Bill Schintler
EF4
Chase target:
Conde, SD (30 miles southeast of Aberdeen).
Timing and storm mode:
Storms with a few supercells will develop in the target area between 4 and 5 PM CDT. An isolated tornado or two is likely.
Synopsis:
Zonal flow will continue over the NRN tier of states over the next 12-36 hours, with slow height falls over the PAC NW. Embedded within the mean flow will be several pieces of energy, with attendant convective complexes. In the LLVLs, a CF will meander in the upper Midwest response to a series of S/WVs and OFBs.
Discussion:
The FCST is challenging due to the uncertain evolution of a late night and morning MCS with attendant OFBs in SERN ND into NERN SD. Ongoing convection S of Jamestown, ND will continue a weakening trend. Current reasoning is that a secondary MCS will fire further W overnight at the nose of a 40kt LLJ between 6 and 8Z. This convection will then track E along the ND/SD border; while producing an OFB that will serve as the focus for renewed convection late in the period on day-2. By 18Z, this boundary should extend along a Watertown to Mobridge line in SD. The synoptic WF will extend from about Morris to New Ulm, MN, during the same time.
The warm sector BL will continue to moisten, owing to both evapotranspiration and a moisture transport of 15-17C H85 dewpoints courtesy of the LLJ. SFC dewpoints will rise to 67-71F during time of initiation where moderate convergence exists along boundaries. Instability will increase as mid-level lapse rates of 8-8.5C/km overspreads this moisture, with MLCAPEs AOA 2500 J/kg. An H5 S/WV along the SRN periphery of the main WLYS will eject EWD with attendant large-scale assent. Storms should initiate E of a SFC low along the OFB over NERN SD, with further development SEWD into CNTRL MN. Additional storms will develop SWWRD later along the CF into NEB. 40 kts of SFC-6km bulk shear along with steep lapse rates will support supercells with large hail and wind. Backed SFC flow E of the low and N of the aforementioned OFB will locally increase hodograph curvatures along the NRN periphery of a 25kt LLJ with SFC-3km SRHs locally AOA 300m2/s2. Additionally, a compact 40kt mid-level streak will locally provide additional shear in the 2-4km layer. Overnight on day-2, a strengthening LLJ and increasing PWAT values will favor backbuilding of storms with one or more MCSs with very heavy rainfall the main feature.
I'm available for nowcasting - PM me.
- bill
10:15 PM CDT, 07/15/08
Conde, SD (30 miles southeast of Aberdeen).
Timing and storm mode:
Storms with a few supercells will develop in the target area between 4 and 5 PM CDT. An isolated tornado or two is likely.
Synopsis:
Zonal flow will continue over the NRN tier of states over the next 12-36 hours, with slow height falls over the PAC NW. Embedded within the mean flow will be several pieces of energy, with attendant convective complexes. In the LLVLs, a CF will meander in the upper Midwest response to a series of S/WVs and OFBs.
Discussion:
The FCST is challenging due to the uncertain evolution of a late night and morning MCS with attendant OFBs in SERN ND into NERN SD. Ongoing convection S of Jamestown, ND will continue a weakening trend. Current reasoning is that a secondary MCS will fire further W overnight at the nose of a 40kt LLJ between 6 and 8Z. This convection will then track E along the ND/SD border; while producing an OFB that will serve as the focus for renewed convection late in the period on day-2. By 18Z, this boundary should extend along a Watertown to Mobridge line in SD. The synoptic WF will extend from about Morris to New Ulm, MN, during the same time.
The warm sector BL will continue to moisten, owing to both evapotranspiration and a moisture transport of 15-17C H85 dewpoints courtesy of the LLJ. SFC dewpoints will rise to 67-71F during time of initiation where moderate convergence exists along boundaries. Instability will increase as mid-level lapse rates of 8-8.5C/km overspreads this moisture, with MLCAPEs AOA 2500 J/kg. An H5 S/WV along the SRN periphery of the main WLYS will eject EWD with attendant large-scale assent. Storms should initiate E of a SFC low along the OFB over NERN SD, with further development SEWD into CNTRL MN. Additional storms will develop SWWRD later along the CF into NEB. 40 kts of SFC-6km bulk shear along with steep lapse rates will support supercells with large hail and wind. Backed SFC flow E of the low and N of the aforementioned OFB will locally increase hodograph curvatures along the NRN periphery of a 25kt LLJ with SFC-3km SRHs locally AOA 300m2/s2. Additionally, a compact 40kt mid-level streak will locally provide additional shear in the 2-4km layer. Overnight on day-2, a strengthening LLJ and increasing PWAT values will favor backbuilding of storms with one or more MCSs with very heavy rainfall the main feature.
I'm available for nowcasting - PM me.
- bill
10:15 PM CDT, 07/15/08
