10/28/04 FCST: IA, MN, NE, SD

[mikegeukes]

Started this forecast thread since SPC has a slight risk for
Thursday for west and central Iowa, southwest Minnesota,
extreme eastern Nebraska and southeast South Dakota.

Supercells and tornadoes are possible as the warm front
lifts northward in this region. Possible severe storms along
dryline from Kansas down to Texas.

Target Cities: Denison IA, Harlan IA (Based on 00Z Model Runs)

Feel free to post your discussions below.

Mike

 

[Ben Prusia]

I might want to add eastern and northeastern Kansas, and northwestern Missouri into this discussion, our supposed and forecasted (both TWX and EAX) cloud cover is gone, it is sunny and bright outside! I am looking at the RUC and the ETA and both are forecasting CAPES of 1500+, the sun will only add more to the forecasted high temperature of 77, I'm thinking it could be up in the 80's as long as the sun stays out, maybe adding more to the instability. Satellites show that cloud cover is breaking up over Topeka and Kansas City. The only thing I can see that will hinder storm development over these areas is cap strength, looks like it could be unbreakable.

I am going to wait and see what could happen in Kansas.

 

[Glen Romine]

I'm not sold on this set up. Current convection across northern plains is in left exit region of upper jet and nose of LLJ, as well as a region of deep WAA. As this shifts to the east, expect the rain to go with it, and leave behind a strongly capped environment. Temps at midlevels are progged to warm during the day - and the sfc convergence at this time appears rather unremarkable during the day, so I have limited prospects for surface based convection. Instead, expect storms to develop on nose of redeveloping nocturnal LLJ during the evening hours over southern MN. Maybe as the day plays out something else will appear to change my mind.

Glen

 

[Andrea Griffa]

I might want to add eastern and northeastern Kansas, and northwestern Missouri into this discussion, our supposed and forecasted (both TWX and EAX) cloud cover is gone, it is sunny and bright outside! I am looking at the RUC and the ETA and both are forecasting CAPES of 1500+, the sun will only add more to the forecasted high temperature of 77, I'm thinking it could be up in the 80's as long as the sun stays out, maybe adding more to the instability. Satellites show that cloud cover is breaking up over Topeka and Kansas City. The only thing I can see that will hinder storm development over these areas is cap strength, looks like it could be unbreakable.

I am going to wait and see what could happen in Kansas.

Overall low level shear might be very favorable for tornadic supercells: we have about 30knots of low level jet (S-SW)and straight wind at the ground level of about 15-20knots(SE); infact cape can grow in the afternoon with value of 1500-maybe 2000 J/Kg. This is well evidenced by 0-1Km Storm Relative Helicity that could reach value of 400-450m2/s2.
Minnesota, Iowa are zones very favorable to chase... 8)
Let's see waht will it be :lol:

 

[Andrea Griffa]

Now SPC changes outlook and take away slight risk:

THOUGH LACK OF LARGE SCALE ASCENT WILL LIMIT
COVERAGE/POTENTIAL FOR THUNDERSTORM DEVELOPMENT OVER THIS
REGION...LOW LEVEL CONVERGENCE AND FAVORABLE
THERMODYNAMIC PROFILES
MAY SUPPORT AN ISOLATED THUNDERSTORM OR TWO LATER TODAY AND THIS
EVENING. SHOULD THIS OCCUR...FORECAST SOUNDINGS INDICATE PARAMETERS
WILL REMAIN FAVORABLE FOR SUPERCELLS. DUE TO LOW CONFIDENCE IN
CONVECTIVE DEVELOPMENT...WILL KEEP SEVERE PROBABILITIES RELATIVELY
LOW ATTM.