SPC Aug 10, 2017 2000 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 10 Aug 2017

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0311 PM CDT Thu Aug 10 2017 Valid 102000Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHWEST KS...OK/TX PANHANDLES INTO NORTHWEST AND CENTRAL OK... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK FROM EASTERN CO INTO KS AND OK... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM FAR EASTERN IA AND NORTHERN IL TO EASTERN WI... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK AREA FROM EASTERN CO AND THE SOUTHERN PLAINS TO LAKE MICHIGAN... ...SUMMARY... Severe thunderstorms are expected this afternoon into tonight across parts of the central and southern Plains. Isolated strong to severe storms are also expected northeastward into part of the upper Mississippi Valley to the southwest Great Lakes region. ...Eastern CO/KS/OK and TX Panhandles and much of OK... Forecast remains on track for two rounds of severe storms to develop/spread east/southeast across the Enhanced risk area, with damaging winds being the greatest threat in that risk area, which extends from southwest KS through the OK/TX Panhandles to northwest/part of central OK. The lead area of storms is ongoing in northwest OK and additional storms will continue to develop over the higher terrain of CO and advance southeast onto the High Plains of CO and into western/southern KS to the southern Plains later this evening/tonight to early Friday morning. Meanwhile, long, straight hodographs across southeast CO into portions of southwest to central KS favor a threat for very large hail, with a 10% significant hail area being added with this outlook issuance. Farther north into northwest KS and southwest NE, severe probabilities have been trimmed southward, given the passage of a convective outflow boundary and cold front in these areas and boundary layer stabilization in the wake of these boundaries. ...Eastern IA/northern IL to eastern WI... Given trends in radar imagery and objective analyses, the Slight risk area and severe probabilities have been expanded some in this region. ..Peters.. 08/10/2017 .PREV DISCUSSION... /ISSUED 1131 AM CDT Thu Aug 10 2017/ ...Synopsis... Low-amplitude cyclonic flow aloft will continue to prevail east of the Rockies today/tonight, while ridging extends northwest from Texas into the Great Basin and Pacific Northwest. Within the cyclonic flow field, a shorter-wavelength trough will continue to cross the upper Mississippi Valley and later the upper Great Lakes region, while smaller/more subtle disturbances shift southeast out of the Rockies and into/across the central U.S. through tonight. At the surface, high pressure will prevail over the eastern and southeastern states. High pressure will also expand southeast across the north central U.S. in the wake of a cold front moving slowly east across the upper Great Lakes/upper Midwest, and southeast across the central Plains and Missouri Valley through 11/12z. Areas along and ahead of this front will be the focus for the primary severe risk this period. ...Eastern Colorado into Kansas/Oklahoma parts of the Texas Panhandle... A complex scenario is evident late this morning across the central Plains vicinity, with a cold front to continue to shift very slowly southward across Kansas and several small-scale perturbations aloft moving east-southeast across the Rockies and into the central Plains vicinity today and tonight. The first of these disturbances is supporting development of a cluster of storms across western Kansas at this time, which will likely continue moving east-southeast while expanding in coverage/breadth. This early band of storms will complicate the forecast in terms of later development in the wake of this convection, with most CAM runs suggesting that later development will be most prevalent/intense near the southern periphery of this storm band, as outflow now across far southwest Kansas and northwest Oklahoma is reinforced. Along with risk for damaging winds and hail associated with this initial storm cluster as it moves east-southeast and grows in coverage, the secondary corridor for later convection possibly evolving along the aforementioned west-northwest to east-southeast outflow boundary may prove to be the zone of greatest severe risk. As such, will introduce 30% wind/ENH risk across a small portion of southwest Kansas, east-southeast into northwest Oklahoma. With moderate CAPE developing through the afternoon and moderately strong west-northwest flow aloft aiding in storm organization, an upscale-growing MCS may evolve through the late afternoon and evening hours. Elsewhere, with backed low-level flow north of the outflow, organized/rotating storms -- and attendant risk for large hail and damaging winds -- will exist across the rest of the SLGT risk area, from the Colorado front range east across much of Kansas and Oklahoma through the evening and into the overnight hours. ...Upper Great Lakes southwest into Missouri... Afternoon heating of the pre-frontal boundary layer will support airmass destabilization sufficient to support development of thunderstorms, with greatest coverage of storms expected from southeast Wisconsin southwestward along the boundary to eastern Iowa/northwest Illinois. Within this area, the strongest mid-level flow is also progged, on the southern fringe of the well-defined upper circulation now moving east across the upper Mississippi Valley at this time per latest water vapor loop. With this zone of stronger flow aloft aiding in potential for organized storms and possibly some upscale/linear growth, risk for damaging winds appears sufficient to support upgrade to 15% wind/SLGT risk. Storms will spread east into the evening, weakening diurnally as they cross Lake Michigan and move into lower Michigan/Indiana. Read more



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