6/6/07 FCST: ND/SD/NE/KS/MN/IA/MO

[MatthewCarman]

Skip what outlook are you looking at? The SPC 3 day outlook only had a 5% chance as of right now for TX and that does not seem like much of a chance to me. I did not look at the wording though just chance for severe weather. Now that could change and probibly will but as of right now I dont see TX getting much. If people want to see a tornado they would most likely have to drive north to NE/SD or mabey KS.

The Mod risk is in western IA/MN aswell. If the storms form in eastern NE/SD wont they make it into IA and MN before dark? You also said if they move faster then the models depict then people would be farther west why is this? I am just trying to get a better understanding of how this works. Also I would think people would want to be infront of initiation so they are not to far west or playing catch up. Is there a good reason to be where the storms are expected to initiate? Thanks for the help anyone who answers my questions.

NWS right now is saying it could be a night time event for some of us and there could be severe weather as far east as the western great lakes before the storms weaken or die out so regardless of where this thing sets up it could be a very long night.

Have to wait and see as this is still 3 days out there.

 

[Oscar van der Velde]

http://lightningwizard.estofex.org/usa.html
The map at the bottom of the page shows the thickness of the layer with parcels having CAPE>50 J/kg and CIN <50 J/kg, so it shows where there is deep moisture and low capping. The 21Z-00Z timeframe Wednesday shows only a narrow zone over NE/SD/ND. But this can be enough, of course, especially with the strong deep convergence signals.

Oscar

 

[Jason McKittrick]

I too have a lot of concerns regarding Wednesday's event. While it is exciting to see a risk area so close to home, I expect that come morning we will see the SWODY2 Mod pulled farther west. This has been the case with just about every event this year.

Just want to point out that the system is still off the west coast and the main energy has come all the way across the Pacific, so it has not been sampled for quite some time. This morning 500mb Analysis shows a strong full latitude negative tilt trough of the west coast. There were a few PIREPS on the west side showing 80knt 500mb flow.

As far as moisture I have spent most of the morning trying to figure out where in the world these 70 degree dewpoints are going to come from. The NAM gridded data showed Austin with a north wind and low 60 Dpts still Tuesday night. It wasn't until I checked the 9z SREF that I found that these 70 dews appear to advect NW from the southern Mississippi Valley region. I would agree that it still seems a little suspect.

The biggest problem I see is timing. With the models slowing things down I wonder if the moisture will be able to advect far enough west to reach the upper level energy needed to erode the strong cap. Otherwise, can you say squall line after dark.

I am planning on chasing Wednesday and FWIW my preliminary target looks to be near Broken Bow Nebraska near the dryline coldfront intersection. Hopefully something will get going before sunset.

 

[cdcollura]

Good day,

Looking at the GFS and ETA roughly 48-60 hours out - I am being redundant to others in this thread - I am seeing severe parameters in eastern / central Nebraska that border (or even exceed) insane!

0z Thursday - Tightly clustered between the GFS and ETA right now, I see winds at the surface SE at 25 knots, south at 50 Kts+ at 850 MB, SW 60-70 at 500 MB, then well over 100 Kts from 300 MB on up from the W then WNW at 250 MB.

Helicity progged to be anywhere from 500 to 750 late Wednesday - Ouch! This is ENVIRONMENTAL helicity - Throw in a boundary and then what?

CAPE pegged ahead of dryline at 5,000 CAPE+ ... Speaking of dryline, dewpoints go from near 70 F to the 20's and 30's across about 1/3 of Nebraska across the middle of the state with a dryline bulge.

Wanna know what kind of EHI this yields - Are you kidding? Take 5,000 CAPE x 500 to 750 Helicity and divide by 160,000 and it gives you a number from 16 to 24!! Tornadoes can form with an EHI from 1 to 2, violent tornadoes with 4 and up - Let alone 24.

The cap will be stout, but I also see 50 CM / S UVV (pegged at both 500 and 700 MB) moving into central Nebraska at 0z as well for Thursday (Wed at about 5-6 PM CDT). I do not see how such an insane upward velocity will not erode any cap - strong or not.

This setup, at least what it looks like now, is more than I have seen in a very long time - Stay safe out there!

I cleared my work schedule for the week (grandma's funeral excuse - works every time) and I am out of Dayton tomorrow and should be near Kansas City at around midnight. Might pull all-nighter driving if adrenaline / anticipation keeps me up all Tuesday night ... Target remains not far from a Beatrice / York line along I-80.

