SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0715 AM CDT Sun Oct 17 2021 Valid 171300Z - 181200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Isolated thunderstorms are possible over south Florida, and some areas southeast of Lakes Erie and Ontario. ...Synopsis/Discussion... In mid/upper levels, a progressive/high-amplitude pattern will continue over the CONUS, south of a splitting flow regime related to the evolution of both eastern and western troughs to closed cyclones. The eastern trough is initially positioned from Hudson Bay over Lake ON to the Carolinas and northern FL. This feature will shift eastward across western/southern QC, NY to New England, and offshore from the Mid-Atlantic and southern Atlantic Coast through the period, while forming an elongated cyclone centered over southeastern Canada. Cold air aloft -- reinforced by northwest-flow shortwave perturbations behind the synoptic trough - will combine with relatively warm/moist boundary layers advecting off parts of Lakes Erie and Ontario, steepening lapse rates enough to yield buoyancy into layers colder than -20C. As such, isolated thunder is possible in some of the convection downwind from those lakes. The surface cold front related to the eastern upper trough was drawn at 11Z across eastern ME to south-central FL. This boundary should exit both ME and south FL by this evening, leaving behind a vast, continental/polar anticyclone covering most of the CONUS east of the Rockies. Despite modest frontal lift and a stable layer between 600-700 mb, rich low-level moisture and diurnal heating may foster a few thunderstorms along and south of the front today over south FL. In the West, height falls aloft are expected as synoptic ridging moves from the Rockies eastward across the Plains States, and a strong synoptic trough now over the Pacific moves ashore between 00-06Z. A closed 500-mb low is progged over the CA/NV line north of RNO by 12Z tomorrow, with difluent mid/upper flow across most of the Rockies, Intermountain region and Great Basin. Sporadic, mainly midlevel convection is possible, and a rogue lightning strike cannot be ruled out. However, the low-level air mass across the region should remain too cool and/or dry to support a general thunderstorm threat. ..Edwards/Leitman.. 10/17/2021 Read more LIVE: spc.noaa.gov
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