6/11/08 FCST: KS/NE/SD/MO/IA/MN

[Michael O'Keeffe]

Since my Tuesday forecast fell through, Wednesday is still looking good. The GFS has been showing a powerful trough ejecting into the C/N Plains the last few days. As of right now the KS/NE border looks juicy with extreme CAPE values, deep moisture, and decent SE 850mb winds. The SPC has outlooked much of the C/N Plains mentioning a higher end severe weather event. With low LCLs, EHIs in the 8-9 range, and good shear on top of the extreme CAPE and good moisture we could very well see a significant severe weather event with tornadoes a good bet.

 

[Darren Addy]

I agree that Wed. is looking good for Nebraska. Cap may be an issue farther down in Kansas, but should be overcome by 00Z in Nebraska. It looks like plenty of moisture will be available. Nice shear should give us some spinning storms. I'm liking the area between Hebron and York for now. Naturally, that could shift with model runs between now and then but, as a Nebraskan, I'm liking what I'm seeing at this point.

 

[Mike Hollingshead]

Ah, the joy of rather cold fronty sfc patterns. Do they have to do this about every chase this year or what? The GFS shows a nice banana sfc low at 18z trying to transition away from that late. NAM to some degree too, with the stronger cold front look in NE ne of the sfc low. That loves to weaken and veer your low levels near the sfc boundary. It won't shock me at all to have NE suck once again, and wind up with another isolated beast in KS, and some other isolated beast on the warm front in MN.

All I know is I'm not at all enthused to chase another setup like I see at this point, for the middle area anyway. I just have a very hard time coming up with anything worth a darn ne of a sfc low like that on/near a ne-sw cold front.

Via both models I'd be in either KS or MN for this one.

I bought a pitch fork the other day. Each day I go outside and stab NE with it.

 

[Matthew Crowther]

12Z NAM is similar to previous runs- deepening surface low pressure in eastern CO in response to a strong trough moving through the northern/central Rockies.
All parameters seem to be coming together for a small tornado event- and this time maybe it will verify. The NAM forecast soundings near HLC are very impressive at 00Z
Thu and the storms will be moving at a more reasonable pace as mid-level winds are in the 40-50 kt range.
Something to watch is the warm 700MB temps suggesting a very stout cap in the warm sector.
Therefore the NE/KS border may be a safer play. Very preliminary target: Norton to Phillipsburg, KS.

 

[afischer]

Haven't looked at this real close yet, but I'm starting to like northern targets (e.g. far northwest IA) based on trends in the GFS. The 12Z run has the cold front arcing N-S once you get up to about Norfolk and northward (more crossover of the deep shear vectors with the boundary)... and only has the cold front progressing eastward at ~20kts during the course of the afternoon and evening. If this verifies and discrete storms form on the cold front, I'd think they could forseeably fire on it and easily move off of it. There will probably be some elevated junk we'll need to get rid of to help destabilize northern targets, of course. Low-level shear is progged to be pretty slick with southeasterly surface flow and 40kt 1km southerly flow progged throughout the warm sector... and very strong MLCAPE (3000+) forecast in northern targets with the richest boundary layer moisture/cooler capping aloft. A glance at the 00Z ECMWF shows a solution (mass fields, anyway) very similar to the 12Z GFS on Wednesday afternoon/evening... it actually looks even a bit better/slower. NAM is sort of similar, though definitely more progressive/strung out/banana-ish at the surface on the north end.

 

[Scott Lincoln]

Just a heads up to anyone planning on chasing in Iowa and parts of eastern Nebraska on Wednesday... Watch for flooded roads!

In Iowa, almost every major river is cresting in the next few days at major or record stage, and there are over-topped roads all across the state. With most smaller streams barely getting below flood stage by mid-week, any rain can quickly cause them to flood rural roads. There are also some bridges that are closed because they need to be inspected. Saylorville Lake is also so backed up that it has closed US30 near Boone, IA.

For a map of all Iowa major road closings:
http://www.511ia.org/




As of right now, it looks to me like the Omaha area has the best crossover of shear and instability. Storm motions in the 30-40mph range shouldnt be too bad for staying with storms, especially as they will likely move almost due east if they get rooted.

 

[Mikey Gribble]

I didn't spend much time on my forecasting, so take this with a grain of salt. I just copied and pasted from my blog again btw...


