9/12/05: FCST: Central/Northern Plains

[nickgrillo]

Relatively deep low pressure will move into Nebraska, bringing in a surface trof during prime heating (18Z-00Z). Excellent speed shear will exist, with the GFS showing winds backing southeast a bit in southern Nebraska. Rich moisture and ample heating will increase instability... with NAM bringing in around >3500J/KG of CAPEs. Helicities across the warm sector will be pretty decent... With the southeast half of Nebraska getting a good 150-300 0-3KM SRH (of course, any storm showing deviant motion could easily see 250-400 SRH). Deep-layer shear will also support severe thunderstorms... Given the strong speed/directional shear which is present in nearly every level (500MB could get a tad better, thou...) - I would have to say supercells are a pretty good bet.

Overall, the setup looks pretty decent... In fact, I would have to say it's Nebraskas best setup in a while :lol: :lol:

EDIT: EDITED TOPIC TO INCLUDE THE REST OF THE CENTRAL/NORTHERN PLAINS

 

[nickgrillo]

Well the 00Z run has tended to bring things closer to reality, I suppose... Also, the NAM has pushed the trof/dryline more west then previous runs. Wind fields don't show much in the way of directional shear, but speed shear is pretty good from the SFC to about 2.5KM AGL. This is good for bow echos, but supercells would require speed shear through the 6KM AGL, in addition to strong directional shear. We still have good moisture, moderate instability and enough shear for severe thunderstorms.

 

[nickgrillo]

GEMPAK-generated SPC type "outlook" for tomorrow: http://midwestchase.com/9_13_06outlook.jpg ...

Ample moisture spread across the warm sector of a nearly stationary frontal boundary, with associated strong low-level shear and strong to extreme instability would lead me to believe there is a pretty good risk for severe thunderstorms. Winds at 500MB are excellent for this area in September, with good westerly 30-40kts across the risk area. I would have to say any established supercell in this vicinity would be capable of a few isolated tornadoes... With the best shot IMO being around the Norfolk / Vermillion area. We shall see...

 

[Scott Currens]

Nice graphic Nick!

I agree with you analysis and I plan on chasing northeast Nebraska tomorrow. The area should have close to 3000 CAPE and sufficient deep layer shear for supercells. If early morning convection leaves an outflow boundary their will be some potential for tornadoes. The main questions I have for tomorrow are cap strength, timing of shortwaves, and positioning of outflow boundaries.

Scott Currens

 

[Dustin Wilcox]

A decent outflow boundary will certainly help tommorow, I have class untill 3:30 but if conditions call for it I may skip the afternoon classes and head North, it doenst take much to get excited after a very dismal season in Eastern Nebraska.

 

[nickgrillo]

Originally posted by Dustin Wilcox
A decent outflow boundary will certainly help tommorow, I have class untill 3:30 but if conditions call for it I may skip the afternoon classes and head North, it doenst take much to get excited after a very dismal season in Eastern Nebraska.

That convection in central Nebraska has moving northeast/east for a while now... I believe this could pretty much be the ticket for some OFBs tomorrow. The new SWODY1 outlook pretty much agrees with my "graphic"... As of this moment, I still really love the Norfolk/Vermillion area for tomorrow. Tomorrow should be one of the first good days for NE in a while...

 

[Dustin Wilcox]

I agree that convection in the Hastings area looks to be intensifying and building south as well, hopefully the clouds quickly clear out in the morning and we'll see a weak cap by afternoon. Lots of Moisture, Dew Point as of 1 am is 69 in Lincoln.
The SPC seems to agree strongly with the graph you posted above.

 

[Edward Ballou]

SPC just released the moderate risk area today.

Best chance in SD I think will be around Yankton to North Sioux City.

However, things are looking much better in NE where higher cape, dew points, a little CIN. Sioux City doesn't look too bad either. The hodograph looks pretty cool. They're definitely right about the shear though. Goodness!

So here I sit at work, watching the situation. The best I'd be able to do is Sioux City by 6-6:30ish.

