380
FXUS63 KUNR 071113
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
513 AM MDT Fri Jun 7 2024

.KEY MESSAGES...

- Showers and thunderstorms expected over most of western SD this
  afternoon with chances for isolated strong to severe storms
  over south central.

- Chances for showers and storms linger through the weekend

- At or above average temperatures through next week

&&

.DISCUSSION...(Today Through Thursday)
Issued at 209 AM MDT Fri Jun 7 2024

Current upper air analysis depicts broad 500mb ridge over the
western US with two developing upper lows: one over central SK/MB
and one over the Great Lakes region. A strong upper level jet
streak (100kt+) stretches from southern SK southeastward into ND,
MN, and WI. At 700 mb, a lee shortwave is developing over central
WY, triggering some light radar returns over central and eastern
WY. Sfc obs in the area are fairly dry (temps in the 60s with
dewpts in the 40s) so it`s doubtful anything is reaching the
ground. Sfc analysis depicts sfc ridge axis centered over SD.
Conditions across western SD are mostly clear save for some high
level cloud cover.

700 mb shortwave will eject over the plains this morning with sfc
low developing over NE/KS. Increasing theta-e over southern SD
with the lift from the shortwave should be sufficient for
development of scattered showers/storms across much of western SD
around and south of I-90. A nose of 500-1500 J/kg ML CAPE will
push its way into south central SD by this afternoon. The highest
shear values are displaced to the north where the strong jet
streak is located, though HRRR and NAM depict 0-6KM shear values
over south central SD this afternoon in the 40-50kt range which is
more than sufficient for rotating updrafts and strong to severe
storm development. The limiting factor here will be high CIN (-50
to -100+ J/kg) and lack of deep layer moisture. Main threats from
any severe storms will be large hail and damaging winds.

Deterministic guidance is still struggling with the evolution of
the upper level pattern through this weekend. The 00z GFS last
night had the upper low staying far to the north in Canada with
the northern plains under mostly zonal flow. The 00z GFS run from
tonight has the upper low over SK/MB pivoting around the Great
Lakes low and going much further south, centering it over ND/SD by
Sunday afternoon. The Euro, NAM, and Canadian have been much more
consistent at keeping the upper low basically stalled out over
southern SK. Regardless ... with better deep layer moisture and
the influence of the jet streak, we could see chances for showers
and storms lingering through the weekend.

Guidance comes into better consensus by the midweek of a
flattening ridge and more zonal flow over the northern plains.
This will translate to mostly dry conditions and above average
temperatures.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 511 AM MDT Fri Jun 7 2024

VFR conditions are expected through most of the forecast period.
Isolated to scattered SHRA/TS can be expected this morning and
again later this afternoon across central SD, especially south
central.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...JC