SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CST Thu Feb 25 2021 Valid 271200Z - 281200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk of severe thunderstorms currently appears negligible across the U.S. for Saturday through Saturday night. ...Discussion... Suppression of an initially prominent blocking high and amplified mid-level ridging across the eastern Pacific appears likely to continue during this period, as a significant short wave trough progresses around its northern periphery, across the northeastern Pacific. A more pronounced split in the downstream flow may develop inland of the Pacific coast, as short wave ridging shifts across British Columbia and adjacent portions of the U.S. Pacific Northwest. By late Saturday night, the leading edge of this regime may begin to translate to the north of a vigorous short wave impulse sharply digging across the Great Basin into the lower Colorado River vicinity of the Southwest. Across and east-northeast of the Rockies, mid-level flow is forecast to trend increasingly confluent, between more prominent subtropical ridging across the Gulf of Mexico into the Southeast and a vigorous short wave impulse pivoting southeastward out of the Arctic. As this perturbation digs across Saskatchewan and Manitoba, an increasingly sheared short wave impulse is forecast to accelerate northeast of the Wyoming/Colorado Rockies toward the Upper Midwest, while a more amplified downstream impulse accelerates east of the Great Lakes into the Canadian Maritimes. Each of these latter features may be accompanied by developing surface cyclones, while cold surface ridging builds beneath the confluent flow across the Great Plains, as far south as the Texas/Oklahoma Panhandle region by 12Z Sunday. The net result of these developments in lower levels is expected to be the evolution and/or reinforcement of a frontal zone near the northern periphery of the mid-level subtropical ridging, from near or south of the Texas Big Bend into the Mid Atlantic Coast vicinity. South/southwesterly low-level return flow, off a still modifying boundary layer over the Gulf of Mexico, will contribute to moistening and destabilization along and north of this front. This will become the focus for areas of scattered thunderstorm development Saturday through Saturday night, with models indicating that warm layers aloft and subsidence will suppress convective development to the south of the front. Models do indicate that southwesterly flow around the 850 mb level may strengthen to 40-50+ kt across the Arkansas/Kentucky/Tennessee vicinity late Saturday afternoon and evening. It might not be out of the question that this could contribute to a risk for organizing storms with the potential to producing damaging surface gusts. However, much may depend on how close convection forms to the surface frontal position (and the depth of the near-surface stable layer below the convection). With this uncertain, and model output still indicating only generally weak destabilization, severe probabilities appear less than 5 percent at the present time. ..Kerr.. 02/25/2021
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