SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1125 AM CDT Fri Jun 20 2025 Valid 201630Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS EVENING AND TONIGHT FROM EASTERN MONTANA...ACROSS MUCH OF NORTH DAKOTA...INTO NORTHERN MINNESOTA.... ...SUMMARY... Severe thunderstorms are likely this afternoon into tonight from far eastern Montana eastward across the northern Plains and into the upper Mississippi Valley. Tornadoes, winds greater than 75 mph, and hailstones greater than 2 inches in diameter will all be possible. ...Eastern MT/ND/MN/WI/Upper MI... No significant changes have been made to the ongoing outlook. Water vapor imagery shows a deepening upper trough over the northern Rockies, with a pronounced shortwave trough entering western MT. Strong lift associated with this trough will overspread eastern MT and western ND this evening, leading to the development of scattered supercell thunderstorms in a region of backed/upslope flow to the north of the surface low. These storms will track eastward through the evening across ND and eventually grow upscale. Very large hail and tornadoes will be possible for the first few hours of this scenario, with an increasing risk of damaging winds with time. An upgrade to MDT risk was considered, but will maintain ENH due to diversity of solutions in various model guidance and uncertainty of corridor of greatest threat. Farther east, an increasingly strong nocturnal low-level jet will help rapid thunderstorm development from eastern ND into MN this evening. Parameters in this area are very favorable for supercells capable of all severe hazards, including very large hail and tornadoes. However, late initiation of storms, warm temperatures in the 850-700mb layer, and rapid storm interactions lend uncertainty regarding the evolution of this activity. Some 12z guidance suggests one or more bowing structures evolve out of this cluster, tracking eastward overnight across MN into WI and Upper MI. ...Western MT... As the aforementioned shortwave trough moves eastward, scattered thunderstorms are forecast to develop off the mountains of western MT. Widespread cloud cover will limit heating/destabilization, but favorable deep-layer shear may support a few rotating thunderstorms. Hail could occur in the strongest storms. ...Southeast Lower MI... A convectively-aided shortwave trough is moving across Lake MI and western Lower MI. This feature may encourage the development of scattered thunderstorms this afternoon over southeast Lower MI and western Lake Erie. These storms could produce gusty winds and hail. ...High Plains... Full sunshine will lead to steep low-level lapse rates and moderate CAPE values this afternoon from southwest NE into eastern NM. Deep mixing will likely result in widely scattered afternoon and evening thunderstorms. This high-based activity will be capable of locally damaging wind gusts. ..Hart/Squitieri.. 06/20/2025