576
FXUS63 KUNR 190521
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1121 PM MDT Wed Sep 18 2024

.KEY MESSAGES...

- Very windy conditions will continue over northwestern South
  Dakota tonight into early Thursday afternoon.
- Elevated fire weather conditions due to low RH Friday
- Cooler this weekend

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 221 PM MDT Wed Sep 18 2024

The vertically stacked low pressure system currently over eastern
Montana will continue to drift to the northeast tonight and on
Thursday.

While the rest of the area will winds decreasing some this
evening, very windy conditions will continue over northwestern
South Dakota tonight into early Thursday afternoon due to the
tight surface pressure gradient nearer the low pressure system to
the north of the forecast area. Subsidence and momentum transfer
associated with LL cold advection and 850mb winds up to 45kts
indicated that surface winds may gust to 40-50 mph. Have expanded
the Wind Advisory in time and area over northwestern South Dakota
to account.

Moisture rotating around the back side of the upper low will
continue to bring some low chances for precipitation over parts of
northeastern Wyoming and northwestern South Dakota through this
evening.

On Thursday, the surface pressure gradient will slowly slacken as
the stacked low continues to move farther away. Slightly cooler
temperatures are expected. On Friday, warm air advection will
support summery MaxTs with a few spots approaching 90F. Over the
weekend into early next week, progressive west/northwest flow
supports a series of waves and fronts. First front moves through
Friday night with noticeably cooler temperatures for the weekend.
Moisture chances remain low with main moisture-laden upper low
passing south of the CWA. Confidence is low with substantial
ensemble guidance uncertainty. Chance of >0.25" QPF over the
weekend <40% over southeast half of the CWA and <20% over the
northwest half. Thus, lowish PoPs scattered about for the long
term forecast.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 1121 PM MDT Wed Sep 18 2024

VFR conditions are expected through the forecast period. Gusty
west-northwest winds will persist tonight into Thursday,
especially from far northeast WY to northwest SD. A few light
showers are expected tonight into early Thursday from far
northeast WY to far northwest SD.

&&

.FIRE WEATHER...
Issued At 221 PM MDT Wed Sep 18 2024

Red Flag conditions over parts of western South Dakota due to
gusty southwest winds and low relative humidity, will improve as
temperatures cool and winds decrease this evening. Some relief
expected Thursday, but elevated fire weather conditions will
return Friday with MinRH 15-30%.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 3 PM MDT Thursday for SDZ001-002-012>014-025-
     072-073-078.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...10
AVIATION...26
FIRE WEATHER...10