10/22/04 FCST: Plains/midwest

I'll keep an eye out for you Tony, I'll be headed to Colby tomorrow. No, I know I'm going the wrong way for the weather, but unfortunately I must attend a wedding. This will ensure a severe weather day on the east side of the state :roll:
 
I'll keep an eye out for you Tony, I'll be headed to Colby tomorrow. No, I know I'm going the wrong way for the weather, but unfortunately I must attend a wedding. This will ensure a severe weather day on the east side of the state :roll:
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Hehehe.. well, hopefully you're right. I'll be passing through Colby at some point tomorrow I'm sure. May make it tonight if my energy holds up, as its only half hour out of Goodland. How far I go tonight is based upon how far I need to go tomorrow. Thanks for the eye and have fun at the wedding. Be watchin' for me shooting passed the Colby exit! Hopefully the gas isn't as expensive as it was in early May. :roll:
 
I'm making a totally different call, and am playing the warm front on the eastern side of things. Most of this is just because I live in eastern Illinois, and have no time for a 7 hour drive to nebraska. But, I kind of like the area along the warm front, right near the intersection of Iowa, Illinois and Missouri. This is around the same area Tom Skilling was harping in his broadcast. Thats only a 2 or 3 hour drive for me, and would certainly be more doable, and enjoyable. So, hopefully both areas, along the warm front, and along the dryline in the west can light up come tomorrow afternoon.
 
In some ways, targeting the WF over CF/DL is attractive from the standpoint that CF will likely be trucking across KS/NE, and because Day 2 also at least eludes to CF movement occurring during the second half to the end of the forecast period. I'm wondering if the WF will trigger more isolated supes before the CF begins its march ... or if this is indeed a situation setting up for cold-core minis, that maybe we'll end up with multiple targets more similar to an April 11, 2001 scenario (by the way, while mini-supe days can be fun, they can also be a real challenge to keep up with). In any case, at least for now it appears that I'll be sticking closer to home tomorrow ... I'm thinking that I'll be in a good place for setting a last minute target when the choices become clearer.

Amos - you are the flip flop king ... LOL. Have fun -
 
For those targeting the warm front... Refering to http://www.wxcaster2.com/CENTRAL_ETA_250M-...VECTOR_30HR.gif and http://www.wxcaster2.com/CENTRAL_ETA_250M-...VECTOR_36HR.gif , the ETA is forecasting 0-6km deep layer shear of only 25-35kts over IA and MO at 18z, increasing to 35-40kts by 0z (sunset). This makes me especially concerned about the occurrence of supercells given the already relatively-scant SBCAPE. Meanwhile, locations neared the mid-level jet streak in OK and KS will likely be characterized by 0-6k shear in the 35-55kts range, which is considerably more conducive to supercell mode, again given the relatively weak-moderate instability forecast. Just something to think about...

EDIT for 18z ETA: The 18z ETA continues the slowing trend and actually keeps a part of the surface low in southwestern NE at 18z tomorrow (http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/eta/18/images/eta_slp_024l.gif ). Part of the problem now is, however, that the upper trough is now going to crash eastern KS, etc, on Saturday morning... In addition the 18z ETA shows the axis of the upper-level jet over northeast NM and western KS, placing much of the original target area (central plains) in the right-exit region, which tends to cause subsidence. However, this may not be entirely bad... For those so inclined, you can reference the following paper:

Rose, Stanley F., Hobbs, Peter V., Locatelli, John D., Stoelinga, Mark T. 2004: A 10-Yr Climatology Relating the Locations of Reported Tornadoes to the Quadrants of Upper-Level Jet Streaks. Weather and Forecasting: Vol. 19, No. 2, pp. 301–309.

The above paper showed that, during the 10-yr period examined (during Apr-June I think) there were still more tornadoes that occurred in the right-exit region than the seemingly more-favorable right-entrance region of the main upper-level jet streak. This seems odd since the right-entrance region is associated with lift, while the right-exit region is associated with subsidence. None the less, it does show that even despite the subsidence provided by the right-exit region via transverse circulation, it is still a favored location relative to the right-entrance region...
 
