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Tuesday, July 13, 2021

SPC Jul 13, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1227 PM CDT Tue Jul 13 2021 Valid 141200Z - 151200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID MISSOURI VALLEY...UPPER MISSISSIPPI VALLEY AND WESTERN GREAT LAKES... ...SUMMARY... Thunderstorms associated with wind damage and isolated large hail are expected on Wednesday from parts of the mid Missouri Valley into the western Great Lakes. Marginally severe storms with strong gusty winds will be possible in parts of the central Plains and Northeast. ...Mid Missouri Valley/Upper Mississippi Valley/Western Great Lakes... An upper-level trough will move from the northern Plains into the upper Mississippi Valley on Wednesday. At the surface, a low will deepen across the central High Plains as a cold front advances southeastward across the central Plains and upper Mississippi Valley. Thunderstorm development is expected to take place along the front during the morning to the north and northeast of the surface low, from northeastern Nebraska into northwest Iowa. These storms should be elevated initially and are forecast to move east-northeastward across the Upper Mississippi Valley during the afternoon. A surface-based convective cluster is expected to develop out of this activity. Other more isolated thunderstorms should develop southwestward along the front in the central Plains. MCS formation will be possible Wednesday evening from parts of the Upper Mississippi Valley into the western Great Lakes. Moisture advection will take place ahead of the front on Wednesday as a 30 to 40 kt low-level jet moves into the upper Mississippi Valley from the southwest. Surface dewpoints are forecast to increase into the lower 70s F in much of the airmass ahead of the front. In response, a pocket of strong instability will likely develop by afternoon across parts of Iowa and Wisconsin. NAM forecast soundings at 21Z from north of Des Moines, Iowa to south of Madison, Wisconsin have MLCAPE in the 3000 to 4000 J/kg range. Wind profiles show directional shear in the low-levels with winds increasing from 30 to 50 kt in the 950 mb to 650 mb layer. This environment will support supercells and organized bowing line segments. Although large hail will be possible with supercells, wind damage should be the more predominant severe threat. The wind-damage threat may become widespread in areas where low-level lapse rates become the steepest. If a cold pool can organize, then a west-to-east swath of wind damage would be possible across the upper Mississippi Valley. ...Northeast... A shortwave trough will move northeastward across the Northeast on Wednesday. A moist airmass will be in place from the Mid-Atlantic into western New England where surface dewpoints should reach the mid to upper 60s F. As surface temperatures warm during the day, the airmass will become moderately unstable. Thunderstorms will develop in the higher terrain of the central and northern Appalachians, with this activity spreading eastward into the lower elevations during the afternoon. The moderate instability combined with steep low-level lapse rates will make strong wind gusts possible with the better organized multicell line segments. The threat should be concentrated during the mid to late afternoon when instability will be maximized. ..Broyles.. 07/13/2021 Read more LIVE: spc.noaa.gov
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