148
FXUS63 KUNR 262331
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
531 PM MDT Fri Apr 26 2024

.KEY MESSAGES...

- Showers and a few thunderstorms possible through the evening hours.

- After a brief lull tonight into Saturday morning, expect
  additional widespread showers to develop Saturday afternoon and
  evening. Heaviest rain expected from western SD into south-
  central SD.

- Cool and unsettled weather gives way to near seasonable
  temperatures with near daily chances of showers under active
  flow aloft.

&&

.DISCUSSION...(This Evening Through Friday)
Issued at 207 PM MDT Fri Apr 26 2024

Water vapor imagery shows prominent shortwave rotating through
central NE this afternoon with plentiful moisture/ascent
overspreading much of the Central and Northern Plains. Further
upstream, a second upper trough axis extends from the Pacific
NW into the desert SW. Surface low pressure is centered over
south-central NE with northerly winds across the forecast area. A
narrow tongue of theta-e rich air resides across far western SD into
the Black Hills where scattered showers/thunderstorms have developed
this afternoon. While the environment is not overly impressive,
sufficient upper level ascent coupled with MUCAPE ~250-750 J/kg will
support transient thunderstorms through the afternoon and evening
hours. A heavier band of rain extends from northern SD into
south-central SD along the northwestern periphery of the low. Showers
will taper off later this evening as the surface low lifts off to the
northeast tonight and shortwave ridging/subsidence overspreads the
forecast area.

After a brief lull late tonight through tomorrow morning, the
western trough will push through the Central Plains late Saturday
into Sunday, becoming centered immediately south of the forecast area
by 12z Sunday. While the best synoptic scale ascent will remain
south and east of the forecast area, sufficient lift and moisture
will be in place for widespread rain across western SD into
south-central SD Saturday afternoon through Sunday evening before
the system lifts into the Great Lakes early Monday. Ensembles
highlight a sharp cutoff in rain potential from NW SD south into
far SW SD, with 85-95% probability of >0.25" of QPF from areas
east and south of Rapid City and much lower probs near the WY/SD
border into NE WY. As temperatures fall below freezing across the
higher elevations of the Black Hills Saturday night, expect to see
some rain/snow mix, although snow accumulations will be light
(<1").

Temperatures will rebound to near-seasonable levels Monday through
next week, although active upper flow will persist with near daily
chances of rain showers. Instability looks muted through at least
the first half of the week, limiting thunderstorm potential although
prob >250 J/kg of SBCAPE increases next Thursday and Friday. The
most recent ensemble cluster analysis begins to diverge during
this period, however with two potential solutions for the latter
half of next week: 1) stronger ridging east of the CWA with SW
flow aloft -> warmer + greater storm chances or 2) more zonal
flow -> cooler/seasonable with best storm chances shunted south.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Saturday Evening)
Issued At 527 PM MDT Fri Apr 26 2024

Showers will taper off this evening. MVFR cigs will spread west
across the SD plains and into NE WY by Sat morning. MVFR cigs will
linger most of the day Sat on the SD plains, with some
improvement to VFR possible.

&&

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

$$

DISCUSSION/KEY MESSAGES...SE
AVIATION...JC