas. The amplitude of this trough is quite low compared to the one that affected these areas on 5/22-5/23, but it does remind me of that setup at least at the surface. Just simply looking at the 500mb presentation on the NAM, I am reminded of major outbreaks of the past. The only issue on Wednesday that I see is a potentially strong cap.

 

[Adam Penney]

This day certainly bears watching, however the stout CAP as mentioned is easily the main issue on this day. Storm coverage would be quite limited, so as far as a "big" tornado outbreak goes, I just don't see it ATTM. I will continue to watch closely however, as the situation becomes clearer in the coming few days.

 

[Matt Grantham]

The cap is definitely a huge question mark at this point, so my choice of words wasn't the best. That's why I hardly ever post in these things. However and storms that develop will certainly have plenty of tornadic potential.

 

[Mike Hollingshead]

Yeah I'm shocked no talk on this one too. I actually just noticed it was this dead.

Here's a "hello" FCST sounding for Beatrice NE at 0z. That'd likely be fun to watch if it verified.

The strong warm front should light up Wednesday afternoon. Cap is actually looking to be gone pretty early along it, if it gets north enough. Dryline might be rather shut down, but se NE/sw IA should light up with at least a couple beasts. The sfc front makes me think of May 10, 2005 a bit in this area. The juice would be a lot better though. I like this better as a chase day than Thursday so far.

Omaha 0z

 

[Darrin Rasberry]

Well, to say the WRF and GFS are in "general agreement" to most of the features of this is like saying me and my insurance company are in general agreement that my windshield is broken. Plenty of disagreement stems past that general point, so I'm not surprised to see the SPC sitting on their hands for this one before highlighting a MDT area.

500mb flow and direction: check. (Speeds eh let's kind of pretend they're fine for now, they're decent but somewhat low storm-relative in forecast ATTM if I'm reading the charts correctly).

850mb's and moisture return/depth are dandy, expecting moisture to not be a problem given the 80's in forecast and low 70's Tds with wind to deliver the goods, if both models are to be believed.

Warm Front Quality INVOF SW IA: WRF says "not very high quality" while the GFS says "sharp." Look at the wind direction and temp dropoff the 00z GFS places in Iowa and compare with the WRF. The winds are northerly and the temp dropoff is significant in the GFS's guess; the WRF has southeasterly flow across all of Iowa and much less of a dropoff temp-wise.

CINH is unreadable on the WRF from the 00z run for some reason, but GFS has it high enough for a possible local event INVOF SE NE/SW IA or even NE KS. CAPE is there on both models, extends less with the GFS's sharper warm front feature, and shear is pretty good. Temps aloft at 700mb are 10-14 degrees on the WRF in this vicinity but are a few degrees cooler on the GFS prog. 850mbs are pretty warm here on both models for what that's worth (if anything).

For now I'm going to wishcast the GFS' opinion, at least until the 12z runs arrive, since it seems like it has a better handle on the strength and definition of the WF IMO. For now, I'm going to box an area from Council Bluffs over to Ottumwa, on over to Lincoln to a point directly south of there on the NE/KS border. This will probably narrow in a couple of hours when I get to see all the details and parameters of the new run. That box might be too far south off the vicinity of the progged warm front boundary just a bit though.

 

[Scott Lincoln]

We need a moderator to add "/IA" to the title of this forecast thread.

Its obvious from SPC forecasts and looking at model data that western Iowa at a minimum is in the threat area for tornadoes. I'd definitely be watching southwest Iowa and southeast Nebraska for tomorrow, but the recent WRF runs that dont break out any daytime precipitation concern me. I dont want to get too detailed in a forecast though, as convection forming in that area today could have major implications for the location of the warm front tomorrow.

