035
FXUS63 KUNR 180905
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
205 AM MST Thu Dec 18 2025

.KEY MESSAGES...

- High fire danger today due to dry conditions and strong winds.

- Very strong northwest winds will decrease through the day today.

- Colder temperatures today and Saturday, but near average for mid-
  December. Otherwise, above average temperatures through
  Christmas.

- Light snow ends this morning. Next chance for light rain/snow
  will be Friday night into Saturday.

&&

.DISCUSSION...(Today Through Wednesday)
Issued at 204 AM MST Thu Dec 18 2025

Several wind gusts over 80 mph have been reported so far, with the
highest gust of 100 mph being reported at the Mud Butte RWIS. These
strong winds will continue as the strong cold front pushes through
the area.

08Z analysis has a stacked low over western North Dakota with water
vapor imagery clearly showing the dry air associated with the cold
front extending from North Dakota through Perkins, Meade and Butte
Counties into the Black Hills. Surface 3-hr pressure rises of 9 to
12 mb have already been reported over eastern Montana and are being
seen behind the front.

Models seem to be in overall good agreement with this system,
indicating 80-100 kt winds between 850-700 mb and 6 to 9+ mb
pressure rises behind the secondary/arctic front. The strongest
winds are expected between now and 16Z today. Winds will diminish
from west to east today.

Along with the wind, there are some light snow showers and upslope
snow behind the front. Froude numbers indicate the majority of the
snow will be before 12Z, with snow ending in most locations by 15Z.

After the winds subside today, weak ridging over the Rockies allows
warm air advection to overspread the forecast area tonight. Models
indicate 850 temps will be 20-25C warmer on Friday than today.

Another clipper system moves through Friday night into Saturday
morning, with light rain/snow across northeast Wyoming, the Black
Hills, and northwest South Dakota. Highs Saturday will be cooler
behind the front and brisk northwest winds will be common across the
South Dakota Plains.

Looking ahead to next week, upper level ridging and southwest flow
will bring warm and dry conditions through Christmas Eve. The ridge
breaks down slightly for Christmas, but 850 temps remain above
freezing.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 948 PM MST Wed Dec 17 2025

A secondary cold front will bring stronger wind gusts from the
northwest reaching 40-70kts at times overnight into Thursday
morning. The front will have isolated snow showers, especially
over the northern Black Hills and far northwestern SD with local
MVFR/IFR conditions. Winds will quickly die down Thursday
afternoon with VFR conditions prevailing.

&&

.FIRE WEATHER...
Issued At 204 AM MST Thu Dec 18 2025

Very strong northwest winds and lower relative humidity (30-45%) will
support near-critical fire weather conditions today, even with
the colder temperatures. Wind gusts will decrease through the day
from west to east.

Temperatures will rebound on Friday as highs in the 50s to low 60s
are expected. Minimum relative humidity will range from 25-45%.
Pre-frontal, breezy southwest winds of 10 to 25 mph will combine
with the warm temperatures to create high fire danger.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...High Wind Warning until 11 AM MST this morning for SDZ001-002-
     012-013-025-041-072-073-078.
     High Wind Warning until 1 PM MST /2 PM CST/ this afternoon for
     SDZ014-026-030>032-042>044-046-047-049-074>077.
     High Wind Warning until 8 AM MST this morning for SDZ024-027>029.
WY...High Wind Warning until 11 AM MST this morning for WYZ059-060.
     High Wind Warning until 8 AM MST this morning for WYZ057.
     High Wind Warning until 5 AM MST early this morning for
     WYZ054>056-058.
&&

$$

DISCUSSION/KEY MESSAGES...Smith
AVIATION...Helgeson
FIRE WEATHER...Smith