Virtual Chase Case #2

[Jason_Politte]

This Virtual Chase Case is done in the style of the Tornado Forecasters Workbook by Tim Marshall and Tim Vasquez. Analyze the data and post your forecast along with a target town. This case may or may not be a day on which tornadoes occurred, and if you think it's a bust day, let that be known as well. An afternoon update will be provided tomorrow afternoon/evening and the solution will be revealed Sunday morning.

Also, if anyone knows or figures out which day this case represents, please do not reveal the answer. Thanks!

Have fun!

SPC Morning Outlook:

VALID 1500Z - 1200Z

THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM
15 NW REJ Y26 30 NNE ATY 20 N STC 55 N IWD 15 WSW CMX 40 NNE GRB
30 E MSN 25 SE DBQ 20 S CID 25 WSW OTM 15 NE STJ 30 SE BIE
35 WNW CNK 45 NE HLC 20 SW BBW 15 S MHN 20 NNE AIA 35 W RAP
15 NW REJ.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM CRP 30 W CLL
10 W TYR 20 SSW PBF 20 SW MEM 30 E JBR 15 ESE P02 40 NW P02
10 SW VIH 45 N SGF 25 W EMP 20 SSW END 55 NW ABI 45 NW DRT.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 55 S MRF ROW
20 ENE CVS 25 SSE LBL 40 NE GCK 35 SSE MCK 25 W IML 30 E CYS
35 SW RWL 50 W MLF 50 ESE TPH 40 WNW BIH 35 ENE SAC 35 ESE MHS
40 N 4OM.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 45 W SSM MBL CGX
30 ENE LAF 25 ENE TOL.

SHORTWAVE TROUGH OVER THE ROCKIES WILL MOVE NEWD ACROSS THE CENTRAL/NRN PLAINS THIS AFTERNOON AND EVENING BEFORE REACHING THE UPPER MS VALLEY BY 12Z WEDNESDAY. ELSEWHERE...UPPER RIDGE WILL REMAIN ANCHORED FROM THE SRN PLAINS TO THE SE U.S.

...CENTRAL U.S...
WARM FRONT OVER NRN KS WILL MOVE/DEVELOP RAPIDLY NWD DURING THE DAY AS STRONG DIURNAL HEATING OCCURS N OF THE FRONT IN THE WAKE OF OVERNIGHT MCS. AS THE UPPER SYSTEM APPROACHES...A PLUME OF VERY STEEP MID-LEVEL LAPSE RATES WILL SPREAD ACROSS NEB AND SD /GREATER THAN 8 C/KM IN THE 700-500 MB LAYER/. THIS WILL CONTRIBUTE TO STRONG INSTABILITY THIS AFTERNOON WITH SURFACE-BASED CAPE VALUES EXPECTED TO EXCEED 3000 J/KG. THUNDERSTORMS WILL REDEVELOP BY
MID-LATE AFTERNOON OVER NEB ALONG RETREATING WARM FRONT AND E OF DEVELOPING LOW CENTER. SHEAR PROFILES WILL BE FAVORABLE FOR SUPERCELL STORMS OVER CNTRL/ERN NEB INTO WRN IA WITH STORM RELATIVE FLOW BEING FAVORABLE FOR A FEW TORNADOES. ACTIVITY WILL LIKELY EVOLVE TO AN MCS THIS EVENING AND MOVE TOWARD THE UPPER MS VALLEY REGION...WITH DAMAGING WINDS BECOMING THE PRIMARY SEVERE THREAT.

A SEPARATE AREA OF SEVERE THUNDERSTORMS IS EXPECTED TO FORM OVER THE BLACK HILLS OF SD THIS AFTERNOON IN UPSLOPE FLOW N OF WARM FRONT. MODELS SUGGEST THAT AT LEAST LOWER TO MID 60S DEWPOINTS WILL POOL ACROSS THE REGION WHICH WILL CONTRIBUTE TO MODERATE INSTABILITY. STRONGLY VEERING WINDS WITH HEIGHT WILL SUPPORT SUPERCELL DEVELOPMENT WITH THE MAIN THREATS BEING FROM LARGE HAIL AND DAMAGING WINDS. THIS ACTIVITY MAY ALSO EVOLVE INTO A SMALL MCS AND MOVE ACROSS THE REMAINDER OF SD THIS EVENING.


