Bill Schintler
EF4
Chase target:
Bennington, OK (20 miles east of Durant).
Timing and storm mode:
Storms will first develop in northeast through east-central OK in the early afternoon hours and then build southwest towards the target area through 4 PM CDT. A few supercell storms will be likely, and cloud bases will be relatively high with hail to golf-ball size the primary severe threat.
Synopsis:
A split flow pattern characterized the synoptic setup with a S/WV in the NRN branch moving E through the Upper-Midwest with a combination of winter precipitation associated with it in MN and WI. Upstream, a 150kt H3 speed max was diving SE into NV with a broad region of divergence in the left-exit region spreading over UT. The SRN stream remained largely S of the CONUS. The details of smaller scale disturbances embedded in the WRN US trough were complicated, with WV imagery indicating several pieces of energy diving SE towards the Four Corners ATTM. In ERN TX, MDLs had earlier trended too moist with BL moisture return, with SFC dewpoints in NERN TX verifying 5F lower then progged. Recent SFC observations are more in line with 06Z MAM progs, however, with 40-45 F dewpoints verifying in ERN TX.
Discussion:
Key FCST concerns are timing of forcing and available SFC moisture. A couple of S/WVs will eject ahead of a 110kt H5 jet in the WRN CONUS. A lead wave will move E through the Red River area during the day Thursday, with a compact zone of strong UVVs spreading onto ERN OK by 00Z. A visual indication of this feature will be a well defined plum of broken CI that will push E through OK throughout the day. The WRN edge of this CI shield will be along I-35 at 18Z, and will reach the OK/AR border by 01Z; while remaining N of the Red River throughout the period. A DL/SFC trough will trail behind the ULVL wave, and forcing along this feature should be sufficient for initiation during the early-afternoon hours
Moisture return is the primary FCST concern. During this period, a SWRLY 40kt LLJ will strengthen and spread a narrow axis of 10-12C H85 dewpoints into NERN TX. By early afternoon, a N/S axis of SC will develop and expand in an area along and E of I-35 in NERN TX. This will be a visual signal that LLVL moisture is pushing N. Initiation will first take place in ERN OK closer to the SFC low in a zone of weak SFC-based instability, and will then build S into extreme NERN TX along and E of a DL/trough into an environment of increasingly favorable moisture but with additionally veering SFC flow.
Steep mid-level lapse rates of 7-7.5C/km and SFC dewpoints of 55-60F along with a 200mb deep moist layer will contribute towards MLCAPEs to 1500J/kG despite modest insolation. Deep-layer shear will exceed 40kts with strong mid-level flow associated with the aforementioned S/WV. Shear in the SFC-2km area will remain largely unidirectional.
- bill
10:30 PM CDT, 03/12/08
Bennington, OK (20 miles east of Durant).
Timing and storm mode:
Storms will first develop in northeast through east-central OK in the early afternoon hours and then build southwest towards the target area through 4 PM CDT. A few supercell storms will be likely, and cloud bases will be relatively high with hail to golf-ball size the primary severe threat.
Synopsis:
A split flow pattern characterized the synoptic setup with a S/WV in the NRN branch moving E through the Upper-Midwest with a combination of winter precipitation associated with it in MN and WI. Upstream, a 150kt H3 speed max was diving SE into NV with a broad region of divergence in the left-exit region spreading over UT. The SRN stream remained largely S of the CONUS. The details of smaller scale disturbances embedded in the WRN US trough were complicated, with WV imagery indicating several pieces of energy diving SE towards the Four Corners ATTM. In ERN TX, MDLs had earlier trended too moist with BL moisture return, with SFC dewpoints in NERN TX verifying 5F lower then progged. Recent SFC observations are more in line with 06Z MAM progs, however, with 40-45 F dewpoints verifying in ERN TX.
Discussion:
Key FCST concerns are timing of forcing and available SFC moisture. A couple of S/WVs will eject ahead of a 110kt H5 jet in the WRN CONUS. A lead wave will move E through the Red River area during the day Thursday, with a compact zone of strong UVVs spreading onto ERN OK by 00Z. A visual indication of this feature will be a well defined plum of broken CI that will push E through OK throughout the day. The WRN edge of this CI shield will be along I-35 at 18Z, and will reach the OK/AR border by 01Z; while remaining N of the Red River throughout the period. A DL/SFC trough will trail behind the ULVL wave, and forcing along this feature should be sufficient for initiation during the early-afternoon hours
Moisture return is the primary FCST concern. During this period, a SWRLY 40kt LLJ will strengthen and spread a narrow axis of 10-12C H85 dewpoints into NERN TX. By early afternoon, a N/S axis of SC will develop and expand in an area along and E of I-35 in NERN TX. This will be a visual signal that LLVL moisture is pushing N. Initiation will first take place in ERN OK closer to the SFC low in a zone of weak SFC-based instability, and will then build S into extreme NERN TX along and E of a DL/trough into an environment of increasingly favorable moisture but with additionally veering SFC flow.
Steep mid-level lapse rates of 7-7.5C/km and SFC dewpoints of 55-60F along with a 200mb deep moist layer will contribute towards MLCAPEs to 1500J/kG despite modest insolation. Deep-layer shear will exceed 40kts with strong mid-level flow associated with the aforementioned S/WV. Shear in the SFC-2km area will remain largely unidirectional.
- bill
10:30 PM CDT, 03/12/08
