014
FXUS63 KUNR 020018
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
618 PM MDT Mon Jul 1 2024

.KEY MESSAGES...

-Severe storms this afternoon and evening

-Daily chances for showers and thunderstorms

-Temperatures near average Wednesday, and slightly below average
the rest of the week

-Warmer and drier this weekend

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 129 PM MDT Mon Jul 1 2024

Upper level analysis has a trough over the Intermountain West with a
ridge over the Central Great Plains, resulting in southwest flow
over the forecast area. Water vapor imagery has a shortwave over
southern Wyoming that is moving into the area. At the surface, there
is a surface low over Lake Oahe and a secondary low near Casper. A
cold front connects to two surface lows, with the front oriented
along the Cheyenne River. Temperatures are currently in the 80s
ahead of the front, with 70s behind the front. Dewpoints are in the
60s.

For this afternoon, shortwave energy will interact with the boundary
and daytime heating to initiate storms. Strong forcing should allow
storms to grow upscale into isolated supercells and convective line
segments, supporting large hail and damaging winds given bulk shear of
35-45 kts. CAPE will be somewhat limited in western SD, but dynamic
forcing should make up for the lack of CAPE. Deeper moisture and
better CAPE will reside over central SD where storms will likely
intensify as they shift east in the late afternoon. Further west
across Wyoming, plenty of shear will be in place for very isolated
supercells, but given conditional nature of convection and limited
CAPE, any severe threat will be isolated. Storms move through pretty
quick this evening and expect they would be out of the area by 02Z.

The surface front will move south of the forecast area tonight, but
another impulse could support shower development along and north of
the front, across the southwest third of the area. Daytime heating
on Tuesday combined with the unstable environment, could lead to
some showers or storms during the afternoon. Temperatures will be
cooler though, with highs slightly below average in the low 70s to
low 80s.

On Wednesday, the upper flow starts our more more zonal, but the
main upper trough starts to dig over Montana and Wyoming ejecting an
impulse across the forecast area in the afternoon. Return flow at the
surface with moisture pooling ahead of the wave will increase
chances for strong to severe storms given sufficient shear
profiles.

The upper trough will linger over the area on Thursday the 4th, with
cool conditions and chances for showers with a cold pool aloft. CAPE
will be limited, hence not expecting any severe weather. Things will
then dry out into the weekend with warmer temperatures.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 616 PM MDT Mon Jul 1 2024

Isolated thunderstorms are possible tonight through Tuesday.
Outside of thunderstorms, VFR conditions will prevail through the
forecast period.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...MLS
AVIATION...13