It seems like I've been saying this a lot lately, but this is another tough forecast. The focus in the near term is Wednesday as a trough ejects into the plains. At the surface a triple point will set up over west central Kansas with a frontal boundary running northeast from there along a Hays, KS to Omaha line. There are two primary areas of interest. The first is the triple point in the ness City area and the other is the front in the vicinity of Omaha. There are clear problems with both the targets, so I am not terribly enthusiastic about the tornado potential right now. I am going to keep this fairly brief BTW, but I will get into it more tomorrow.
The triple point in west central Kansas actually looks pretty good before you start digging a little deeper. A surface low over SW Kansas will back winds ahead of the triple point and a sharpening dryline and/or a bulge are likely just south of the boundary intersection. Storms forming near the triple point and dryline bulge area will be in an environment characterised by strong instability and deep layer shear near 50kts (supercells are likely). Hodographs are actually quite nice and are certainly supportive of tornadic supercells. KHYS forecast sounding is showing 1km SRH of 185, 1km SR winds near 30kts and 5km SR winds at 23kts, so as far as wind shear goes everything looks good. My huge concern is a large t-td spread which results in high LCL heights and strong DCAPE. The same Hays sounding is showing DCAPE near 1800 and MLLCL heights over 2000m. That is going to be seriously detrimental to the tornado threat if it verifies. LCL heights will be slightly lower right along the front, especially near and after dark, but they are still going to be quite high. right now I would put the tornado threat at 5% ahead of the triple if I were SPC. Another potential target in this area is north central Kansas where overnight convection may lay down an outflow boundary. If this can happen and the boundary can maintain itself throughout the day (backing winds north of it) storms may be able to fire along the OFB/frontal interesction in the afternoon. In theory LCL's will be a little lower and when you add the preexisting vorticity of a boundary into the equation amazing things can happen, so I would think storms in this area would pose a tornado threat, but this is a huge If at this time and it likely won't verify.
Further North near Omaha and ENE of there better moisture and lower surface temps will keep LCL heights quite low and the tornado threat will be higher as a result. I looked at the hodograph for Harlan, Iowa and it didn't look very good at 00Z for some reason, but it improves by 03Z. Regardless, very strong instability and deep layer shear near 50kts will again create a favorable environment for supercells. The tornado threat is a little uncertain to me right now. I am a little worried that low-level winds may veer slightly and I am also worried a little by a lack of curvature in the Harlan hodograph, but going off the wind field maps everything looks OK, so I'm a little confused. I will look into this more tomorrow and figure it out, but right now I would put a 10% tornado probability from Omaha East into Iowa.
I will post the next forecast tomorrow some time.

 

[Darrin Rasberry]

WRF 48 HR: A banana-shaped SLP at 12 WED feature will split into two areas; one area of 990mb will exist in Western Kansas, while another 1000mb feature will exist in W MN. At 00z, a frontal boundary is shown from NW KS to SC NB curving north through east of Sioux City/Falls in IA. This moves yesterday's prog somewhat eastward. The feature(s) will have plenty of time to draw deep moisture and warm air into the area.

A cold front connecting the two low pressure regions, and a warm front attendant to the MN low, will be the focus for development. The SPC is currently counting on outflow boundaries as of yesterday's forecast, but since such boundaries are not easily predictable, potential with these will be assessed as the day grows closer. The cold front will be sharper alongside the Sioux City area, and will be somewhat sharp in the NW KS area.

Winds will back (through time) along the entire CF boundary. The Sioux City area and the N Kansas area have the most directional backing, which will potentially increase the directional shear. Wind speeds will increase, with direction remaining the same, as the evening progresses into the night along the northern target and the SFC Low drifts south into NW IA.

850 SPD will remain southerly along the entire boundary, and will increase significantly during the evening. 700 spds will be stronger and will veer nicely with the 850s down south, but will be a bit slower and not turn as significantly INVOF the northern target. 500 spds will be decent for both areas, again with nice directional veering, and will back (with time) alongside the rest of the aloft winds in response to the UL Low situated in Montana. There is an indicator of higher vorticity INVOF the northern target, but remains pretty weak; however of course that's not the only indicator of lift. Vertical velocities through all the heights are a bit unreadable in the southern area, but may indicate a possible initiation point in the northern target to the east of Sioux City.

And woah, did the instability kick the bucket in a day on the WRF: whereas 4000+ SBCAPE was predicted over the "old" target E of Omaha yesterday, 3000-3500 is all it musters now, but if it holds that of course will certainly do. EHI's max out on Earl's page for both the southern and the northern target.