I hope whatever develops Wednesday afternoon / evening does not have Hallam in it's sights again ;-P

 

[Skip Talbot]

Skip what outlook are you looking at?

From the Day 3:

CAP MAY BE BREACHED LOCALLY ALLOWING ISOLATED STORM DEVELOPMENT
ALONG DRYLINE AS FAR S AS SRN KS/OK/WRN N TX.

The Mod risk is in western IA/MN aswell. If the storms form in eastern NE/SD wont they make it into IA and MN before dark? You also said if they move faster then the models depict then people would be farther west why is this? I am just trying to get a better understanding of how this works. Also I would think people would want to be infront of initiation so they are not to far west or playing catch up. Is there a good reason to be where the storms are expected to initiate? Thanks for the help anyone who answers my questions.

Sorry, that was a typo on my part. The models are too fast usually, not the system. Meaning that you often see the upper level winds arrive later, and dryline further west, than what the models show earlier on. I've edited my original post. March 28 was a good example this year.

If storms fire near O'Neill, its going to take them a few hours to cross to the Missouri. So it'll be nightfall if we have initiation after 0z, or some daylight left if the storms fire late afternoon.

You'll want to be on these storms at initiation because, given the extreme instability and very favorable shear, there will be explosive development. They may go severe within minutes of appearing on radar. You're not going to want to be more than a half hour from where these storms fire or you may miss the first round of tornadoes. Although this isn't necessarily the end of the world as cyclical supercells and long track tornadoes are possible.

 

[Chris Hayes]

Per the latest runs of the GFS and ETA I'm going to have to move my target further west. From Central SD southward into NC NE there seems to enough weaker CINH for storms to fire near the dryline bulge. I'm in Wakeeney Kansas right now, and will probably be leaving here tommorow afternoon and going to North Platte and staying the night at the Ramada Inn, because of their WiFi. I'll stay up and look at the day 1, and computer models, and make the final targeting decision early on Wed before we leave.

 

[nickgrillo]

Looking at days like these makes me pissed off that I had to sit out on one of the most active and successful seasons that most chasers have seen in years...

From my glimpses at the models... Surface-based CAPE is progged to be extreme (e.g. 4000-5500) over much of the region ahead of the dryline, given the extremely high low-level theta-e being advected beneath steep mid-level lapse rates aloft. You rarely see that kind of CAPE juxtapositioning with those kind of low/deep-layer shear profiles (NAM has 450-700j/kg 0-3km SRH across much of the warm sector by later in the evening). Lack of stronger lift on a synoptic-scale should prohibit too much activity from shooting off at once, particularly areas further south along the dryline, with the degree of upper-level divergence and mid-level DPVA aloft helping to increase convergence near the surface. Obviously any storm that develops in this environment would become supercellular and have the potential to produce a violent tornado and extremely large hail.

 

[Mike Hollingshead]

I'm moving my target to Valentine NE. Anymore I'll take the gfs thought's over the nam. It suggest a good hop west. Both models shut off Nebraska south. It'll be interesting to see what tonight's run does as far as the cap, since yesterday morning's run had the healthier cap, followed by less capping on the 0z run.

As far as magically appearing dews, wouldn't some of this come from the advancing front and backed sfc winds ahead of it, pooling/pinching the moisture?

Edit: Also worth mentioning for those that like space and/or auroras, and are out chasing, it might be worth monitoring the monster and rather active, sunspot, rotating into position. That'd be a dream shot, storms and auroras.

 

[Adam Lucio]

I too have cleared my work and social schedule for the remainder of the week.

I ran out of grandmas so the funeral excuse no longer works

Hoping my partner does the same, would leave Chicago Tuesday night, I might stay pretty close to the state line around NE/SD, and hopefully I dont find myself in Cherry county! poor road network!

Will then follow the system home to Chicago by Thursday/Friday. [Unless of course it stalls, hey I can dream can't I?]

Best of luck to everyone and be safe! This may be the last decent potential outbreak this year, altho The medium-range pattern does indeed look interesting! I thought May ended 4 days ago?

Im thinking a teaser round of storms may fire first, much like in Kansas on May 5th. The dry line wont wake up till late afternoon, tho i hope this is not the case.

