SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0655 AM CST Tue Dec 22 2020

Valid 221300Z - 231200Z


Thunderstorms are not expected through tonight.

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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