SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1149 PM CDT Wed Oct 07 2020 Valid 091200Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FRIDAY INTO FRIDAY NIGHT ACROSS THE NORTH CENTRAL GULF COAST VICINITY... ...SUMMARY... A few tornadoes may accompany the landfall of Hurricane Delta, mainly across parts of southeastern Louisiana Friday afternoon and evening. ...Synopsis... Models continue to indicate that the main belt of westerlies across the mid-latitude Pacific into North America may begin to undergo amplification during this period. It appears that this will 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 the northern U.S. Great Plains. Downstream of the ridging, a short wave trough is forecast to dig across northwestern Ontario. Within a lingering weaker branch, split off to the south of the stronger flow, a short wave trough, with an embedded mid-level low, may gradually begin to progress into southern California and adjacent areas of the Southwest. As this occurs, some eastward progression of weak downstream troughing east of the southern Great Plains is expected, though mid-level ridging across the subtropical western Atlantic into parts of the Southeast may hold firm. In response to these developments, Hurricane Delta is forecast to continue accelerating northward, then northeastward, around the periphery of the ridging, before the mid-level circulation center becomes increasingly absorbed within the mid-level trough, as it progresses inland of the Louisiana Gulf coast. Delta is expected to be in the process of weakening as it makes landfall by early Friday evening, and more rapid weakening probably will ensue as it continues inland across Louisiana, late Friday evening through daybreak Saturday. In advance of Delta, and ahead of the weak mid/upper troughing emerging from the southern Great Plains, seasonably high precipitable water content likely will advect north-northeastward in a plume off the northwestern Gulf of Mexico. However, relatively dry/potential cool boundary-layer air as far south as portions of the Gulf coastal plain may be initially slow to modify. ...Gulf Coast... At the outset of the period, it still appears that surface dew points near or just above 70 F may be confined to immediate coastal areas, though perhaps a bit farther inland across southeastern Louisiana than other areas, to the north of Hurricane Delta. Across the remainder of the Gulf coastal plain, surface dew points may generally be in the mid/upper 60s F, with mid 70s F dew points mostly well offshore. Given the warm mid-level environment initially present, and advecting inland with Delta, mid 70s surface dew points probably will need to advect inland to contribute to sufficient boundary-layer destabilization to support an appreciable risk for tornadoes. Forecast soundings in recent model runs are increasingly suggestive that this is possible, at least in a corridor inland of southeastern Louisiana coastal areas, just in advance of and with the landfall of Delta. East-northeast and east of the low-level circulation center, enlarging, clockwise-curved low-level hodographs in forecast soundings also appear increasingly conducive to tornado potential, in the presence of weak boundary-layer layer instability, perhaps by mid to late Friday afternoon. The tornado threat may persist into Friday evening, before probably diminishing overnight. ..Kerr.. 10/08/2020
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