Severe Storm Outlook Narrative (AC)
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000
ACUS48 KWNS 270900
SWOD48
SPC AC 270859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Wed Mar 27 2024

Valid 301200Z - 041200Z

...DISCUSSION...
An upper trough/low should continue to move south-southeastward over
the western states on Day 4/Saturday. Over much of the central
CONUS, upper ridging should generally prevail, with a gradual
northward advance of low-level moisture across the southern Plains.
Although a plume of elevated instability should accompany this
moisture return, a cap is expected to suppress robust convective
development Saturday. On Day 5/Sunday, the upper trough/low over the
western CONUS should slowly advance eastward across the Southwest.
But, there are still some differences in various guidance with the
evolution of this trough/low. Some GEFS ensemble members show a
slower ejection, with a closed 500-mb isohypse remaining over the
West. Other members align more with the deterministic ECMWF is
showing a more open wave, but with a positive tilt into the
northern/central Plains. Another potentially complicating factor is
a northern-stream upper trough, which may phase with the
lower-latitude trough and help induce stronger cyclogenesis across
the mid MS Valley/Midwest around Day 6/Monday.

Even with these continued differences, it appears that severe
potential should gradually increase from Sunday into Monday across
parts of the southern/central Plains, mid MO into mid MS Valleys,
and perhaps also into the OH Valley/Midwest. For Sunday, some severe
potential may be focused across parts of MO into IL along and near a
sharpening surface warm front. Mid-level height tendencies look to
remain neutral through Sunday evening across this area, with
nebulous large-scale ascent. Even so, low-level warm advection may
help initially elevated convection to develop across MO in a
moderate instability and strong deep-layer shear environment. If
this occurs, then some severe threat may continue eastward into IL
through Sunday evening. At this point, too much uncertainty exists
regarding thunderstorm initiation and coverage to include a focused
15% severe area for Sunday.

A larger area of severe potential may be realized on Monday from
parts of the southern/central Plains into the mid MS and OH Valleys.
This will be largely dependent on the timing of ejection of the
upper trough over the Southwest, and whether it can phase any with a
northern-stream trough moving southeastward out of central Canada.
Regardless, a broad warm sector, with 60s surface dewpoints, should
be in place from TX/OK east of a dryline and northward to a warm
front located somewhere in the vicinity of the OH Valley. The exact
placement of these surface features remains rather uncertain Monday,
as does the potential strength and northeastward track of a surface
low across the mid MS and OH Valleys. Deep-layer shear appears
strong enough to support organized severe thunderstorms, and
consideration was given to adding a broad 15% severe area for
Monday. But, there still seems to be too much spread in possible
solutions with the upper trough to introduce an area yet.

Finally, some severe threat may continue on Day 7/Tuesday along and
ahead of a cold front moving across parts of the Southeast and
eastern states. But, predictability remains very low at this
extended time frame.

..Gleason.. 03/27/2024


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