 

[Van DeWald]

Am thinking that a polygon bounded by KGBD to KRSL to KSLN could be the sweet spot for Wednesday afternoon/evening, with tornadic storm development 00z-03z, if you believe the Nam that is. It's now forecasting 0-6km bulk shear is pushing 60kts, while 0-1km shear increases to about 40 kts by 03z in this area. 0-1km EHI increases to 10+ in this area with 0-1km helicity increasing to 460 and LCLs are forecast to drop to 600-800m. Dependent on where the front ends up though. Looks like RUC is still focusing things in the quad-state intersetion of NE/KS/MO/IA though.

 

[afischer]

The synoptic pattern forecast tomorrow aftn/eve certainly has some strong resemblences to past violent afterdark tornado events in the central plains. If a "nice" mesoscale surface pattern emerges over KS (e.g. properly oriented quasi-stationary front, etc) and the area can stay north of the fairly hallacious cap moving out into the southern plains tonight/tomorrow... it could get quite scary as Van stated. If a well-timed impulse can offer synoptic scale support and/or keep the 700mb thermal ridge a bit suppressed, that would be good too. As of now I'm kind of worried about the cap magnitude (and how far significantly rich moisture will back up into central KS). Accordingly, another good target may emerge farther northeast away from the hotter cap, if an OFB materializes or if the front is oriented right... maybe southwest IA. We'll know a lot more about both targets tomorrow a.m. after these rounds of storms have moved through.

 

[Mike Hollingshead]

Well, 0z GFS is in and it's a lot more kind on morning/early afternoon precip. So it's further north with the front, which will be a much better scenario. I could see the GFS being closer to reality(crossing fingers anyway). Seems like the last couple runs of the NAM just started inserting that boundary shoving morning crap. If it winds up north, it would likely be crazy into the night, the way both models really crank up and back the low level jet. That 15c 700mb line really races ne after dark, so if it does end up further south in KS, night time craziness may be saved a bit. Either route, as long as it's I70 north, there's a window for some nice supercells along the warm front or any OFB.

 

[Bill Schintler]

Chase Target for Wednesday, June 4

Chase target:
Fairview, KS.

Timing and storm mode:
Surface-based convection will fire at 4 PM CDT, with supercells and a few tornadoes possible.

Synopsis:
Zonal pattern will amplify over the next 24hrs as the WRN CONUS trough digs. A compact but potent vort max will race though IA between 12-18 Z while a secondary impulse approaches from the SW late in the period. SFC low pressure will strengthen over SWRN KS/SERN CO and a SFC WF will extend SE and then E along the IA/MO border through 00Z. This evening, area and upstream soundings (TOP, OAX, LBF, and DDC) indicated steep mid-level lapse rates. Recovery should take place in wake of convection ongoing in KS/OK with strong SRLY SFC/H85 flow tomorrow. The latest GFS has a poor handle on ongoing convection in KS. Latest MDL trends place the WF and associated features further S, which seems reasonable given ongoing convective trends in MO.

Discussion:
FCST is complicated by the evolution of elevated convection early in the period and resulting boundaries and cloud cover during the day. A small MCS should develop in the morning in ERN KS, and track NE into NWRN IA. Partial clearing will take place from SW to NE, allowing for rapid destabilization with SFC dewpoints of around 70F beneath steep mid-level lapse rates of 8C/km. Attention theb turns to SFC-based convective initiation along and just N of a WF where a WSWRLY 25kt LLJ overspreads 10kt ERLY SFC flow. All forms of SVR WX are likely with 50kt of deep-layer shear and SFC-3km SRH’s of 300m2/s2 coincident with 2000J/kg of 100mb MLCAPE and LCL levels of 800m AGU. Storms will evolve into an MCS and track E though IA and into IL, assisted by a strengthening LLJ.

Please feel free to PM me for nowcasting.