...MIDDLE MS VALLEY/LOWER OH VALLEY...
ALTHOUGH NOCTURNAL MCS HAS DISSIPATED ACROSS MO...SATELLITE IMAGERY SHOWS A REMNANT MESOSCALE VORTICITY CENTER. THIS FEATURE WILL MOVE EWD DURING THE DAY AND THERE IS SOME CONCERN THAT THUNDERSTORMS COULD REDEVELOP IN ASSOCIATION WITH THIS SYSTEM. ALTHOUGH SHEAR PROFILES ARE EXPECTED TO BE RELATIVELY WEAK...AIRMASS WILL BECOME MODERATELY TO VERY UNSTABLE WITH DAYTIME HEATING. WE WILL MONITOR
CONVECTIVE TRENDS ACROSS PORTIONS OF MO/SRN IL/KY AND SRN INDIANA DURING THE DAY FOR A POSSIBLE UPGRADE TO SLIGHT RISK THIS AFTERNOON.

12z Maps:
12z surface obs
850 mb analysis
700 mb analysis
500 mb analysis
250 mb analysis

12z Soundings:
Aberdeen, SD
Rapid City,SD
Omaha, NE
North Platte, NE
Denver, CO
Topeka, KS
Dodge City, KS

Satellite:
National IR (sorry, no visible)

Radar:
12z Central Plains Radar Composite
12z Northern Plains Radar Composite

 

[David Wolfson]

I only have a mezzo-positive feeling about this setup for tornados. The tor potential will depend on more focused low-level shear and jet than exists so far. The warm front in southern NE is in frontolysis. It looks to re-form arcing up through southeastern SD as short-wave action lowers pressures to the lee of the Black Hills, and move north and northwestward to the east of the Missouri River through the late afternoon and evening. Anything much south of I-90 has more messy-scale severe potential than tor potential without the forcing and shear possible further north IMO.

Target: Huron, SD, but be watching the obs for afternoon frontogenesis. Could be heading more west and north. FWIW.

Thanks for the puzzle, Jason!

 

[Jason_Politte]

Originally posted by David Wolfson
Thanks for the puzzle, Jason!

You're welcome David, and thank you.

I had hoped there would be more interest considering the positive reaction to the last case I posted. Regardless, here's the afternoon update for you and anyone else who might want to jump in. I'll extend the deadline for the solution to tomorrow night.

1745z National IR Satellite
18z Surface Obs

Updated SPC Outlook:

VALID 1930Z - 1200Z

THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 20 NW MLS 40 WNW Y26 20 N STC 55 N IWD 15 WSW CMX 40 NNE GRB 30 E MSN 15 NE STJ 45 NE HLC 20 NNE AIA SHR 20 NW MLS.

THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 25 SE CEW 30 SW TOI 40 WNW ABY 25 SE SAV ...CONT... 35 NNW DAB 20 SSW CTY.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM CRP 30 W CLL 10 W TYR 20 SW MEM 15 ESE P02 10 SW VIH 25 W EMP 55 NW ABI 45 NW DRT.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 55 S MRF ROW 25 SSE LBL 35 SSE MCK 30 E CYS 35 SW RWL 50 W MLF 50 ESE TPH 40 WNW BIH 35 ENE SAC 35 ESE MHS 40 N 4OM.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 45 W SSM MBL CGX 30 ENE LAF 25 ENE TOL.


LATEST SURFACE ANALYSIS SHOWS A DOUBLE WARM FRONT STRUCTURE ACROSS PORTIONS OF THE NORTHERN AND CENTRAL PLAINS. THE SOUTHERN FRONT EXTENDED ALONG THE KANSAS/NEBRASKA BORDER...AND THE NORTHERN FRONT
LAY ALONG THE NEBRASKA/SOUTH DAKOTA BORDER. WATER VAPOR IMAGERY SHOWS SPEED MAX MOVING THROUGH THE MEAN TROUGH INTO SOUTHWESTERN NEBRASKA.

