Day 4-8 Severe Weather Outlook Issued on Aug 22, 2020
Updated: Sat Aug 22 09:01:02 UTC 2020
Day 4 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
15 %
225,504
76,000,358
New York, NY...Philadelphia, PA...Detroit, MI...Baltimore, MD...Boston, MA...
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
Tue, Aug 25, 2020 - Wed, Aug 26, 2020
D7
Fri, Aug 28, 2020 - Sat, Aug 29, 2020
D5
Wed, Aug 26, 2020 - Thu, Aug 27, 2020
D8
Sat, Aug 29, 2020 - Sun, Aug 30, 2020
D6
Thu, Aug 27, 2020 - Fri, Aug 28, 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 220859
SPC AC 220859
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Sat Aug 22 2020
Valid 251200Z - 301200Z
...DISCUSSION...
Medium-range models are relatively consistent in depicting a surface
cold-frontal advance across the Northeast Day 4/Tuesday, as
upper-level troughing amplifies as it moves across eastern Canada
and the adjacent northeastern CONUS. A strong deep-layer wind field
accompanying the strengthening upper system, and at least modest
destabilization ahead of the front from New England south to the
central Appalachians and the Mid Atlantic suggests widespread storms
and associated severe risk -- mainly in the form of damaging winds.
On Day 5/Wednesday, models depict a somewhat subtle short-wave
trough moving across the north-central U.S., cresting the broad
ridge over central portions of the country. In response, a low is
expected to evolve along trailing portions of the eastern U.S. cold
front over the Dakotas region. With some retreat of the cold front
northward into the Great Lakes ahead of this low, some
war-advection-induced thunderstorm development is expected -- mainly
during the evening, within a region of ample deep-layer shear.
Isolated severe risk would appear to be possible, but will refrain
from an areal inclusion at this time.
Beyond Day 5, uncertainty increases. Extratropical remnants of
Marco and Laura will likely be moving into the central U.S., though
differences in timing/location of these systems complicate
synoptic-scale pattern evolution. As such, no areal highlights for
severe-weather potential will be included beyond Day 5 at this time.
..Goss.. 08/22/2020
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