(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 040938
SPC AC 040938
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0338 AM CST Sat Feb 04 2017
Valid 071200Z - 121200Z
Model differences/uncertainty persist at this time, with respect to
evolution of the large surface storm system to move across the
eastern third of the U.S. Day 4/Tuesday. However a somewhat more
consistent depiction of major features within the ECMWF and GFS
permits what appears to be a reasonable ability to highlight a 15%
severe risk area from roughly the mid Ohio Valley southward into the
central Gulf coastal region. Within this area, somewhat modest but
sufficient CAPE development should occur ahead of a
strengthening/advancing cold front -- particularly from the Ohio
Valley southward -- to permit development of fairly robust updrafts
by afternoon. Though what appears likely to be a westerly component
to the low-level warm-sector flow field should limit tornado
potential, large hail and locally damaging winds will be possible --
with potential for both rotating storms and lines/line segments.
Convection should eventually weaken overnight, especially over
northern parts of the risk area as storms move into a less-unstable
environment. Risk may linger farther south, as storms move into the
southern Appalachians overnight.
By Day 5/Wednesday, greater uncertainty exists, with the GFS
depicting the front to have moved off the Atlantic and Gulf coasts
by midday, while the ECMWF lingers a trailing, west-to-east portion
of the front over the Gulf Coast States/Carolinas through the
afternoon. Given these differences, will not highlight a risk area
at this time for Day 5.
Risk appears minimal for Day 6, but potential for convection could
increase into the central U.S. Day 7 and into the East Day 8 as the
next storm system shifts out of the Rockies. Model differences are
substantial enough with respect to the details, however, that no
risk areas will be considered at this time.
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