SPC Jun 19, 2017 0730 UTC Day 3 Severe Thunderstorm Outlook

By Newsroom America Feeds at 19 Jun 03:48

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0246 AM CDT Mon Jun 19 2017 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF KANSAS AND NEBRASKA NORTHEAST INTO SOUTHERN MINNESOTA AND IOWA... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE TEXAS PANHANDLE AREA INTO THE CENTRAL PLAINS AND PARTS OF THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Isolated to scattered severe thunderstorms are possible across the middle Missouri Valley southwestward into the southern High Plains on Wednesday. ...Synopsis... A mid-level anticyclone will remain over the Desert Southwest while the stronger belt of flow will be confined to the northern tier of states on Wednesday. A 500-mb speed max will move from MT through the northern Plains and into the Upper Midwest during the period. In the low levels, a weak surface low/triple point will develop near the NE/SD border with an attendant warm frontal zone, while a cold front pushes east across the northern portion of the Great Plains and the primary low over Canada occludes. A lee trough will move east into the central Plains. Tropical-related convection will likely organize in the Gulf of Mexico with increasing thunderstorm coverage. ...middle MO Valley into the central-southern High Plains... The eastward advection of an elevated mixed layer is forecast over the central Plains into western parts of IA and adjacent portions of SD/MN during the day. Increasing boundary-layer moisture and heating will contribute to a very unstable airmass over the middle MO Valley by late afternoon. A capping inversion will likely erode in part due to strong heating and weak convergence along the cold front. Southerly low-level flow veering to moderate westerlies in the midlevels will likely result in 30-45 kt effective shear from the middle MO Valley southward into the central-southern High Plains---sufficient for storm organization. MLCAPE in excess of 3000 J/kg is expected from northern KS northeast into western IA/southeast SD and a mix of supercells and severe multicells are expected. Large to very large hail will be the initial threat along with some tornado risk, perhaps developing where richer low-level moisture/stronger low-level shear is forecast (near the IA/SD/NE border). Very steep lapse rates will also be conducive for severe gusts with the more intense downdrafts, with this threat maximizing during the evening. The LLJ is forecast to strengthen during the evening and possibly aid in maintaining a severe risk into the overnight hours across parts of the Midwest, as storms move towards the MS River and develop within an intensifying warm-air-advection regime in the western Great Lakes overnight. ...central Gulf Coast... The outer rainbands from the developing Gulf of Mexico tropical system may begin to overspread coastal areas of the central Gulf Coast on Wednesday. Considerable uncertainty remains regarding the forecast track of the tropical system (refer to the National Hurricane Center for the latest forecast). Nonetheless, it appears low-level easterlies will intensify on the outer envelope of the amassing convection per latest forecast guidance. Will defer the possible delineation of a low-probability severe risk until uncertainty regarding the overall scenario decreases. ..Smith.. 06/19/2017 Read more



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