...NORTHERN PLAINS/WESTERN GREAT LAKES...
WARM FRONT WILL CONTINUE TO LIFT SLOWLY NORTHWARD ACROSS THE PLAINS AND UPPER MISSISSIPPI VALLEY TODAY AND TONIGHT. AS THE FRONT RETREATS...AN INCREASINGLY UNSTABLE AIRMASS WILL MOVE INTO THE OUTLOOK AREA. CURRENT SURFACE OBSERVATIONS SHOW DEWPOINTS CLIMBING INTO THE MIDDLE AND UPPER 60S. AS A RESULT...MODERATE TO STRONG INSTABILITY EXTENDS FROM SOUTHEASTERN MONTANA...ACROSS NORTHERN NEBRASKA INTO IOWA. SURFACE BASED CAPE VALUES IN THESE AREAS ARE
IN THE 1500 TO 3500 J/KG RANGE.

THUNDERSTORMS HAVE ALREADY DEVELOPED OVER THE HIGHER TERRAIN OF MONTANA INTO SOUTH DAKOTA THIS AFTERNOON. THIS ACTIVITY CONTINUES TO MOVE EASTWARD/NORTHEASTWARD INTO THE AXIS OF HIGHER INSTABILITY. VAD WIND PROFILES ACROSS THE AREA SHOW STRONGLY VEERING WINDS...INDICATING A POSSIBILITY FOR ISOLATED SUPERCELLS...ESPECIALLY AS THE STRONGER WINDS CONTINUE TO SPREAD EASTWARD INTO THE PLAINS.
LARGE HAIL AND DAMAGING GUSTS ARE LIKELY WITH SOME OF THESE STORMS. ISOLATED TORNADOES ARE ALSO POSSIBLE GIVEN THE VEERING PROFILES AND DEGREE OF INSTABILITY.

ADDITIONAL STORMS ARE LIKELY TO DEVELOP IN THE VICINITY OF THE
RETREATING WARM FRONT THROUGH THE AFTERNOON ACROSS NEBRASKA AND SOUTH DAKOTA. VAD WIND PROFILES OVER EASTERN NEBRASKA INTO IOWA SHOW FAVORABLE SPEED AND DIRECTIONAL SHEAR FOR ORGANIZED SUPERCELLS. THIS ACTIVITY SHOULD EVOLVE INTO AN MCS LATER THIS EVENING AND CONTINUE EASTWARD MOVEMENT INTO THE WESTERN GREAT LAKES REGION.

 

[Bill Tabor]

Well I must say I typically use a LOT more stuff than this to forecast - namely model data; however given this and limited time for the fun of it I'll take a 'swag' at it:

This looks like a doable supercell / tornado day to me. I didn't print this out and draw a bunch of lines to really get down and dirty to analyze it but I am drawn to the surface low of 056 with backing winds at 18z in northern KS and the frontal boundary between KS and NE. Earlier precipitation in the day in eastern NE may leave some outflow boundaries to work with as well. I see this frontal boundary lifting northward throughout the afternoon with 700mb temps per 12z sounding between 8 and 12 later in the day. I'd say some capping in place, but if breakable would lead to explosive development given surface temperatures near 90 and dewpoints near 70 in northern KS. These winds expected to be in south central NE later that afternoon in position under the upper jet which is also inbound to the south central NE area. I would consider an enhanced risk for severe thunderstorms along an area from southern central NE extending into southern IA. A moderate risk bounded by North Platte, Hays, Maryville, Des Moines, Sioux City.

Probably my favorite initial place for tornadoes would be centered over Kearney, NE and I would plan on working ENE toward IA. Hopefully Kearney would end up being on the front, ne of the low, and under the upper jet (assisting in lift and helping to overcome cap). Perhaps there would also be a dewpoint bulge in this area as the surface shows some lowered dewpoints to the SW toward CO that may be inbound at 18z. I would also be looking for old storm boundary interactions.

Edit: In case my third paragraph wasn't succinct enough let me spell it out....

Target = Kearney, NE

 

[nickgrillo]

Based on the limited data - I'd probably head for the GRI/Kearney area myself...

 

[Karen Politte]

Well - I haven't looked at the afternoon update yet because I wanted to play around with this in the correct order and make it a bit more of a challenge.

From what I saw in the morning, at 8.30am over a great hotel breakfast, the warm front in northern KS interested me and it is progged to translate rapidly northwards. A nice zonal wave is forecast to eject out across NE/SD for this chase day, with more than adequate 500mb flow. Moisture in the morning is a bit scatty and we have an ongoing MCS, but things should become much more focused during the day.

I'm worried about the Iowa target.

I take my orange juice in the little platic cup from the hotel and get myself to Broken Bow's library in the Nebraska Sandhills by 9.00am. Should be interesting.....

