Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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298 ACUS01 KWNS 242001 SWODY1 SPC AC 242000 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Mon Jun 24 2024 Valid 242000Z - 251200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN THE UPPER MS VALLEY ACROSS SOUTH WI... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SEPARATELY IN EAST NC... ...SUMMARY... Scattered severe thunderstorms are expected over parts of the Upper Midwest late this afternoon into tonight. A corridor of potentially widespread destructive wind gusts could develop over parts of Minnesota into Wisconsin. ...20Z Update... Overall forecast scenario remains valid with potential for an intense, bowing MCS this evening into tonight. With continued spatiotemporal differences among recent guidance for initial supercell development, confidence is below-average for further increases in severe probabilities along the north-northwest to south-southeast oriented MLCAPE gradient over the Upper MS Valley. In addition, the likely orientation of the MCS with respect to the instability gradient suggest the significant severe wind threat may be relatively confined owing to abundant warm-moist sector MLCIN to the west and diminishing instability to the east. The corridor previously highlighted, that is centered on a portion of the Upper MS Valley into south WI, remains the most probable zone for potentially destructive wind gusts. ..Grams.. 06/24/2024 .PREV DISCUSSION... /ISSUED 1131 AM CDT Mon Jun 24 2024/ ...Upper Midwest... A weakening MCS continues to track eastward across central MN, associated with a shortwave trough over southern Canada. Extreme instability will develop along the southern fringe of this MCS and accompanying cloud shield, with hot/humid conditions leading to MLCAPE values over 4500 J/kg by late afternoon across southwest MN. Very warm temperatures aloft will likely suppress convective development in this volatile air mass, but strengthening southwesterly low-level winds by early evening will enhance warm advection and likely lead to thunderstorms over central MN. Initial storms will be supercellular, with forecast soundings showing ample low level and deep-layer shear to support a risk of very large hail, damaging winds, and a few tornadoes. As the evening progresses, most morning CAM solutions indicate that the cluster of supercells will grow upscale into a fast moving bowing MCS. However, there is considerable diversity regarding the track of the most intense storms. Given the very warm temperatures aloft, it seems likely the storms will track southeastward along the thermal gradient - across central/southern WI and into northern IL. The potential exists for a corridor of widespread and occasionally significant (exceeding 65 kt) wind damage, so have upgraded to ENH. The low-level air mass will become increasingly less unstable as the storms move across Lake Michigan and into northern IN by early Tue morning, suggesting a weakening trend. ...Central High Plains... Scattered high-based showers and thunderstorms are expected to develop over the central Rockies and Black Hills today and spread eastward into parts of SD/NE/KS. Hot surface temperatures and inverted-v profiles will support a risk of gusty/damaging winds with this activity for a few hours early this evening. ...Eastern NC/SC... A surface front is sagging southeastward across NC today, with a very moist and moderately unstable air mass in place ahead of the front. Thunderstorms are expected to form in this environment, with sufficient westerly flow aloft to help organize the storms and promote a risk of damaging wind gusts. Given the amount of heating that is occurring in eastern NC, and morning guidance showing substantial coverage of storms, have added a SLGT risk for parts of this area. $$