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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.


Wednesday, July 26, 2023

SPC Jul 26, 2023 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0101 AM CDT Wed Jul 26 2023 Valid 261200Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE GREAT LAKES... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL PLAINS... ...SUMMARY... Severe thunderstorms associated with wind damage and isolated large hail will be possible today in parts of the southern Great Lakes region. A severe threat is also expected in parts of the central Plains. ...Southern Great Lakes... A large mid-level anticyclone will remain across much of the southwestern and south-central U.S. today. To the northeast of this feature, a shortwave trough will move eastward across the north-central U.S. Ahead of the shortwave, a complex of thunderstorms will likely be ongoing at the start of the period over the upper Mississippi Valley. A moist airmass with surface dewpoints in the 70s F will be in place across parts of the upper Mississippi Valley eastward into the Great Lakes. As surface temperatures warm, strong instability will likely develop from northern Illinois eastward into lower Michigan. The complex of storms is forecast to move east-southeastward into the stronger instability during the late morning and early afternoon. A linear MCS is expected to develop and move through the southern Great Lakes region this afternoon. A mid-level speed enhancement, associated with the shortwave trough, will move east-southeastward into the Great Lakes this afternoon. This feature will help to create moderate deep-layer shear across much of the region, making conditions favorable for severe storms. RAP forecast soundings in southwest Lower Michigan at 21Z have MLCAPE near 3000 J/kg, 0-6km shear around 35 knots, and 0-3 km lapse rates approaching 7 C/km. This should be favorable for wind damage along the leading edge of the convective complex. The greatest wind-damage threat will be associated with bowing line segments. In addition, the wind profile will support supercell development with storms that remain discrete. A large-hail threat will be possible with supercells. Also, forecast soundings have 0-3 km storm-relative helicity reaching 250 to 300 m2/s2 in parts of lower Michigan by late afternoon. This suggests that a tornado threat may develop. The MCS is expected to eventually outrun the stronger instability, making the severe threat more isolated by early evening. ...Central and Northern Plains... A mid-level anticyclone will remain in place across the Desert Southwest and southern Plains today. A shortwave trough to the north of the anticyclone will move eastward into the central High Plains this afternoon. At the surface, upslope flow is forecast across parts of western Kansas and central Nebraska, where surface dewpoints are expected to be in the 50s F. As surface temperatures warm ahead of the shortwave trough, an axis of moderate instability is forecast to develop across far southern Nebraska. Thunderstorms will likely initiate along the western edge of the stronger instability, and move eastward across the central Plains this afternoon. RAP forecast soundings along the instability axis in south-central Nebraska have MLCAPE near 2000 J/kg, 0-6 km shear around 40 knots, and low to mid-level lapse rates near 8.5 C/km. This environment will be favorable for damaging wind gusts associated with high-based short multicell line segments. In addition, high-based supercells with isolated large hail will also be possible. Further to the north across the northern Plains, an axis of instability is forecast to develop ahead of a cold front moving through the western Dakotas. Along the instability axis, MLCAPE in the 500 to 1000 J/kg combined with moderate deep-layer shear and steep lapse rates may be enough for a marginal severe threat in the afternoon. ..Broyles/Squitieri.. 07/26/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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