- bill
11:00 PM CDT, 06/03/08

 

[Mark Farnik]

The 1300 Day 1 SPC outlook just upgraded portions of northern Kansas/southern Nebraska into southwestern Iowa and northwestern Missouri to Moderate Risk. Latest indications are the cap will persist until late in the day, when convection will initiate near the surface low in far eastern CO/northwestern KS/southwestern NE. As the storms move east towards evening, a significant tornado threat may emerge near and east/northeast of the surface low along the warm front in a corridor from Oakely, KS to Clarinda, IA as the 700 mb temps cool off and a 65 knot south/southwesterly low level jet develops. The Hays 03z sounding is crazy, showing 3000 j/kg of CAPE, LI of -9, SRH values of 587 and BRN Shear values of 29! I think the best play for tornadic supercells before dark will be in north central Kansas near and just northeast of the surface low, where shear and instability values will be maximized near the surface low/warm front intersection. My preliminary target for the day is good ol' WaKeeney, KS, seeing as that vicinity has been a veritable tornado magnet this year.

 

[Tim Marshall]

TARGET: Hays to Great Bend KS. TIME OF DEPARTURE FROM SALINA: Noon. A classic severe weather set-up today for KS. This morning's surface low near Pratt should wash out as a new low begins to form on the lee side of the Rocky Mountains. PROS- Ample surface moisture is already in place and should push westward in backed flow toward the western portion of the state. However, a dryline is expected to mix eastward with a bulge forming south of I-70 vicinity by 00Z per RUC. An unusually strong east-northeast mid-level jet will steer storms quickly to the northeast reaching I-135 by evening. CONS- Strong cap over OK and S KS noted on morning soundings and the lack of convergence along the boundary in KS. We will be back in SLN tonight. TM

 

[scott r currens]

I have to work till 3PM so I have a significant geographic bias to my forecast. That being said I really like what I am seeing from 12Z RUC along the KS/NE border. An uncapped WF with >3000 CAPE and excellent LLwinds can be ignored. The only weakness in the flow is at 500mb but that has increased some since last night’s runs. The biggest problem I see is targeting CI along the WF. It's a big area and I don't see any reason to favor one section of it over another. With my late start satellite and radar will likely guide me to my final target.

Departure: Leavenworth, KS at 3PM
Target: Marysville, KS to Hebron, NE

 

[Warren Faidley]

Interesting forecast today, as far as picking the exact spot for "isolated" initiation vs. cap bust, vs. rapid, late afternoon, early evening rapid development with multiple storms to work around at dusk/dark. Think I'll play a safe mode and target I-70 in n-central KS or areas just south, (Great Bend) with an option to drop south, north or back slightly to the SW if things look more isolated there. Sat. loop and surf. map will be major forecast tools today. Hoping extra soundings will be launched today.

Good luck, safe travels.....

W.

 

[Jeff Snyder]

I'm having a tough time picking a target based on the 12z NAM, 12z RUC, and 00z explicit-convection WRF runs. The warm front is a screaming "come here" target, and the NAM is ~50-60 mi farther S with the warm front than the 12z RUC is (just N of I70 vs. N of the KS/NE border). Deep-layer shear should be just fine for supercells pretty much everywhere, and the easterly winds on the N side of the warm front produce some pretty tempting hodographs. For example, check out the CNK forecast sounding for 00z this evening (based on 12z NAM). A second potential target is farther south, from near PTT to WWR. Morning soundings and profilers show strong mid-level flow over this area (and just upstream), but the primary question seems to be the degree of moisture along the dryline down there by late afternoon; the RUC wants to mix out much of the good juice, while the NAM keeps 65+ Tds along the dryline down there. The explicit convection runs each forecast convection in that corridor this evening, and the 12z NAM also shows QPF by 0z there as well. LCLs will likely be higher down there owing to hot sfc temps required to deplete the convective inhibition associated with ~13F 700mb temps. Low-level shear all over the warm sector should go bonkers by 3z (as expected), but the southern target may stabilize more quickly after 0z.

Right now, we're in GBD, a fine place to play "monkey in the middle" for the next few hours. I guess I'll wait to see what the sfc obs show with regards to Tds in far NW OK later this afternoon. IF that moisture starts to mix out (or be shunted eastward), then I'll argue for blasting NNE to play the warm front near the NE/KS border.