870
ACUS48 KWNS 190850
SWOD48
SPC AC 190849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Sun May 19 2024

Valid 221200Z - 271200Z

...DISCUSSION...
...Day 4/Wed - Southern Plains to the Ohio Valley...

An upper low over the Upper Midwest will develop east/northeast
across the Great Lakes and Ontario on Wednesday. A broad area of
enhanced mid/upper southwesterly flow will persist across the
region. At the surface, strong low pressure over MN/WI will occlude
and slowly pivot north/northeast into Ontario. A cold front will
shift east across Lower MI/IL/IN, while the southern extent of this
boundary stalls, or returns a bit north from southern MO into
OK/northwest TX. Convection may be ongoing Wednesday morning along
the cold front, with destabilization ahead of the boundary across
the Ohio Valley occurring during the day. Further south, convective
evolution is more uncertain. However, a very moist and unstable
airmass is expected. Thunderstorms may be ongoing during the morning
and persist as an MCS through the afternoon, or convection may
develop along a surface dryline or residual outflow. While some
uncertainty remains in details, a corridor of severe potential
appears likely given the presence of a surface boundary, sufficient
vertical shear, and a moist/unstable boundary layer.

...Day 5/Thu - Southern Plains/ArkLaTex and the central
Appalachians/Mid-Atlantic vicinity...

A subtle upper shortwave impulse is forecast to eject from the
southern Rockies/northern Mexico toward the Mid-South vicinity on
Thursday. As this occurs, a surface dryline will surge east,
becoming positioned from near the OK/TX border southward into
central TX by evening. A very moist and unstable airmass will be in
place ahead of the dryline and convection is likely. With time an
MCS may develop and move southeast across the risk area during the
evening hours.

Meanwhile an upper low over Quebec and attendant trough will
overspread much of the northeastern U.S. on Thursday. A surface cold
front is expected to develop southeast across the area and a line of
thunderstorms may pose some severe risk to the region. Confidence in
the location of 15 percent severe coverage is low, precluding
probabilities at this time.

...Days 6-8/Fri-Sun...

Lower-amplitude and generally weaker flow is expected across much of
the CONUS on Friday and Saturday. A seasonally moist airmass will
persist across the southern Plains to the Mid-MS Valley during this
time, and a weak shortwave impulse migrating through westerly flow
aloft may be a focus for strong to severe storms across parts of the
Plains/MO Valley. However, spread among guidance is fairly large and
confidence is low.

By the end of the period on Sunday, some guidance suggests a strong
upper shortwave trough will eject into the southern Plains. However,
guidance varies in the timing of this feature (some on Saturday,
some on Sunday) as well as in the strength of the trough, resulting
in low predictability.

..Leitman.. 05/19/2024