Day 4-8 Severe Weather Outlook Issued on Oct 17, 2020
Updated: Sat Oct 17 08:54:02 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
Tue, Oct 20, 2020 - Wed, Oct 21, 2020
D7
Fri, Oct 23, 2020 - Sat, Oct 24, 2020
D5
Wed, Oct 21, 2020 - Thu, Oct 22, 2020
D8
Sat, Oct 24, 2020 - Sun, Oct 25, 2020
D6
Thu, Oct 22, 2020 - Fri, Oct 23, 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 170852
SPC AC 170852
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Sat Oct 17 2020
Valid 201200Z - 251200Z
...DISCUSSION...
...Tuesday/Day 4 and Wednesday/Day 5...
The medium-range models are in good agreement on Tuesday, moving an
upper-level trough across the central United States. A surface low
is forecast to develop in the southern Plains as moisture return
takes place across the south-central states. Thunderstorm
development will be possible Tuesday afternoon and evening along the
northern edge of the moist sector from the central Plains into the
mid Mississippi Valley. Although an isolated severe threat may
develop at that time, the models keep instability relatively weak
that far north suggesting the potential could remain marginal.
The moist airmass is forecast to continue advecting northward on
Wednesday with an east-to-west gradient of moisture setting up from
the lower Missouri Valley into the Ohio Valley. This will be the
favored corridor for thunderstorm development Wednesday afternoon
and evening. Although deep-layer shear will be strong along this
corridor, instability is forecast to remain weak suggesting any
severe threat would again be marginal.
...Thursday/Day 6 to Saturday/Day 8...
Model solutions diverge on Thursday with some advecting the moist
airmass into the Upper Midwest with others keeping the moist sector
further south. As an upper-level trough moves into the central and
northern Plains on Thursday, thunderstorm development will be
possible along the northern edge of the moist sector once again. A
large variance in the amount of forecast instability among the
solutions makes uncertainty substantial on Thursday. If enough
instability can develop along the northern edge of the moist sector,
then an isolated severe threat would be possible.
On Friday and Saturday, the models move a cold front southeastward
from the mid Mississippi Valley into the Southeast. Thunderstorm
development will be possible along the front each day. However, the
models are currently forecasting weak instability ahead of the
front. This combined with substantial uncertainty makes
predictability quite low late in the Day 4 to 8 period.
..Broyles.. 10/17/2020
CLICK TO GET WUUS48 PTSD48 PRODUCT
weather.gov 
@NWSSPC
