07/12/04 FCST: Central & Northern Plains

Mike Hollingshead

Capping could prove to kill this day, but I think there is plenty of potential in place for a thread. Eastern SD, sw MN, nw IA, and ne NE look a wee bit unstable and this time the shear looks to be more over the instability. 35-40knts at 500mb. SFC to 850 rather weak but that is to be expected this time of year. We really really need to get a storm up in this kind of instability and shear.

http://www.wxcaster.com/modelskewt.php3?mo...&STATIONID=ksux

Sioux City. EHI of 9.3...lol. Flow is better nw of this location. I just grabbed this one cause I think extreme instability is so cool.

Cape progged as high as 8300 in nw IA with a nice veering profile. An ok sfc boundary is shown in place as well...and temps should be closer to the convective levels. LCL's could be high too, but there IS plenty of moisture and this may actually not be too big of an issue even with sfc temps in mid 90s. Thoughts?

Mike
 
Interesting difference in Eta forecast soundings, especially when it comes to CAPE and CINH.

Example below is for Sioux City Iowa
This is from the Eta: 00Z 11 SUN JUL 04 run
for the 48 hour forecast period: Valid 00Z TUE 13 JUL 04

Earl Barkers Model Page:
http://www.wxcaster.com/modelskewt.php3?mo...&STATIONID=ksux
http://mgweather.com/SUX5.png
CAPE: 8139.2 CINH: -34. 7 BEST CAPE: 6578.0 ML CAPE 5853.9

Plymouth State College:
http://mgweather.com/SUX.gif CAPE: 3602 CINH: 146

The Storm Machine and the University of Wisconsin both identical
http://mgweather.com/SUX3.gif CAPE: 4778 CINH: 087
http://mgweather.com/SUX4.gif CAPE: 4778 CINH: 087

Wright-Weather which I cannot post: CAPE 6710 CINH: 069
Another source told me, CAPE is around 5000 for SUX

Its late, I forgot to see what the Eta BUFKIT sounding would be for SUX
Just wanted to show what a difference you can get in calculating CAPE
on forecast soundings from a variey of sources on the internet.

Mike
 
I've noticed that Earl's sounding based indices have some major flaws, and may have played a roll in several recent busts as I know a number of folks use his stuff quite heavily (so did I as I love the clarity of the sounding outputs).

CAPEs of 8000+ J/kg are impossible (at least on this planet)...let alone 6000. Even accounting for "cornbelt-itis" and using surface based CAPE, the indices and lifted parcel on that sounding don't make sense. A mean boundary layer CAPE still yields an impressive 5000 or so J/kg, but I think that the Eta is suffering from it's tendency to convectively parameterize too much and erode any thermal inversions.

With that said, Sioux City would certainly be my pick late Monday. Thermally induced surface trough, extreme instability and incredible deep layer shear underneath belt of westerlies should support a small but intense area of convection in that region. Even a fairly decent tornado threat early given CAPEs and low level turning...but strength of upper flow and cold pool generation suggests if this event goes...it would likely evolve into one helluva bow echo. The only negative factor I see is that the soundings produced are ignoring a nose of mid level thermal ridging that's partially the cause of the pressure falls in the first place. Convective parameterization may be heating the boundary layer too much and eroding a cap that could limit coverage/longevity of convection. If I had the means, I would probably go for it.

Evan
 
Been a quiet day on this thread...

Based on the 0z Eta, looks like some kind of weak surface low sets up during the afternoon in northeast NE with significant instability pooling along a NW-SE axis from the Sioux Falls area down into western/central IA.

By 0z, w-nw 500mb flow of 30-40 kts is just poking into the NE IA MN SD border region overlaying fairly weak sw 850mb flow maybe in the 10-15 kt range. 0-3km SRH is in the 100-150 range yielding respectable EHI values of roughly 3-4 over the instability axis. 0-6km shear is into the 30-40 range which is decent as well.

