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- SPC AC 191647
- Day 1 Convective Outlook
- NWS Storm Prediction Center Norman OK
- 1147 AM CDT Fri Jul 19 2019
- Valid 191630Z - 201200Z
- ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS
- EAST-CENTRAL MINNESOTA AND NORTHERN WISCONSIN...
- ...SUMMARY...
- A regional outbreak of severe thunderstorms with the possibility of
- strong tornadoes and widespread significant wind damage is expected
- from central Minnesota across northern Wisconsin during the mid/late
- afternoon into tonight.
- ...Upper Midwest/Great Lakes...
- A regional outbreak of severe thunderstorms is expected later this
- afternoon into tonight. That said, some specific uncertainties
- remain with the timing details/exact sub-regional corridor of peak
- severe-weather risk given capping/warm temperatures aloft and
- uncertainty with the decay of the cloud shield from the earlier MCS
- across South Dakota.
- A very strong summertime belt of westerlies exists across the
- northern tier of the CONUS, with 50-100 kt westerlies noted between
- 500/250 MB in 12Z upper-air data spanning Montana to the
- Dakotas/Minnesota. Where storms develop/increase later today, this
- very strong belt of winds aloft will be influential in storm
- organization including supercells and potential evolution of a
- fast-moving MCS (possible if not likely derecho) later
- today/tonight.
- Consult Mesoscale Discussion 1523 regarding midday details across
- western Minnesota. Additional surface-based thunderstorm development
- may emanate from the ascent/differential heating related to the MCS
- remnants, focusing downstream surface-based severe potential across
- central Minnesota. An extremely unstable air mass (MLCAPE >4000
- J/kg) will continue to become established from southeast Southeast
- South Dakota through central/southern Wisconsin as the elevated
- mixed-layer overspreads surface dew points rising into the mid to
- upper 70s. A surface cyclone over central South Dakotas should track
- towards the Twin Cities through early evening. Strong low-level
- convergence near/northeast of this cyclone along the warm front
- should sustain surface-based storm development across central into
- east-central Minnesota.
- Intense supercells are likely to develop rapidly, with an attendant
- threat for all severe hazards including the possibility of a strong
- tornado or two amid 50-60 kt effective shear and 0-3 km SRH >300
- m2/s2. The very warm/moist thermodynamic profiles will also support
- generation of strong cold pools which should eventually yield a
- bowing, forward-propagating MCS across northern Wisconsin into parts
- of northern Lower and Upper Michigan. Strength of the vertical shear
- suggests the potential for intense bowing segments capable of
- yielding a derecho with significant/widespread severe wind gusts.
- ...Lower Great Lakes/Northeast States...
- Have upgraded parts of the region for thunderstorm-wind related
- potential this afternoon into evening. This will be related to the
- possible east-southeastward persistence of a complex of storms
- across Ontario and additional scattered development that is expected
- in the lee of the Lower Great Lakes. The ambient air mass will be
- moderately to strongly unstable but the region will generally be
- south of the stronger westerlies aloft. The overall expectation is
- for predominantly multicellular, outflow-dominant storms capable of
- isolated damaging wind gusts this afternoon and evening.
- ...South Dakota tonight...
- Another round of 700-mb warm/moist advection will occur tonight
- within a tight baroclinic zone well north of a surface front arcing
- across Nebraska into northeast Wyoming. Large elevated buoyancy and
- strong effective shear will support a risk for isolated large hail.
- While storms will generally tend to be elevated, there may be some
- wind damage potential if upscale quasi-linear growth occurs late
- tonight as storms progress east-southeastward across South Dakota.
- ..Guyer/Wendt.. 07/19/2019
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