SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0655 AM CST Tue Dec 22 2020 Valid 221300Z - 231200Z ...NO THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms are not expected through tonight. ...Synopsis/Discussion... A high-amplitude and progressive synoptic pattern will shift eastward over the CONUS this period, behind a trough exiting the Atlantic Coast. A synoptic trough, initially evident in moisture- channel imagery from the Canadian Rockies across the inland Pacific Northwest to northeastern/central CA -- will both amplify and broaden its wavelength through the period. By 12Z, a full-latitude trough is expected from central Canada across the Great Plains to northern MX, with cyclonic flow at 500 mb from the Great Basin to the Mississippi Valley. At the surface, an area of low pressure was analyzed near the MT/AB border, with cold front southwestward across southern ID to northern CA. By 00Z the surface cyclone should move/redevelop eastward to the Dakotas, with cold front southwestward toward the Four Corners area. By 12Z tomorrow, the front should extend from a deepening low over MN across IA, northwestern MO, southeastern KS, southwestern OK, the TX South Plains, and east-central NM. The cold front related to the departing eastern CONUS trough is well offshore from the Atlantic Coast, and has crossed the Gulf. Airmass modification behind this front is underway, but will remain far from mature through the period. Modest moisture return through tonight will result in 50s F surface dew points into portions of OK, and 60s in central/south TX. However, the air mass encountered by the cold front before 12Z should be too incompletely modified, and thermally stable, to support thunderstorm formation. ..Edwards.. 12/22/2020
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