Yes, I've been ignoring the obvious capping issue thus far....looks like the ETA is building some pretty stout 700mb temps into the 12-14C range by mid-day in the Sioux Falls region but then knocks them down to 10-12C by 0z as the shortwave approaches. So, does anybody buy the Eta initiation of storms in the NE-SD border counties by 0z or is this too optimistic? I see the latest GFS seems to be keeping things a few counties north of here. It will be interesting to see what effect, if any, some of this overnight activity might have as far as setting up outflow boundaries and such.

At least I like the looks of extreme instability combined with a nearby surface low. Maybe Sioux City to Yankton corridor and hope for initiation before dark? Or is this just too far south? Thoughts?
 
Environment Canada is calling for some more T-Storm action in northern Alberta and Saskatchewan again. Southern Manitoba looks ripe for some action as well.

If I wasn’t working, i'd keep my eye on the Winnipeg area and strait south from there into the US as well. However it's a little too far for me to chase, lol.
 
Some questions from the inexperienced...

1. Why do you tend to always look at the 48 hour skew-T, why not look for target times of storm development?

2. I've come to understand CAPE is an important term and found the definition on the internet, what are some other terms and definitions or do you know of some place I could find them?

Edit: Good site: http://www.theweatherprediction.com/thermo/parameters/

3. For someone like me, can I trust the percentage of Supercell potential?

4. Is anyone going to be out in SE SD tonight - perhaps Brookings to Sioux Falls area?
 
SWW in SD

NWS has posted a SWW for a large portion of Eastern SD and Western MN.

NWS STORM PREDICTION CENTER NORMAN OK
1055 AM CDT MON JUL 12 2004

THE NWS STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR PORTIONS OF SOUTHWEST MINNESOTA
NORTHEAST AND EAST CENTRAL SOUTH DAKOTA EFFECTIVE THIS MONDAY MORNING AND AFTERNOON FROM 1055 AM UNTIL 400 PM CDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

bdef697e46c422442ceea2b99aade190.gif
 
Edward, I just post those because they give all the info for one area in one url. At 48hrs it's best just to gather an idea of what could be in place, then worry about more confined target areas later. One problem with that supercell potential is it's figuring there is convection in that spot at that time. If there are no boundaries for convection other then a cold front it's likely you will see no supercells. Cold fronts are bad. One thing early on to learn is finding surface boundaries/convergence as you have to have that for storm development. They are rather easy to locate. Places that give you moisture convegence images are probably the easiest but they don't always update very often. This one is every hour...

http://www.spc.ncep.noaa.gov/exper/mesoana...sis/s1/mcon.gif

Going off that right now, I'm likley heading to Mitchel SD soon.

http://wwwghcc.msfc.nasa.gov/GOES/GOES1631...04194vIMjUd.jpg

Interesting boundary on satellite going nw to se, but there doesn't seem to be much sfc convergence along it. Still, thinking of heading to where that intersects the cold front and sfc low...or se of that location.

I'll guarantee a tornado box in se SD and east this afternoon...lol.
 
Today we have a moderate risk for SE Manitoba and a slight risk for SE Saskatchewan. The spinning action on radar has moved from the Edmonton area over to the Saskatoon area. Since it is my day off work, hopefully I can be as lucky as the other chasers yesterday in SE Sask. Watches have been posted along the SK/MAN border at this hour. Tornadoes are most likely in southern/central Manitoba although it might be impossible to chase central Manitoba due to lakes and trees, I have never been there so maybe it could be a fun fishing trip or something. I think I will stay around here though since it will be hot and muggy and possibly unpredictable like yesterday around Edmonton where another tornado was reported. Several chasers caught a tornado also yesterday in SE Sask. Even talk of chaser convergence in Saskatchewan???? :shock:

Jared
 
Tornado watch issued for Prince Albert and areas east of there. Pop up cells north of Saskatoon have changed direction since noon so I think I will go see if these "funnels" that were reported are scud or what.
 
