Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
633 ACUS03 KWNS 020719 SWODY3 SPC AC 020718 Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0218 AM CDT Thu Oct 02 2025 Valid 041200Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY AFTERNOON AND EVENING ACROSS PARTS OF WEST CENTRAL NEBRASKA...CENTRAL AND EASTERN SOUTH DAKOTA...SOUTHEASTERN NORTH DAKOTA...AND NORTHWESTERN MINNESOTA... ...SUMMARY... Strong thunderstorms may impact a corridor across parts of the northern Great Plains late Saturday afternoon or evening, accompanied by at least some risk for severe wind and hail. ...Discussion... Downstream of building mid/upper ridging, perhaps including an evolving high across the northeastern Pacific, large-scale mid/upper troughing is likely to be maintained across the Southwest through Great Basin vicinity. However, a notable short wave impulse pivoting across the Great Basin at the outset of the period is forecast to accelerate across the Rockies toward the northern Great Plains Red River Valley, as mid-level troughing digs across the Canadian Prairies. The lead impulse may tend to weaken as mid-level flow trends more confluent near the central international border vicinity Saturday night. However, models suggest that substantive further deepening of surface troughing is probable northeast of the Front Range into far northwestern Ontario before this occurs. It appears that this might include the evolution of a compact embedded surface cyclone across parts of central South Dakota toward southeastern North Dakota late Saturday through Saturday night, but there remains substantive spread within/among the model output concerning this and other developments. ...Northern Great Plains... Beneath a plume of initially warm and capping elevated mixed-layer air, a narrow corridor of stronger surface heating and deeper boundary-layer mixing along/ahead of the surface trough probably will provide the primary focus for thunderstorm development with the most appreciable severe weather potential. Although models suggest that CAPE will be more marginal northeast of the Front Range through central South Dakota than farther to the northeast, due to lower boundary-layer moisture content, thermodynamic profiles along the entire corridor are forecast to become characterized by steep lower/mid-tropospheric lapse rates with sizable temperature/dew point spreads by late afternoon. Subsequent south-southwesterly low-level jet intensification (including 50-60+ kt around 850 mb through mid to late evening) will support potential for severe surface gusts, as convection develops in response to forcing for ascent and contributes to downward momentum transport. The extent to which this potential may be maintained beyond a couple of hours window remains unclear, as a cold front surging out of the high plains and overtaking the surface trough might quickly undercut the stronger late afternoon/early evening thunderstorm development. ..Kerr.. 10/02/2025 $$