Day 4-8 Severe Weather Outlook Issued on Dec 10, 2020
Updated: Thu Dec 10 09:37:02 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
Sun, Dec 13, 2020 - Mon, Dec 14, 2020
D7
Wed, Dec 16, 2020 - Thu, Dec 17, 2020
D5
Mon, Dec 14, 2020 - Tue, Dec 15, 2020
D8
Thu, Dec 17, 2020 - Fri, Dec 18, 2020
D6
Tue, Dec 15, 2020 - Wed, Dec 16, 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 100935
SPC AC 100935
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0335 AM CST Thu Dec 10 2020
Valid 131200Z - 181200Z
...DISCUSSION...
A progressive/moderate amplitude flow field aloft is progged across
the U.S. through Day 8, with medium-range models in reasonably good
agreement through Day 6 (Tuesday Dec. 15), with respect to
synoptic-scale evolution.
During this first three days of the period, low-amplitude troughing
-- rotating around the eastern fringe of a large northern Canada
polar vortex -- is forecast to gradually depart northeastward/away
from the northeastern states. Meanwhile, a second short-wave trough
-- initially over the Plains -- is forecast to move quickly eastward
across the Southeast Day 4 (Sunday Dec. 13) and then off the
Atlantic Coast through the first half of Day 5. This feature will
be followed by the next in a series of troughs, which will move
inland over the West Day 4, across the Intermountain region and
eventually into the Plains through Day 5, and then eastward to the
Mississippi Valley region through Day 6.
Both of these two, aforementioned troughs will be accompanied by
associated surface cyclogenesis. However, at this time it appears
that a cool/stable boundary layer will remain across the southern
Plains/Southeast, and thus the primary surface low tending to evolve
just offshore of the Gulf Coast -- along the main west-to-east zone
of baroclinicity (separating the cool continental air from the Gulf
airmass).
Given this evolution, any severe weather potential would appear to
be limited to the Florida Peninsula, and that risk appears too low
at this time to warrant any introduction of severe-weather
probabilities.
..Goss.. 12/10/2020
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