Jason deserves all the credit for taking the TIME and the EFFORT to put studies like this online for us to think about.

KR

 

[Karen Politte]

Right - well the time to get into position is here. I haven't read any of the other posts on this thread - I'm going completely on my gut feeling.

I found it impossible to ignore the developing surface cyclone in northwestern KS/southwestern NE, with the southerly warm front draped across this region. With 82/66 at McCook and 79/68 at Holdredge - both with good easterly components to their winds - all factors point towards this zone as my no. 1 area of interest today. I'm no longer interested in targets further north or east - and this might land me with egg on my face when the reults are revealed.

But - I enjoy going out on a limb and hoping to be the odd one out who lucks out - so here I go.

At mid-morning it became clear to me that today wasn't about to be totally clear cut - and I may as well commit and hope for the best. I waved goodbye to Broken Bow and took Gene and Tim (who are having way too much fun today as I drive) down to the I-80 corridor. We ate lunch in Kearney and filled up, then sidled down towards Holdredge by around 1.00pm.

We plan to tool around between Holdredge and McCook all afternoon - not going very far until we see something that really catches our eyes - like initiation on the NE side of this developing low.

KR

 

[David Wolfson]

What a difference six hours makes. Not exactly a warm front yet, but the deeper moisture is nosing into southeast SD and backed winds are beginning to crank. I like the dry punch just starting to come off the mountains in Casper and Cheyenne. I don't want to be too far east nor am I eager to get lost west of the Cheyenne River Reservation.

New target: Gettysburg, SD, with the feeling I'll be seeing Selby before the night is over.

 

[Gabe Garfield]

Thanks for putting this together, Jason!

I have to agree with Karen's assessment right now...looks like a day to play the low. Wind fields look pretty decent, especially across the southern part of the plains, based on the 12z obs. Looks like the shortwave trough responsible for the morning convection exited by 18z and left subsidence and an outflow boundary in its wake. The outflow boundary would be the obvious play on a day like this, but I'm also slightly curious about parts of South Dakota which had significantly backed winds and good moisture.

Target: Arapahoe, NE

Gabe

 

[Aric Cylkowski]

Thanks for the Chase Case, Jason.

Ok, the change in the IR looks very good to me around the Wichita, KS area. The earlier sounding from Dodge City looked promising, but the cap and cinh had me a tad concerned. However, I got a gut feeling that the Witchita, KS area is a good place to be.

Target: Wichita, KS

 

[Jeff Snyder]

Moisture and surface winds look appealing in SD, but the very backed mid-upper level flow is worrying me. I'm not sure I buy the 400-500mb Rapid City wind obs on the 12z sounding, since they don't match well with the more backed mid-upper level flow of surrounding sites. Regardless, with S/SE mid-upper level flow in the Dakotas, I'm wanting to play a little farther south.

The nicely backed flow and generally mid-upper 60 Tds in central and southern NE catch my eye. Flow, at 12z, aloft is adequate and not too backed, while, at the surface, dewpoint depressions are in the 10-15 degree range, yielding sufficiently-low LCL heights for me to think tornadoes. There seems to be a pocket of drier low-level air in northcentral and norhteastern NE, as evidenced by the low-60 Tds, so I'd like to stay nearer I80 if possible. There doesn't appear to be a super well-defined dryline in place, as the only real dry air is located in extreme sw KS and into the western OK/TX panhandles. That said, the westerly surface wind at Goodland, KS, certainly catches my eye, raising the possibility of enhanced surface convergence or possible "dryline" bulge. With very steep lapse rates per the 12z Denver sounding advecting over this area courtesy of the sw flow aloft, mid-upper 60 Tds with temps near 80 (or slightly higher with a few more hrs of heating), southern NE looks pretty good... Let's look a little farther south...

Those stations in KS west of I-135 generally have surface winds with a westerly component, which is likely a result of convective mixing and boundary layer deepening. This is likely the culprit for the slightly lower Tds in this area (low-mid 60s are common). Where mixing is less prevelant, surface winds are more backed and moisture more plentiful, as can be seen with the upper-60s to low-70s Tds and se sfc winds generally east of I135 in eastern KS. This looks pretty good, but surface temps are considerably higher down here, yielding larger T-Td and higher LCLs. And, with a couple more hours of heating, I'd be worried that even this moisture may begin to mix out, considering the very shallow moisture depth as seen on the 12z soundings from DDC and TOP.

