Bill Schintler
EF4
Chase target:
Sanborn, MN (30 miles W of New Ulm).
Timing and storm mode:
Renewed convection should initiate at 5 PM CDT, and the primary weather feature will be supercells with large hail to golf-ball size. A few short-lived tornadoes will also be possible.
Synopsis:
ULVL analysis indicated persistent broad ridge over the CNTRL and SRN CONUS with strongest SWRLY H3 flow of 70 kts spreading into MT ATTM. Divergence and lift ahead of this wave will strengthen and accelerate movement of a CF in the Upper-Midwest during the day Saturday. At the SFC, dewpoints of around 70F were in place over SWRN MN while the 00Z MPX sounding indicated good moisture depth. Several convective complexes were ongoing in NEB, in MN, and in the Dakotas. Activity over NEB and SERN SD will experience a weakening trend over the next few hours, while the MCS in NERN SD should strengthen and move E into MN as the LLJ focuses into that area. Overall model performance with ongoing convective trends is poor with feedback issues.
Discussion:
A 40kt LLJ and associated WAA will assist in the maintenance of a large area of elevated convection overnight, which will be ongoing Saturday morning along and N of US-212 in MN. This should, in turn, push an OFB S to about US-14 by early afternoon. An extensive cloud shield should erode from SW to NE as the afternoon progresses, allowing for strong insolation. Following renewed SFC-based storm initiation, LLVL shear may be enhanced near the intersection of the aforementioned OFB and the CF where SFC-3km SRH’s may exceed 300m2/s2 beneath a veering 30kt LLJ. This could increase a tornado threat despite high LCL levels of 1500m-1700m AGL.
A significant concern will be the cap strength as a 15C H7 thermal ridge noses into SWRN MN. Given sufficient clearing of convective debris along with forcing along the CF/OFB, convective temperatures in the low-90 should be reached. An EML sounding should result as steep lapse rates from upstream soundings (BIS, ABR, LBF) advect over the mid-level thermal ridge. This will combine with 70F-75F SFC dewpoints with a 100mb deep moist layer to realize MLCAPE’s AOA 4000J/kg.
- bill
11:41 PM CDT, 08/10/07
Sanborn, MN (30 miles W of New Ulm).
Timing and storm mode:
Renewed convection should initiate at 5 PM CDT, and the primary weather feature will be supercells with large hail to golf-ball size. A few short-lived tornadoes will also be possible.
Synopsis:
ULVL analysis indicated persistent broad ridge over the CNTRL and SRN CONUS with strongest SWRLY H3 flow of 70 kts spreading into MT ATTM. Divergence and lift ahead of this wave will strengthen and accelerate movement of a CF in the Upper-Midwest during the day Saturday. At the SFC, dewpoints of around 70F were in place over SWRN MN while the 00Z MPX sounding indicated good moisture depth. Several convective complexes were ongoing in NEB, in MN, and in the Dakotas. Activity over NEB and SERN SD will experience a weakening trend over the next few hours, while the MCS in NERN SD should strengthen and move E into MN as the LLJ focuses into that area. Overall model performance with ongoing convective trends is poor with feedback issues.
Discussion:
A 40kt LLJ and associated WAA will assist in the maintenance of a large area of elevated convection overnight, which will be ongoing Saturday morning along and N of US-212 in MN. This should, in turn, push an OFB S to about US-14 by early afternoon. An extensive cloud shield should erode from SW to NE as the afternoon progresses, allowing for strong insolation. Following renewed SFC-based storm initiation, LLVL shear may be enhanced near the intersection of the aforementioned OFB and the CF where SFC-3km SRH’s may exceed 300m2/s2 beneath a veering 30kt LLJ. This could increase a tornado threat despite high LCL levels of 1500m-1700m AGL.
A significant concern will be the cap strength as a 15C H7 thermal ridge noses into SWRN MN. Given sufficient clearing of convective debris along with forcing along the CF/OFB, convective temperatures in the low-90 should be reached. An EML sounding should result as steep lapse rates from upstream soundings (BIS, ABR, LBF) advect over the mid-level thermal ridge. This will combine with 70F-75F SFC dewpoints with a 100mb deep moist layer to realize MLCAPE’s AOA 4000J/kg.
- bill
11:41 PM CDT, 08/10/07
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