Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 20 2025 19:55:56 ACUS01 KWNS 201955 SWODY1 SPC AC 201954 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Fri Jun 20 2025 Valid 202000Z - 211200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM FAR EASTERN MONTANA...ACROSS MUCH OF NORTH DAKOTA TO NORTHERN MINNESOTA... ....SUMMARY... Severe thunderstorms are likely late 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. ....20z Update Northern Plains... Confidence in the overall convective evolution of storms expected today and tonight remains low. Recent observations and CAM guidance show potential for isolated supercell development within a focused low-level upslope regime across far eastern MT and southwestern ND. Current expectations are that isolated storms may develop late this afternoon and track eastward along the stationary front in eastern MT and southern ND with a risk for all hazards. Given this potential, the Slight Risk has been expanded southwestward toward the MT/WY/SD border where strong heating and low-level convergence are being maximized near the surface low. Farther east across ND and western MN, confidence in surface-based storm initiation remains quite low owing to warm 700 mb temperatures (13-16 C) and mid-level ridging. However, very strong heating and mixing (max sfc temps near/exceeding 100 F to the south) may provide enough ascent for isolated high-based storm development in the early evening. Should they remain surface-based, they will mature within an extremely buoyant, and very strongly sheared air mass supportive of significant severe weather including; very large hail and tornadoes. A perhaps more plausible scenario is for scattered storm initiation from strong low-level warm advection, courtesy of a 40-60 kt low-level jet, later tonight across central/eastern ND. Likely elevated, these supercells would pose a risk for large to very large hail and damaging gusts before growing upscale along the front into the western Great Lakes overnight. Should this occur, one or more organized bows with significant damaging winds and a couple tornadoes is possible. Given the conditional risk and resulting uncertainties, the outlook remains largely unchanged. ....Florida... Scattered thunderstorms have developed along typical sea breeze boundaries across the FL Space Coast to near Tampa Bay. Moderate to large CAPE (2000-3000 J/kg of MLCAPE) will continue to support strong pulse updrafts through this evening. Some of these storms could produce an isolated damaging gust or small hail However, very weak mid and upper level flow suggests storm organization is unlikely and the threat will likely remain below 5%. ...Lyons.. 06/20/2025 ..PREV DISCUSSION... /ISSUED 1125 AM CDT Fri Jun 20 2025/ ....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. $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .