SPC May 19, 2017 2000 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 19 May 2017

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Fri May 19 2017 Valid 192000Z - 201200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NORTH TEXAS AND SOUTHERN OKLAHOMA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE SOUTHERN PLAINS TO THE MID MISSISSIPPI VALLEY... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE OHIO VALLEY... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF TEXAS TO SOUTHERN NEW ENGLAND... ...SUMMARY... Severe thunderstorms are possible this afternoon into tonight across parts of the central and southern Plains through portions of the Ozark Plateau and middle Mississippi Valley. Particularly across parts of northern Texas into southeastern Oklahoma, some of these may be accompanied by large hail, damaging wind gusts and a couple of tornadoes. ...Portions of the southern Plains... No significant changes are made to the ongoing risk areas. A somewhat nebulous convective evolution lends some uncertainty regarding the severe potential this afternoon and evening. Nonetheless, surface heating and dew points in the upper 60s/lower 70s are maintaining moderate surface-based buoyancy across portions of north Texas into southeast Oklahoma. Across this area, large hail (with an isolated report over 2 inches in diameter), damaging winds, and a couple tornadoes remain possible. Farther north into central Oklahoma, while air mass recovery has been stunted by convection to the south, storms developing over northwest Texas will potentially push east/northeast and pose a threat of large hail. ...Portions of the Ohio Valley... The Slight Risk is expanded farther east, as a stationary front focuses convection along/ahead of a larger-scale complex progressing east. Mixed-layer CAPE around 500-1500 J/kg and sufficient westerly flow aloft will support a few damaging wind gusts. A tornado may be possible as well in the vicinity of the front, where storm-relative helicity may be slightly enhanced. ..Picca.. 05/19/2017 .PREV DISCUSSION... /ISSUED 1115 AM CDT Fri May 19 2017/ ...Synopsis... Within the southern branch of split westerlies emanating from the mid-latitude Pacific, models continue to indicate that large-scale troughing will gradually redevelop northeastward out of the Intermountain West and Rockies into the Plains, with an embedded closed low migrating out of the Colorado Rockies into the central Plains. At the same time, a significant upper trough within the northern branch appears likely to dig across the Canadian Maritimes and New England. In between, mid/upper ridging is forecast to build north and east of the middle Mississippi Valley through the Great Lakes and Mid Atlantic region. In lower-levels, a significant surface cold front associated with the northern branch trough has advanced into the Northeast, Ohio and middle Mississippi Valleys, and central/southern Plains. While this front is stalling across the central Plains into the Ohio Valley, it is expected to advance across the remainder of New England and northern Mid Atlantic Coastal areas by late tonight. Across the Plains, in response to forcing associated with the southern branch impulse, modest surface frontal cyclogenesis appears possible later today into tonight, from parts of western Oklahoma through the middle/lower Missouri Valley. ...Central and southern Plains into middle Mississippi Valley... The ongoing southward frontal surge across the Texas Panhandle and south Plains, the presence of significant outflow from prior convection across the Ozark Plateau into the Red River area, southward into northwest Texas, and the presence of considerable ongoing storm development above/to the cool side of this outflow across northwest Texas into Oklahoma, all are adding uncertainty to severe weather potential for today into tonight. Ongoing storms across northwest Texas appear to be supported by warm advection on the northern periphery of a plume of warmer and more strongly capping elevated mixed layer air. Little further northeastward advection of this air mass may occur, and this may remain the focus for the primary thunderstorm development through the remainder of this period, as a short wave impulse pivots northeast of the southern Rockies. The eventual upscale growth of a large mesoscale convective system appears possible this afternoon and evening across northern Texas into southeastern Oklahoma. In the presence of thermodynamic profiles characterized by steep mid-level lapse rates and moderately large CAPE, large hail and damaging wind gusts are expected. Deep layer and low-level shear may remain sufficient to support a risk for tornadoes, particularly with any initial discrete supercell development, and possible continuing supercell development near or just ahead of the evolving convective system. Farther north, into the central Plains, potential for significant destabilization is becoming more unclear, but the developing frontal wave may provide another focus for strong/severe storm development late this afternoon and evening. If sufficient destabilization can occur, deep layer wind fields and shear probably will become supportive of organized storm development, including supercells. ...Ohio Valley into Mid Atlantic and New England... Low severe probabilities have been extended northward into parts of southern New England, where the pre-frontal environment now appears at least conditionally supportive of storms capable of producing severe wind/hail. Farther south and west, into the Mid Atlantic and Ohio Valley, more uncertainty exists concerning severe storm potential, in the presence of rising mid-level heights beneath the building upper ridge. However, it appears at least possible that forcing associated with a remnant convectively enhanced impulse, could support and enhance thunderstorm development near the stalling front across the middle Ohio Valley region this afternoon. Read more



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