Bill Schintler
EF4
Chase target:
Harrisburg, Nebraska (in the southwestern tip of the panhandle).
Timing:
Storms will initially fire along the front range of the Rockies near the Colorado and Wyoming border at 3 PM MDT. Storms will later move towards the deeper moisture of the target area through 5 PM.
Synopsis:
Primary WX maker today was a strong CF that had pushed S into WI, SERN MN, NWRN IA, and NEB by mid-afternoon. Visible satellite from 22Z – 01Z also indicated a 100 mile wide A-CU band parallel to and 50 miles behind the SFC front, indicative of returning moisture flow aloft with insentropic lift along the 310K SFC. Mostly linear convection had fired along the front in WI through IA under weak flow aloft. Further W, several other areas of strong convection had fired in SERN CO into ERN NM, apparently in response to lift provided by a compact H3 speed max now approaching WRN KS. Moderate SWRLY H3-H5 flow AOA 30kts over ERN CO and NEB was pushing the northern edge of these cloud tops over SERN SD. Model guidance so far has had a poor handle on the ULVL flow between H8 and H5. SFC moisture return in the wake of the CF has commenced with ERLY flow S of a high-pressure centered over WRN SD, and dewpoints of 50-55F were found in an up-sloping zone in from NERN CO into the NEB panhandle S of I-80.
Discussion:
Difficult forecast as the outcome depends on subtle details of the ULVL forcing and possibly residual OFBs from ongoing convection in CO. Current thinking is that convection will first initiate over the front range of the Rockies near the WY/CO/NEB border, and then expand to the E and NE into the deeper moisture of the NEB panhandle. S of I-76 in CO, it is expected that one or more areas of CI canopy persisting throughout the day will limit insolation somewhat there. Given modest instability and shear, overall storm mode appears to be high-based multicell clusters with a few rotating updrafts possible in embedded cells. Expect advection of steep lapse rates indicated on RIW and GJT 00Z soundings over deepening moisture in the WRN NEB panhandle, resulting in MLCAPEs to range from 1000J/kg over NERN CO to 250J/kg N of I-80 in NEB. It appears as though a compact H5 wave, now over CNTRL CA and NV, may increase deep-layer shear to 30 kts locally.
- bill
[FONT="]10:30 PM CDT[/FONT]
Harrisburg, Nebraska (in the southwestern tip of the panhandle).
Timing:
Storms will initially fire along the front range of the Rockies near the Colorado and Wyoming border at 3 PM MDT. Storms will later move towards the deeper moisture of the target area through 5 PM.
Synopsis:
Primary WX maker today was a strong CF that had pushed S into WI, SERN MN, NWRN IA, and NEB by mid-afternoon. Visible satellite from 22Z – 01Z also indicated a 100 mile wide A-CU band parallel to and 50 miles behind the SFC front, indicative of returning moisture flow aloft with insentropic lift along the 310K SFC. Mostly linear convection had fired along the front in WI through IA under weak flow aloft. Further W, several other areas of strong convection had fired in SERN CO into ERN NM, apparently in response to lift provided by a compact H3 speed max now approaching WRN KS. Moderate SWRLY H3-H5 flow AOA 30kts over ERN CO and NEB was pushing the northern edge of these cloud tops over SERN SD. Model guidance so far has had a poor handle on the ULVL flow between H8 and H5. SFC moisture return in the wake of the CF has commenced with ERLY flow S of a high-pressure centered over WRN SD, and dewpoints of 50-55F were found in an up-sloping zone in from NERN CO into the NEB panhandle S of I-80.
Discussion:
Difficult forecast as the outcome depends on subtle details of the ULVL forcing and possibly residual OFBs from ongoing convection in CO. Current thinking is that convection will first initiate over the front range of the Rockies near the WY/CO/NEB border, and then expand to the E and NE into the deeper moisture of the NEB panhandle. S of I-76 in CO, it is expected that one or more areas of CI canopy persisting throughout the day will limit insolation somewhat there. Given modest instability and shear, overall storm mode appears to be high-based multicell clusters with a few rotating updrafts possible in embedded cells. Expect advection of steep lapse rates indicated on RIW and GJT 00Z soundings over deepening moisture in the WRN NEB panhandle, resulting in MLCAPEs to range from 1000J/kg over NERN CO to 250J/kg N of I-80 in NEB. It appears as though a compact H5 wave, now over CNTRL CA and NV, may increase deep-layer shear to 30 kts locally.
- bill
[FONT="]10:30 PM CDT[/FONT]
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