557
FXUS63 KUNR 271653
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1053 AM MDT Fri Jun 27 2025

.KEY MESSAGES...

- There is a slight risk (level 2 of 5) for severe thunderstorms
  this afternoon and evening, mainly east of the Black Hills. Main
  hazards will be large hail (quarter size or larger) and
  damaging wind gusts.

- Hotter temperatures are expected today, with highs climbing into
  the 90s for most.

- Heat shifts east on Saturday, with widespread showers and
  thunderstorms anticipated late Saturday into Sunday.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 217 AM MDT Fri Jun 27 2025

Water vapor imagery tonight shows brought, modest troughing and
associated enhanced deep moisture over much of the western CONUS. An
embedded upper low center is evident near the WA/BC border, with an
attendant disturbance extending into the northern Rockies. Closer to
home, a cluster of storms continues to shift eastward across
northwestern SD. Though largely elevated, occasional gusts of 40-50
mph have been observed within and behind this convection, and
subsevere hail likely accompanies the strongest cores. This activity
is supported by low-level warm air advection and convergence near
the nose of a 30-35 kt low-level jet focused over the NE panhandle,
per latest SPC mesoanalysis. The strongest activity will likely
traverse Ziebach County later in the overnight/very early morning
before departing the area and gradually weakening as the low-level
jet diminishes. Outside of the storms, it`s a pleasant night, with
locally warm temperatures (lower 70s) in locations such as Newcastle
and Edgemont owing to easterly downslope winds.

Midlevel trof and associated speed max, along with attendant low-
level trof, cross the region this afternoon and evening. Most
favorable environment for explosive convection capable of severe
hazards continues to be projected to remain east of the Black Hills
and largely east of our area. 00z HREF mean SBCAPE of 2-3+ kJ/kg
coupled with 0-6 km shear vector magnitudes of 30-40 kt are present
from central NE northward thru central SD by late morning,
expanding/shifting northeastward with time thru the afternoon. Dry
midlevel air will translate to deep, well-mixed boundary layers and
high LCLs over much of the area, which will limit tornado potential
outside of our far eastern tier (i.e., around Dupree to Winner).
However, the high LCLs may increase the potential for damaging
winds. Similarly, relatively modest low-level shear will further
limit tornado potential, but hodographs look favorable for very
large hail formation. Altogether, the primary hazards over most of
the area will be large to giant hail and damaging winds, potentially
locally significant. The time frame of the primary severe threat
will be fairly limited--from around 20z thru 04z or so. However, a
secondary weak disturbance moving through zonal/slightly
southwesterly flow aloft later in the evening may support additional
shower/storm activity contingent on evolution of convection earlier
in the day.

Surface trof slowly shifts eastward tomorrow night thru early
Saturday, effectively stalling over the region just south of our
area. Low-level north/northeast flow should allow for moisture
recovery in the wake of today`s convection. As an upper jet streak
passes north of the area, Q-vector convergence associated with the
right entrance region should promote ascent over the lingering
baroclinic zone late Saturday into Saturday night, leading to
widespread shower and thunderstorm activity. Compared to tomorrow,
CAPE will generally be lower, but shear will be improved, especially
across our western zones. As such, it will be another day to watch
for potential severe hazards. Low-level shear remains very weak, so
primary threats will be hail and wind. Storm chances continue into
Sunday as a more notable midlevel trof is carved out over the north
central CONUS. Though not currently in the SPC Convective Outlook
for Sunday, some longer duration CAMs do suggest a favorable
environment for severe across southwestern and south central SD by
Sunday afternoon.

Southeast to northwest oriented ridging builds over the
Plains/Rockies on Monday in the wake of the aforementioned trof.
Rising heights at all levels on Monday will likely limit convective
activity; however, northwest flow aloft and increasing CAPE from
Tuesday onward should support at least isolated convection each day,
some of which could be severe. Relatively mild temps on Sunday will
also give way to warmer/hotter conditions as height/thermal ridging
extend into the region.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 1050 AM MDT Fri Jun 27 2025

Around 21z, ISO TSRA are expected to develop over portions of
western SD and central SD. In addition to localized IFR/LIFR
conditions, the strongest storms will be capable of large hail
and erratic wind gusts in excess of 50 kt. Much of this TSRA
activity will diminish by 06z. After 06Z, some LLWS could develop
across central SD.

&&

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

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...Pojorlie