-- Discussion containing changed information from previous version are highlighted. --
639
FXUS63 KUNR 120811
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
211 AM MDT Wed Jun 12 2024

.KEY MESSAGES...

- Near to above average temperatures through Thursday with a few
  late day/nighttime showers and thunderstorms possible.

- A more unsettled pattern returns Friday, with daily chances for
  storms into early next week.

&&

.DISCUSSION...
-- Changed Discussion --
(Today Through Tuesday)
Issued at 211 AM MDT Wed Jun 12 2024

RAP reanalysis depicts largely zonal flow at the upper levels
with 700 mb shortwave over southwestern SD/NE/WY. Region of
500-1500 J/kg ML CAPE extends across most of western SD into
portions of northeastern WY. Radar and satellite imagery show
ongoing convection over southeastern MT tracking eastward towards
northwestern SD. Some storms have also fired off in central and
eastern SD. If the storms in southeastern MT maintain strength,
should expect them to move into northwestern SD within the next
hour or so.

Thermal ridge extends up into the northern plains this afternoon,
resulting in a very warm day across the CWA. Largely westerly
flow at the mid and lower levels will facilitate compressional
heating, resulting in even warmer temps towards south central SD
and over the plains east of the Black Hills. Some areas may breach
the 90 degree mark for the first time this year. Dry airmass will
be in place with afternoon RHs dipping into the upper teens
across portions of northeastern WY into southwestern SD and from
20 to 30 percent across the rest of western SD. Light winds and
green fuels preclude any fire weather concerns at this time. By
the afternoon ML CAPE across south central into southwestern SD
and the Black Hills will reach 500-2500 J/kg with the higher
instability further east. 0-6km shear will range from 30-50kt
which is sufficient for rotating updrafts if an updraft were to
form. However, the lack of any appreciable deep layer moisture and
source of lift will preclude any storm and therefore any severe
threat at this time.

Upper low/deepening trough over the northern Pacific begins to
make its way onshore by Thursday with a ridge building over the
western US, resulting in another warm and dry day for the CWA.
Weak lee shortwave and sfc trough will develop and affect the
region Friday, resulting in chances for showers and storms Friday
afternoon. Axis of strong instability extends into western SD and
northeastern WY Friday afternoon with ML CAPE of 1000-2000 J/kg
across most of western SD into the Black Hills and far
northeastern WY. With 0-6km bulk shear of 25 to 45kt, could see
isolated strong to severe storms Friday afternoon.

Guidance is generally in consensus of troughing over the western
US by the end of the weekend into early next week. This will
bring unsettled and relatively cooler conditions (highs in the
upper 60s to 70s) to the region the beginning of next week.
-- End Changed Discussion --

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 514 PM MDT Tue Jun 11 2024

Isolated showers are possible after 06z tonight mainly across
northwestern and central SD. Otherwise, VFR conditions are
expected through the TAF period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...13