3/22/11 FCST: IA/NE/KS/MO

[Jeff Duda]

Just a quick look at SPC's 700 mb analysis.

http://www.spc.nssl.noaa.gov/obswx/maps/700_110322_00.gif

If this is the initialization tonight, be prepared for more errors and junk forecasts being thrown out by the models. The height contours are pretty far off from where they ought to be (i.e. parallel to the winds.) Garbage in, garbage out.

You must see something I don't. What makes you say the analysis is wrong? There can be ageostrophy in 700 mb flow. Compare the analysis from SPC to that on the RAP site: www.rap.ucar.edu/weather/upper/upaCNTR_700.gif . There are slight differences, but I wouldn't say there is something obviously wrong here. I would say there is one hell of a cap for late March, though, pretty much throughout the Plains and Midwest. It will take some arrival of cooler mid-level temps to get anything to go with this kind of warmth above the surface (with the exception, of course, of very strong low-level/surface forcing).

 

[Derek Weston]

Surprised to see the SPC this optimistic. Hadn't been monitoring this one too closely. Looking at the NAM.... it isn't as optimistic as the SPC where instability is concerned... nevertheless... as long as we're at least able to get marginal instability -- north of 1000 j/kg, lets say -- through a broad enough sector... I think we see some tornadic supercells. I'm seeing some nice, large hodographs near center state and points west. Great shear out in front of the triple point. Severity of this episode is going to depend on moisture and resulting instability, naturally. Could see this one going moderate should Iowa clear out and heat up well enough. Will monitor closely as day progresses.

 

[Greg Blumberg]

Jeff, that's a good point about the ageostrophy at that level. I suppose terrain could significantly influence the wind direction given how high up the terrain is. The thing that stuck out to was the near perpendicular SLC wind vector to the height contours. That says to me strongly ageostrophic, and I don't see anything that would cause such a reading. The other thing was suspicious were the winds at Elko, NV and Boise, ID. Westerly winds at 35 knots to southeasterly at 10 knots (the profiler at that time too says 5 knots) between a distance of ~200 miles I'd say is questionable. Also, I would have brought the 294 contour down more towards the southern portion of Nevada because of the -10 C in Elko and the 963 ob in Las Vegas, NV.

Agreeing with Derek regarding SPC's decision to go MDT. From a synoptic viewpoint, the setup seems to be very prime for severe weather and even echos some of the classic models for tornado outbreaks (http://www4.ncsu.edu/~nwsfo/storage/cases/19840328/dynamicsvrsetup.jpg). From what I can tell in the water vapor imagery, we have the polar jet and the subtropical jet both playing a part in this setup. I can easily see the IA/MO mid-levels cooling with the approach of the shortwave trough. Additionally, from the soundings there doesn't seem to be a whole lot of significant deep cloud cover in the IA/MO area, so getting surface heating shouldn't be a problem. Even upstream from the target area, there's not a lot of cloud cover.

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/refc_f24.gif

This little gem of a model run has been passed around quite a bit in the past few hours. I have to say that it does seem very possible to see something like this tomorrow. The biggest problem will be those pesky 850 mb winds being too badly veered. Mixing down dry air + poor low level directional shear doesn't bode well for tornadic activity. Looks like another day of watching the wind profilers/VADs!

 

[Ryan Pfannkuch]

4-county target area as of 8am: western IA: Cass, Audubon, Guthrie, Adair

First chase of 2011...and I hope everybody has their jet-packs ready! As others have pointed out, the veered low level flow south of the warm front and resultant near-unidirectional wind profiles has currently got me favoring the IA/eastern NE area more so than down the dryline over eastern KS as I was considering yesterday. Not to mention I don't particularly want to mess with the KC metro or northern MO road options. Based on a blend of various short term models, a roughly 990mb sfc low should be along the MO River near Tekamah NE/Onawa IA around 22z, anchoring a fairly classic triple point for these parts for this time of year. My biggest concern is where will things initially fire? The 0z 4km WRF-NMM clearly breaks things out BY 21z several counties west of the MO River into eastern NE, while the RUC holds the cap through 21z and the HRRR shows a few storms streaking across southeast NE by 22-23z.

Clearly as a chaser you have to seriously consider storm motions in this kind of setup, which should be from the WSW at 40-50 MPH. Considering that you can get behind things in a heartbeat, I am prone to playing well ahead of the "firing line" and letting things come to me for awhile, but of course at the ever-present risk of missing something back to the west during the early stages. That's why my target area reflects a bit of a middle ground with great road options all directions. If the classic arc of convection extends SE from the sfc low by 00z, I-80 could be a great east option for trying to get ahead of storms flying up from the southwest. Although not a true cold core setup aloft, the sfc features suggest that the chase strategy will be very similar to one, so for now will aim for being roughly 75-100 miles ESE of the sfc low in the 22-02z time frame, and adjust as necessary. Storm mode will be key for tornado potential, as storms closer to the sfc low could easily be forced into a line quicker but with better access to stronger low level shear, while storms farther S-SE often remain a bit more isolated but in a more veered low level regime. Targeting can be so tricky in these setups for sure.

Again, with storm motions of 40-50 MPH I would strongly advise targeting a few counties east of where you might "ideally" be and plan your moves carefully because 1 shot at storm intercept might be all you get.