370
FXUS63 KUNR 190335
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
935 PM MDT Thu Jul 18 2024

.KEY MESSAGES...

- Near average temperatures with a daily chances for thunderstorms
  through the weekend. Isolated strong to severe storms possible.

- Trending warmer and drier for the first half of next week with
  periods of elevated fire weather conditions.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 211 PM MDT Thu Jul 18 2024

Current analysis shows upper ridge continuing to build over the
western CONUS. At the surface, high pressure is centered over the
Midwest with a weak trough along the Rockies, which is resulting
in southerly return flow over the South Dakota side of the
forecast area. Dewpoints are in the 50s to lower 60s over western
SD and in the mid-30s to mid-40s over northeastern Wyoming.

Steep lapse rates and convergence over the Black Hills continue to
produce periodic weak radar returns, However, weak forcing and
marginal shear has so far kept the convection from persisting.

With continued heating expect to see some thunderstorm development
during the rest of the afternoon into this evening, mainly over
the higher terrain of eastern Wyoming and the Black Hills. With
MLCAPE of 500-1500J/KG, an isolated severe storm is possible,
mainly over and near the central/southern Black Hills this
afternoon/early evening. Thunderstorm coverage will increase
later tonight with the combination of a shortwave moving into
eastern Montana and increasing theta-e advection on the nose of a
developing low level jet. Thunderstorm chances will continue
through the day on Friday as the shortwave crosses western South
Dakota mid-day. Buoyancy and shear will be sufficient for a few
robust updrafts with a severe wind/hail threat later tonight into
Friday.

The upper ridge will become more amplified over the weekend with
northerly flow aloft over the Plains. Embedded impulses will keep
small chances for thunderstorms in forecast each day. Early next
week, an upper trough will move into Pacific NW, nudging the ridge
eastward toward the Northern Plains. This will bring warmer/drier
conditions. With that, periods of elevated fire weather
conditions are expected.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 932 PM MDT Thu Jul 18 2024

A disturbance crossing the CWA overnight will bring scattered high
based showers/storms, with brief MVFR visibility in heavier
precipitation. Additional storms will develop Friday afternoon,
especially over south-central SD, with VFR conditions in any
stronger to severe storms.

&&

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

$$

DISCUSSION/KEY MESSAGES...10
AVIATION...Johnson