With all this said, I'm going to have to side with Karen and Gabe. Strong instability should develop across southern NE as the afternoon progresses. In addition, southeasterly surface winds below relatively strong southwesterly flow aloft will yield shear profiles favorable for supercells, while low LCLs aid the tornado risk. Strong diffluence aloft is also nice to see. My target is very close to Gabe's, so I'll pick a slightly different city. I'm a little worried about going too far into SW NE, given the mostly-cloudy skies at McCook. Kearney looks appealing, but I want to play a tad south of there.

Target: Holdrege, NE

 

[brody_clifton]

My target town would be Rose, NE, denoted by the X on the map below.

<img src= "http://24.211.196.156/case2/target_town.bmp" />

I would expect the southern warm front to eventually make its way at least into southern NE if not central, and if so Rose would be just north of this front but hopefully far enough south of the northern front by kickoff time to be out of the grudge caused by warm air advection.
From the infrared sat. image and from the SPC mentoning, the black storm icons on the map indicate generally where convection has already fired by early afternoon in eastern MT sse to western SD, with the dark blue arrows estimating cell movement. I would expect storms to continue to fire farther down the line south of these, eventually into western NE (the blue storm icons on the map).
The short wave speed max mentioned by the SPC and the mid level 50kt max shown on the 12Z 500MB map moving into southwestern NE at lunch should be nosing into north central NE about the time the western NE cells begin to approach the this area, enhancing 0-6 km shear and hopefully setting the stage for one or two strong low level mesos.
However, I would be keeping my eye out for any tail end charlies firing south of my target town and jump on those asap, unless theyre all the way down in KS then I'll just stay put near the warm front.

 

[Bill Tabor]

Originally posted by brody_clifton
My target town would be Rose, NE, denoted by the X on the map below.

:lol: Rose, NE? LOL! Couldn't you have picked a smaller town? Rose looks just like a bump in the road. Had to use Streetatlas to find it.

 

[Jason_Politte]

Solution

First, thanks to all who participated in this chase case. I hope it’s found to be educational.

This day was June 23, 1998, a day many chasers will recognize from mainly one piece video, the Columbus, NE wedge tornado AKA “the crazy farmer video.â€￾ With the dual warm front structure, this was indeed a complicated forecast and probably an even tougher chase for those out this day.

Two main areas of interest emerged, the first being just north of Rapid City, SD as a tornadic supercell developed within the left exit region of the upper-level jet. Tom Warner documented this cell, and his chase account for the day can be found at:

http://www.atmosphericwildlife.com/severe/...998/980623.html

The second area of development occurred ahead of the northeast moving sfc low in an area of backed flow near the Columbus, NE area as a prolific tornado producing supercell formed before 00z. Mike Umscheid and Jay Antle were able to catch this storm from Grand Island in time to observe one of the tornadoes it produced. It's interesting to notice some of the same thought processes occurring in both his chase account and this thread.

http://web.archive.org/web/19991018212504/...n23/account.htm

Photo by Jay Antle:

Another tornado was reported in association with the convection in south central South Dakota.

Data from the event as it unfolded:

SPC Storm Reports

Maps:
22z surface obs
23z surface obs
00z surface obs
850 mb analysis
700 mb analysis
500 mb analysis
250 mb analysis

Satellite:
2345z National IR

Radar:
23z Central Plains Radar Composite
23z Northern Plains Radar Composite
00z Central Plains Radar Composite
00z Northern Plains Radar Composite
01z Central Plains Radar Composite
01z Northern Plains Radar Composite

Jason

 

[Bill Tabor]

Having been in the general target area the day before, I arrived near the target town of Kearney, NE by 19z. Sitting NE of the low and near the warm front as it worked it's way north and the low moved northeast I was able to detect cu forming on vis sat to my NE which fit my moderate risk between NE / IA. As expected I quickly shot ENE toward the town of Columbus along highway 30 where I also witnessed the 'crazy farmer' and the wedge tornado.

I'm eating virtual steak tonight baby! I ran into a few of you at that cafe later that night where we all swapped stories. :lol:

In retrospect (and reality), back on June 23rd '98 I was probably stuck at home in Austin because of work. My DBA job didn't allow me to get out much. I wasn't too good at forecasting then either but was trying to pick it up. A lot has happened since then. I'm sure it was a helluva chase!