 

[cdcollura]

Good day,

I ran out of grandmas so the funeral excuse no longer works

Yeah, I know ... But if you work at a different company (contracting) frequently, they do not know your two grandmothers passed at the last job. Also, I ALWAYS used my "grandmother" who was already passed away - This one passed last year - Lying about an alive relative dying is bad luck.

Getting back to the setup ... Models often shift east and west a bit.

The disturbance coming into California and the pacific West coast looks really impressive. I can imagin those Japan / Asian airlines flights are getting a nice tailwind coming into SFO - And paying for it flying the other way.

I also noticed that this first trough just clearing the east coast now did an absolutely horrible job at scouring away any moisture behind it.

 

[Brian Stertz]

I too have moved my target a bit further westand closer to the Nebraska stateline...between Winner and Mitchell SD...the ETA has remained very consistent with popping that area REAL hard. Based on the violent tornado checklist I have for my pre-chase forecasting...most parameters are checked and underscored. By the time this supercell or multiple supercells get up towards the Mitchell SD area...these should be full fledged mega supercells capable of baseball hail and strong to violent cyclical tornado families. Looks like a wild time ahead !!

 

[Jim Bishop]

I think Jeff makes some great points about the moisture return, LCL height, and associated capping--looking at the way dewpoints plummet Wednesday night in the warm sector is enough to make my toes curl. I share his concerns, and would add to that that even with dewpoints in the 68-70 degree range, the capping is still very, very substantial, with only a narrow corridor of low CIN, even over SD/NE. To really kill the cap and allow for sustainable convection into the nighttime hours a la May 4/5 of this year, mixed-layer dewpoints more in the 71-73 range are necessary, which is not going to happen.

So given that it looks like moisture return won't be stellar given the strength of the cap, what if the models are overdoing 700mb temps and the cap is not really what it's advertised to be? This would hardly be unprecedented, but this time the cap looks all too realistic. After baking under a ridge Tuesday, all the hot air from the Rockies is rapidly advected east by intense 700mb flow ahead of the trough on Wednesday. That's obviously favorable for steep mid-level lapse rates, but in this case is too much of a good thing, I think.

As a consequence, I think Wednesday will not be a record-breaking, monster outbreak, simply because there won't be enough storms for that to happen as the cap is too much of a limiting factor. That said, the shear and instability are obviously out-of-control, so wherever storms are able to fire and sustain themselves (most likely a few cells in SD/northern NE), I'd certainly expect them to tornado in short order. Wish I could go up there, but there'd have to be no obvious negatives to get me to go to SD during the week. With the models forecasting a huge cap in place over the vast majority of the warm sector despite a bullish moisture forecast, I'm going to have to take a pass.

I have the same concerns about the cap. From my experience anytime your 700mb temps get to 14-16C you need a pretty good vort max moving through the region to help break the cap. Based on the WRF/GFS areas north of I-80 should break the cap. But I still tend to think the storms would be fighting the cap, at least initially. Otherwise Northern Nebraska into South Dakota looks very conducive for tornadoes.

 

[Brandon Goforth]

Yes, things are looking rather nice up north. Too bad the cap will probably be too strong down into OK, so I will probably play the southern/central regions of Kansas to stay closer to home since this is the only chase day I will have this week. I would expect 1 or 2 isolated supercells into southern Kansas.

 

[Jared Farrer]

I am going to be heading out from central to north central IN, if anybody doesnt want to chase alone. I know some of guys are from around here i.e. ohio, indiana, and IL. This system isnt one you want to miss!! So if anybody wants to go take it from me and ready the work excuses pack the gear and just do it! For all you once in awile chasers out there, trust me and go!!

 

[Ben Prusia]

18Z NAM model data is in and it is looking kinda tasty from points of Kearney-Grand Island, NE northward into South Dakota for some severe thunderstorm development. The model shows the dryline up to Grand Island, NE and points along US Highway 281 by 0Z Thursday in a slightly faster moving storm system than that progged by the 12Z run. Right now, I will balance each model run, the 12Z GFS and the 12/18Z NAM models and I believe that storms should fire along the dryline from Valentine to Kearney with points further south having a harder time. Nothing new really to add as all of the severe parameters are still as strong as previous model runs, and I believe that any storm that can fire will quickly become tornadic.

I still will stick to my planned target area of along and just slightly north of I-80 and as far west as Kearney.