851
FXUS63 KUNR 200822
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
222 AM MDT Sat Jul 20 2024

.KEY MESSAGES...

- Isolated thunderstorms possible through Monday with near average
  temperatures.

- Haze smoke filled skies from Canadian fires

- Hot and dry middle to end of the week with elevated/critical
  fire weather conditions possible

&&

.DISCUSSION...(Today Through Friday)
Issued at 139 AM MDT Sat Jul 20 2024

Current surface map places weak high pressure across the Northern
Plains. A few mid clouds linger around the Black Hills with some
patchy fog developing in south central South Dakota. Upper level
ridge across the Intermountain West into the Canadian Rockies
remains in place through Monday with relatively weak north-
northwest flow across the Northern Plains. Steep low/mid level
lapse rates and residual low level moisture will provide a bit of
buoyancy across the area today. Weak impulse crossing the area
late today/tonight should bring some isolated thunderstorms. A
strong storm or two is possible over the southern Black Hills
where low level convergence/upslope flow is maximized. Similar
setup on Sunday with another impulse crossing the area. Weak
shear should limit severe weather threat. Visible Satellite from
yesterday afternoon shows extensive smoke filled skies across
Central Canada into the Northern Plains. With the north-northwest
flow aloft, the hazy skies will continue across the area.

Upper trough moves into the Pacific Northwest early in the coming
week, nudging the upper ridge eastward into the Northern Plains.
Low level thermal ridge spreads into the Northern Plains bringing
hot temperatures for the last half of the week. Ridge breaks down
late in the week, with potential for cold front late in the
forecast period. On the plains, LREF is showing areas with 30-50%
probability of temperatures >100F Thursday/Friday.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 912 PM MDT Fri Jul 19 2024

Mainly VFR conditions are expected through Saturday. The
exceptions will be near isolated thunderstorms overnight with
brief MVFR visibility, and isolated to scattered thunderstorms
Saturday afternoon/evening with brief MVFR conditions. There is
also a low probability of early morning fog in central SD.

&&

.FIRE WEATHER...
Issued At 139 AM MDT Sat Jul 20 2024

Warm and dry conditions continue through the forecast period. An
upper level ridge will bring hot temperatures by mid week. the upper
ridge breaks down Thursday/Friday with cold front moving through
Friday...with some uncertainty as to the timing of the cold
front. However, pre-frontal environment will be hot and dry with
some locally windy conditions possible. This will result in
elevated to critical fire weather conditions, especially across
northeastern Wyoming and far western South Dakota. Temperatures
ahead of the front will be in the 90s to around 100. LREF is
giving 50-90% probability of relative humidity less than 15%
across northeastern Wyoming and far western South Dakota with
30-50% probability of wind gusts greater than 25 mph on Thursday.
The Hot-Dry-Windy Index ensemble members suggest that there`s
about a 30% chance of exceeding the 90th percentile in the pre-
frontal environment.

&&

&&

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

$$

DISCUSSION/KEY MESSAGES...7
AVIATION...Johnson
FIRE WEATHER...7