SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 PM CDT Thu May 15 2025 Valid 160100Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE GREAT LAKES AND NORTHERN OHIO VALLEY... ...SUMMARY... Severe thunderstorms are expected across parts of the upper Mississippi River Valley and Great Lakes this evening. Tornadoes, some of which could be strong, very large hail and damaging winds will be possible. Severe thunderstorms are also expected later this evening into tonight from the the lower Ohio Valley into the Ozarks. ...Upper Mississippi Valley/Great Lakes/Ohio Valley... The latest water vapor imagery shows a mid-level low over the eastern Dakotas, with a diffluent pattern over the upper Mississippi Valley and western Great Lakes. A 500 mb jet is analyzed from the Ozarks into western Illinois. At the surface, a front extends southward from southern Wisconsin into central Illinois. To the east of the boundary, surface dewpoints are in the 60s F. MLCAPE is estimated to be from near 2000 J/kg in far southeast Wisconsin to about 4000 J/kg in western Indiana. Ahead of the instability axis, a line of severe storms is moving across Lake Michigan. Further south, storms are developing along the western edge of the stronger instability from south of Chicago southward into east-central Illinois. The current thinking is that the convection over Lake Michigan will move across the remainder of Lake Michigan, and remain severe as it moves eastward into western Lower Michigan. Wind damage will be likely along the leading edge of this convective line, with gusts above 75 mph possible. A few tornadoes may develop with rotating cells embedded in the line. Large hail will also be likely with the more intense embedded supercells. The storms in northeastern and east-central Illinois are expected to move into western Indiana this evening, where strong instability, and 0-6 km shear near 50 knots will be favorable for severe storms. Mesoscale analysis currently has Significant Tornado Parameter ranging from 3 to 5 over much of central and northern Indiana. As low-level shear continues to increase over the next couple of hours, a tornado threat may develop with supercells that remain semi-discrete. The more intense supercells will also have a threat for very large hail, potentially greater than 2 inches in diameter. Wind damage will also be likely along the leading edge of a line that is expected to become more organized later this evening. Further south into southern Illinois and southern Indiana, large-scale ascent will be limited. However, moderate instability is present and low-level flow will strengthen this evening. This could support isolated to scattered severe storms late this evening with large hail and wind damage as the primary threats. ...Ark-La-Tex/Western Tennessee Valley... A mid-level jet, analyzed by the RAP, will overspread the Ark-La-Tex from late this evening into the overnight period. The jet is located above a moist airmass that extends southeastward from the Ozarks into the Gulf Coast States. Across this airmass, the RAP has MLCAPE in the 2000 to 3500 J/kg range, with moderate deep-layer shear in place. As large-scale ascent associated with the exit region of a mid-level jet increases, scattered convective development will become likely. The greatest potential for storms will be from northeastern Arkansas eastward into Kentucky, along the northern edge of the stronger instability. Large hail and wind damage will be possible with the stronger cells, mainly after midnight through late in the period. ..Broyles.. 05/16/2025