SPC Sep 13, 2017 0600 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 13 Sep 2017

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1134 PM CDT Tue Sep 12 2017 Valid 131200Z - 141200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk of severe storms appears negligible today through tonight. ...Synopsis... The stronger mid-latitude westerlies appear likely to remain north of much of the Canadian/U.S. border area through this period, but models indicate that some further amplification of upper troughing is possible along a positively tilted axis across the western Canadian Prairies into the Pacific Northwest. As this occurs, a closed low, within a weaker but still amplified belt of westerlies emanating from the subtropical eastern Pacific, is forecast to accelerate across the central/southern California coast through the southern Sierra Nevada/Mojave Desert by late tonight. At the same time, a broader downstream closed low may undergo considerable deformation, as subtropical ridging remains strong across the Caribbean into western Atlantic. The most prominent embedded perturbation, the remnants of Irma, is expected to gradually turn northeastward around the periphery of the ridge, toward the upper Ohio Valley and central Appalachians region, while an increasingly sheared impulse to the southwest pivots east/southeast of the Texas coast. ...East of the Rockies... A substantive influx of moisture on southerly flow could contribute to sufficient destabilization for widely scattered late afternoon and evening thunderstorm activity across parts of the central and southern Florida Peninsula. Otherwise, generally weak destabilization and/or weak forcing for large-scale ascent appears likely to result in limited thunderstorm potential. ...Pacific Coast into Rockies... Mid/upper support for large-scale ascent is expected to focus highest thunderstorm probabilities along the Sierra Nevada, and across northern portions of the Great Basin into the mountains of northwestern Wyoming and adjacent portions of Idaho and Montana. But weak to modest destabilization probably will contribute to scattered afternoon and evening thunderstorm activity southward/eastward across the Colorado Plateau and southern Rockies. Within any of this sizable area of the West, thermodynamic conditions could locally become sufficient to support a risk for marginally severe hail and/or locally strong surface gusts. However, due to expected sparse coverage and lingering uncertainty concerning a more specific risk area, severe probabilities of less than 5 percent have been maintained for today and tonight. ..Kerr/Cohen.. 09/13/2017 Read more



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