SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1246 AM CDT Tue Jul 27 2021 Valid 281200Z - 291200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF WISCONSIN... ...SUMMARY... Thunderstorms associated with severe wind gusts, isolated large hail and a couple tornadoes will be possible from Wednesday into Wednesday night across parts of the upper Mississippi Valley and Great Lakes region. Marginally severe storms could also occur in the central Appalachians and Mid-Atlantic. ...Upper Mississippi Valley/Great Lakes... A large area of high pressure will remain over the western and central United States on Wednesday, with northwest mid-level flow located from the upper Mississippi Valley to the eastern Seaboard. At the surface, a low will move across the upper Mississippi Valley as a cold front advances southward across the northern Plains. A warm front should be located across the western and southern Great Lakes region. Along and to the south of the warm front, surface dewpoints will likely range from 70 to 75 F, with moderate to strong instability developing by afternoon. Model forecasts move a subtle shortwave trough from southern Canada into the Great Lakes region as a 40 to 50 kt low-level jet moves across the upper Mississippi Valley. Convective initiation is expected to take place at the northwestern end of the instability corridor and to the north of the low-level jet during the afternoon. This convection should organize quickly with a severe complex of storms moving southeastward across Wisconsin during the late afternoon and early evening. It appears that MCS development will take place in the evening. NAM forecast soundings along the track of the MCS near Madison, Wisconsin show an impressive thermodynamic and kinematic environment. MLCAPE is forecast to peak near 4000 J/kg across central Wisconsin late Wednesday afternoon with 0-6 km shear in the 60 to 70 kt range. This combination of instability and shear will likely be favorable for a linear MCS associated with damaging wind gusts. A northwest-to-southeast swath of wind damage may occur across parts of northern, central and eastern Wisconsin. As the MCS moves southeastward into lower Michigan during the late evening, a wind damage threat should continue. A couple of tornadoes and some hail will also be possible along the track of the MCS, mainly with supercells that develop within the MCS itself. The wind-damage threat could persist into the early overnight period across the lower Great Lakes region. ...Central Appalachians/Mid-Atlantic... An upper-level trough is forecast to move southeastward across the Northeast on Wednesday. A moist airmass will likely be in place across parts of the central Appalachians, where moderate instability is forecast to develop by afternoon. Although large-scale ascent will not be that strong, isolated convective initiation should take place in the higher terrain as surface temperatures warm up. In addition to the instability, deep-layer shear will be strong enough to contribute to a marginal severe threat. A few marginally severe gusts will be possible in the mid to late afternoon as low-level lapse rates become steep. ..Broyles.. 07/27/2021
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