Bill Schintler
EF4
Chase Target for Thursday, May 27:
Jordon, MT (Garfield county, 115 miles northeast of Billings).
Timing and storm mode:
Storms should initiate between 6 and 7 PM MDT. Storm motion will be towards the northeast at 20 mph. Supercell storms and a tornado or two is likely.
Synopsis:
The ERN CONUS ridge should amplify slightly over the next 24 hours, which will slow eastward progression of a WRN CONUS ULVL system. Upstream 00Z soundings (SLC, GJT, and RIW) indicate nearly dry-adiabatic mid-level lapse rates. The 00Z NAM has initialized slightly high with regard to SFC dewpoints, which were verifying in the low- to mid-50’s F in ECNTRL MT. MDLs do appear to have a handle on present convective trends in ERN MT.
Discussion:
A WF in ERN and NERN MT will provide the focus for a variety of severe WX Thursday afternoon. Capping will remain strong through 22Z, especially over the SERN portion of MT, owing to subtle H5 ridging and a ridge of 10C plus H7 temperatures. By late afternoon, however, large-scale assent increases as the exit region of a 60kt H5 streak ejects form the WRN CONUS trough and overspreads the area. H7 omegas locally increase to -6uB/s after 00Z. A band of AC cloudiness will edge eastward from CNTRL MT after 23Z. Virga from this cloud deck may cool mid-levels through evaporative cooling enough to aid in weakening of the cap. S of I-94 in SERN MT, however, diurnal convection should remain inhibited due to capping.
Once storms initiate, moderate to strong instability and shear will support a wide spectrum of severe WX. Steep mid-level lapse rates of 8-8.5 C/km and SFC dewpoints of 60-65 F will support SBCAPEs AOA 2000 J/kg. Deep-layer shear will increase to 40-50 kts with the approach of the aforementioned H5 streak. SFC-3km SRH AOA 200m2/s2 will exist along and N of the boundary as southerly H8 flow surges over easterly or northeasterly SFC flow. LLVL directional shear will slowly increase between 00Z and 03Z as the LLJ strengthens and shifts W into ERN MT. Storms will travel parallel to or along the boundary, instead of crossing over to the N side of the WF while becoming elevated, as is often the case with similar setups. Therefore, cells should continue to tap into moist BL air in an environment with large clockwise-curved hodographs and LCLs of 1000-1200m AGL.
- Bill
9:34 PM CDT, 05/26/10
Jordon, MT (Garfield county, 115 miles northeast of Billings).
Timing and storm mode:
Storms should initiate between 6 and 7 PM MDT. Storm motion will be towards the northeast at 20 mph. Supercell storms and a tornado or two is likely.
Synopsis:
The ERN CONUS ridge should amplify slightly over the next 24 hours, which will slow eastward progression of a WRN CONUS ULVL system. Upstream 00Z soundings (SLC, GJT, and RIW) indicate nearly dry-adiabatic mid-level lapse rates. The 00Z NAM has initialized slightly high with regard to SFC dewpoints, which were verifying in the low- to mid-50’s F in ECNTRL MT. MDLs do appear to have a handle on present convective trends in ERN MT.
Discussion:
A WF in ERN and NERN MT will provide the focus for a variety of severe WX Thursday afternoon. Capping will remain strong through 22Z, especially over the SERN portion of MT, owing to subtle H5 ridging and a ridge of 10C plus H7 temperatures. By late afternoon, however, large-scale assent increases as the exit region of a 60kt H5 streak ejects form the WRN CONUS trough and overspreads the area. H7 omegas locally increase to -6uB/s after 00Z. A band of AC cloudiness will edge eastward from CNTRL MT after 23Z. Virga from this cloud deck may cool mid-levels through evaporative cooling enough to aid in weakening of the cap. S of I-94 in SERN MT, however, diurnal convection should remain inhibited due to capping.
Once storms initiate, moderate to strong instability and shear will support a wide spectrum of severe WX. Steep mid-level lapse rates of 8-8.5 C/km and SFC dewpoints of 60-65 F will support SBCAPEs AOA 2000 J/kg. Deep-layer shear will increase to 40-50 kts with the approach of the aforementioned H5 streak. SFC-3km SRH AOA 200m2/s2 will exist along and N of the boundary as southerly H8 flow surges over easterly or northeasterly SFC flow. LLVL directional shear will slowly increase between 00Z and 03Z as the LLJ strengthens and shifts W into ERN MT. Storms will travel parallel to or along the boundary, instead of crossing over to the N side of the WF while becoming elevated, as is often the case with similar setups. Therefore, cells should continue to tap into moist BL air in an environment with large clockwise-curved hodographs and LCLs of 1000-1200m AGL.
- Bill
9:34 PM CDT, 05/26/10
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