SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1124 AM CDT Fri Mar 21 2025 Valid 211630Z - 221200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not forecast today. ...Iowa Vicinity... An upper shortwave trough will move across the Midwest today and tonight, with increasing deep-layer west/northwest flow associated with this feature overspreading the region. Boundary layer moisture will remain scant ahead of an east/southeast moving cold front sweeping across the Lower MO/Mid-MS Valley this afternoon and evening. Nevertheless, very cold temperatures aloft (near -25 C at 500 mb, as sampled by 12z regional balloon observations), will support steep midlevel lapse rates. Additionally, surface heating into the mid 50s to low 60s will support steepening low-level lapse rates. These steep lapse rates amid cold temperatures aloft should be sufficient for SBCAPE values up to 300 J/kg. As such, isolated high-based, low-topped thunderstorms are expected this afternoon and evening from the Mid-MO Valley into the Mid-MS Valley. Given the dry boundary layer and near 30-40 kt flow between 850-700 mb, convection may locally enhance already gusty surface winds, and a few stronger gusts near 40-45 kt may occur, especially across southeast Iowa into northwest IL. A couple instances of small hail/graupel also could accompany this activity. ...Pacific Northwest/Northern Rockies... An upper shortwave trough will move across the region tonight. Cooling aloft will support steepening lapse rates and sufficient destabilization to support isolated lightning flashes. ..Leitman/Halbert.. 03/21/2025