6/17/09 FCST: NE / KS / IA / MO/SD

[Jeff Snyder]

I'm actually a quite interested in tomorrow's forecast, partly because I think it will be the final chase of the season for this OKC-based chaser. The upper ridge builds across the southern Plains as the stronger flow aloft shifts northward. Moisture will hang around (as we expect for this time of year), and surface temps in the low 90s north of a weak sfc front will lead to extreme instability again tomorrow (MLCAPE >4500 j/kg) across northeastern KS, far southeastern NE, perhaps extreme southwestern IA, and much of the northern 1/2 of MO. The 12z NAM continues to forecast southeasterly surface flow through the day north and east of a Kearney, NE, to Topeka, KS line, which, with ~40 kt 500 mb flow, results in 40 (near I70) to 55 kt (near I80) deep-layer shear. In fact, both the GFS and NAM have what looks like a dryline bulge pointing towards Salina by 0z; nicely backed southeasterly surface flow exists north and east of said feature. Finally, some warm (>14 C) 700mb air will try to approach from the southwest, but the 12z NAM and GFS indicate the 14C isotherm will stay along and just south of I70 by 00z. The NAM also indicates a potential weak vort max approaching the area during the afternoon; the NAM has an area of convection by/before 0z in northeasern KS.

Low-level shear is nice but nothing to write home about by 00z (~250+ m2/s2 0-3km SRH in northeastern KS at 0z), but it does rapidly increase thereafter. For example, check out the CAPE/SRH plot valid at 3z Thursday (i.e. Wednesday evening) HERE. The LLJ cranks up and veers a bit by 6z; I'd rather it stay backed to southerly .

My initial target is somewhere in far northeastern KS or southeastern NE, with storm motion to the east. Some potential exists in the "bent back" area all the way to the southwestern NE / northeastern CO border, too.

 

[Chris Allington]

Jeff,

I've been watching this too and not thinking the cap would break... however, now as you mention the higher 700 & 500 mb temps area confined down along the I-70 corridor. I like the extreme CAPE (4000-4500 j/kg) due to low 70s dews and low 90s temperatures, and a nice theta-e ridge nosing into extreme SE NE, that with localized convergence along the weak warmfront I think may be able to pop something. If it does the better mid-level westerlies and SEly surface winds give some great turning with height, but low level winds are rather anemic.

We will likely start out somewhere on the KS/NE border and see if we can break the stout cap sometime in the late afternoon. Say maybe HWY 77 near the Beatrice area.

 

[Brandon Sullivan]

Ive been looking at this also.. The 4KM WRF doesn't show any precip developing in the northeast KS area, but im not always sold on forecast radar anyways. The NAM however shows some precip over Northeast KS.

CINH looks to be eroded by 00z, and the Lid Strength Index is well down into breakable levels..

Pretty much nailed my thoughts, also note the Theta E axis nosing into the area. Nice little kink at H7, further supporting the idea of convection materializing. At this time I would target right along the Surface Boundary in southeast Nebraska..

I have a feeling it will all go into an eastward propogating MCS once the LLJ cranks, and veers overnight.

 

[Andrea Griffa]

I'm pretty impressed by tomorrow's setup and overall by the quantity of energy ready to be ingested by storms. I didn't see 80F of dew by a lot of time on dupage maps. Actually it is not so common to see by WRF more than 5000 J/Kg so widespread in the territory. I think Ruc is gonna get crazy tomorrow.
Nice mid level shear well oriented with the dry line, coupled with 20-25 knots of LLJ coming to the south-east; not to mention the quite sharp dry line bulging in NE Kansas and the very strong cap that will be in place. Extreme cape could make up for the lack of substantial low level shear.
This could result in isolated supercells capable of producing extremely large hail and also a couple of strong tornadoes IMO in NE KS and SE NE.

Wish I could be there. Good luck and stay safe, you guys.

 

[Jeff Duda]

I don't know if I agree with the NAM's output of 80F dewpoints (granted in one spot) near St. Joeseph, but it is going to be quite sultry out there. 12Z models seem to suggest highly (i.e., they put a "GO HERE!!!" X) right around Beatrice. Additionally, if 850 winds stay backed in that area like they are progged to, helicity will be good, as 700 mb winds are SW at 25-30 kts.

