Bill Schintler
EF4
Chase target:
Sutherland, NE (17 miles west of North Platte).
Timing and storm mode:
Storms will initiate over the Front Range of the Rockies by early afternoon, and then develop northeast towards the target area through 7 PM CDT. Additional storms will develop further northeast; towards the Rose, NE area. High-based multicells will be the primary mode, with a few isolated supercells possible. Winds to 70 mph will be the primary severe threat. In the event of insufficient moisture return where dewpoints fail to reach about 55F, a bust is likely.
Synopsis:
The stacked Hudson Bay low will finally shift to the E while the ULVL flow transitions to an increasingly zonal regime. LLVL moisture was very limited at 00Z, as noted on LBF and upstream DDC soundings. Moisture was confined to areas S of the KS and OK border, with AMA and OUN showing deep moisture. During day-2, a SFC low with attendant moisture return will develop in NERN CO. The WRF and SREF more optimistic with regard to moisture return then is the GFS, which is also slower with the return of a moisture nose in the SFC-2km AGL layer in WRN KS into SWRN NEB. Upstream soundings (RIW, DNR, and SLC) indicate very steep mid-level lapse rates; and it will be differential advection of LLVL moisture from the S, and steep lapse rates from the W, that will result in an EML as well as a capped environment. A SFC boundary trailing NE from the low into SWRN into NCNTRL NEB should serve as a focus for convection by early evening.
Discussion:
Storms will initiate over the Rockies during the afternoon, and ULVL winds will carry anvils from this convection to the ESE. Therefore, CI blow off from early convection should not affect insolation in the target area. SFC temperatures will be moderated by upslopping flow, with higher temperatures possible immediately NW of the boundary where downslopping takes place along with H85 temperatures in the 28-30C range. Capping will be strong, with H7 temperatures in the 13-15C range, however locally strong forcing associated with a compact mid-level S/WV should be sufficient for initiation of SFC/based convection by late afternoon with SFC temperatures in the neighborhood of 95F. Strong UVM should increase SFC convergence along the boundary extending NE from the low.
Hodograph curvatures in the SFC-3km layer should increase to 200m2/s2 by early evening as a SSWRLY LLJ strengthens over SRLY or slightly backed SFC flow. Additionally, SFC-6km shear should reach 35kts with the aforementioned S/WV, and this should be sufficient for storm organization. Moisture return is a concern, with BL dewpoints in WRN NEB, NERN CO, and WRN KS currently in the 30-40 F range. Indications suggest that sufficient moisture return will take place given healthy SRLY flow on day-2. With help of very steep lapse rates associated with the EML, MLCAPES will increase to a modest 1000J/kg owing to shallow moisture layer and persistent mixing. If moisture fails to verify, diurnal convection is unlikely. In that case, elevated convection will initiate in the Broken Bow area after 04Z as the LLJ focuses there. During the overnight hours, a LLJ will increase to 50 kts while aiding in the maintenance of a large MCS that will track E through NEB while reaching the MO river by 12Z in a weakening state.
I'm now available for nowcasting - PM me...
- bill
9:15 PM CDT, 07/13/08
Sutherland, NE (17 miles west of North Platte).
Timing and storm mode:
Storms will initiate over the Front Range of the Rockies by early afternoon, and then develop northeast towards the target area through 7 PM CDT. Additional storms will develop further northeast; towards the Rose, NE area. High-based multicells will be the primary mode, with a few isolated supercells possible. Winds to 70 mph will be the primary severe threat. In the event of insufficient moisture return where dewpoints fail to reach about 55F, a bust is likely.
Synopsis:
The stacked Hudson Bay low will finally shift to the E while the ULVL flow transitions to an increasingly zonal regime. LLVL moisture was very limited at 00Z, as noted on LBF and upstream DDC soundings. Moisture was confined to areas S of the KS and OK border, with AMA and OUN showing deep moisture. During day-2, a SFC low with attendant moisture return will develop in NERN CO. The WRF and SREF more optimistic with regard to moisture return then is the GFS, which is also slower with the return of a moisture nose in the SFC-2km AGL layer in WRN KS into SWRN NEB. Upstream soundings (RIW, DNR, and SLC) indicate very steep mid-level lapse rates; and it will be differential advection of LLVL moisture from the S, and steep lapse rates from the W, that will result in an EML as well as a capped environment. A SFC boundary trailing NE from the low into SWRN into NCNTRL NEB should serve as a focus for convection by early evening.
Discussion:
Storms will initiate over the Rockies during the afternoon, and ULVL winds will carry anvils from this convection to the ESE. Therefore, CI blow off from early convection should not affect insolation in the target area. SFC temperatures will be moderated by upslopping flow, with higher temperatures possible immediately NW of the boundary where downslopping takes place along with H85 temperatures in the 28-30C range. Capping will be strong, with H7 temperatures in the 13-15C range, however locally strong forcing associated with a compact mid-level S/WV should be sufficient for initiation of SFC/based convection by late afternoon with SFC temperatures in the neighborhood of 95F. Strong UVM should increase SFC convergence along the boundary extending NE from the low.
Hodograph curvatures in the SFC-3km layer should increase to 200m2/s2 by early evening as a SSWRLY LLJ strengthens over SRLY or slightly backed SFC flow. Additionally, SFC-6km shear should reach 35kts with the aforementioned S/WV, and this should be sufficient for storm organization. Moisture return is a concern, with BL dewpoints in WRN NEB, NERN CO, and WRN KS currently in the 30-40 F range. Indications suggest that sufficient moisture return will take place given healthy SRLY flow on day-2. With help of very steep lapse rates associated with the EML, MLCAPES will increase to a modest 1000J/kg owing to shallow moisture layer and persistent mixing. If moisture fails to verify, diurnal convection is unlikely. In that case, elevated convection will initiate in the Broken Bow area after 04Z as the LLJ focuses there. During the overnight hours, a LLJ will increase to 50 kts while aiding in the maintenance of a large MCS that will track E through NEB while reaching the MO river by 12Z in a weakening state.
I'm now available for nowcasting - PM me...
- bill
9:15 PM CDT, 07/13/08
Last edited by a moderator:
