(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 170735
SPC AC 170735
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0235 AM CDT Tue Jul 17 2018
Valid 201200Z - 251200Z
...DISCUSSION...
...Friday/Day 4 and Saturday/Day 5...
The medium-range models are in much better agreement early in the
Day 4 to 8 period. The ECMWF, GFS, Canadian and UKMET move an
upper-level trough across the mid Mississippi Valley on Friday and
show the moist sector in the base of the trough. This would imply
that moderate instability will be in place by Friday afternoon
across parts of Missouri and Arkansas extending eastward into
western parts of the Ohio and Tennessee Valleys. An isolated severe
threat would be possible Friday afternoon along the northern edge of
the strongest instability from near St. Louis, MO eastward to the
Cincinnati, OH area. For Saturday, the models move the upper-level
trough slowly eastward and again show the moist sector in the base
of the system. The models would suggest an isolated severe threat
will be possible across parts of the Ohio and Tennessee Valleys
Saturday afternoon. Any severe threat would be probably remain
marginal due to the relatively weak deep-layer shear forecast.
...Sunday/Day 6 to Tuesday/Day 8...
The models continue to move the upper-level trough slowly eastward
across the eastern U.S. from Sunday to Tuesday. Thunderstorms would
be possible each day from near the upper-level trough eastward
across the moist sector. For Sunday, the greatest potential for a
marginal severe threat would be in the central Appalachians. The
threat would shift eastward into the Mid-Atlantic on Monday and
appears likely to diminish by Tuesday as the upper-level trough
becomes less amplified. Also, a marginal severe threat can not be
ruled out in parts of the central and northern Plains from Sunday to
Tuesday but model spread is large and forecast uncertainty is high.
..Broyles.. 07/17/2018
CLICK TO GET WUUS48 PTSD48 PRODUCT
weather.gov 
@NWSSPC
