SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1120 PM CST Thu Jan 28 2021 Valid 291200Z - 301200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for severe thunderstorm appears negligible across the U.S. today and tonight. ...Synopsis... The upper trough near the Pacific coast this morning will intensify and develop eastward toward the southwestern U.S. through the first half of the period, becoming oriented over the southern/central High Plains by Saturday morning. Isolated thunderstorms may be ongoing across parts of southern California at the beginning of the period, near the exit region of an intense mid/upper jet streak at the base of the trough. Cold temperatures aloft will support steep lapse rates, resulting in a few hundred J/kg MUCAPE. These conditions will spread eastward across the lower Colorado Valley and lower desserts of southern AZ during the afternoon and evening and isolated thunderstorms may continue as midlevel moistening allows for continued weak instability. Further east, height falls ahead of the upper trough will result in surface cyclogenesis over the central/southern Plains late in the period. Southerly low level return flow will bring modest increases in near-surface moisture across parts of the southern Plains. However, this moisture will remain shallow and a midlevel warm/dry layer will persist between 850-650 mb. This will prevent surface-based convection from developing, but forecast soundings show steep midlevel lapse rates and a deep, saturated layer above 650mb. As stronger ascent shifts eastward into the Plains toward the end of the period, isolated elevated thunderstorms are possible. ..Leitman.. 01/29/2021
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