 

[Matthew Piechota]

weds and thurs look pretty good. southeast NE to northeast KS look primed, say beatrice to topeka or just north around holton. 500 flow near 40kts out of the west with back 850s in the area near 20kts so shear is pretty good. GFS has higher dews then the WRF but they should be able to get to the near mid 60's with a good theta-e axis right into the area with MLCAPE values possibly up near 4000 or better. both models are breaking out precip at 0z, GFS is farther north into southeast NE and WRF has precip in northeast KS.

Its to far for me to chase tomorrow but I will hopefully be chasing somewhere closer on thursday. for tomorrow, I would probably play somewhere west of nebraska city right on the border. I would guess tomorrow will be a moderate at some point in the day. really looks good for some tornadoes, maybe one or two sig tors.

 

[Bill Schintler]

Chasing Target for Wednesday, June 17

Chase target:
Sutton, NE (20 miles east of Hastings).

Timing and storm mode:
Supercell storms should form by 5 PM CDT, with a full spectrum of severe weather expected, including a few tornadoes. Individual storms will track east at 15 mph. During the evening hours into the overnight, storms will evolve into a derecho and race east through NE and IA (similar to KS on Monday).

Discussion:
Strong instability should develop along and N of a WF extending E from low pressure in WRN KS as steep mid-level lapse rates of 8-8.5C/km overspread a 150mb-deep well-mixed BL with SFC dewpoints of 65-70F. Warm mid-level temperatures S of the KS/NEB border should inhibit any convection as the ULVL ridge builds. An area of elevated convection should be ongoing by 18Z in NWRN NEB. This will dissipate and move N and E of the area by mid-afternoon.

Some uncertainty remains concerning details of a number of compact disturbances that will rotate overh the area within anticyclonic ULVL flow. Indications are that an H5/H7 disturbance will arrive in SWRN NEB by 21Z, with surface-based initiation shortly thereafter along the NEB/KS border during the period of peak insolation. A canopy of CI will arrive in the area from CO, signaling the approach of this wave.

Surface-based storms should rapidly become severe given the degree of instability and shear. SFC-5km shear should locally increase to 50-60kts with the approach of the aforementioned wave. Furthermore, hodograph curvatures along and north of the boundary will become extremely large as the BL begins to decouple and the LLJ strengthens and veers over backed SFC flow. During the evening hours and overnight, the nose of a 40kt LLJ will aid in the maintenance of a large storm complex that will track E through NEB and then IA.

- Bill

PS: feel free to contact me via PM for nowcast support.

10:55 PM CDT, 06/16/09

 

[Nick Hartley]

I think it would be wise to add Eastern South Dakota to the thread for tomorrow. Initation will take off around 2 or 3 PM much like today. All the ingredients seem to be in place for a classic South Dakota tornado event and will carry on into Thursday. Plus there appears to be some wind backing an event and a series of shortwaves in the mix. I think an area from 6E5 (De Smet) to BKX (Brookings) towards PQN (Pipestone, MN) will be the intitation point with storms moving slowly east and north and building south as the day progresses.

 

[John Farley]

I agree Nebraska looks like the best play tomorrow. Too far for me, so I am watching the band of very good instability that both the NAM and the GFS (but especially the NAM) have from around Omaha southeastward to just west of St. Louis. There is good directional shear in this area too, especially along the boundary (not sure if it is really the synoptic warm front or the leftover boundary from this morning's convection and cold pool, moving northeastward). In any case, it looks like capping will be a big limiting factor in this area, as neither model breaks out significant precip in this area, despite the high to extreme instability. But if something does manage to fire and sustain itself for a while along the boundary, I would think a very impressive supercell could occur. In other words, probably nothing, but if something does happen, it could be quite a show. I will be watching this are closely and looking at the morning models to see if there is any trend toward breaking out some precip in this area.

 

[Chad Cowan]

Looks like a solid 15% hatched tor and 45% hatched hail MDT risk for much of Nebraska and portions of western Iowa and possibly even extreme northeast Colorado. Maybe even a 45% hatched wind over Iowa/ northern Missouri on the 01z update once it's clear where the MCS will track. You don't see this amount of moisture, instability and shear in the same spot very often. Low-level shear really cranks up after 0z so I'm hoping the cap holds until around then which it looks like it will. I'm expecting multiple supercells along I-80 in NE possibly extending into wrn IA. After the tornadic sups line out there could be some tornadic LEWPs embedded in the MCS given the magnitude of the shear.

