Bill Schintler
EF4
Chase target:
One mile north of Ashby, NE (50 miles north of Ogallala). This is in the sandhills, however a relatively flat and open area exists just north of Ashby.
Timing and storm mode:
Elevated storms should fire by late afternoon in eastern WY into western SD, and then become surface-based through 6 and 7 PM MDT in the target area. A few supercell storms will be possible early in the evening, before an evolution into one or more clusters of elevated storms. Storm motion will be to the east and southeast at 20 mph.
Synopsis:
Ridging was in place over all but the extreme western continental US, while the remains of TD Fay continue to spin away in the southeast. Looking upstream, a deepening trough was located over the Pacific Northwest. At the surface, an axis of moisture had worked into the northern high plains, with dewpoints at or above 60F noted over western NE. Isolated convection fired over eastern WY and CO in response to a compact wave within anticyclonic upper-level flow. This activity should diminish overnight with the loss of daytime heating and lack of low-level jet focus. The trough will continue to deepen and move to the east over the next 24 hours.
Discussion:
The primary surface low will remain in southern CAN, while a secondary lee low strengthens over the NE panhandle. Capping will remain strong owing to the EML, with mid-level lapse rates of 9-9.5 C/km by 00Z. Subsidence will remain the rule with the area located between two shortwaves. By early evening, assent will increase as the second wave overspreads the western Dakotas and the cold front surges east. A harbinger of this assent will be an area of CI that will reach the NE panhandle by 00Z. The late timing of this cloud deck should not impact insolation. Rapid cooling of the mid-levels will occur with H7 temperatures falling from 15C to 10C over a period of several hours.
Deep-layer sheer will remain weak with the area well south of the strongest H5 flow, however low-level directional shear will increase with increasingly backed low-level flow beneath the western periphery of a southwesterly low-level jet. Ample instability is indicated, with MLCAPEs approaching 2000J/kG due to aforementioned steep lapse rates over surface dewpoints of 60-63F throughout a 50mb deep moist layer.
- bill
10:00 PM CDT, 08/25/08
One mile north of Ashby, NE (50 miles north of Ogallala). This is in the sandhills, however a relatively flat and open area exists just north of Ashby.
Timing and storm mode:
Elevated storms should fire by late afternoon in eastern WY into western SD, and then become surface-based through 6 and 7 PM MDT in the target area. A few supercell storms will be possible early in the evening, before an evolution into one or more clusters of elevated storms. Storm motion will be to the east and southeast at 20 mph.
Synopsis:
Ridging was in place over all but the extreme western continental US, while the remains of TD Fay continue to spin away in the southeast. Looking upstream, a deepening trough was located over the Pacific Northwest. At the surface, an axis of moisture had worked into the northern high plains, with dewpoints at or above 60F noted over western NE. Isolated convection fired over eastern WY and CO in response to a compact wave within anticyclonic upper-level flow. This activity should diminish overnight with the loss of daytime heating and lack of low-level jet focus. The trough will continue to deepen and move to the east over the next 24 hours.
Discussion:
The primary surface low will remain in southern CAN, while a secondary lee low strengthens over the NE panhandle. Capping will remain strong owing to the EML, with mid-level lapse rates of 9-9.5 C/km by 00Z. Subsidence will remain the rule with the area located between two shortwaves. By early evening, assent will increase as the second wave overspreads the western Dakotas and the cold front surges east. A harbinger of this assent will be an area of CI that will reach the NE panhandle by 00Z. The late timing of this cloud deck should not impact insolation. Rapid cooling of the mid-levels will occur with H7 temperatures falling from 15C to 10C over a period of several hours.
Deep-layer sheer will remain weak with the area well south of the strongest H5 flow, however low-level directional shear will increase with increasingly backed low-level flow beneath the western periphery of a southwesterly low-level jet. Ample instability is indicated, with MLCAPEs approaching 2000J/kG due to aforementioned steep lapse rates over surface dewpoints of 60-63F throughout a 50mb deep moist layer.
- bill
10:00 PM CDT, 08/25/08
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