SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0215 AM CDT Wed Oct 07 2020 Valid 091200Z - 101200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE FRIDAY INTO FRIDAY NIGHT ACROSS PARTS OF SOUTHEASTERN LOUISIANA...SOUTHERN MISSISSIPPI AND SOUTHWESTERN ALABAMA... ...SUMMARY... At least some risk for tornadoes may accompany the landfall of Hurricane Delta, across parts of the southeastern Louisiana, southern Mississippi and southwestern Alabama coastal plain, mainly Friday night. ...Synopsis... Amplification within the westerlies across the mid-latitude Pacific into North America may commence during this period. This may include a digging mid-level trough to the west of the Pacific Northwest coast, and building large-scale ridging across the Canadian/U.S. Rockies through the Canadian Prairies and much of the Great Plains. In a lingering branch split off to the south of the stronger flow, weaker mid-level troughing is forecast to shift into the Southwest, perhaps with an embedded closed low migrating into southern California by late Friday night. Downstream, Hurricane Delta is forecast to accelerate north-northeastward, inland of the northwestern Gulf coast by Friday evening, with the mid-level circulation center gradually becoming absorbed within weak troughing slowly shifting east of the southern Great Plains. This probably will be accompanied by the influx of seasonably high precipitable water content within a plume across and just east of the lower Mississippi Valley. However, relatively dry/ potentially cool boundary-layer air as far south as the Gulf coastal plain early Friday may be slow to substantively modify. ...Gulf Coast... Latest model output generally suggests that surface dew points near or just above 70F may initially be confined to immediate coastal areas, perhaps inland some across parts of southeastern Louisiana, to the north of Hurricane Delta at the outset of the period. Across the remainder of the Gulf coastal plain, surface dew points may generally be in the mid/upper 60s F, with mid 70s+ F mostly well offshore across the western Gulf of Mexico. Given the warm mid-level environment advecting inland with Delta, mid 70s F surface dew points will probably need to be advected inland to contribute to sufficient boundary-layer destabilization to support an appreciable risk for tornadoes, northeast and east of the inland migrating low-level circulation center. At this time, most guidance suggests that lower 70s F dew points may be advected inland in a small/narrow plume wrapping into the circulation center, across parts of southeastern Louisiana, southern Mississippi and adjacent southwestern Alabama, with mid 70s F dew points lagging near/south of immediate coastal areas. Given the forecast strength of the system as it approaches landfall, it is possible that this is underdone, but the risk for tornadoes with Delta still seems largely conditional at this time. ..Kerr.. 10/07/2020
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