Bill Schintler
EF4
Chase Target for Monday, August 4
Chase target:
Iowa Falls, IA (between Waterloo and Fort Dodge).
Timing and storm mode:
Storms should fire at 3 PM CDT. Supercells will be likely early in evolution, with a transition to a progressive derecho by mid-evening. This derecho will race east and southeast through eastern IA and then IL, reaching the Mississippi at 11 PM CDT.
Synopsis:
The main flow band will exist along the NRN tier of states while a number of compact pieces of ULVL energy will travel from W to E well S of the jet stream. MDLs differ on the details and timing of these features, with the GFS lagging the WRF by 5 hours.
Discussion:
Moisture is somewhat problematic with drying PROGGED at 850mb over MO. MDLs do, however, indicate LLVL moistening in IA between 18Z and 00Z. This is largely due to corn early August corn dewpoints, in addition to convergence along the stationary front. The WRF is running too high with moisture in IA, and SFC dewpoints should verify in the low- to mid-70’s F in most areas by the time of storm initiation, contributing to MLCAPEs of 2000J/kg. Locally higher dewpoints should also pool along and just N of the SFC boundary between I-80 and US-20 in ERN IA, which will enhance instability in this area. Capping will again be strong, with H7 temperatures in the 11-13C range. Strong H9-H8 WAA will take place across the boundary, resulting in UVM which will aid in overcoming CIN.
Strong shear in the SFC-H7 layer is progged, due largely to a 40kt H7 speed max. During the evening hours, a rear inflow jet will develop and storms should evolve into a progressive derecho and race through ERN IA and into IL along the quasi-stationary WF parallel to and between US-20 and US-30 in IA.
- bill
10:30 PM CDT, 08/03/08
Chase target:
Iowa Falls, IA (between Waterloo and Fort Dodge).
Timing and storm mode:
Storms should fire at 3 PM CDT. Supercells will be likely early in evolution, with a transition to a progressive derecho by mid-evening. This derecho will race east and southeast through eastern IA and then IL, reaching the Mississippi at 11 PM CDT.
Synopsis:
The main flow band will exist along the NRN tier of states while a number of compact pieces of ULVL energy will travel from W to E well S of the jet stream. MDLs differ on the details and timing of these features, with the GFS lagging the WRF by 5 hours.
Discussion:
Moisture is somewhat problematic with drying PROGGED at 850mb over MO. MDLs do, however, indicate LLVL moistening in IA between 18Z and 00Z. This is largely due to corn early August corn dewpoints, in addition to convergence along the stationary front. The WRF is running too high with moisture in IA, and SFC dewpoints should verify in the low- to mid-70’s F in most areas by the time of storm initiation, contributing to MLCAPEs of 2000J/kg. Locally higher dewpoints should also pool along and just N of the SFC boundary between I-80 and US-20 in ERN IA, which will enhance instability in this area. Capping will again be strong, with H7 temperatures in the 11-13C range. Strong H9-H8 WAA will take place across the boundary, resulting in UVM which will aid in overcoming CIN.
Strong shear in the SFC-H7 layer is progged, due largely to a 40kt H7 speed max. During the evening hours, a rear inflow jet will develop and storms should evolve into a progressive derecho and race through ERN IA and into IL along the quasi-stationary WF parallel to and between US-20 and US-30 in IA.
- bill
10:30 PM CDT, 08/03/08
