SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0233 PM CDT Sun Oct 25 2020 Valid 252000Z - 261200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...20Z Outlook Update... Some adjustments were made to the categorical/10 percent probability of thunderstorms lines, mostly to account for latest trends concerning destabilization evident in observational data and a general consensus of the various latest model output. Across the Carolinas, a categorical risk for thunderstorms is being maintained, but probabilities may not be much more than the minimum 10 percent threshold. Stronger forcing for ascent associated with low amplitude troughing is in the process of shifting north-northeast of coastal areas. General subsidence in its wake has already overspread much of South Carolina, but insolation within a residually moist air mass, south of cool air currently nosing southward to the lee of the southern Appalachians, has supported weak boundary-layer destabilization. This is contributing to some deepening convective development, particularly near Orangeburg SC as of 1930Z. It might not be out of the question that this activity could still briefly intensify into a weak thunderstorm or two late this afternoon. ..Kerr.. 10/25/2020 .PREV DISCUSSION... /ISSUED 1100 AM CDT Sun Oct 25 2020/ ...Synopsis... A weak midlevel trough will move east-northeastward over the Carolinas today, and an associated surface cold front will move southward across the Carolinas in its wake. There will be a window of opportunity for isolated thunderstorms today in the zone of ascent across eastern NC, and where surface heating/destabilization will be greater along the front into central SC (prior to the onset of subsidence late today). Farther south, the threat for occasional thunderstorms will persist across south FL within a tropical moisture plume (PW values in excess of 2.3") that extends north-northeastward from tropical storm Zeta in the western Caribbean Sea. Downstream from an amplified northeast Pacific ridge, and midlevel trough will continue to dig southward over the Great Basin. A confluent northern stream will help maintain a large/cold surface high immediately east of the Rockies, with the consolidated baroclinic zone on the leading edge of the cold air mass expected to extend from southwest TX to southeast OK by the end of the period. Isolated thunderstorms will be possible later this afternoon into tonight in the vicinity of the Four Corners in the zone of ascent of ascent preceding the Great Basin trough, and in advance of an ejecting southern-stream now just off the southern CA coast. Farther east, elevated thunderstorm development is expected the last 3-6 hours of the forecast period in response to strengthening warm advection and destabilization atop the shallow cold air mass across northwest TX and OK from 06-12z.
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