Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0749 AM CDT Fri Jun 09 2017 Valid 091300Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO TONIGHT FOR PARTS OF THE NORTHERN PLAINS... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK AREA...FROM SOUTHEASTERN MONTANA TO NORTHWESTERN MINNESOTA... ...SUMMARY... Strong to severe thunderstorms, capable of large hail, damaging winds, and perhaps a couple tornadoes, will be possible across the northern Plains today through tonight. ...Northern Plains through tonight... Within a belt of cyclonic mid-upper flow over the northwestern CONUS, embedded speed maxima will eject east-northeastward from the northern Rockies/Great Basin to the northern Plains by Saturday morning. An associated surface cyclone will develop slowly eastward across ND, as boundary-layer dewpoints in the 60s are drawn northward across the Dakotas (and augmented by evapotranspiration) beneath steep midlevel lapse rates. The elevated mixed layer plume will act to cap the boundary layer until mid-late afternoon, when convective initiation becomes probable across central ND in association with deeper surface mixing and low-level ascent along a surface trough. Moderate-strong buoyancy (MLCAPE ranging from 1500-3000 J/kg from north to south across central ND)and effective bulk shear in excess of 40 kt will support a risk for supercells late this afternoon/evening. Somewhat large temperature-dewpoint spreads suggest that large hail/damaging winds will be the main risks. However, substantial low-level shear/hodograph curvature and somewhat lower spreads along the north edge of the warm sector in north central ND could support a couple of tornadoes. Some of the afternoon convection could persist into early tonight and spread as far east as northwest MN with an associated hail/wind threat. A few clusters/bands of thunderstorms may also form by early tonight near and just northeast of the higher terrain in southern MT/northern WY, and spread northeastward to ND overnight. Isolated damaging winds and/or large hail could occur with the strongest storms along and on the immediate cool side of a surface cold front. ..Thompson.. 06/09/2017Read more
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