247
FXUS63 KUNR 200416
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1016 PM MDT Sun May 19 2024

.KEY MESSAGES...

- Widespread showers late Monday/Monday night. Locally heavy rain
  over south central South Dakota.

- Active pattern continues through the end of the week and
  into the holiday weekend.

&&

.DISCUSSION...(This Evening Through Sunday)
Issued at 240 PM MDT Sun May 19 2024

Current surface analysis shows low pressure just east of the
Black Hills, with warm front extending east across southern SD and
a cold front trailing to the southwest across WY. A surface
trough/dryline extends south from the low across the central into
southern high Plains. Upper level analysis shows a pair of low
pressure systems over southern Canada, with a shortwave trough
across the northern Rockies into the northern high Plains.
Additional energy extends further south across the Rockies. Skies
are variably cloudy with showers and storms developing early this
afternoon across eastern WY, southwest SD, and the NE panhandle.
Temps are mostly in the upper 60s to around 80 degrees across the
area, warmest over far southern SD. Winds are gusty from the south
to southeast across a good portion of south central SD.

A fairly active afternoon/early evening is in store for portions of
western into central SD as the surface low moves slowly east near
the I-90 corridor during this time. Most of the short range models
and CAMS show storms continuing to develop near and along the
surface trough as it moves east through the late afternoon and early
evening. A severe thunderstorm watch was issued earlier this
afternoon for most of southwest into central SD until 02z. Latest
analysis shows moderate buoyancy ahead of the low and to the south
of the warm front across locations mostly east of the Black Hills at
this time, with MLCAPE values to around 1000 j/kg to the southeast
of the Black Hills. Shear is modest in most areas, with the more
favorable values either behind the front to the north and west or
well south/southeast across the central Plains. However, they could
be sufficient for at least short-lived supercells or some more
organized multicells to develop. Activity is starting to focus
relatively quickly along the surface trough over southwestern SD as
it tracks east into central SD by the early evening. Main time
period for severe storm potential across southwest SD will be from
now until about 5 or 6 PM MT, with areas further east toward central
SD mostly from 4 to 7 PM MT (5 to 8 PM CT). Strong wind gusts and at
least marginally severe hail will be the main threats from any
severe storms, with wind likely becoming the bigger threat late this
afternoon and early evening. A few lighter showers/thundershowers
could linger later into the evening across western SD, but remaining
activity should end by midnight.

After a brief period of quiet weather later tonight into Monday
morning, showery weather develops for Monday afternoon into Tuesday
as a larger trough moves across the western US and active
southwesterly flow develops from the Rockies into the Plains.
Showers still look to be most numerous across southern portions of
the forecast area, I-90 and southward, with some thunder also
possible. At least some locally heavy rain is possible across south
central SD, probabilities of an inch or more at or above 50 percent,
as the heaviest rainfall likely tracks from northern NE to southeast
SD. There could even be a little bit of snow across the highest
elevations of the Black Hills later Monday night into Tuesday
morning. Highs Monday and Tuesday will drop back to below average
levels, mostly in the 50s and 60s.

The rest of the week and the holiday weekend looks to be unsettled
at times with near seasonable temperatures as near zonal flow brings
occasional shortwave disturbances across the Rockies and Plains. The
best and most widespread chances for showers and storms later in the
week looks to be Thursday afternoon into Friday. There is some
potential for stronger storms later Thursday across at least eastern
portions of the CWA. The weekend looks seasonably warm, with highs
in the mid 60s to mid 70s.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1013 PM MDT Sun May 19 2024

Breezy northwesterly winds will continue behind cold front
overnight, gusting to over 35 kts on portions of the SD plains.
Winds will gradually decrease Mon morning. VFR conditions can be
expected overnight into Monday. Chances for showers will increase
from west to east across northeast WY and southwest SD during the
late morning and afternoon on Monday, with local MVFR conditions
expected in the afternoon.

&&

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

$$

DISCUSSION/KEY MESSAGES...26
AVIATION...JC