Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 240849
SWOD48
SPC AC 240847

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0347 AM CDT Fri Mar 24 2017

Valid 271200Z - 011200Z

...DISCUSSION...
...Monday/Day 4...
The medium range models begin the day 4 to 8 period with an
upper-level trough across eastern parts of the southern Plains. This
upper-level trough moves into the lower Mississippi Valley on
Monday/Day 4 with an axis of instability located just ahead of the
trough oriented along the Mississippi River by midday. The ECMWF and
GFS solutions suggest that scattered thunderstorms will develop
along the instability corridor during the early afternoon. Although
uncertainties exist concerning instability, it appears that
deep-layer shear associated with a belt of stronger mid-level flow,
rounding the base of the trough, will be sufficient for an isolated
severe threat. Will continue with an area including eastern
Arkansas, much of central and northern Mississippi into southwest
Tennessee.

...Tuesday/Day 5 and Wednesday/Day 6...
The ECMWF and GFS solutions continue in fairly good agreement on
Tuesday/Day 5 with an upper-level low forecast to develop over the
southern Rockies. Both models advect low-level moisture into the
southern Plains with a dryline developing during the day on Tuesday.
Although afternoon convection along the dryline may remain isolated,
the window for convective initiation should be extended into the
evening and overnight period when convective coverage should
increase as the upper-level system approaches. Moderate instability
along with strong deep-layer shear is forecast to be in place across
west-central Texas and far southern Oklahoma suggesting a severe
threat will be possible. A well-developed low-level jet late Tuesday
night into Wednesday/Day 6 should maintain an organized severe
threat. It appears that large hail, wind damage and a tornado threat
will be possible as a linear MCS organizes and moves across the
southern Plains from Tuesday evening into Wednesday afternoon. The
models are in good enough agreement to add a 15 percent contour in
west-central Texas and far southern Oklahoma for Tuesday and from
eastern parts of the southern Plains into the Arklatex for
Wednesday.

...Thursday/Day 7 and Friday/Day 8...
The ECMWF and GFS move the upper-level trough into the lower
Mississippi Valley on Thursday/Day 7 with a corridor of instability
located in the central Gulf Coast region. This combined with
moderate to strong deep-layer shear could support a severe threat
during the day on Thursday. The models move the upper-level trough
into the southern Appalachians on Friday/Day 8 where an isolated
severe threat would be possible. However, will not issue a severe
threat area on Thursday or Friday due to uncertainties concerning
the evolution of the upper-level trough and instability.

..Broyles.. 03/24/2017


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