Chase target for August 3
Chase target:
Brookings, SD
Timing:
Storm initiation 3 PM CDT.
Storm intensity:
Low-end severe storms, with isolated hail to golf-ball size, and winds to 70 MPH.
Discussion:
A fairly complicated WX setup is in place across the upper-Midwest this morning. At the surface, a synoptic surface trough extends along an ADC/YKN/LXN line; the CF appears to extend along an ABR/9V9 line in SD; while numerous mesoscale boundaries are in place throughout the area as a result of ongoing and decaying convection and MCS’s. Ongoing convection in the HON and ULM areas will produce outflow boundaries that will be key in this afternoons convection. By 20Z, an E-W oriented boundary should extend from ULM/BKX/9V9 line, with locally backed surface flow north of this feature. This should serve to produce more favorable low-level shear then 12Z guidance suggests, although the RUC hints at this feature.
Upstairs, SWRLY flow is spreading into the Dakotas, with a couple of embedded S/WV’s and increasing vorticity advection throughout the region. WV imagery suggests a small-scale region of UVV along an MBG/DO7 line, and another near PIR/PHP in SD. Ample instability (SBCAPE’s to 5000J/kG/MLCAPE’s to 3500J/kG) by mid-afternoon, coupled with decent deep-layer shear of 30kts and SFC-1km SRH’s locally to 200m^2/s^2 along and just N of the aforementioned outflow boundary will support storm organization. Dewpoint spreads in excess of 20F will keep cloud bases on the high side, minimizing tornado threat.
- bill
