478
FXUS63 KUNR 090348
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
948 PM MDT Wed May 8 2024

.KEY MESSAGES...

- Remaining cool and unsettled with showers and possibly an
  isolated thunderstorm through Thursday.

- Warmer and drier conditions expected for the weekend.

- Cool and unsettled weather returns for the beginning of next
  week.

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 213 PM MDT Wed May 8 2024

Nearly vertically stacked surface to 500hpa low will continue to
slowly meander south across the area this evening and overnight
with the vast majority of the precipitation falling west and east
of the CWA. Neutral to weak WAA occurring on the backside of low
(depicted via 700hpa theta-e analysis) is still contributing to
isolated-scattered showers across mainly southwestern SD.
Ensembles show that there should be a slight decrease in the
overall PoPs early this afternoon with a notable increase in PoPs
later this afternoon and into the evening. Of question is what
form will the precipitation take in the Black Hills. The only area
where the ensemble mean points to a solid snow forecast is the
northern Black Hills, generally above 6000 feet. Below that, while
the ensemble means have higher probabilities for snow, the rain
probabilities are non-zero. Then...areas below highway 385 have
all rain probabilities. Ensembles also show lowering probabilities
heading toward 12z Thursday as temp advection turns more neutral
and low gets further south of the area.

Attention then turns to the rest of Thursday as a pretty well
pronounced 700hpa trowel moves west across the state. Upper flow
turns a bit more northeasterly and 850hpa temps warm from +2 to +4
C at 00z Thursday to +4 to +6 C by 12z Thursday. MUCAPE values
from 250-500 J/Kg traverse from east to west with this trowel as
well...mainly along and south of I-90...so a mention of thunder is
also warranted with the showers. The risk of snow in the hills
also diminishes as 2 meter temps warm to near 40 F by late morning
and ensemble probabilities turn more toward rain vs snow by the
late morning. Breezy conditions are still expected through the day
Thursday.

For the weekend, 500hpa Pacific ridge flops into the midwest,
compressing the low south where it eventually becomes cut off in
the desert southwest. Surface high pressure drops southward into
the region...relaxing the winds with 850hpa temps warming into the
teens C by Sunday. Except for minor chances of Black Hills
showers/thunder...it should be a dry Friday & Saturday for much of
the area. Another weak wave drops through the 500hpa flow later in
the day Sunday, so cant discount any pcpn chances associated with
that feature. A stronger trough passes through Monday & Tuesday as
broad cyclonic flow develops again over much of the northern
CONUS. This will lead to a soggy start next week with expected
below normal temps.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 945 PM MDT Wed May 8 2024

Scattered rain showers will persist overnight into at least the
first half of Thursday. This will bring mainly IFR conditions
over northeastern WY, the Black Hills, and far western SD.
Conditions will slowly improve throughout the day Thursday, and
then VFR conditions should take hold for most places tomorrow
evening.

&&

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

$$

DISCUSSION/KEY MESSAGES...Hintz
AVIATION...Bunkers