05/29/04 FCST: Central Plains

[Gabe Garfield]

Whoa...

I'm not exactly sure why the Day 3 probabilistic outlook only has 25%....and not even hatched. LOL. The text doesn't seem to match the rather heavy wording. It cracks me up how matter-of-fact Thompson's tone is in the discussion...it's like he is writing"Well, the model forecasts show 'Day After Tomorrow' conditions will develop in the southern and central plains. Mutliple wedges are likely, including a few wedges side by side..." while yawning. :lol:

Moving on...

What already appeared to be a very potent weather situation has become increasingly more ominous with the 18z ETA run. It stacks up like this:

Synoptic Setup:
Negatively tilted longwave trough
Surface low in SW to WC Kansas
Warm front extending NE into N. Kansas and SE Nebraska.
"Cold front" (not much of one) extending SW from the low into Colorado
Dryline extending south from surface low into W. Oklahoma and W. N. Texas

Instability:
Dewpoints - Upper 60s-Low 70s (perhaps even mid-70s) over the S. and C. Plains.
SBCAPE - 2500-3500 j/kg over the S. and C. Plains (most likely much higher..being conservative here)

Wind Shear:
Surface - SSE-SE at 15-20 kts
850 mb - S at 40-55 kts (00z run had up to 45 kts)
700 mb - SW at 40 kts
500 mb - WSW at almost 40 kts (it will likely be better if we can get a decent s/w)
250 mb - WSW at 70-75 kts

Convective Inhibition:
CINH less than -50 j/kg along and east of the dryline and locally down to 0 j/kg.

Synoptically speaking, this is the type of weather situation that I would draw on my notebook paper when I got bored in class....in other words, the perfect system. Of course, this isn't that yet...but it has the potential to get very bad across the central United States on Saturday.

Gabe

 

[Chris Hayes]

with all the talk of an outbreak, is this looking like an April 26 91/march 13 1990 outbreak? I'm not familiar with the synoptic conditions of those days.

 

[Jeff Snyder]

Re: Whoa...

I'm not exactly sure why the Day 3 probabilistic outlook only has 25%....and not even hatched.
Gabe

Gabe,
The Day 3 Outlook can only go to 25% unhatched... Day 2 can go to 45% hatched...

I agree with Gabe's take on the situation. I'd like 500mb winds to be a little stronger, but I've heard that the ETA has bias towards underforecasting shortwave strength / mid-level flow strength for forecasts >24-36 hrs in advance (the HPC Model Diagnostic Discussion mentioned this a couple of days ago I think). Strong mid-level flow would give us slightly stronger mid-level SR flow, which would help move potential storms away from the HP spectrum and into the classic part of the spectrum. However, such winds have proven sufficient at other times this year and will likely mean that we chasers could tripod the storms, in contrast to the "gotta keep moving" mentality that was necessary during the storms of "First Ten Days of May" (sounds like a movie, eh?) last year... I'm worried about the ETA mixing out the 70 Tds over OK, which is yeilding model-forecast CAPE of only 2500-3000 over OK -- obviously sufficient for tornadoes, but not typical of the synoptically-evident tornado outbreaks... 18z ETA does show 0-3km helicity values >400 east of I-35 in OK... I like OK because the better upper-level flow stays mainly in OK, and decreasing northward. Cap strength doesn't appear to be an issue, and will likely be less of an issue if we can keep 70 Tds in the OK part of the warm sector...

 

[Chris C Sanner]

Day 3 (saturday) looks like the kind of setup you see only in ideal situations in the classroom or such. Right now, I'm heavily favoring Oklahoma because of the attendant risk of more discrete storms, but the cap won't be as strong as earlier was thought, so there may be more storms to deal with. If the 70s TDs don't mix out, we're looking at a huge day. I know I'm not saying anything new for everyone, but what else is there to say? One thing, I hope these things will stay out of populated areas, but when setups like this occur, its unavoidable. I hope the TV and Radio can keep everyone covered, especially since a lot will be on the lakes or traveling through.

 

[Robert Dewey]

with all the talk of an outbreak, is this looking like an April 26 91/march 13 1990 outbreak? I'm not familiar with the synoptic conditions of those days.

