Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1253 AM CDT Mon Aug 17 2020 Valid 181200Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHWEST...AND CENTRAL HIGH PLAINS VICINITY... ...SUMMARY... Isolated severe thunderstorms -- accompanied by risk for damaging winds -- are forecast to spread across parts of the Northwest on Tuesday, from the eastern Oregon vicinity into parts of western Montana. A couple of severe storms may also occur over the central High Plains vicinity. ...Synopsis... The general western trough/eastern ridge pattern within the upper flow field will continue over the U.S. Tuesday, though some breakdown on the northern fringe of the ridge -- i.e. over the northern Intermountain region is expected. This will occur as numerous cyclonic disturbances continue moving in an anticyclonic arc across western Canada and the northwestern CONUS. Meanwhile in the East, troughing will remain in place -- expanding southward/deepening a bit through the period. At the surface, a weak cool front extending from New England to the Ohio Valley early, is expected to shift southeastward across the central and southern Appalachians, while high pressure expands across much of the central and eastern U.S. in its wake. Farther west, while lee troughing will generally persist across the High Plains, high pressure will prevail across a large portion of the Intermountain region. ...The northwestern states... Showers and thunderstorms are forecast to develop diurnally once again across parts of the northwestern U.S., as daytime heating results in ample high-based CAPE, and terrain-induced convective development is enhanced by mid-level disturbances moving through fast southwesterly flow aloft. Given the belt of fast (35 to 45 kt) mid-level southwesterlies, rather rapid storm motion combined with the deep/dry mixed layer suggests potential for locally strong/damaging gusts with a few of the more intense/sustained cells into the evening hours. ...The central High Plains area... Though boundary-layer capping and what appears to be rather featureless anticyclonic north-northwesterly flow aloft around the eastern fringe of the ridge should limit convection coverage, a few afternoon storms may evolve -- initially most likely to initiate over the higher terrain. With time, any storms that can become sustained will likely shift toward lower elevations -- aided by enhanced north-northwesterly winds aloft atop low-level southerlies. Given the available CAPE, and this flow configuration with height, cold pool development would likely yield one or two forward-propagating clusters, that could produce more widespread damaging winds than currently expected. However, will introduce only 5% probability at this time, as it appears most likely that convective coverage will remain limited. ..Goss.. 08/17/2020Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_0600.html
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