Day 4-8 Severe Weather Outlook Issued on Aug 23, 2020
Updated: Sun Aug 23 08:56:03 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, Aug 26, 2020 - Thu, Aug 27, 2020
D7
Sat, Aug 29, 2020 - Sun, Aug 30, 2020
D5
Thu, Aug 27, 2020 - Fri, Aug 28, 2020
D8
Sun, Aug 30, 2020 - Mon, Aug 31, 2020
D6
Fri, Aug 28, 2020 - Sat, Aug 29, 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 230854
SPC AC 230854
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Sun Aug 23 2020
Valid 261200Z - 311200Z
...DISCUSSION...
Model-to-model forecast consistency between the GFS and ECMWF --
which appears reasonable at the start of the Day 4-8 period --
deteriorates with time beginning roughly Day 5, at least in part due
to differences with respect to the inland/extratropical evolution of
tropical system Laura. As such, forecast confidence/certainty
likewise decreases steadily with time.
Day 4/Wednesday, the fast belt of weakly anticyclonic westerly flow
will persist over the northern U.S., with small-scale/embedded
disturbances continuing to move through the fast flow field.
However, with these features depicted as being subtle/weak in the
models, any possible area or areas of 15% or greater severe weather
coverage/concentration is difficult to discern at this time.
Meanwhile, landfall of Laura is currently expected to occur Day 4,
though combination of track and intensity uncertainty precludes
highlighting a risk area at this time.
By Day 5/Thursday, model differences begin to increase. The GFS
shows a fairly substantial short-wave trough moving into the
north-central U.S., and corresponding surface response in the form
of cyclongenesis. As this low moves northeastward toward the Upper
Mississippi Valley Thursday night, an associated/southward advance
of a cold front across the northern Plains is depicted -- which
would likely be accompanied convective potential. However, the
short-wave trough -- and thus surface response -- remains notably
weaker in the ECMWF forecast.
Beyond Day 5, as remnants of Laura shift into the interior central
U.S., the pattern evolution becomes increasingly uncertain, such
that no risk areas will be delineated at this time, through the
forecast period.
..Goss.. 08/23/2020
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