However, MLLCLs look stupid high for the southern target, where the cap will also be tough. Independent of OFBs, my boxes for targets are, by order,

#1 50m radius Storm Lake IA (concerns: theft from crud that may quickly develop along possible OFBs straight to the south in the area where CINH falls quickly; HP mess)
#2 50m radius Beatrice NE (concerns: theft from southern target show-stopper, no immediate reason for a special lift source - "field goal bust", HP mess)
#3 50m radius Hays KS (concerns: high LCLs and temp, stouter cap than up north)

EDIT: GFS choice is not listed due to the College of DuPage site not having the 00z runs yet for some reason. Will update a choice based on GFS alongside a new WRF target at this time tomorrow. Since I am new at this, any criticism of this forecast is appreciated and even needed; please PM me with comments if you have time.

 

[Kenny Drake]

I agree with Mike Gribbles assessment. The timing is a little off with this system, as the trough becomes negatively tilted as a smaller s/w ejects around the base of the main trough near or just after dark. This will be the feature that will allow the low LCL areas along the warm front in MN/IA to initiate, however after dark. Along with the timing issue (for the warm front play) earlier convection will likely ruin the low levels along and just south of the warm front throughout the day. Farther south and west into S.C. NE and KS the cap is going to be a major concern with 850 temps likely approaching 25C. The moisture will likely mix out quite a bit along and just ahead of the dryline towards the late afternoon and evening. NAM shows this well with less than 60F dewpoints by 00Z along the dryline from N.C. KS southward. Another issue in NE will be the orientation of the cold front not favoring discrete cells. The front is progged to be oriented northeast to southwest with storm movement possibly parallel to the front. This is where the warm front action in S. MN and N. IA may yield more of a discrete mode with the warm front oriented more west to east. Personally, I would hope something goes up in NW IA based on the 00Z NAM run. The NAM ejects the s/w fairly rapidly after the 00Z timeframe so my best guess would be MCS mayhem by or just after sunset.

The 00Z GFS run has the 500mb trough wrapped up more than the NAM does. This would obviously inhibit the warm sector mid-level forcing quite a bit. The GFS does show a s/w eject out of the main trough farther south but well into the overnight hours into Thursday.

All in all, I'm not too impressed by this system yet. If this was 2006 I would be going insane, but given 2008 it is not much. I would say high end SLIGHT and near-warm front MOD if the 00Z NAM verifies.

 

[Scott Weberpal]

I'm fairly high on the prospects of supercells and potentiall strong tornadoes in W. IA tomorrow. NAM shows continuing convection in MN north of the WF throughout the day which should create a diff heating and/or OFB further south. Sfc winds remain backed as the trof approaches from the west, and scattered supercells should develop north of the 10c H7 line from SW IA into SW MN. Not sure if the WF in MN will be the play yet, but if clearing occurs early enough, I'll be blasting north out of Iowa to play the WF.

The NAM has been very consistent with this solution for many runs now, and given the event is within 36 hours, I have fairly high confidence for tornadic supercells in W. IA tomorrow. Current target is Fort Dodge to Sioux City.

 

[Mike Hollingshead]

Just a tiny bit of cape forecast in western IA tomorrow.

Atlantic IA 21z (wow almost 400 is 0-3km cape....guess that's to be expected with so much though)

Vent in the upper levels not so great tomorrow, but maybe the diffluent flow will help. I still don't know if I am in love with tomorrow yet. Via the NAM the northern portion of the front isn't n-s till later, but the cap is shown eroding really early(gone in Tekamah by 18z). 18z it's ne-sw and the sfc isn't really backed much. Hopefully morning convection can leave a good ofb in IA somewhere. That or hope it there isn't much morning convection and there's a good warm front to chase.

I guess looking at RAP's cape/cin prog at 18z that area it's removed is tiny, and just happens to be at the Tekamah sounding I looked at. What I did notice was just how fast it's knocking down the 700 temps between 18z and 0z. Should be some seriously explosive updrafts tomorrow, if nothing else. I just hope they aren't in a fast forming ne-sw line by 3pm.

Look at the 700 temps/winds at 18z.
http://www.wxcaster2.com/CENTRAL_ETA_700_GPHTMPWINDRH_30HR.gif

Then look by 0z.
http://www.wxcaster2.com/CENTRAL_ETA_700_GPHTMPWINDRH_36HR.gif

Can see that 700mb warming/cap on the Fremont sounding at 18z.
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=030&STATIONID=kfet

Guess I just get the feeling a whole lot of storms are going to go at once and in a hurry tomorrow. Then again, that degree(no pun intended) of 700mb cooling seems a little questionable to me.

