SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK 0816 PM CDT Fri Jun 20 2025 Valid 210100Z - 211200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NORTH DAKOTA AND MINNESOTA... CORRECTED AREA MENTIONED IN FIRST SENTENCE OF THIRD PARAGRAPH OF DISCUSSION ...SUMMARY... A significant swath of severe winds is expected this evening and tonight from the northern Plains eastward into the upper Mississippi Valley. ...Northern Plains/Upper Mississippi Valley... Water vapor imagery currently shows a shortwave trough moving through the northern High Plains. Near the trough, a line of strong to severe thunderstorms is ongoing across western North Dakota and far northwestern South Dakota. As these storms move eastward across the northern Plains this evening, a 60 to 70 knot mid-level jet will move northeastward through the Dakotas. Lift associated the left exit region of the jet, combined with a strongly unstable airmass over the eastern Dakotas and western Minnesota will be favorable for vigorous convective development. In response, the ongoing storms are expected to grow upscale into a fast-moving severe MCS. The MCS is forecast to track eastward across far northern South Dakota, North Dakota and north-central Minnesota this evening. At the surface, a 991 mb low will move northeastward across northern South Dakota this evening. A tongue of very moist air with surface dewpoints in the lower to mid 70s F will move northward into southeastern North Dakota and central Minnesota this evening. Within this moist airmass, strong instability is analyzed by the RAP with MLCAPE in the 4000 to 5000 J/kg range. The ongoing line of severe storms will move into this strong instability, and gradually intensify over the next couple of hours. RAP forecast soundings along the expected track of the MCS in southeastern North Dakota this evening have moderate to strong deep-layer shear, long and looped hodographs and steep mid-level lapse rates. This should be favorable for supercells with large hail, wind damage and tornadoes. A strong tornado may occur. Supercell development will be most likely among cells that remain semi-discrete. However, a line is expected to become more organized, which will make severe wind gusts likely along its leading edge. Gusts above 80 mph will be possible ahead of the more intense parts of the line. A Derecho may develop across parts of the northern Plains and upper Mississippi Valley this evening into tonight. As the MCS moves into south-central North Dakota over the next few hours, some short-term model forecasts develop discrete cells further to the east near the moist axis in the vicinity of the ND-SD-MN triple point. These storms are forecast to quickly expand in coverage and move across northwest and north-central Minnesota, ahead of the approaching MCS. These storms will likely be supercellular, and be associated with large to very large hail, wind damage and possible tornadoes. A consolidation of the two areas of convection will likely take place late this evening, with the severe MCS continuing to track eastward across north-central Minnesota. A wind-damage swath is expected as far east as northern Wisconsin and the western Upper Peninsula of Michigan. Wind gusts of 85 to 105 mph will be possible along parts of the MCS track. ...Southern Rockies/Central High Plains... Water vapor imagery shows southwest flow over much of the south-central U.S. A subtle shortwave trough appears to be located in the southern Rockies, where convection has increased in coverage over the last couple of hours. These storms will continue to move northeastward into the High Plains this evening. Forecast soundings from northeast New Mexico into northwest Kansas early this evening have very steep low to mid-level lapse rates. This will likely support a marginal threat for severe gusts, as the cells move into the stronger instability over the High Plains. ..Broyles.. 06/21/2025