8/3/07 FCST: SD / NE

[Michael O'Keeffe]

Well tomorrow looks like a possible Blacks Hills upslope setup. The SPC has issued a 30% for the area east of the Black Hills mentioning the possibilty of supercells with tornadoes! CAPE will be decent, but helicity looks good as well as some good loopy hodogrpahs. Tds will be relatively high in th low 70s, but most likely upper 60s. There would be good SE winds just east of low. If I were to chase which I might I'd target Kadoka, SD for starts.

 

[Zach Chappell]

Yea i agree However I think it may be a linear type event.With maybe a Strong squall like MCS going through.It for sure will be a heavy rain event with pwats extreme.I think storms will fire along the black hills multicell 's at first then get out by Kadoka area and form into a squall line and move northeast.No way to really predict it but NCEP radar sim as well as other models do have this acting like a derecho.Which would not be bad either

 

[Colin Davis]

Gotta agree with Michael here. NAM putting a great area of directional shear just E of the Black Hills...setup really spells supercells and tornadoes to me. At least for awhile. Should be some great turning in the low levels...and won't be too far from the 90 corridor, I don't think.

Not really thinking there's enough instability to drive a derecho. The term really is overused, though.

Actually considering making the drive and chasing both days, should the 500 temps on Saturday become more favorable...

 

[Bill Schintler]

Chase target for Friday, August 3

Chase target:
Martin, SD (50 miles SW of Murdo).

Timing and storm mode:
2 PM CDT. Elevated storms will be ongoing in western SD prior to this time, and surface-based convection will take place at around 2 PM in the target area. A few medium-based supercell or rotating storms will be possible during the few hours following surface-based initiation. Storms will later evolve into a large convective complex which will track to the east through SD during the evening hours, and severe wind to 70 mph will be the primary severe threat during this time.

Synopsis:
UA analysis indicated ridge over the WRN CONUS with the strongest H5 flow located north of the border in CAN. A mid/upper circulation was located S of the main WRLYs over NERN NV, and convection over WY was associated with this feature. Some steepening of mid-level lapse rates along with cooling mid-level temperatures was also occurring, as noted on LKN and BOI soundings. Significant LLVL moisture was in place and a developing SERLY LLJ was transporting 15C H85 dewpoints towards NWRN NEB.

Discussion:
An upsloping pattern will develop while the aforementioned H7/H5 circulation over NEV opens up and translates through SD on Friday as a compact 35kt H5 speed max. Shear parameters should be ample for storm organization as 40 kts of SFC-6km shear overspreads the area while 30-40kts H85 SRLY flow over backing SFC winds will contribute towards unseasonably impressive hodograph curvatures. Attainable instability will be limited by marginal mid-level lapse rates however MLCAPEs should reach 1500J/kG given generous LLVL moisture with SFC dewpoints in the 65F range. Given an elevation of over 3000 ft, very high theta-E values will be achieved. In the morning hours, elevated convection should be ongoing over WRN SD. During the mid-afternoon hours, SFC-based convection should fire along a SE/NW oriented SFC convergence/trough boundary as CIN is removed. During the morning hours, a large CI shield will be present over WRN NEB, and this will thin/lift to the E through the late morning hours, allowing for strong LLVL heating to occur. Further N, over much of WRN SD, extensive mid- and ULVL cloudiness should remain throughout the key heating hours while inhibiting insolation there and also increasing a SFC baroclinic zone along the NEB/SD border with lower LCL levels just to the N.

- bill
[FONT=&quot]12:00 AM CDT, 08/03/07[/FONT]