Current target...home Too bad reality seems to be a state further come the next day

The juice and sfc reminds me a little of last Saturday. Big difference is a lot less low level veering this time. So, I still fear the "IL" storm(maybe MN/WI this time) and the "KS" storm...like last Saturday. A "not-to-new" outflow boundary a ways into IA would rule tomorrow. I fear any OFB's in IA tomorrow will wind up too fresh/cold.

I was thinking the other day. IA really does rule for chase terrain and roads. Looking at a map...it's going to be very hard to top for paved road options, while being in tornado alley. At least if you aren't in the county near the rivers at each end.

 

[Bill Schintler]

Chase Target for Wednesday, June 11

Chase target:
20 miles east of Omaha.

Timing and storm mode:
Surface-based storms should fire between 4 and 5 PM CDT, with supercells and all modes of SVR WX possible.

Synopsis:
The flow aloft will become increasingly amplified as the ULVL low over WRN MT shifts S and E over the next 36 hours. SFC low pressure in ERN SD by 18Z tomorrow will weaken as a secondary low becomes established over SWRN KS, resulting in increasingly backed SFC flow over WRN IA.

Discussion:
During the overnight hours, two convective complexes will develop in a zone of isentropic lift along 305-310K SFCS at the nose of the LLJ, and track though the area while laying out boundaries that will ultimately affect tomorrow’s mesoscale setup. The first MCS will develop in NERN KS after 04Z and should track E through NRN MO and SRN IA overnight. This will probably evolve out of the ongoing convection over NRN KS. A second, initially post-frontal, MCS will develop in NCNTRL NEB after 07Z and eventually track E into NERN NEB and WRN IA. By noon, this elevated convection should have pushed E of the region with partial clearing. A storm outflow enhanced WF will be located along a Norfolk, to Omaha, to Maryville, MO line at 20Z.

By early afternoon, dewpoints will climb into the lower 70’s. LLVL directional shear should be maximized beneath a 45kt SSWRLY LLJ where backed SFC flow exists, with SFC-3km SRH’s increasing to 300m2/s2 and SFC-1km to 200m2/s2, after 01Z. SFC-6km shear will increase rapidly as a 50kt H5 speed max overspreads the area. Tornado probabilities will increase with MLLCL’s in the 1000m AGL range early in storm evolution, with MLLCL’s decreasing to 800m between 02Z and 04Z.

PM me for (free) nowcast support.

- bill
10:00 PM CDT, 06/10/08

 

[Brian Stertz]

Favorably looped hodographs on ETA forecast after 21z across SE Nebraska and SW Iowa with 3-5 EHI's yield some good hope for tornadic supercells. Just watch out for flooded roads either pre-existing or areas getting soaked and then flooding again. I do not think this area has recovered much from the last round of torrential rainfall. May have to once again watch that Concordia-Beloit-Belleville KS area for a monster supercell with a possible boundary interaction leftover from tonight's action. It looks like this is also an "area of higher interest" by later this evening.

 

[Scott Weberpal]

Not sure what to make of the 09z RUC with veered sfc flow well into Iowa. If I were to pick a target based on what I see, the Fort Dodge area may not be bad. Hopefully the 12z RUC or NAM will give a better solution than what I'm seeing.

 

[Bill Hark]

Very good setup for severe weather but unfortunately, this is another one of those two target days. Approaching trough from the west will produce 50-60 500 mb sw winds across Nebraska, Iowa and most of Kansas along with a strong low level jet from the S to SW. The NAM shows the best backing of surface winds in northeastern MO, southern Iowa and Northeastern Kansas while the RUC is less enthusiastic about surface backing except farther east into central Iowa and MO. Presumable, there will be some backing close to the surface low, forecast by both the NAM and RUC to be in SW Kansas by 00Z. The NAM has a narrow axis of 2500 to 3000 CAPE from near Dodge City, northeastward to Iowa with a bullseye in central Iowa by 00Z while the RUC shows the axis in a north-south orientation from northeast Kansas and extreme southeast Nebraska southward. My two targets (take with a grain of salt since I am not out chasing) are Nebraska City and Rush Center, KS. Although the waiting will be difficult as storms fire southeast Nebraska into Iowa, I think the Kansas target is good for later, better and more isolated storms.
Target: Rush Center, adjusting according to the position of the surface low and approaching cold front.

Bill Hark