Sunrise 5:47 AM   Sunset 7:53 PM Moonrise 12:00 AM   Moonset 7:37 AM

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FXUS63 KUNR 270408 AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1008 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 06Z TAFS Through 06Z Saturday Night)
Issued At 1005 PM MDT Fri Apr 26 2024

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. Isolated showers are also possible. Widespread MVFR/IFR conds are expected Sat night on the SD plains as a low pressure system crosses the region and rain develops.

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

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