773
FXUS63 KUNR 152222
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
422 PM MDT Sun Sep 15 2024

.KEY MESSAGES...

- Very warm through Tuesday with near critical fire weather
  conditions
- Strong thunderstorms with a marginal chance for a few severe
  storms possible very late this afternoon into the evening
- Pattern change mid to late week with cooler weather likely,
  along with better chances for precip at times, especially
  Tuesday night

&&

.DISCUSSION...(This Evening Through Sunday)
Issued at 1227 PM MDT Sun Sep 15 2024

Water vapor shows upper trof digging on the west coast with ridge
amplifying over the Northern Rockies/Northern Plains. Strong
short wave is ejecting across western CO. At the surface, weak low
is over the Black Hills with boundary extending eastward across
western SD.

Ejecting short wave will move into the area this evening, with
showers/storms developing across far southwest SD by very late
this afternoon then spreading north/east through western/central
SD this evening/overnight. While there could be a few stronger to
severe storms early on, the later arrival along with marginal
bulk shear values should limit the overall severe threat.
However, precipitable waters will be on the increase into the
neighborhood of 150%+ of normal, so efficient rain can be expected
with any stronger activity. Precip should end by morning in our
eastern zones.

Short wave ridge in wake of tonight`s short wave will bring warm
and drier conditions for Monday. Gusty southerly winds will
develop on the plains east of the Black Hills, especially towards
south central SD. High temps will be well into the 80s, with 90s
south/east of the Black Hills.

Large upper trof will work slowly east across the western CONUS
early to mid week. Ejecting upper low will lift through the
Central Rockies Tuesday, with strong/broad forcing bringing a band
of widespread showers/storms to the area Tuesday night. Models
have been very consistent with this scenario for multiple days
now, so confident is quite high.

Cooler and somewhat drier conditions then expected for the last
half of the work week as upper low lifts west and north of the
area. Precip chances for very late in the week and weekend are
questionable at this time as models are not very consistent with
the details of the broad trof as it crosses the Plains. However,
confidence is high that much cooler weather will accompany the
trof.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 420 PM MDT Sun Sep 15 2024

Thunderstorms with local MVFR/IFR conditions are expected over
parts of western South Dakota this evening, spreading into
central SD overnight. Some thunderstorms may produce small hail
and gusty winds. Otherwise, VFR conditions will prevail.

&&

.FIRE WEATHER...
Issued At 1227 PM MDT Sun Sep 15 2024

Elevated to near critical fire weather conditions expected
through at least Monday, especially over northeastern WY and far
southwest SD where minimum relative humidities will dip to 10-20%.
There is a small chance that southwest winds could mix deep
enough to produce some areas of critical conditions over northeast
WY and southwest SD Monday afternoon, but the stronger winds
should remain east of the Black Hills where RH will be higher. A
wetter and cooler pattern will develop mid to late next week.

&&

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

$$

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