Bill Schintler
EF4
9:49 PM, 07/14/07
Chase target:
McClusky, ND (52 miles southeast of Minot).
Timing and storm mode:
Surface-based storm initiation at 4 PM CDT. A few isolated supercell storms will be likely within the first few hours following initiation, with hail to golf-ball size the primary severe risk. During the evening hours, an elevated MCS will track from northeastern ND into western MN. This MCS will reach the Twin Cities at 11PM CDT.
Synopsis:
Little change in the large scale pattern with Hudson Bay ULVL low and strong ridge in the WRN CONUS. At the SFC, storms fired during the late afternoon hours along a pre-frontal trough from NRN MO into NERN KS, and this activity should weaken with the loss of daytime heating. Further NW in NERN MT, an MCS appears to be associated with a vort max rounding ULVL ridge. This feature should also weaken with loss of insolation and lack of a significant LLJ. An environment of steep mid-level lapse rates was noted over WY and MT, as indicated on the TFX and RIW soundings, and this will be advected towards to east into ND on Sunday. As of often the case with a persistent NWRLY flow pattern, the SFC moisture layer is shallow in most locations in the Upper Midwest, owing mainly to evapotranspiration.
Discussion:
On Sunday, slow cyclogenesis will take place over WRN ND in response to a few S/WV’s embedded in 40-50 kt NWRLY H5 flow. Associated with this feature will be a developing SFC boundary, possibly enhanced by outflow from the aforementioned MT MCS, which will be located along US-2 in WRN and CNTRL ND during the mid-afternoon hours. Early in the period, elevated convection will be ongoing along the H85 WF north of the CAN border, and this feature will shift towards the SE during with time while SFC-based convection develops along the SRN periphery of this storm complex. Lift will be enhanced locally in the right-entrance region of a 50kt H5 streak. During the early- to mid-afternoon hours, a thin veil of anvil CI should overspread points along and NE of a line from the NW corner to the SE corner of ND, and this may also aid in differential heating. Along and N of this line, SFC dewpoints should increase into the low-60’s F, while in the SWRN half of ND, the shallow moisture layer will mix out as dewpoints decrease to the mid-40’s. H7 temperatures of 10C coupled with H5 temperatures of -10C will result in moderate mid-level lapse rates of around 8C/km; which when combined with a shallow moist layer will result in MLCAPE’s of 500-1000J/kg. Impressive shear parameters may somewhat offset the marginal instability, as deep-layer (SFC-6km) shear will exceed 40kts beneath the stronger H5 flow, while an increasingly NWRLY LLJ on top of WRLY/SWRLY SFC flow will result in impressive hodograph curvatures. Model consensus has been poor with this system, with the NAM much stronger with the SFC features. The GFS appears to have a better handle on ULVL features and SFC moisture and resulting instability.
- bill
Chase target:
McClusky, ND (52 miles southeast of Minot).
Timing and storm mode:
Surface-based storm initiation at 4 PM CDT. A few isolated supercell storms will be likely within the first few hours following initiation, with hail to golf-ball size the primary severe risk. During the evening hours, an elevated MCS will track from northeastern ND into western MN. This MCS will reach the Twin Cities at 11PM CDT.
Synopsis:
Little change in the large scale pattern with Hudson Bay ULVL low and strong ridge in the WRN CONUS. At the SFC, storms fired during the late afternoon hours along a pre-frontal trough from NRN MO into NERN KS, and this activity should weaken with the loss of daytime heating. Further NW in NERN MT, an MCS appears to be associated with a vort max rounding ULVL ridge. This feature should also weaken with loss of insolation and lack of a significant LLJ. An environment of steep mid-level lapse rates was noted over WY and MT, as indicated on the TFX and RIW soundings, and this will be advected towards to east into ND on Sunday. As of often the case with a persistent NWRLY flow pattern, the SFC moisture layer is shallow in most locations in the Upper Midwest, owing mainly to evapotranspiration.
Discussion:
On Sunday, slow cyclogenesis will take place over WRN ND in response to a few S/WV’s embedded in 40-50 kt NWRLY H5 flow. Associated with this feature will be a developing SFC boundary, possibly enhanced by outflow from the aforementioned MT MCS, which will be located along US-2 in WRN and CNTRL ND during the mid-afternoon hours. Early in the period, elevated convection will be ongoing along the H85 WF north of the CAN border, and this feature will shift towards the SE during with time while SFC-based convection develops along the SRN periphery of this storm complex. Lift will be enhanced locally in the right-entrance region of a 50kt H5 streak. During the early- to mid-afternoon hours, a thin veil of anvil CI should overspread points along and NE of a line from the NW corner to the SE corner of ND, and this may also aid in differential heating. Along and N of this line, SFC dewpoints should increase into the low-60’s F, while in the SWRN half of ND, the shallow moisture layer will mix out as dewpoints decrease to the mid-40’s. H7 temperatures of 10C coupled with H5 temperatures of -10C will result in moderate mid-level lapse rates of around 8C/km; which when combined with a shallow moist layer will result in MLCAPE’s of 500-1000J/kg. Impressive shear parameters may somewhat offset the marginal instability, as deep-layer (SFC-6km) shear will exceed 40kts beneath the stronger H5 flow, while an increasingly NWRLY LLJ on top of WRLY/SWRLY SFC flow will result in impressive hodograph curvatures. Model consensus has been poor with this system, with the NAM much stronger with the SFC features. The GFS appears to have a better handle on ULVL features and SFC moisture and resulting instability.
- bill