Interestingly the NCEP forecast reflectivity blows up a supercell at 23z right in the heart of the 15C 700 temps on the dryline in south-central KS. Something to keep an eye on, but the best upper support is well north of there.

 

[Jeff Snyder]

Chad -- I agree that it certainly looks to be more than a simple 5% tor prob day! The 6z SWODY1 tend to be a bit conservative since there are often mesoscale details to sift through after overnight convection, but I think tomorrow falls in line with a solid 15% hatched tor prob day.

I think Dan Dawson and myself may give Ma Nature one more go tomorrow somewhere near the NE/KS border N of SLN and/or adjacent parts of southeastern Nebraska. I know forecast soundings from models can (and do, often) look much better than verifying soundings, but I'm not sure how you can look at something like the this sounding near BIE valid 3Z (from tonight's 00z NAM) and not get excited. I know there is some near-surface stability in that (and nearby) soundings, but I'm not sure that would deter an established supercell with well-determined vertical perturbation pressure gradients, and there may well be some enhanced mixing in the inflow of the convection that can help mix out that near-surface stable layer (or, at least, that's my hope). At 00z, I like anywhere N of I70 in northeastern KS and southern NE, but the rapidly strengthening and veering LLJ after 00z makes me a bit hesitant to target something in Kansas (the forecast hodos get a bit odd-looking as 850mb flow increases beyond the 500 mb flow). As such, I'm leaning a bit more towards the southeastern NE area (not sure we can make it to south-central NE in time). The 00z EMC 4 km and NSSL 4km WRF runs both initiate convection in southern NE by 23 UTC, which is an encouraging sign!

Hopefully, given the solid 5+ weeks of chasing I just finished, Mother Nature can pull off a good one tomorrow!

 

[Craig McPeck]

Looking at the latest data(even though i happen to always be outta town on the best days in my area)it appears if i was going, i would target along I-80 from Grand Island to just west of Omaha before a Derecho Forms with excessive winds like a couple days ago. Wether is a tornado or damaging wind storm, their will be some damage somewhere

 

[Michael O'Keeffe]

Based on the 12z RUC I am liking the Beatrice to Marysville area. Nice convergence with ESE surface winds with some sort of wind shift line suggests storms could initiate there. The CAPE is extreme there as well as the rest of S NE and I also like the SE 850s in SE Nebraska. The RUC goes crazy with the precip so hopefully things pop which looks probable as the CAP should be gone by 21z or so. Either way looks pretty dang good!

 

[Derrick Herndon]

No denying that this is the best setup for East and Southern Neb of the year. One thing I am concerned about is that this am's models runs are showing the cap eroding sooner, shortly after 18Z. RUC and NAM suggest storms out West will continue to propagate East along boundary and eventually become surface based. Not sure I am as crazy about that solution. But they also show additional development south of the boundary. In any case I do not see any the models being shy about firing something. I see the 12Z RUC is farther south with its dryline bulge, just North of DDC while NAM is up close to the NE border. Not sure how important that feature is for today. It looks like the NAM is stronger with flow from 850-700 and thus advects/mixes the bulge more to the Northeast. A more North solution could act to intensify the surface low through diabatic heating and thus strengthen and back the low levels a bit. This seems to be reflected in the NAM's slightly lower pressures for the low. It would also move the bulge away from the warmer mid level temps. For me it looks like a target near Hastings.

 

[Andrea Griffa]

As we did think yesterday Ruc is totally out of control today with huge values of cape well widespread in a very big portion of Ne and Ks. Actually I'm so impressed by the new run of WRF: it sounds like a very nice day today.
In comprison with RUC, WRF shows a quite sharp dry line extending to South NE with backing low level winds in south central/ SE Nebraska. A quite strong mid level flow is confirmed for SE Nebraska and N Kansas; also LLJ is so good for both direction and speed in South Nebraska and it is forecasted to strenghten dramatically after 00Z enhancing the tornado potential in SE Nebraska and NE Kansas by 6.30-7pm. Not to mention the good cap that will be in place making some selection. Without thinking too much, this case reminds me may 29 2008 a little bit.