2/9/2009 FCST: KS/NE/IA

[jshields]

yeah auburn looks good to me, and better yet its only about 70 miles from omaha! the 0Z run of the gfs is a little better in the placement and the speed of the dry slot coming through during peak heating hours, however the nam is still the best model in terms of developing more cape and clearing earlier. the nam showed 500 J/kg sbcape on monday afternoon and about 180 J/kg of 0-3km CAPE, which is plenty for mini sups, by 21Z over se nebraska and ne kansas, but the gfs still didn't develop any appreciable amounts of cape at all. it stinks that it still gets dark by a little after 6pm. the new day 2 outlook is out and is still mentioning the possibility for monday afternoon over ne kansas, eastern ne, and western iowa.

 

[Darrin Rasberry]

GFS/WRF diverging on the nature and tightness of the low; if the WRF is to be believed, I'd hang around east of Beatrice and hope that bridge across the Missouri that's south from Omaha is STILL not out. I don't like the GFS' vote of no confidence for instability in that area, presenting <250 CAPE for the Beatrice region in a VERY narrow tongue (and none at all extant at 18z's prog), but it puts some later, heavier instability out by Red Oak, IA, making me wonder whether a like chance exists for that portion of the area in question should a broken squall not fire early. I'm still learning forecasting, but I'm betting the confidence about the clearing regarding the early morning junk (specifically, the dry intrusion that's to provide the broom) will likely have to wait until tomorrow to assess with greater precision.

Of course the only nonzero prob day for tornadoes has to be on the exact same day I scheduled a doc's appointment months ago, when I expected neg-ten temps to still be reigning over the area and my top worry about the weather being whether I'll get frostbit or bust my head from slipping on the sidewalk on my way to the appointment, with all tornado possibilities being consigned safely to Arklatech. In short: since this is the only day in February I can't chase because I'd have to wait three months for another appointment time (and thus three months for meds), enjoy your photogenic tubes across the countryside.

 

[Brian Stertz]

Still looks to me like the Auburn-Nebraska City NE area and points northeast for tomorrow's target zone. Decent steep lapse rates...fairly strong background vorticity...favorable SRH and LCL...with the only wildcard being some solid afternoon clearing to help boost things. At this point I would have the tornado risk tomorrow afternoon & early evening nailed down to 30 e/w of a line from Harlan NE to Maryville MO...with my target spot being Nebraska City with a bridge across to SW Iowa available for pursuit. Forecast ne storm motions of 35-40mph should not make for too difficult of chasing these low topped wonders.

 

[Dustin Wilcox]

Intriguing enough for me to have the camera’s charged. The 12Z NAM was another favorable trend, with the sfc low now proged at about 3-4mb lower than the previous run. Per the 12KM, dp’s look to be around 47-51 obviously every degree will be of great importance, big difference between 47 and 51 on a day like this. By 18Z a nice Dry Slot looks to be racing NE engulfing the extreme SE NE area, by 21Z the NAM has decent instability across extreme SE NE with 0-3km CAPE values around 200j/kg, even hints at upwards of 500j/kg SBCAPE and LI‘s -2, indicative of good clearing, this clearing has temps creeping up to near 58-60, 21Z AFK skew-T shows a convective temp of 58.7. As Brian mentioned favorable LCL’s and SRH values (300-400m/s). The 12KM Base Reflectivity product picks up on an arc of convection forming along the Dry Slot around 21Z near and just East of Lincoln, before racing the arc east across the river by 0Z. I’m still not excited about my chances at seeing anything to exciting tomorrow, but there is only one way to break this mini sup drought I seem to be stuck in…

 

[Michael O'Keeffe]

The 18z NAM is looking even better than the 12z NAM with SBCAPE reaching close to 750 j/kg and 0-3km CAPE exceeding 250 j/kg near Lincoln. We will be chasing tomorrow and as of right now E NE/W IA could be in for some nice cold core action, or at least mini sups with a decent threat for tornadoes IMO.

 

[jshields]

The 18z NAM is looking even better than the 12z NAM with SBCAPE reaching close to 750 j/kg and 0-3km CAPE exceeding 250 j/kg near Lincoln. We will be chasing tomorrow and as of right now E NE/W IA could be in for some nice cold core action, or at least mini sups with a decent threat for tornadoes IMO.

yes the 18Z NAM is definitely way better! i too will be out somewhere is se nebraska waiting for the clearing and dry slot to punch through

 

[Dick McGowan]

Not much of a cold-core system depicted by the NAM any more. But the warm sector is looking like it might work out. A mid level dry slot should clear things out allowing for decent destabilization SE of the surface low by 21z.

I wish this were 100 miles either side of the river, but it's not....hopefully things slow down a little for tomorrow.

http://www.twisterdata.com/data/mod...1_2009020900_F21_PLI_30_0_MB_ABOVE_GROUND.png

See everyone there.

 

[Michael O'Keeffe]

I noticed that too, but it could still be a good mini supercell warm sector event. With the nice lifted indicies and good CAPE values for early February, not to mention the decent shear, my dad and I will still probably head out since the tornado threat still appears decent.

