Chase target for Monday, July 16
9:48 PM CDT, 07/15/07
Chase target:
Delhi, IA (30 miles west of Dubuque).
Timing and storm mode:
Storms will fire between 2 and 3 PM CDT. Storm mode will be medium- to high-based multicellular storms which should remain below severe limits.
Synopsis:
A couple of H3 S/WV’s were noted in NWRLY flow. Divergence in association with a lead wave over ERN SD/NEB has been associated with a cluster of storms in CNTRL NEB. This storm complex will propagate to the S for several more hours into an increasing 20kt SRLY LLJ. A stronger upstream wave has been responsible for a variety of severe WX with ongoing storms in ERN ND this afternoon and evening. Model progs radar extrapolation, and Corfidi vectors take this complex on a SERLY track overnight though MN. In IA, ERLY SFC flow has commenced in the WRN half of the state, while dewpoints were 60-65F throughout the state. Moisture depth is shallow in most areas of the Upper-Midwest; however an axis of deeper moisture extended from OK into ERN NEB/WRN IA as indicated by 15C H85 dewpoints. A WRLY LLJ will transport this moisture towards ERN IA overnight. Upstream soundings (MPX, ABR, BIS) also indicated modest mid-level lapse rates.
Discussion:
Over the next several days, the ridge over the WRN CONUS will continue to build to the N, causing a blocky pattern to evolve. In the short term, one more day of active WX is on tap for the Upper-Midwest, and then a quiet pattern will resume for the first part of the week. The MCS presently approaching WRN MN will track SE through MN overnight and then into extreme NERN IA and WRN WI by 12Z. This in turn will push an E/W-oriented OFB S into US-20 in ERN IA by 18Z, which should provide a focus for storm development by 20Z. The strongest deep-layer shear will be located well to the north of the instability axis in ERN IA and NRN IL, however backed flow N of the OFB will locally enhance SRH’s in this area. Instability will be limited by aforementioned modest lapse rates, with MLCAPE’s AOB 1000J/kg.
- bill