Day 4-8 Outlook

Day 4-8 Outlook Image

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0253 AM CST Sun Dec 06 2020

Valid 091200Z - 141200Z

An upper ridge will spread eastward across the Plains toward the MS
River on Day 4/Wed as a shortwave trough digs south and east across
the Pacific Northwest and northern Rockies. At the same time, the
persistent cut-off upper low off the southern CA/northern Baja coast
will develop eastward along the international border. This will
bring increasing chances for rain and perhaps a few thunderstorms to
portions of the southwestern U.S. Wednesday and Thursday. 

By Day 5/Thu, the northern Rockies trough and the southwestern upper
low will merge into a larger-scale trough, and eject eastward from
the Rockies into the Plains by early Day 6/Fri. In response, lee
cyclogenesis is forecast over the southern/central Plains. Strong
southwesterly deep layer flow will overspread the southern Plains
into the mid MS Valley late Thursday, and southerly Gulf return flow
will develop across the south-central U.S. As this system shifts
eastward through Day 6/Fri and Day 7/Sat, thunderstorm potential
will increase across portions of the southern Plains into the lower
MS Valley, and perhaps as far north as the mid-MS/lower OH Valleys.
However, severe potential is uncertain. The quality of low level
moisture return could be limited to a small portion of the Sabine
and lower MS Valleys, and may be ill-timed with the passage of the
upper trough and surface cold front. Additionally, medium range
guidance varies in the intensity of the developing surface cyclone,
and in timing of the eastward-advancing cold front from the Plains
into the Midwest. As such, predictability is too low to include any
severe probabilities.

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