LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0739 AM CDT Sat Sep 02 2023
Valid 021300Z - 031200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Organized severe thunderstorms are not expected.
...Synopsis/Discussion...
In mid/upper levels, the main belt of westerlies will remain largely
confined to Canada and the Great Lakes/Northeast this period --
well-removed from optimal low-level moisture still relegated to
portions of the Gulf Coast States and southward. South of those
westerlies, a split, blocky pattern will persist, with minor
adjustments from yesterday. Although a high aloft will remain over
the south-central Great Plains, a small, cut-off cyclone now
centered near SHV should meander west-northwestward toward the Red
River region north of DFW. General thunderstorms will remain
possible to its southeast, over much of the Gulf Coast region, amid
difluent flow, lift near residual low-level frontal zone across the
region, and rich low-level moisture.
Elsewhere, a prominent, cut-off, mid/upper-level cyclone is apparent
in moisture-channel imagery over much of OR, CA and NV, with a
center near Cape Mendocino. For most of the period, the cyclone
will meander near its present position, while weakening very
gradually. Near the end of the period, as a northern-stream
shortwave trough moves quickly southeastward down the BC Coast, the
cyclone will begin to open up and shift slightly eastward, heralding
its substantial deamplification and acceleration on day 2.
...Lower Colorado River Valley to Great Basin....
Widely scattered to scattered thunderstorms are expected through
this evening over a large area of the interior West, likely peaking
in coverage late this afternoon. This potential will be associated
largely with a broad plume of nearly southerly deep-layer flow east
of the cyclone, and associated moisture transport and warm
advection. Two areas of interest exist with conditional potential
for isolated severe gusts or hail, but not organized/focused enough
for an outlook area this cycle:
1. Lower Colorado and Imperial Valley regions, where the greatest
buoyancy will exist amid strong diabatic heating and rich low-level
moisture (upper 60s to mid 70s F lower-elevation surface dewpoints).
Those factors, along with a deep troposphere, will yield negligible
MLCINH beneath 2000-3000 J/kg MLCAPE and strongly difluent mid/
upper-level flow southeast of the coastal cyclone. However, deep-
layer flow will be weak, along with vertical shear, limiting
organization. Strong pulse downdrafts may occur from the most
intense multicell convection.
2. Central/northern NV, where afternoon heating, moisture and
instability will be more limited than farther south, but still
perhaps adequate for some surface-based convection. Some of the
resulting thunderstorms may exhibit at least transient supercellular
characteristics in closer proximity to the eastern part of the
cyclonically enhanced flow field aloft, where 35-45 kt effective-
shear magnitudes and 500-800 J/kg MLCAPE are possible. Lack of
greater buoyancy for that shear suggests that any severe threat
remains too isolated and conditional for an outlook area.
..Edwards/Leitman.. 09/02/2023
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