346 ACUS02 KWNS 201732 SWODY2 SPC AC 201730 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Fri Jun 20 2025 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE NORTHERN GREAT LAKES INTO NEW YORK AND NORTHERN PENNSYLVANIA... ...SUMMARY... Strong to locally severe storms are possible Saturday from the northern Great Plains into the Upper Midwest and Great Lakes. ...Synopsis... An amplifying pattern will occur on Saturday with a trough strengthening across the west with a ridge building across the eastern CONUS. Surface high pressure will be present across the eastern CONUS with lee troughing across the central and northern Plains ahead of the strengthening western CONUS trough. ...Great Lakes into the Northeast... A strong MCS will likely be ongoing at the beginning of the period across northern Wisconsin/western Upper Michigan. This MCS will likely continue east through the morning with some wind/hail threat across Upper Michigan and northern Lower Michigan before eventually moving into Ontario. If this MCS continues to track along the instability gradient, it could eventually arrive across western/central New York during the afternoon/evening. However, this threat is conditional given stronger forcing farther north in Canada and strong building heights across the Northeast. Additional thunderstorms may develop along the trailing outflow/composite boundary during the afternoon as strong instability builds into the northern Great Lakes. However, building heights aloft should mostly suppress convection, with only isolated storm coverage expected, if at all. If any storms can develop, the environment would be very favorable for large hail, severe wind gusts, and perhaps a tornado. ...Northern Plains into the Upper Midwest... Very strong instability is expected to build across the northern Plains on Saturday afternoon/evening. Very warm 700mb temperatures (16C) and building heights aloft should keep thunderstorm activity suppressed for much of the period. However, strong heating could allow for isolated storm development which would likely be supercellular with a hail and wind threat if this conditional threat does materialize. A few strong to potentially severe storms may be ongoing at the beginning of the period across eastern Montana as a weak mid-level trough traverses the region. Storm activity will likely remain limited across eastern Montana for much of the day as heights build aloft. However, additional storms may develop early Sunday morning as troughing starts to advance east. Limited instability is the primary limiting factor, but if sufficient instability can develop, a few strong to severe storms may be possible (12Z NSSL WRF). ..Bentley.. 06/20/2025 $$