You can find the conditions for many significant outbreaks here - http://www.spc.noaa.gov/staff/hart/outbreaks/

Looks like this system will rapidly deepen between Saturday and Monday...With ETA showing the low bombing out in the Midwest...With probably a good tornado outbreak in the Plains, translating into a pretty intense derecho, possibly rivaling the May 31, 1998 event across the Midwest/Great Lakes, if the ETA holds true...

Robert

 

[Jeff Snyder]

Well... looking at the latest 0z ETA (LOL), the threat of signficant outbreak continues. The ETA continues with a widespread area of very strong low-level shear (+400 m2/s2 0-3km SRH) mainly east of I-35 in eastern KS and ne OK. Mid-level flow forecast remains a little weak, but doable. The ETA continues to mix out the 70 degree Tds in OK and KS, more so than previous model runs. This could spell some pretty big trouble for chasers, given the forecast CAPE remains less than the typical (whatever typical means) synoptically-evident outbreaks, w/ CAPEs generally in the 3500-4000 range. Additionally, the mixing out of the 70 Tds leads to a pretty strong (very strong) cap over the area of best low-level shear by late afternoon -- eastern KS and ne OK. If the CINH of 100-180 verifies, we're not gonig to get the signficant outbreak that we otherwise could have. However, if we can keep those 70 Tds, it'll up the CAPEs and drop the CINH to breakable levels, which would allows cells that move/propagate off the dryline to move into the region of very (almost scary) low-level shear...

P.S. -- of course it' encouraging to read "AT THIS TIME, IT
APPEARS CONDITIONS WILL BE FAVORABLE FOR AT LEAST ISOLATED TORNADOES OVER CENTRAL AND SOUTH CENTRAL KANSAS SATURDAY LATE AFTERNOON AND EVENING" from the pm updated HWO from ICT.

 

[Austin Ivey]

Well, I'm flying to OKC tomorrow afternoon and I'm still very encouraged by the discussion on this thread, conversations with my chase partners and the 0z ETA run. Good Tds mixing out is a possible issue, but I like how the 48hr ETA forecast shows a moisture "bubble" or pooling in NE KS of some 70 dews. Of course this could be some sort of spatial/meteorological error attributable to grid scale feedback or something (hopefully not). Also the surface forecast map is downright awesome.

MSLP/WINDS:
http://www.rap.ucar.edu/weather/model/eta4...hr_sfc_mslp.gif

DPs(moisture pooling in NE KS?):
http://www.rap.ucar.edu/weather/model/eta4...hr_sfc_dewp.gif

I will be anxious to read the new Day 2 tomorrow as well as all the new AFDs and HWOs from offices in the approximate target area in the mernin.

 

[Kevin Scharfenberg]

It looks like a large part of the plains will be vulnerable to tornadic supercells Saturday.

The eta prog for 18Z Saturday shows a large area of 68-70 dewpoints along and ahead of the dryline in KS/OK and surrounding states. The CAPE is progged to be on the order of 4000, and deep mixing ratios on the order of 14-16 g/kg support these numbers (note, this deep tropical moisture has made it ashore as of 00Z tonight at BRO, CRP and LCH). At the 00Z time step, convection has broken out in the eta model, and due to the way convection is parameterized, the dewpoints and especially the CAPE drop some in the model by 00Z Saturday night. This is known eta model behavior to eat the instability up too quickly when thunderstorms are initiated, so it is not a big concern to me right now.

Wind shear looks good to excellent over a large area. Rapid pressure falls should be ongoing, so the isallobaric forcing should allow the winds near the surface to back. With 40-50 kts from 1km-6km, and 65-70 kts at anvil level, shear will be more than sufficient for tornadic supercells over a large area.

The cap is strong, but not overly so. In fact, I would prefer a strong cap on a day like Saturday, to help the moisture pool along the immediate dryline boundary and to pump the instability up as far as possible before initiation.

I suspect the biggest problem for Saturday is not whether to play, but where. There will probably be a legitimate tornado threat over a rather large area, as was the case Monday.

 

[Amos Magliocco]

Well, after learning to pronounce Bee-yah-triss in true Snoop Dogg style and finding our favorite lodging of all time in the region (can't say where lest Martin Lisius file it away in his Rolodex at the Tempest Command & Control Center), it would only be appropriate to return to the scene of my crime, the place I left my chasing heart and soul a few days ago. So I'm rooting for Hebron as a target (have not looked at models tonight). I will drive to the center of Thayer County and sit cross-legged, guru style, until I am lifted by a tornado and carried back to Indiana. I'll never leave my target again.

Tonight, I bought a cowboy hat at the Denton Cracker Barrel for good luck. It actually fits and looks silly enough that I hope the storm gods are satisfied with my hubris.

Okay, so I don't have to send a PM to myself about superfluous posts in Target Area, I'll say that when I looked at the 12Z ETA, I saw moisture pooling in southeast NE and a strong dry punch working into north central Kansas, perhaps a little more south than where it was on the 24th, as the low was further south as well. Still I could see the warm front making the border and storms just north of the baroclinicity winding up along the border or just south, if that makes any sense. Maybe I'm looking for a way to initiate in Nebraska. I feel silly since the rest of you are talking about Kansas. Perhaps the 12Z is already way obsolete? I'll have to look.

Anyway, lots of energy, nearly-bombing synoptic sfc low, warm front draped that-a-way, dryline moving this-a-way---what's not to love?

 

[mikegeukes]

Day 2 just came out, Moderate risk for Saturday

0236 AM CDT FRI MAY 28 2004
THERE IS A MDT RISK OF SVR TSTMS ERN NEB/WRN IA INTO CENTRAL AND
ERN KS AND NWRN MO...

Mike

 

[Shane Adams]

In similar cavalier spirit to Amos, I'm looking at the area from Concordia to Beatrice, favoring the former. I too was burned twice last week by (Sat)moving from my original target and (Mon) playing too far east and ignoring the dryline. I will play the dryline just south of the TP Saturday, and will anchor myself into the ground wherever I decide to make my final target Friday night/early Saturday morning.

The dryline has been magic the past week, and I see no reason for this trend not to continue.

 

[Gabe Garfield]

I know this sounds regionally biased (it is--sort of), but I believe the best parameters for significant tornadoes will be located in SC Kansas and NC Oklahoma based on the forecast position of the best 500 mb and 250 mb winds. Also, everyone has been talking about the "big cap", but the last 3 or 4 ETA runs have been consistently eroding the cap along the entire dryline. In fact, the May 28 06z run of the ETA shows CINH values down to zero across the dryline in Oklahoma and breaks out precip almost down to N. Texas.

NWS OUN said this in their morning AFD:
"ALTHOUGH THE BEST FORCING... AND MOST WIDESPREAD TSTM ACTIVITY... WILL INITIALLY BE NORTH OF THE AREA... WE BELIEVE THAT HEATING... AND POSSIBLY A WEAK UPPER WAVE... MAY SUPPLY ENOUGH FORCING TO ALLOW AT LEAST A FEW STORMS TO BUST THE CAP"

I believe the dryline will light up at least as far south as N. Oklahoma.

Gabe

 

[Joey Ketcham]

I'm definately going to head out Sat. I might stick around the Wichita area so I'm centrally located with interstates running in all directions. Though my decision won't be definate until later tonight.

 

[Austin Ivey]

another thing I am liking about tomorrow is the possibility of full insolation beginning at sun-up or shortly thereafter. after skimming the model runs and AFDs it appears the UL ridge currently in place across the SPs will preclude the formation of any convective complex today/this evening in the area. Therefore, we might not have to contend with cloud debris in the morning (except for possibly some stratus due to moisture advection that will quickly burn off). Thus, even greater chances the CAP could break farther south. Opinions?

 

[John Cameron]

with all the talk of an outbreak, is this looking like an April 26 91/march 13 1990 outbreak? I'm not familiar with the synoptic conditions of those days.

I dont recall all the numbers for 4/91. But, the LI on the morning sounding for ICT was -12.




have a nice day