SPC Jul 27, 2024 1730 UTC Day 2 Convective Outlook

[NorthGeorgiaWX]

SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1223 PM CDT Sat Jul 27 2024

Valid 281200Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE CENTRAL AND NORTHERN PLAINS...

...SUMMARY...
Scattered severe thunderstorms are expected across portions of the
central/northern Plains on Sunday.

...Synopsis...
The overall synoptic regime is forecast to largely remain stagnant
over the next 24-48 hours with persistent mean west to southwesterly
upper-level flow across much of the central and western CONUS.
Multiple mid-level impulses are noted in early-afternoon water-vapor
imagery across the western U.S., but the most influential feature
for Sunday's severe weather potential appears to be a weakening
shortwave trough migrating across the northern Great Basin. This
feature should phase with a second shortwave trough entering the
Pacific Northwest as they eject into the central and northern Plains
by Sunday afternoon. As this occurs, strengthening flow aloft
combined with modest broad scale ascent ahead of the mean mid-level
trough axis should result in a deepening lee surface trough along
the High Plains, with the potential for two surface cyclones across
western SD and western NE. The surface trough will likely act as a
dryline by late afternoon as it shifts east and impinges on the
western periphery of a plume of 60-70 F dewpoints currently in place
over the Plains. Thunderstorm development will likely be focused
along this boundary as well as in the vicinity of the surface lows
and along a residual cold front across the upper MS River Valley
region. 

...South Dakota into Minnesota...
Consensus among latest model solutions suggests that confidence
remains relatively high in the development of an organized surface
low across western SD by tomorrow afternoon. A trailing cold front
will likely stall by late morning with some northward advancement as
a warm front by mid/late afternoon across central to northern SD.
Initially high-based thunderstorms developing in the vicinity of the
deepening low or along the sharpening surface trough/dryline will
likely pose a severe wind threat as they develop within a relatively
dry/well-mixed environment. Intensification appears probable as they
migrate east into the higher theta-e air mass where MLCAPE is
forecast to be upwards of 2000-3000 J/kg. While mid-level flow will
not be overly strong (around 30 knots), east/southeasterly low-level
flow will likely result in effective bulk shear values between 30-40
knots. Consequently, a few supercells appear possible with an
attendant risk for large hail. Low-level veering within the warm
frontal zone appears sufficient to support a tornado concern, but
this potential may be highly conditional on realizing a relatively
discrete storm mode without undercutting outflow. Additional
thunderstorm development is anticipated along the residual frontal
boundary across southeast ND into northern MN, but displacement from
better flow aloft should limit the potential for long-lived
organized convection.

Some solutions - most notable the 12 UTC HRRR - hint at the
development of a mature MCS along the warm front that propagates
into the upper MS River Valley by early morning Monday. This
scenario appears plausible given an adequate environmental parameter
space and a favorable deep-layer flow orientation with the warm
front; however, forcing for ascent is expected to be relatively weak
given the low-amplitude nature of the upper wave with low confidence
in convective coverage. Furthermore, the potential MCS should be
relatively displaced from the low-level jet axis further to the
southeast. Ensemble guidance also suggests this is a low-probability
scenario with only weak/non-coherent signals in QPF, UH, and updraft
probability fields. 

...Nebraska into Kansas...
A similar convective environment is expected to be in place further
south into NE and KS by Sunday afternoon. Forcing along the surface
trough and in the vicinity of a secondary surface low over
west/southwest NE should support a few initially discrete,
high-based cells with the potential for upscale growth into one or
more organized clusters by early evening. Ensemble consensus shows a
similar signal for convective coverage and severe wind potential
across portions of southern NE into far northern KS as compared to
portions of SD. As such, 15% wind probabilities have been extended
south to the general vicinity of the secondary surface low to
account for this potential.

..Moore.. 07/27/2024

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