237
FXUS63 KUNR 072310 AAA
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY...UPDATED
National Weather Service Rapid City SD
510 PM MDT Sat Jun 7 2025

.KEY MESSAGES...

- Gusty NW winds in store for Sunday for the western SD plains

- A return to more summer like temperatures next week

- Upper flow regime by mid-week supports a more active weather
  pattern beginning the middle of next week.

&&

.UPDATE...
Issued at 509 PM MDT Sat Jun 7 2025

Previous forecast is on track and minimal changes were needed. We
added slightly more temporal resolution to precipitation
probabilities with pre-frontal weak convection now confined to
locations south of I-90, and midlevel frontogenesis-driven light
showers not beginning until later this evening. With sub-cloud
layer remaining fairly dry later this evening and into the night,
and forcing being modest at best, we still have high confidence
than rainfall amounts will be light from the west-northwest to
east-southeast oriented bands of precipitation that develop.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 221 PM MDT Sat Jun 7 2025

Current map shows strong 500hpa low spinning across nrn Sask with
lead trough now pushing through western SD. Minor s/w in northwest
flow behind trough moving through MT. Associated surface trough
along the SD/WY border with NW winds behind feature and SW winds
ahead of feature. Main sfc cold front back in MT where strongest
3-hrly pressure rises are located.

Aforementioned surface trough/cold front will sweep eastward
across  the region this afternoon as upper low continues to drop
southeast into the Great Lakes region. Surface dwpts...while not
overly impressive ahead of the cold front, are generally in the
mid 50s. Grand Ensemble shows SBCAPE values this afternoon from
300-400 J/kg. Ensemble values are non-zero for convective chances
for the remainder of the afternoon, although will admit most are
less than 20% or even 15%. Isolated thunder seems to cover very
well. Wind wise, both NAM/GFS showing 3-hrly pressure rises by 00z
behind front of 3-5mb. Ensemble chances are only 20% of seeing
wind gusts > 40mph across the far nrn counties and that is only
for an hour or two. Feel that gusts may tickle the lower bounds of
wind advry critieria in a few places briefly, but see no need to
issue any wind headlines for this evening as winds will settle
down into breezy category overnight.

Overnight into Sunday models remain fairly certain of a strip of
pcpn  setting up from WY counties into SW SD overnight through
12z Sunday. This seems to line up fairly well with 700hpa theta-e
ridging seen in both the GFS & NAM. There is also some minor
850-700hpa 2-D frontogenesis that takes place along this area as
well overnight. Ensemble probabilities in this area range from
20-50%. This area of pcpn moves out of the area aft 12z Sunday,
with thoughts then turning to the winds again. With 500/700 and
850hpa winds well linked, another breezy/windy day is in store
across western SD. Ensemble guidance shows probabilities for wind
gusts exceeding 40mph in the 50%+ range, but less than 50mph
through about 21z Sunday in the favored squeeze areas of western
SD. Sustained winds of 30+mph are in the same probability range.
Could be a need for a wind advisory across much of the plains
Sunday morning-afternoon. Additionally, inherited grids had
already introduced some smoke from Canadian wildfires into
forecast for Sunday. With strong NW-N flow aloft, see no reason to
remove the mention.

Monday through the remainder of next week, models remain
consistent on a warming trend as upper flow transitions from NW to
zonal to SW flow by the end of the week. Nice thermal ridge pushes
into the region Tuesday, which could be the warmest day of the
week with highs 10 to 15 degrees above normal. As trough digs
across the western CONUS, waves will eject into the plains
beginning mid-week. This is usually a more favorable pattern for
severe/active weather. Models seem to pick up on the usual BH
afternoon convection beginning Wednesday through the end of the
week. Right now there are differences in timing/strength of the
individual short waves as they traverse the region. 850Hpa temps
fall mid-week back into the middle teens, but begin to warm again
toward next weekend.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 509 PM MDT Sat Jun 7 2025

Fairly high confidence in VFR conditions continuing. The more
robust isolated/scattered convection with possible brief
visiblity/ceiling reductions have remained east of TAF sites and
any precipitation later this evening should be from a midlevel
cloud deck (~10,000 ft). So, any associated impacts to aviation
should be minimal. Primary impact through mid-evening will be
strong wind gusts up to 35 knots from the northwest until mixing
subsides and winds decrease later this evening.

&&

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

$$

UPDATE...Bowers
DISCUSSION/KEY MESSAGES...Hintz
AVIATION...Bowers