Day 4-8 Severe Weather Outlook Issued on Dec 6, 2020
Updated: Sun Dec 6 08:55:03 UTC 2020
Day 4 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 5 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 6 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 7 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 8 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
D4
Wed, Dec 09, 2020 - Thu, Dec 10, 2020
D7
Sat, Dec 12, 2020 - Sun, Dec 13, 2020
D5
Thu, Dec 10, 2020 - Fri, Dec 11, 2020
D8
Sun, Dec 13, 2020 - Mon, Dec 14, 2020
D6
Fri, Dec 11, 2020 - Sat, Dec 12, 2020
(All days are valid from 12 UTC - 12 UTC the following day)
Note: A severe weather area depicted in the Day 4-8 period indicates 15%, 30% or higher probability for severe thunderstorms within 25 miles of any point.
PREDICTABILITY TOO LOW is used to indicate severe storms may be possible based on some model scenarios. However, the location or occurrence of severe storms are in doubt due to: 1) large differences in the deterministic model solutions, 2) large spread in the ensemble guidance, and/or 3) minimal run-to-run continuity.
POTENTIAL TOO LOW means the threat for a regional area of organized severe storms appears unlikely (i.e., less than 15%) for the forecast day.
Forecast Discussion
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 060853
SPC AC 060853
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0253 AM CST Sun Dec 06 2020
Valid 091200Z - 141200Z
...DISCUSSION...
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.
..Leitman.. 12/06/2020
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