121
FXUS63 KUNR 161554
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
954 AM MDT Mon Sep 16 2024

.KEY MESSAGES...

- Very warm through Tuesday with elevated fire weather conditions
- Strong storm system late Tuesday/Tuesday evening brings
  marginal/slight risk of severe weather
- Pattern change end of the week with cooler weather likely

&&

.DISCUSSION...(Today Through Sunday)
Issued at 218 AM MDT Mon Sep 16 2024

08z surface analysis had low over southeast MT with meso-low over
K2WX per KUDX radar loop. Water vapour loop had shortwave over
southwest half of CWA with convective cluster ahead of it moving
northeast. Bigger picture has upper low over northern CA, which is
the main concern for the short term.

Today/tonight, shortwave ridge moves in behind shortwave with
well-defined subsidence. Leftover buoyancy expected. While the
chance of precipitation is not zero during peak heating today, not
enough confidence to pinpoint any areas for introduction into
forecast. Gusty southerly winds develop on the western SD plains
this afternoon, persisting into tonight. Strongest winds over
south-central SD where low level jet develops tonight. Wind gusts
40-45mph likely. Day shift can take a look at necessity of wind
advisory if it looks like winds will persist into Tuesday.
Temperatures will be near guidance.

Tuesday, upper low ejects into eastern MT with pronounced
synoptic forcing ahead of it per negative tilt. Deepening surface
low over southeast MT expected with fast moving trailing cold
front late afternoon/evening. Buoyancy not that impressive ahead
of cold front, but synoptic forcing should support high-based
thunderstorms racing across WY into western SD. Many CAMS showing
strong/severe outflow wind potential resulting in marginal/slight
risk of severe thunderstorms over the CWA. Should be quite the
dynamic system to watch on satellite/radar with a 25-50% chance of
>0.25" QPF. Temperatures will reach guidance east of the Black
Hills, but greater uncertainty over northeastern WY/far western SD
per cloud cover/precipitation timing.

Wednesday through next weekend, upper trough/cyclonic flow not
looking as well-defined as previous ensemble guidance has
depicted. Cooler temperatures still foreseen per west/northwest
flow aloft spinning a series of disturbances through the northern
plains resulting in almost daily PoPs. Chance of >0.25" QPF
during any 24-hour period is low.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 953 AM MDT Mon Sep 16 2024

VFR conditions will continue through the TAF period.

&&

.FIRE WEATHER...
Issued At 218 AM MDT Mon Sep 16 2024

Elevated fire weather conditions expected through Tuesday
afternoon, especially over northeastern WY and far southwest SD
where minimum relative humidities will dip to 15-25%. Gusty
southerly winds are expected on the SD plains today. A sharp cold
front will move through late Tuesday with gusty southerly winds
ahead of it and gusty southwesterly winds behind it. A band of
strong/severe thunderstorms (with good chance of wetting rains)
will accompany the front. Cooler weather then expected for the
end of the week into next weekend, but the chances of significant
precipitation have waned.

&&

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

$$

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