Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1149 PM CDT Wed Apr 26 2017 Valid 271200Z - 281200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF THE GREAT LAKES REGION SOUTHWARD TO THE SOUTHEAST STATES... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF SOUTHEAST CO...WESTERN/SOUTHERN KS...THE TX/OK PANHANDLES...NORTHERN OK... ...SUMMARY... Isolated severe wind gusts may accompany thunderstorms from portions of the Great Lakes region to the Southeast States today into this evening, and across portions of the central and southern Great Plains late this afternoon into this evening. ...Synopsis... Deep surface low pressure is forecast to advance from the vicinity of Lake Michigan northward into Ontario, associated with a northward-advancing shortwave trough embedded within the eastern rim of broadly cyclonic flow covering the Central and Western States. A cold front will arc south from the low to the north-central Gulf Coast vicinity and westward. The South-Central States portion of the front is forecast to weaken and develop northward in response to surface lee cyclogenesis over the central High Plains -- enhanced by the emergence of a midlevel speed maximum from the central/southern Rockies vicinity. ...Portions of the Great Lakes region southward to the Southeast States... Comparatively stronger deep ascent accompanying the northward-advancing shortwave trough is forecast to become increasingly displaced to the north of richer moisture within the low-level cyclone's warm sector. This will tend to marginalize the severe potential through the period. Nevertheless, storm coverage and intensity are forecast to gradually increase through the diurnal heating cycle along and ahead of the front, with an extensive corridor of eastward- and northeastward-moving clusters of storms across the Marginal Risk area. Isolated damaging wind gusts should be the primary hazard with this activity. The strongest pre-frontal buoyancy related to the richest low-level moisture characterized by middle/upper 60s dewpoints will be confined to portions of central SC into GA and vicinity. While effective shear around 30-40 kt and modest low-level directional shear may support a few rotating updrafts, weakening low-level ascent will tend to limit updraft sustainability and keep any severe risk isolated. Farther north, diurnal gains in buoyancy will be muted by cloud coverage and more scant moisture return northward to the Great Lakes region and vicinity. However, sufficient low/midlevel flow could encourage momentum transport capable of supporting locally damaging wind gusts. Storms across the Marginal Risk area will weaken during the evening as they spread across an area from western NY southward to the SC piedmont. ...Portions of southeast CO, western/southern KS, the TX/OK Panhandles, northern OK... Strengthening deep ascent associated with the aforementioned speed maximum, including isentropic ascent related to lee cyclogenesis, will support the development of convective clusters in the steep-lapse-rate environment across the High Plains by late afternoon. Convection will subsequently spread eastward along a zone of frontogenesis through the evening hours. A dearth of moisture return will greatly stunt buoyancy. However, long/looping hodographs amid sufficient buoyancy and the steep lapse rates may support a few bowing convective segments capable of isolated severe wind gusts. ..Cohen/Leitman.. 04/27/2017Read more
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