NWS just released:

TORNADO WATCH NUMBER 612 IN EFFECT UNTIL 900 PM CDT.

IN SOUTH DAKOTA THIS WATCH INCLUDES 16 COUNTIES...

SDC003-009-027-035-043-061-067-083-087-099-125-127-135-130200-
IN SOUTHEAST SOUTH DAKOTA THIS WATCH INCLUDES 13 COUNTIES...
AURORA...MINNEHAHA...DAVISON...HANSON...MCCOOK...LINCOLN...TURNER...
DOUGLAS...HUTCHINSON...YANKTON...BON HOMME...UNION AND CLAY

An hour till I get off work...grrr
 
Tower's are goin up, but they're calling for a nice squall line. I'm headed out towards Aberdeen anyways, maybe I'll see a reports thread. Wish me luck!

EDIT:
STRONG STORMS ARE EXPECTED TO CONTINUE DEVELOPING
WITHIN LOW LEVEL CONVERGENCE ZONE FROM SOUTH CENTRAL SD ESEWD INTO SERN SD/NERN NEB. AIR MASS HAS BECOME VERY UNSTABLE WITH MLCAPE OF 2500-3500 J/KG. WINDS VEER AND INCREASE WITH HEIGHT RESULTING IN STRONG DEEP LAYER SHEAR SUPPORTIVE OF SUPERCELL DEVELOPMENT. IN ADDITION...SRH AND LCL PARAMETERS SUGGEST THREAT FOR POSSIBLE TORNADOES AS CELLS PROPAGATE EWD AND SEWD INTO THE EVENING HOURS

MAYBE I won't go so far away. don't want to miss the tube a couple miles from home :D
 
Could we get a NOW thread up and running?

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE SIOUX FALLS SD
403 PM CDT MON JUL 12 2004

THE NATIONAL WEATHER SERVICE IN SIOUX FALLS HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHEAST GREGORY COUNTY IN SOUTH CENTRAL SOUTH DAKOTA

* UNTIL 430 PM CDT

* AT 403 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO OVER GREGORY
COUNTY...OR ABOUT 13 MILES WEST OF PICKSTOWN...MOVING SOUTH AT 10
MPH.
 
This might belong in a 'NOW' thread, but what magnificent low level rotation on that storm on the South Dakota/Nebraska border. LBF radar picking up nearly 100 kts of shear at the base velocity, and it's the first storm of the day with the atmosphere to itself. So much for the 12-13 C 700 mb cap..
 
This might belong in a 'NOW' thread, but what magnificent low level rotation on that storm on the South Dakota/Nebraska border. LBF radar picking up nearly 100 kts of shear at the base velocity, and it's the first storm of the day with the atmosphere to itself. So much for the 12-13 C 700 mb cap..

unfortunately the storm is right on the cusp between those two radars, so those velocity readings are probably coming from the mid-upper levels of the storm, rather than at the base. still quite an impressive upper mesocyclone
 
I would guess that the LBF radar is intercepting the storm at about 5000 ft for its base velocity, which to me, is still pretty low in the storm, and picking up 100 kts of shear (latest scan is down to about 75 kts) at that level is indicative that a pretty strong mesocyclone is in place with the storm. Given other factors such as near storm environment of EAST winds at ONL, 70 degree dew points, and bulk shear in excess of 45 kts, and it looks like that storm is going to have a pretty decent chance to be tornadic, even if a little high based. If nothing else we should get some impressive hail reports from this storm.
 
Should be a NOW thread, 2.50 inch hail reported in Charles Mix and Gregory Counties SD.
The beam height is more like 15K and its 120 miles away from the North Platte radar for the Boyd County storm.

Mike
 
The storm has taken a hard right turn and is now heading due south towards Spencer, NE. It also appears to be developing a slight hook echo in the west quadrant. I hope people in this area are heeding the warnings. My niece’s future husband (next month) has family in this area.
 
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