6/5/09 FCST: KS/CO/OK/NE

[Skip Talbot]

I've been monitoring the evolution of this setup on the models for over a week now, and I believe we finally have enough run to run consistency and agreement between models to say that we've got a chase op on Friday, June 5.

The GFS is indicating a much more classic setup than we've had for the past few weeks: a dryline over the plains with a broad area of SW flow. Moisture is still in the process of advecting into the plains. It should be well estabilished in OK and TX by Friday, but we'll be struggling to get into the mid 60's in KS it looks like. Even so, modest cape values under a 50-60 knot 500 mb jet, with excellent veering with height, should create an environment favorable for discrete supercells. With the weakening cap and upslope flow on the higher elevations of western KS and eastern CO, we should have more than enough ingredients in play to fire off a few supercells. Given the modest moisture I'd expect an LP storm mode. The resulting higher LCL's might limit tornado potential, but directional shear could counter that.

Further south into OK, there also exists good veering with height and much better instability. However, the cap looks solid here and with upper level flow further north and the lower elevations, we probably won't have enough lift or forcing to break the through. OK and TX look like they will stay sunny, but with this event still a ways out, we should watch this area closely.

I'd favor areas along I-70 in western KS and eastern CO where moisture is wrapping around a forecasted elongated surface low. This target will shift as the event approaches though...

 

[Skip Talbot]

Well, the WRF is in range for this setup. The overall placement of the dryline, trough as well as the quantities of moisture and shear are very similar to the GFS solution. Given this agreement, it looks likely that we'll see some supercells over the risk area of eastern CO and western KS. One big difference in the WRF, however, is its showing much less instability, barely hitting 1000 J/Kg on the CO/KS border. The cap, however, is also weaker, so I guess its a trade off. It looks like the main problem with this setup is going to be meager moisture. In the higher elevations, dewpoints may only be in the upper 50's or lower 60's, while further southeast into central KS we have better moisture, but surface temps will be much higher (approaching 90). This is going to produce very high LCL's. Friday might be a structure day with beautiful, discrete high plains sups and large hail, but with meager moisture and high LCL's tornadoes may be sparse.

 

[cdcollura]

Good day all,

I definitely am excited about Friday (6/5) as it should be "the day before the day". The moisture will be just nosing in to the area of upper air dynamics with a cap in place, however, one must consider that this area (NE CO / NW KS / SW NE) is at and above 5,000 feet MSL - Meaning the UPSLOPE into this area should overcome any capping.

I see great shear, moderate CAPE (1500 or so), and developing Colorado low / lee trough backing the surface winds for a really impressive LP supercell chase opp. LP Supercell tornadoes are rare, but can happen, especially with this type of setup.

 

[Steve Polley]

I have posted a preliminary forecast on my blog site. Also think that NE should be added to the forecast thread as well.

http://mesoextreme.blogspot.com/

 

[Skip Talbot]

I'm still liking Friday for a high plains supercell chase in eastern CO. The 0z WRF is out and plotting a tongue of 60 degree dewpoints flowing in along I-70 resulting in Cape values over 2000. A 40-50 knot mid level jet should provide enough shear to maintain supercells. High LCL's of around 1500-1750 and almost non existant low level shear should inhibit tornado development, however. With 200-300 3km SRH values, we may see a few LP motherships out there with huge hail. The composite reflectivity is firing off what looks like a nice storm between 21z and 0z on the CO/KS border. The same feature was present on the 18z run as well.

 

[Mikey Gribble]

I pretty much agree with Skip. Good structure, but high LCL's and weak flow throughout the 0-6km layer will preclude any sort of a tornado threat. If there wasn't going to be good directional shear from the backing surface winds I wouldn't even go.
I also don't think I'm buying 60td. Maybe they'll get close, but I don't know. Like Skip mentioned you may get some good structure shots and I'd head out if it was close to home.

Saturday has my attention now. I wrote a forecast off tonights 00Z for both Friday and Saturday on my blog if you are interested http://loadedgunchasing.com/blog1/

 

[Bill Schintler]

Chase Target for Friday, June 5

Chase target:
Imperial, NE (about 50 miles southwest of North Platte).

Timing and storm mode:
Storms will initiate over the Front Range during the afternoon, and then develop further east in the target area through 6 PM CDT. Supercell storms with a tornado or two appears possible.

Synopsis:
The CA ULVL low will open up and merge with the NRN stream over the next 12-36 hours. Cyclogenesis will commence over ERN CO and then in NWRN KS in response to H5 height falls over NV, contributing to upslope flow N of a sharpening frontal boundary along the KS/NEB border. Unlike the case today in ERN CO where convergence was weak at best, we will finally see strong convergence along a boundary.

Discussion:
A warm front extending E from low pressure over ECNTRL CO will provide the focus for strong to severe convection Friday afternoon and evening. A few storms will be ongoing Friday morning over the Nebraska Sandhills area, and will push east of the area as the LLJ veers and weakens. Broken CI, signaling the approaching trough, will overspread CO and WRN NEB during the afternoon and will somewhat inhibit insolation – expecially N of I-80 in the sandhills where thicker cloud cover will exist, some of this from anvils blown off from earlier convection in WY. A narrow axis of 60’s F dewpoints will develop along the frontal boundary as convergence increases, however capping will remain strong in this area through 00Z owing to an inversion around 700mb. Initial thunderstorm development will be in SERN WY and then further S over the Front Range W of Denver to Fort Collins. Convection may later extend S and E to the Palmer Ridge by mid-afternoon. After 22Z, large scale assent arrives in WRN NEB and convection will rapidly develop E into the instability axis.