Target Area: Sioux City to Norfolk to Columbus

 

[Chris Allington]

Well some brief overnight/ morning convection and sprinkles have given way to some overcast skies here in Omaha, but looking at Vis sat images shows clearing working into central NE. As of 9 AM were sitting at 73/ 68 here at my school. If I had to pick a target right now it would probably be around the Columbus to Norfolk areas.

 

[Bill Schintler]

Chase target for September 12

Chase target:
30 mi. west of Sioux Falls, SD.

Timing:
4 PM CDT.

Storm mode:
Supercell storms early in storm evolution, later evolving into an MCS through the early evening hours. A full spectrum of severe weather will be possible, including tornadoes.

Discussion:
This morning, a series of waves were lifting NEWRD ahead of WRN CONUS trough. Ongoing convection in MN and SD appears to be associated with the first two S/WV’s, while a third wave was ejecting out of SERN CO. At the surface, low pressure was centered between SNY and LBF, with a WF extending NEWRD along an ANW to YKN and SHL line where it was convectively reinforced. Extensive cloudiness was in place, however erosion was taking place from the SW throughout NEB and insolation should not be an issue today. Also noteworthy was a ST band across CNTRL NEB, clearly showing healthy moisture advection towards the target area.

Today, the surface boundary will lift slightly NWRD as a WF, reaching a VTN to HON line by early afternoon as a S/WV approaches the area. A potential negative today is the timing of the S/WV and strongest mid-level winds relative to the best instability axis, with today’s NAM guidance lifting it much more rapidly through the area so the best shear may be found E of the target area. RUC is slower with the timing of this feature, and suggests deep-layer shear to 45 kts. This, in combination with nicely turning hodographs below 2 km and great thermodynamics with SBCAPE’s to 4000J/kG and LI’s in the –10C range will support storm organization. Tornado threat is also present with forecasted cloud base heights in the 800m range N of the boundary.

- bill

 

[Dustin Wilcox]

Clouds have burned off in Lincoln, I have not been able to find any boundarys from last nights convection (if any finds one plz point it out) as of now I am looking at leaving Lincoln and heading slowly North to the Columbus area.

 

[Mike Hollingshead]

I'm torn between heading northwest to the area near Spencer NE or heading wsw down I-80 to the Kearney area. Low level clouds are rapidly increasing in nc NE and I don't know if I like that area because of this now. The way the sfc has looked I'm not sure I'd count on nice backing along that front. I'm getting more and more tempted to get closer to the nose of that little dryline bulge(ne of it) that is progged around the sc part of the state. This is also right along the southern edge of the more extensive low level grunge going on. Actually looking at it a bit more, maybe just north of Kearney seems like a decent place. That 850 needs to back soon and quit scouring out moisture. I don't like the looks of that on the spc meso page. Hmmm, maybe better to go north along that front. If it backs soon(llj), which I think it should, my bet will be on the Kearney area. Time to shoot the gap and head due west down 91 and look at things again in a few hours. Good luck to all.

 

[Mike Hollingshead]

I don't even like the looks of the "bulge" on the 15z ruc. CAPE progs of it are more due to the scouring than they are the sfc features bulging. I think a person's safer bet today is to just get to c-nc/ne NE along that front out there and see what happens. Thinking less and less of that "bulge". Thinking less and less of the whole day, lol.

 

[Mike Hollingshead]

Well, I'm liking the better clearing in se SD. You can watch the better moisture convergence(and curl back to the west with it) on satellite around the Ainsworth area or maybe just northeast of there. I'm back to the Spencer NE thought and just hoping the low level clouds clear off with further heating, which they should(crossing fingers). Spencer NE it is.

 

[Dan Christianson]

Vermillion SD, Yankton and Sioux City ... ill be targeting northeast NE, maybe dreams do come true i was thinking of this setup the last 2 days and i had a dream i was in northeast ne chasing a tornadic supercell lol... all my dreams consist of friggin tornadoes, inital target Vermillion SD, good luck to everyone. Mike H. make up your mind which is it?


Nice clearing of the clouds now, heat rising and i can feel action in the air for today"