Very Large Hail Threat in Colorado as Training Storms Trigger Flash Flooding Across Midwest

Overview

• The NWS Storm Prediction Center issued Severe Thunderstorm Watches 670 and 671 on Saturday for portions of the Plains and eastern Colorado with primary hazards of damaging winds to about 75 mph and isolated large to very large hail.
• SPC said on Sunday that the immediate severe focus moved to northeast and east‑central Colorado where a strong upper‑level vorticity max and steep lapse rates could support supercells with hail over 2.00 inches and a few severe wind gusts.
• The Weather Prediction Center flagged expanding, locally training convection across eastern Iowa, northern Illinois and parts of Indiana that could produce localized 3–5+ inch totals overnight and a high likelihood of flash flooding in low‑lying and urban areas.
• WPC also issued multiple mesoscale discussions for southern Ohio, western and central West Virginia, the High Plains and the Black Hills noting very high precipitable water, short‑duration rates near 1–2+ inches per hour, and greater flood sensitivity because soils and streamflows are already elevated.
• Forecasters cautioned that small changes in storm placement, back‑building or outflow interactions will control where the worst impacts occur, that some watches (for example WW672) may be ended early as severe threat wanes, and that people should follow local NWS warnings and radar updates.