Thanks Jeff - - - I'm sure you're already aware of this, but we have to keep in mind that the parameters for a favorable mini environment are significantly different from those of a typical supercell chase ... SBCAPE can be significantly reduced on these days, and the resulting CAPE/shear combination often appears much smaller than what we usually think is acceptable. Some of Jon Davies' study material is pretty helpful: http://members.cox.net/jondavies1/tornado_...sprcll_tors.htm

Tomorrow I would be more concerned with the two ingredients Jon mentions:

*A core of cold air aloft nearby, resulting in steep lapse rates and CAPE closer to the ground, suggesting potential for increased stretching in low levels.

*A well-defined boundary extending east or southeast from a surface low, providing focus and vertical vorticity (significant horizontal vorticity from SRH may or may not be detectable in the environment, although any detectable SRH will add to the potential for tornadoes)
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Any thoughts from anyone experienced in this type of setup would be greatly appreciated. Since this is usually an early spring setup, we don't cover it a lot in here - - -
 
For those targeting the warm front... Refering to http://www.wxcaster2.com/CENTRAL_ETA_250M-...VECTOR_30HR.gif and http://www.wxcaster2.com/CENTRAL_ETA_250M-...VECTOR_36HR.gif , the ETA is forecasting 0-6km deep layer shear of only 25-35kts over IA and MO at 18z, increasing to 35-40kts by 0z (sunset). This makes me especially concerned about the occurrence of supercells given the already relatively-scant SBCAPE. Meanwhile, locations neared the mid-level jet streak in OK and KS will likely be characterized by 0-6k shear in the 35-55kts range, which is considerably more conducive to supercell mode, again given the relatively weak-moderate instability forecast. Just something to think about...
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Perhaps the 'weaker' shear over the weaker CAPE isn't that bad - I would be affraid that if the shear was too strong, and the updrafts would get ripped apart. With slightly weaker shear, the updrafts (from what little available energy exists) would have an easier time rising... So, while the risk does appear low, I don't think that the weaker shear is necessarily a 'kill-all' so to speak. Anyway, with CAPE of 1700J/KG (off the 18Z ETA) over western IA, and rather strong low level helicities, I could see supercells developing.

BUT, if you were referring to eastern IA - Things don't look so good for supercells - CAPE doesn't even show up on the 18Z ETA, and as Jeff said, the flow there is much weaker than about 100 miles further west. I suspect any supercells would become linear long before reaching this area...
 
It's fun to look at last night's eta's progged cape for tonight at 7 and compare it with what is actually happening via spc meso page.
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You took the words right out of my mouth...I was just about to say. :lol:

CAPE is going to be much more significant than advertised by the ETA, IMO. The 70 F isodrosotherm is almost to C. Ok already!!! Will be real interesting to see tonight's OUN sounding (to see just how deep the moisture is).

Also, a substantial lee cyclone has formed just east of Denver with surface winds up to around 20 kts in the vicinity of the low (compared to < 10 kts earlier today). Warm advection should begin in a hurry tonight. Also, compare the position of the surface low with the 12 z ETA forecast (ETA had the sfc low in ND at this time). Furthermore, 850 mb winds are significantly more backed than the ETA forecast this morning (Purcell profiler showing south winds just below 850 mb).

All this said, I think the tornado threat is much more significant in the central and southern plains than previously advertised.

Gabe
 
Just noticed this courtesy of Gabe... This is EXACTLY why I have very little faith in the ETA forecast...

The first graphic is the 6hr forecast from the 12z ETA valid at 18z today. The second graphic is the 18z RUC 0hr analysis (in other words, what things actually looked like at 18z today). Remember, the ETA foreast is ONLY a 6hr forecast.

[Broken External Image]:http://www.tornadocentral.com/now/12z6hrETAMSLP.gif
[Broken External Image]:http://www.tornadocentral.com/now/18zRUCAnalysis.gif

No low near DEN (which may be an analysis issue to begin with, but still)... The actual lee-side trough is pretty significantly underestimated by the ETA. If the 6hr forecast didn't fare well, how are we to trust the 24-36hr surface forecast for anything? LOL...
 
Wow, folks have been busy posting a lot on this topic today. Surprised to see so much discussion still on the ETA - many have noted how poorly it is representing things - and the folks at HPC still don't like how the ETA is performing with this event:

http://kamala.cod.edu/ncep/latest.fxus10.KWNH.html

As some have mentioned - I think also that the WF may end up as the best play tomorrow. These events are favored for torns as you get into the midwest - and with the weaker forcing should favor more discrete cells. Of course, tornadic potential is less certain on WF events until mesoscale features come out - but if I were free to chase I'd be looking toward southern IA.

Glen
 
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