(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.
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 200828
SPC AC 200828
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0328 AM CDT Mon Mar 20 2017
Valid 231200Z - 281200Z
...Day 4 to Day 6...
The medium-range models begin the day 4 to 8 period with an
upper-level ridge in the central U.S. and an upper-level trough over
Baja California. This system is forecast to move quickly
northeastward across the Desert Southwest and into the southern
Rockies on Thursday/Day 4. A dryline is forecast to setup in the
southern and central High Plains by late afternoon where isolated
severe thunderstorms will be possible into the evening. However,
will not add a severe threat area yet due to uncertainties
concerning the quality of moisture return and exact timing of
large-scale ascent entering the high Plains Thursday evening.
The dryline is forecast to sharpen on Friday/Day 5 and move eastward
across the southern Plains during the day. The best chance for
thunderstorm initiation would be in the late afternoon from
east-central Oklahoma south southwestward into the north-central to
northeast Texas. The ECMWF and GFS solutions are in good agreement
with this scenario and the models provide support for the idea of a
line of thunderstorms organizing into a wind producing linear MCS.
If this where to occur based on the timing of the models, a line of
storms would move east southeastward across the Arklatex Friday
evening, into the lower Mississippi Valley overnight crossing the
central Gulf Coast States during day on Saturday/Day 6. Based on
this scenario, will maintain a 15 percent contour from eastern parts
of the southern Plains into the Arklatex. Will expand this area
eastward into the lower Mississippi Valley and add a new 15 percent
contour in the central to eastern Gulf Coast States for Day 6.
...Day 7 to Day 8...
On Sunday/Day 7 and Monday/Day 8, large differences exist between
the ECMWF and GFS solutions. The ECMWF emphasizes the development of
a negatively tilted upper-level trough in the southern and central
Plains while the GFS emphasizes the upper-level trough just upstream
from the Carolinas. A severe threat could develop ahead of either of
these two systems. However, due to large model differences,
uncertainty is too great to warrant adding a 15 percent area late in
the forecast period.
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