FCST soundings indicate impressively large hodograph curvatures along and N of the KS/NEB border through 00Z; with directional shear further increasing during the evening as the LLJ strengthens. LCL heights fall rapidly after 01Z. The SPC SREF ensemble indicates a Significant Tornado parameter approaching 2 between 00Z and 03Z. By late evening, storms will grow into a large complex and track E between I-80 and the KS/NEB boarder, at the nose of a 40-50kt LLJ.

- Bill
KD0DJG
www.twistertoursusa.com
11:27 PM CDT, 06/04/09

 

[Brandon Sullivan]

Target Area

Will keep it short and sweet here...

Target: Sidney, Nebraska

This region above will be on the nose of the low level moisture tongue, this combined with the thermal profiles will yield low LCL's over the area. Instability should reach 1500-2000 (Varying By Model) which will be sufficient.

Kinematically the region will have more than favorable turning winds with height.

Although I do not always buy into forecast reflectivity.. 4 KM WRF does develop a nice Supercell right over this area...

Good Luck All!

 

[Bill Hark]

I am cautiously optimistic about late Friday afternoon/evening for pretty supercells and possibly tornadoes. The NAM shows a narrow area of 60 degree dewpoints in NE Colorado and SW Nebraska though the GFS is slightly less bullish with predicted dewpoints to around 55. This corresponds to an area of backing surface winds and later formation of a lowin NW Kansas. There will also be SE winds at 850 level in NE Colorado. CAPE will be up to 1500 in that area, again if you believe the NAM. Looking at the 700 mb temps, I think the cap will be an issue south of I-70 though the NAM does show precip further south by 00Z. Mid level flow will be decent though I would like it a bit higher. Currently forecast from 30-40 by 00Z. Right now, I still think moisture will be the biggest limiting factor. Currently, dewpoints are only in the low 50’s and high 40’s across Kansas (2:15 AM CDT). I would target Julesburg in northeastern Colorado at present.

Bill Hark

 

[Larry J. Kosch]

Add NE to FCST Thread

I really think we should add NE to the FCST Thread!

Last night, on the Weather Channel, Mike Bettes said that SW Nebraska gets a "5" on the TCI (Tornado Condition Index) scale. That is the highest mark given out on this new scale so far this season!!

Plus the fact, in the previous posts, other chasers have indicated they have targets in NE or plan to chase in NE.

The SPC has targeted nearly all of NE as a slight risk for severe weather today.

Do I need to say more, HMMM?? I think this could be the start of a "harvey wallbanger" type of weekend for storm chasers. I foresee a tornado outbreak, with numbers possibly reaching 40-50. And we could have a few EF-4s!!


EDIT: OK, OK I was streching things a bit. No way anybody can "predict" a few EF-4s, or any EF-0s for that matter. Sorry my bad. I'm getting a few lumps on my head from the hail stones falling on me!!

 

[Darren Addy]

No question NE should be in this thread.

Interesting thing in the LBF (North Platte, NE) forecast discussion from early morning:

A NICE FETCH OF SUBTROPIC MOISTURE EXTENDS FROM BAJA
MEXICO ALL THE WAY NORTHEAST INTO WYOMING AND CO.

This is a new one on me, (but I still consider myself a newbie). It appears that concentrating only on Gulf moisture return may be inadequate in accessing this particular setup. Thoughts?

The SPC has targeted nearly all of NE as a slight risk for severe weather today.

But to be fair, at least the eastern half of NE is included due to an after-dark MCS that will move through. The isolated storms will be earlier and mostly (if not exclusively) in the western half of NE.

 

[Patrick Martin]

Nebraska should definitely be added to this thread! I'm in agreement with Bill that Julesburg CO will make an excellent starting point for today. From a look at the 0z NAM and latest RUC, we get a good fetch of moisture piling into the end of the Cheyenne Ridge by late afternoon and we are already starting out with dp's around 50 this morning. Don't think that mid 50's by afternoon will be unrealistic. Also noticed that the NAM wants to run a tongue of favorable helicity down into the wrn NE panhandle and NE CO by late afternoon as well. The Denver area currently has a ceiling of clouds, but vis satellite shows that nern CO is clear so we'll get good heating which should be able to overcome the cap by late afternoon.

Earlier this week felt that a more easterly chase was in the cards and glad that I arranged for the day off today and even happier it's not far at all. I'll be heading out later this morning and my initial target is Julesburg but feel pretty certain will be in SW NE before the day is out. Good luck to all chasing today.

 

[Andrew Stoller]

That mid level tropical moisture plume could substantially limit today's potential as it has a cirrus shield/mid level clouds totally blocking insolation into northeast CO.

 

[terra seright]

UM, What about the Texas Panhandle??

Dryline is setting up....They're talking 40% chance of severe TS action.....

Sorry, I'm not a forecaster, and I deeply appreciate what you guys do in this forum....but someone had to bring it up!

 

[Darren Addy]

CAP is expected to be too strong the farther south you go along the dryline.

NAM has a good looking model skew-t for KIML (Imperial, NE):

Only negative would be the LCL heights. However, if you look at the NAM projected LCL heights for the same time frame (00z) you'll see a nice area of lower LCLs just north of there: