Bill Schintler
EF4
Chase Target for Tuesday, July 27:
Motley, MN (45 miles northwest of St. Cloud).
Timing and storm mode:
Elevated storms will be ongoing in the northwestern third of MN throughout much of the day. Surface-based convection should develop along an outflow boundary between 4 and 5 PM CDT. Supercells, with a tornado or two, will be possible with the initial discrete storms. Storms will eventually evolve into a line by early evening as the cold front pushes east. Storm motion will be towards the east at 25 mph.
Synopsis:
00Z analysis indicates a number of impulses embedded within a zonal flow along the US/CAN border. A couple of large storm complexes over ND appear to be associated with one such disturbance. This impulse is well depicted in the water vapor loop. Storms will continue in this area overnight giving increasing isentropic uplift on the 310K surface at the nose of a strengthening low-level jet. The warm sector is recovering, as indicated by deep moisture through 850 mb on the 00Z ABR and OAX soundings. Meanwhile, upstream soundings (BIS, GGW, and RAP) show nearly dry-adiabatic mid-level lapse rates. Differential advection of moisture from the south and steep lapse rates should result in a very unstable but capped air mass over MN on Tuesday.
Discussion:
A seasonally strong shortwave and associated cold front will be the focus for strong to severe storms Tuesday afternoon and evening. Elevated convection should be ongoing north of US 10 in northwestern MN during the morning hours within a zone of warm air advection. Further to the south, the warm sector will remain capped until after 4 PM due to warm mid-level temperatures associated with the EML. By late afternoon, a compact area of lift associated with a shortwave will arrive. Discrete storms should develop southeast of an advancing cold front along an outflow boundary from the earlier MCS. Rotating updrafts appear likely given strong instability and shear early in storm evolution before a transition to a linear mode.
Steep mid-level lapse rates coupled with surface dewpoints just above 70F will yield SBCAPEs in excess of 2500 J/kg. The surface flow will remain veered; however, considerable (SFC-3km) SRH in excess of 200m2/s2 should exist given a nearly westerly low-level jet. Additionally, low-level directional shear may be locally enhanced along and north of the aforementioned outflow boundary. The area also lies along the southern periphery of a compact 70kt H5 jet max, with a resulting 40-50 kts of deep-layer shear sufficient for storm organization.
Bill Schintler
9:39 PM CDT, 07/26/10
Motley, MN (45 miles northwest of St. Cloud).
Timing and storm mode:
Elevated storms will be ongoing in the northwestern third of MN throughout much of the day. Surface-based convection should develop along an outflow boundary between 4 and 5 PM CDT. Supercells, with a tornado or two, will be possible with the initial discrete storms. Storms will eventually evolve into a line by early evening as the cold front pushes east. Storm motion will be towards the east at 25 mph.
Synopsis:
00Z analysis indicates a number of impulses embedded within a zonal flow along the US/CAN border. A couple of large storm complexes over ND appear to be associated with one such disturbance. This impulse is well depicted in the water vapor loop. Storms will continue in this area overnight giving increasing isentropic uplift on the 310K surface at the nose of a strengthening low-level jet. The warm sector is recovering, as indicated by deep moisture through 850 mb on the 00Z ABR and OAX soundings. Meanwhile, upstream soundings (BIS, GGW, and RAP) show nearly dry-adiabatic mid-level lapse rates. Differential advection of moisture from the south and steep lapse rates should result in a very unstable but capped air mass over MN on Tuesday.
Discussion:
A seasonally strong shortwave and associated cold front will be the focus for strong to severe storms Tuesday afternoon and evening. Elevated convection should be ongoing north of US 10 in northwestern MN during the morning hours within a zone of warm air advection. Further to the south, the warm sector will remain capped until after 4 PM due to warm mid-level temperatures associated with the EML. By late afternoon, a compact area of lift associated with a shortwave will arrive. Discrete storms should develop southeast of an advancing cold front along an outflow boundary from the earlier MCS. Rotating updrafts appear likely given strong instability and shear early in storm evolution before a transition to a linear mode.
Steep mid-level lapse rates coupled with surface dewpoints just above 70F will yield SBCAPEs in excess of 2500 J/kg. The surface flow will remain veered; however, considerable (SFC-3km) SRH in excess of 200m2/s2 should exist given a nearly westerly low-level jet. Additionally, low-level directional shear may be locally enhanced along and north of the aforementioned outflow boundary. The area also lies along the southern periphery of a compact 70kt H5 jet max, with a resulting 40-50 kts of deep-layer shear sufficient for storm organization.
Bill Schintler
9:39 PM CDT, 07/26/10
