Bill Schintler
EF4
Storm Chasing Target for Tuesday, July 14
Winnebago, NEB (12 miles south of Sioux City, IA)
Timing and storm mode:
Storms will fire after 6 PM CDT, with a supercell or two likely early in storm evolution before a transition to a linear complex. The desired storm may be a “tail-end charlie†along the developing line.
Discussion:
A difficult FCST as tomorrow’s event depends on how ongoing MCSs evolve overnight. First in line is an arc of rain with embedded thunder currently entering NERN NEB through NWRN IA. This is apparently associated with weak isentropic upglide along the 305K SFC along with a lead mid-level shortwave, and should continue to weaken as it outruns moisture transport at the nose of the LLJ focused further W. Several areas of strong convection are ongoing from WRN KS through the Dakotas. Current radar trends suggest a slow weakening of storms in NEB and KS, and an increase in intensity and coverage in ERN SD. This is supported by both the NAM and GFS with drive the bulk of the MCS activity from the Dakotas into WRN MN and NWRN IA through 12Z, with one or two smaller convective complexes further S in NEB and KS. The focus for day-2 storms should be near the intersection of an outflow boundary resulting from tonight’s activity, and an advancing CF which is more of a wind shift as little temperature gradient exists across the boundary.
A large area of elevated convection will be ongoing during the morning hours in western MN, the eastern Dakotas, and into NWRN IA. This moves E and weakens during the late morning into early afternoon hours as the LLJ refocuses further S. Partial clearing takes from W to E, allowing for destabilization; with strong evapotranspiration from maturing corn crops. Capping will be strong given a mid-level thermal ridge, with H7 temperatures AOA 15 C nosing in to the OMA to SUX area, and only slightly lower at around 12C in NERN NEB/SERN SD at mid-afternoon. Instability and deep-layer shear will increase after 20Z with mid-level CAA as the shortwave approaches, with SFC-6km shear approaching 60 kts. Renewed convection may occur first ahead of the CF along an outflow boundary draped across SWRN IA, located from just N of Omaha to Lamoni at 18Z; and then retreating to the N, oriented along a SUX to DSM line by 21Z. Warm temperatures should limit southerly growth of storms down the line, with little development S of US-20 in IA. Backed LLVL flow will exist along and NE of the OFB, with enhanced hodograph curvatures along with LCL’s in the 800-1000m AGL range.
- bill
11:07 PM CDT, 07/13/09
Winnebago, NEB (12 miles south of Sioux City, IA)
Timing and storm mode:
Storms will fire after 6 PM CDT, with a supercell or two likely early in storm evolution before a transition to a linear complex. The desired storm may be a “tail-end charlie†along the developing line.
Discussion:
A difficult FCST as tomorrow’s event depends on how ongoing MCSs evolve overnight. First in line is an arc of rain with embedded thunder currently entering NERN NEB through NWRN IA. This is apparently associated with weak isentropic upglide along the 305K SFC along with a lead mid-level shortwave, and should continue to weaken as it outruns moisture transport at the nose of the LLJ focused further W. Several areas of strong convection are ongoing from WRN KS through the Dakotas. Current radar trends suggest a slow weakening of storms in NEB and KS, and an increase in intensity and coverage in ERN SD. This is supported by both the NAM and GFS with drive the bulk of the MCS activity from the Dakotas into WRN MN and NWRN IA through 12Z, with one or two smaller convective complexes further S in NEB and KS. The focus for day-2 storms should be near the intersection of an outflow boundary resulting from tonight’s activity, and an advancing CF which is more of a wind shift as little temperature gradient exists across the boundary.
A large area of elevated convection will be ongoing during the morning hours in western MN, the eastern Dakotas, and into NWRN IA. This moves E and weakens during the late morning into early afternoon hours as the LLJ refocuses further S. Partial clearing takes from W to E, allowing for destabilization; with strong evapotranspiration from maturing corn crops. Capping will be strong given a mid-level thermal ridge, with H7 temperatures AOA 15 C nosing in to the OMA to SUX area, and only slightly lower at around 12C in NERN NEB/SERN SD at mid-afternoon. Instability and deep-layer shear will increase after 20Z with mid-level CAA as the shortwave approaches, with SFC-6km shear approaching 60 kts. Renewed convection may occur first ahead of the CF along an outflow boundary draped across SWRN IA, located from just N of Omaha to Lamoni at 18Z; and then retreating to the N, oriented along a SUX to DSM line by 21Z. Warm temperatures should limit southerly growth of storms down the line, with little development S of US-20 in IA. Backed LLVL flow will exist along and NE of the OFB, with enhanced hodograph curvatures along with LCL’s in the 800-1000m AGL range.
- bill
11:07 PM CDT, 07/13/09
