666
ACUS48 KWNS 170900
SWOD48
SPC AC 170858

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0358 AM CDT Fri May 17 2024

Valid 201200Z - 251200Z

...DISCUSSION...
...Day 4/Mon-Day 5/Tue -- Central/Southern Plains to the Midwest...

Increasing southwesterly deep-layer flow will overspread much of the
southern/central Plains by Monday afternoon/evening ahead of a
deepening upper trough across the western U.S. Subtle lead shortwave
impulses will eject across the KS/NE vicinity after 21-00z Monday
night as a surface front drops southeast across the northern Plains.
Rich boundary-layer moisture will spread northward across OK/KS as
at least weak surface cyclogenesis occurs over the central High
Plains. This overall pattern will support some severe potential
somewhere from NE/KS/OK to the Lower MO Valley into early Tuesday.
However, uncertainty remains given the subtle nature of ejecting
shortwave impulses and the potential for ongoing convection Monday
morning, leaving some questions over smaller-scale details.
Nevertheless, enough consistency exists to introduce a 15 percent
severe probability for Monday evening/overnight ahead of the surface
front across portions of the central Plains vicinity. Given
uncertainty, this area may shift in the coming days.

On Tuesday, the upper trough is expected to eject east/northeast
across the Plains to the Mid/Upper MS Valley. A deepening surface
cyclone will lift northeast from KS to the Upper Midwest as the
trough ejects over the region, and a cold front will push
east/southeast. A very moist/unstable and favorably sheared
environment will exist from eastern KS/OK to the upper Great Lakes
ahead of the surface low and upper trough. Organized convection is
expected across a broad area. This area likely will change some in
coming days given mesoscale uncertainties tied to likely convection
in the Day 4/Mon time frame continuing into Day 5/Tue.

...Day 6/Wed -- Ohio Valley to the Mid-South...

By Wednesday the upper trough is forecast to lift northeast from the
Mid/Upper MS Valley to Ontario/Quebec. Large-scale ascent will
quickly shunt north of the international border. The surface cold
front is expected to become more diffuse as the surface cyclone also
shift north into Canada. Still, moderate deep-layer southwesterly
flow will overspread a moist boundary layer across the Ohio Valley,
and some severe potential may persist. Confidence is too low to
include probabilities at this time, but may be needed in subsequent
outlooks.

With southward extent into the Mid-South vicinity, some severe
potential could also persist given an expected moist/unstable
airmass and potentially ongoing morning MCS. However, upper-level
support will not be as favorable heading into the afternoon hours,
and confidence is too low for severe probabilities at this time.

...Days 7-8/Thu-Fri...

Forecast guidance is not in as good agreement by the end of the
forecast period. The overall pattern may become less amplified and
more quasi-zonal. However, some guidance does indicate at least some
weak shortwave impulses migrating through westerly flow,
particularly across the southern Plains vicinity. Trends will be
monitored as a potential area of interest could develop across
portions of the southern Plains around Day 7/Thu.

..Leitman.. 05/17/2024