Wow check out the SBCAPE at 21z and the 0-3km CAPE at 21z.
http://beta.wxcaster.com/models/eta/central/CENTRAL_ETA212_ATMOS_CAPE_21HR.gif
http://beta.wxcaster.com/models/eta/central/CENTRAL_ETA212_0-3KM_CAPE_21HR.gif

 

[Bill Schintler]

Chase Target for Monday, February 9

Chase target:
Murray, IA (40 miles S of Des Moines)

Timing and storm mode:
A large area of precipitation with embedded convection will affect the area through the morning hours, with partial clearing by early afternoon. Low-topped supercells should then fire along an advancing dryline by 3 PM with hail to 1 inch the primary severe threat. A brief tornado or two cannot be ruled out, especially before 6 PM

Discussion:
00Z analysis indicates a deepening trough over the Four Corners area, which will become increasingly negatively-tilted as it ejects through CO and into NE by 00Z Tuesday. The 00Z NAM appears to have a handle on SFC and H85 moisture in IA and MO; although the GFS is too bullish with SFC dewpoints in SERN KS. The TOP and SGF soundings indicate a 200mb deep moist layer over a shallow dry layer.

A large area of stratiform precipitation with embedded convection should fire in a zone of WAA and STG forcing within the left-exit region of an 110kt H3 streak. This precipitation will push rapidly NE with partial clearing in its wake as a dry slot pushes in, and by mid-afternoon, the WF will push N into SERN IA while reaching an Oskaloosa to Washington line by 00Z. An axis of dewpoints of 50-55F will nose into SRN IA. A trailing DL will race E into SWRN IA by late afternoon and should be the focus for discrete storm development.

Modest SFC-based instability is indicated, with SBCAPE’s AOB 500J/kg between 21Z and 00Z. The BL will rapidly decouple after 00Z with loss of daytime heating. An additional negative for convection will be a surge of dry air above H8 that will become entrained in already weak updrafts, especially SE of a DSM to ALO line. Deep-layer shear AOA 50 kts along with SFC-3km SRH well in excess of 300m2/s2 is FCST; and this may partially offset the lack of instability for increased SVR potential over an area of limited aerial coverage. An SPC significant tornado parameter of one along with a supercell parameter of three is advertised.

- bill
10:48 PM CST, 02/08/09

 

[Darrin Rasberry]

I'd be inclined to hang out closer to the SFC LOW and pick Mr. Schintler's target, but my only concern is that the SPC's point about snow coverage in northern IA killing the tornado potential could translate down here as well, where it's still patchy and generally cold - it was totally covered just a few days back. Don't have much experience with ... err, chasing in the snow, so I can't regard myself as an expert in the matter beyond extending the SPC's recent logic on the effect on SBCAPE. Plus, Dick McGowan's 0-3km map seems indicative of this around the important 21z frame - I think *some* lower level cape is needed for a setup like this, especially if the CC assumption is fading out. Red Oak, IA is still my horse, down to the NE tip of KS.

 

[Mike Umscheid]

This is an interesting setup. Surface features respond to mid/upper level forcing... so that being said.... warm front convergence will be moving rapidly north during the day. Current extrapolation of the 400mb PV anomaly and water vapor dry anomaly (which at 1015z was already across the TX Panhandle) suggest that by ~ 18z this feature will be at or just north of OMA. This thing is moving FAST... therefore surface is going to look different hour by hour. Surface dry advection from dry intrusion influences will likely be impacting OMA area by 18-20z (I think the NAM is under doing the dry advection when compared against the GFS and 09z RUC).... The 09z RUC has the best surface frontogenesis/convergence and theta-E ridge nosing up toward NW Iowa by 21z close to where the model has snow cover (how far south does snow pack extend?). Watch out for that dry intrusion... it's very easy to get caught too far south on a day like today. I honestly don't like waves moving this fast. I wouldn't want to play anything along the dry intrusion convergence/pacific cold front... too much dry entrainment for my liking. Ideally, I'd like to be as close as possible to the surface low/vorticity center which will be farther northwest near the SD/NE border around Winner to Valentine... but for this event it will be too cool/stable with too much stratus in that area.. after all it is Feb 9th! I doubt there will be low-topped tornadoes today.

 

[Matt Gingery]

I intend on playing the limited timing on this situation. I will likely be just north of Topeka in the Holton Ks. area. I feel the best daytime destabilization will take place across NE Kansas, as morning convection quickly exits. Given the timing, and the thought that the instability will quickly die off this early evening, I would suspect the tornado threat to be confined to SE Nebraska, and NE Kansas. Once these descrete low topped supercells do their thing in these areas the main threat will be small hail and winds to 60mph across Iowa and areas of NW Missouri. 21Z to 24z from Beatrice Nebraska, to Topeka on to the NE to the Iowa line. I am with the snow cover theory as well. Good luck to everyone.

 

[Darrin Rasberry]

By miracle, my doc had a 9:45 cancellation. I'll be at Red Oak, perhaps itching to drop SW juuuuust a bit more to catch that earlier cape tongue that the RUC is showing. There's a fat one that appears right over Mr. Schintler's target (the fattest of the day) at 00z, so I'm still keeping SC IA in mind for 21-00. In other words, I'll be hoping in vain while returning home to upload pictures of bust stratus to the report thread while some poor rabbit goes thump-thump-thump under my car for hundreds of miles after meeting my driver's side tire.

 

[Chad Cowan]

We've got a pretty strong dry punch on the backside of this squall line that is pushing north and east pretty quickly. It is doing a good job of clearing out the backside. I'm going to be targeting Holton, KS and likely points north and west. My ChaserTV stream will be up, there is a link at my homepage: chasethestorms.com

 

[Mike Peregrine]

The wind is something else. The high rise I work in is swaying noticeably today and the glass on the windows is bowing in and out.

Severe thunderstorm watch for this line of storms approaching western Missouri out of Kansas. The "occasionally can and do produce tornadoes" language has been included. If Mike U is correct, this is one of those dynamic days that will prove difficult logistically. I think if I were to pick a target, I'd shoot for northeast Kansas/southeast Nebraska today ... Beatrice to Marysville maybe. Hope you all are successful and have fun out there.