SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0102 AM CDT Wed Jun 28 2023 Valid 291200Z - 301200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID TO UPPER MISSISSIPPI VALLEY...OHIO VALLEY AND SOUTHWESTERN GREAT LAKES... ...SUMMARY... A severe threat, with a potential for wind damage, large hail, and perhaps a tornado or two appears likely to develop on Thursday across parts of the mid to upper Mississippi Valley, Lower Ohio Valley and southwestern Great Lakes. An isolated severe threat will likely develop across parts of the central Plains and central Rockies. ...Mid To Upper Mississippi Valley/Ohio Valley/Southwestern Great Lakes... A mid-level anticyclone will be in place across the southern U.S. on Thursday. To the north of the anticyclone, mid-level flow will be westerly from the central High Plains eastward into the southern Great Lakes, as an upper-level trough moves eastward across western Ontario and the upper Mississippi Valley. In the Upper Midwest, a 45 to 55 knot mid-level speed max will translate eastward through the flow. At the surface, a cold front will advance southeastward toward the western Great Lakes, providing a focus for convective initiation. A moist and unstable airmass will be in place ahead of the low across much of the Mississippi Valley extending eastward into the lower Ohio and Tennessee Valleys. Surface dewpoints across the moist airmass will generally be from the mid 60s to the mid 70s F. Scattered thunderstorms will likely develop across much of this airmass during the afternoon, with two or three clusters persisting into the early to mid evening. MCS development will be possible. NAM Forecast soundings in central Illinois at 00Z/Friday, along the instability corridor, have MLCAPE near 3500 J/kg, with 0-6 km shear around 50 knots, and 700-500 mb lapse rates near 8 C/km. This environment will be favorable for supercells with large hail. Hailstones greater than 2 inches in diameter will be possible across much of northern and central Illinois, where the combination of shear and instability is forecast to become maximized. A tornado or two may occur across this same area, where 0-3 km storm-relative helicity is forecast to reach 200 m2/s2. Supercells are expected to be the favored mode early in the event, but a transition to linear mode may take place. Cold pool development would increase the wind-damage potential with any line segment that can become organized. A severe threat will be possible during the early to mid evening across parts of the lower Ohio Valley. ...Central Plains/Lower to Mid Missouri Valley... An upper-level ridge will be in place on Thursday across the central U.S., as a mid-level anticyclone remains anchored over the south-central states. At the surface, a quasi-stationary front will likely be in place across the central Plains, with an east-to-west corridor of maximized low-level moisture located from northwest Missouri to northeastern Colorado. Moderate instability will develop across the moist airmass by afternoon. Thunderstorms are expected to form in the higher terrain and in the High Plains across eastern Wyoming and western Nebraska during the late afternoon. The storms will like develop south and eastward into northeastern Colorado and southern Nebraska during the evening. Thunderstorm should continue into the overnight period across the central Plains extending eastward into the lower to mid Missouri Valley. Along the instability axis from southeast Wyoming into southwestern Nebraska, models suggest that MLCAPE will likely reach the 1000 to 2000 J/kg range by early evening. This, along moderate to strong deep-layer shear should be favorable for an isolated severe threat, with large hail and strong wind gusts. Although the severe threat could be marginal, a potential for isolated severe storms could continue into the late evening and early overnight as warm advection causes storm coverage to increase near the front. Further east into the lower to mid Missouri Valley, deep-layer shear is forecast to be considerably stronger, suggesting the severe threat could be greater during the evening and early overnight. Large hail and isolated damaging wind gusts would again be the primary threats. ..Broyles.. 06/28/2023
