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FXUS63 KUNR 071722 AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1022 AM MST Thu Dec 7 2023

KEY MESSAGES
218 AM MST Thu Dec 7 2023

- Gusty southwest winds today across parts of northeastern WY and southwestern SD.

- Gusty northwest winds developing later today across northwestern SD, continuing into Friday.

- Light precipitation today and Friday, resulting in a few inches of snow over the northern Black Hills by Friday evening.

DISCUSSION
(Today Through Wednesday)
Issued at 218 AM MST Thu Dec 7 2023

Upper level analysis shows ridging over the central states and a trough over the west coast. At the surface, low pressure is over northern MT, the surface trough stretches over the western Dakotas, and a cold front is approaching from the west.
Southwesterly winds are starting to become gusty across parts of northeastern WY, but the high winds over the southern Hills/foothills have not yet materialized. Temperatures across much of the CWA are still mild, especially across the downsloped areas, where there are some 50s at 2 AM.

Winds are still expected to increase this morning across northeastern WY and southwestern SD as the surface trough crosses the area. Based on forecast soundings and the potential for 50+ kt wind gusts to mix down, along with NBM 50th percentile showing wind gusts of 50+ kts today, have issued a High Wind Warning for parts of northeastern WY, and have also upgraded Fall River County to a Warning. As the surface low shifts into central ND this afternoon/evening, strong northwesterly winds will develop across northwestern SD, behind the first cold front. Have issued a Wind Advisory mainly for northwestern SD tonight, but included areas to the south as well, because winds there will increase Friday behind a secondary cold front. May need to expand the advisory in time and area later, but aimed to not complicate wind headlines more than they already are. Breezy to strong winds look to continue through Saturday.

Along with the cold fronts, some light precipitation is expected.
Light rain showers will be possible today, with some light snow in the Black Hills. As colder air moves in Friday, light snow will be possible across much of the CWA. Accumulations will be little to none on the plains; however, with Froude number between 1 and 2 Friday afternoon and evening over the northern Black Hills, 1 to 3 inches of snow will be possible. Breezy winds will result in some patchy blowing snow as well.

As for temperatures, today will be another mild day. Friday will be noticeably cooler, and then widespread 30s/40s for highs settle in for the weekend and early next week.

After this windy trough shifts eastward late this weekend, no significant weather systems are expected through early next week.
Expect dry conditions and lighter winds through Tuesday.

AVIATION
(For the 18Z TAFS Through 18Z Friday)
Issued At 1017 AM MST Thu Dec 7 2023

VFR conditions will continue for most places through the TAF period. The exception will be MVFR and local IFR conditions this afternoon and evening over the northern BLKHLS and parts of northeastern WY/northwestern SD as some rain and snow showers move across those areas. MVFR and local IFR conditions will again move into northwestern SD after 12z Friday, reaching into northeastern WY and the northern BLKHLS from 15-18z. In addition, gusty west- southwest winds will be found across much of the area today.
Winds will shift to the northwest this evening and continue to be gusty through the night.

FIRE WEATHER
Issued At 218 AM MST Thu Dec 7 2023

Today will be another mild day, with highs in the 50s and 60s.
Relative humidity will dip to around 25 to 35%. Strong west to southwest winds are expected today, especially across parts of northeastern WY and southwestern SD. Gusts of 50 to 60+ mph are expected, which will result in elevated fire weather conditions (and Very High to Extreme Fire Danger). Breezy to strong winds are expected again Friday into Saturday, although the temperatures will be cooler and the relative humidity will be slightly higher. Still, elevated fire weather conditions will continue with the strong winds.

UNR WATCHES/WARNINGS/ADVISORIES
SD...Wind Advisory from 2 PM this afternoon to 5 PM MST Friday for SDZ001-002-012-013-078.
Wind Advisory from 5 PM this afternoon to 5 PM MST Friday for SDZ014-031-032-043-073.
Wind Advisory until 5 PM MST /6 PM CST/ this afternoon for SDZ026-030-042-044-046-047-076-077.
High Wind Warning until 5 PM MST this afternoon for SDZ027-041- 075.
High Wind Warning until 11 AM MST this morning for SDZ028-029- 074.
WY...High Wind Warning until 5 PM MST this afternoon for WYZ055-058.

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