(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 240901
SPC AC 240901
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0401 AM CDT Wed May 24 2017
Valid 271200Z - 011200Z
Despite some differences on timing, latest GFS and ECMWF are
generally consistent in the low-amplitude mid-level flow evolving
into a broadly cyclonic flow regime at the beginning of the Day 4-8
time frame. A very moist air mass will be in place from the
central/southern Plains to the southeast states.
A strongly unstable air mass will exist south of a frontal boundary
that will likely extend from the southern Plains into the Ohio
Valley Saturday afternoon. The MCS expected to move across portions
of the central Plains on Day 3 may undergo diurnal intensification
on Saturday as it moves east to the north of the boundary in the
presence of strengthening mid-level flow and ascent with an
approaching impulse. Such a scenario casts some uncertainty on
downstream development as discrepancies are already noted with
latest guidance regarding the position of the front. Nevertheless,
it appears probable that additional development will occur near the
front during the afternoon from the Ozarks southwest across eastern
Oklahoma/northeast Texas, with more isolated development possible
along the dryline extending into southwest Texas. Given a strongly
sheared/unstable environment, supercell and linear storm modes are
anticipated with all severe hazards possible, though details will
depend on the evolution of the mesoscale influences with inherent
low predictability at this time. Expanded/higher severe
probabilities will likely be needed in subsequent outlooks.
A composite frontal boundary extending from the vicinity of the
Great Lakes into central/southern Texas will serve as the focus for
strong/severe thunderstorm development, with additional storms
possible near a warm front from the Great Lakes into the
mid-Atlantic region. Predictability regarding placement of 15
percent coverage areas remains too low for this outlook.
...Day 6/Monday and Beyond...
Thunderstorms will once again develop along a weakening frontal
boundary from New England south/west through Gulf Coast region and
south Texas. Some severe risk will exist, though with continued low
predictability at this extended time frame.
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