SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Tue Oct 21 2025 Valid 212000Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE SOUTHERN GREAT LAKES... ...SUMMARY... Isolated strong to locally severe gusts are possible this afternoon over parts of the southern Great Lakes. ...20Z Update... Minimal changes were made with this update. The MRGL risk area was trimmed behind an eastward-moving band of low-topped convection in southeast Lower MI, where temperatures have dropped into the lower 50s. As these storms continue eastward across the remainder of far southeast Lower MI and northern OH this afternoon, strong to locally severe gusts (45-60 mph) will remain possible -- aided by steepened pre-convective boundary-layer lapse rates and 35-40-kt flow below 2 km AGL (per VWP data). Farther south, the TSTM area was trimmed behind the southeastward-moving cold front in the Southeast, and in the southern Appalachians where convection has generally outpaced the remaining buoyancy. ..Weinman.. 10/21/2025 .PREV DISCUSSION... /ISSUED 1125 AM CDT Tue Oct 21 2025/ ...Synopsis... Morning water-vapor loop and upper-air data indicate a midlevel low tracking east-southeastward over the upper Midwest -- accompanied by cold 500-mb temperatures (around -28C). This feature will continue eastward across the Great Lakes through the period, while a cold front moves from the Upper OH Valley to the Atlantic Coast. Within the base of the midlevel low, an embedded vorticitiy maximum will move across the Lower Great Lakes through the afternoon, while a related surface front/wind shift overspreads IN, OH, and Lower MI. ...Southern Great Lakes... In the wake of a weakening band of showers along the departing front over the upper OH Valley, mostly clear skies will promote boundary-layer heating/steepening low-level lapse rates (shallow inverted-V profiles) beneath the midlevel cold pocket -- yielding marginal destabilization across parts of northern OH and southeast Lower MI. As widely scattered convection along the secondary surface front/wind shift spreads/develops into this environment, a modest uptick in updraft intensity is possible this afternoon. Given strong deep-layer flow flanking the midlevel low, isolated strong-locally severe convectively enhanced wind gusts (45-60 mph) will be possible during the late afternoon into early evening time frame. Small hail will also be possible with any shallow cellular convection. ...Central Gulf Coast vicinity... A warm, moist, and uncapped air mass ahead of the tail-end of the cold front will support isolated thunderstorms across parts of east TX into southern LA this afternoon. While moderate surface-based buoyancy and around 25 kt of effective shear could promote a couple strong storms along the front, warm temperatures aloft and minimal large-scale forcing for ascent should generally limit upward accelerations in updrafts.
