SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Fri Sep 14 2018 Valid 142000Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND TONIGHT ACROSS PARTS OF EASTERN NORTH CAROLINA... ...SUMMARY... A risk for a few tornadoes continues this afternoon across parts of eastern North Carolina, and into tonight, mainly near southeastern North Carolina coastal areas. ...Discussion... No change was made to the previous outlook. ..Smith.. 09/14/2018 .PREV DISCUSSION... /ISSUED 1115 AM CDT Fri Sep 14 2018/ ...Synopsis... Much of the nation to the east of the southern Rockies will remain under the influence of a broad subtropical ridge through this period. Models indicate that there will be some amplification of short wave ridging on its northwestern periphery, across parts of the northern U.S. Rockies through the central Canadian/U.S. border area, downstream of a significant short wave impulse digging into amplified larger-scale troughing across the eastern Pacific/Pacific coast. Within the easterlies, to the south of the subtropical ridge axis, Hurricane Florence is forecast to continue a very slow southwestward migration across parts of southeastern North Carolina into northeastern South Carolina. A much weaker wave is expected to gradually shift westward inland of the Texas/northeast Mexico Gulf coast, into the lower Rio Grande Valley. ...Southern Mid Atlantic coast... Given the motion of Florence with respect to the coast, boundary layer instability supportive of continuing potential for low-level mesocyclones with a risk for tornadoes appears likely to remain confined roughly to its outer northeast quadrant. This may mostly continue to be associated with stronger convective bands pivoting off the Atlantic into the North Carolina coastal plain. This risk appears maximized roughly near the periphery of the 40-50+ kt flow around the 850 mb level, which will gradually shift southwestward and may begin to shrink. By late this evening into the overnight hours, the primary lingering risk area may become more focused near southeastern North Carolina coastal areas. ...Northern Minnesota and adjacent areas... On the southernmost fringe of the westerlies (near the northwestern periphery of the mid/upper ridge), models suggest that modest destabilization, associated with moisture return above a northward advancing frontal zone, may become sufficient for scattered vigorous thunderstorm development tonight. This appears most likely to initiate in the 03-06Z time frame, aided by ascent associated with low-level warm advection accompanying an 850 mb jet strengthening to 30+ kt. On the northern periphery of warmer and more strongly capping elevated mixed-layer air, the environment may become conducive to convection accompanied by a risk for marginally severe hail, particularly with initial development.
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