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000
FXUS63 KUNR 252030
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
230 PM MDT Thu Apr 25 2024

.KEY MESSAGES...

- Thunderstorms continue this afternoon and evening with heavy rain,
  some hail, and gusty winds expected.

- Fairly widespread rainfall at times from Friday through much of
  the weekend, especially the Black Hills and eastward.

- Warmer and drier conditions move in for much of next week.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 228 PM MDT Thu Apr 25 2024

Current surface analysis shows low pressure over far east central
WY, with Pacific cold front stretching from far western ND to far
eastern WY. Upper level analysis shows trough over the Great
Basin to Four Corners region, with developing low pressure over
northeast AZ. Skies are variably cloudy, with the most clouds over
northeast WY and far western SD. KUDX radar shows scattered to
numerous showers and thunderstorms from northeast WY to the Black
Hills area and northwest SD as stronger energy aloft pushes
through western portions of the CWA. Temps are mostly in the 60s
and lower 70s, with some 50s over the Black Hills and rain cooled
areas. Brisk southeasterly winds are gusting to over 35 mph across
central SD, with lighter and more variable winds to the west.

Active weather pattern taking shape for the next several days as a
couple of upper level systems cross the region. Any severe weather
potential will be confined to the next several hours, with the
heaviest rain potential expected through Friday as the first upper
low approaches and passes over the region. Most favorable CAPE this
afternoon has been over and east of the Black Hills, ahead of the
front, with values around 1000 j/kg. Shear is rather weak in many
areas, so individual storms have been pulsy in nature and not very
long-lived, producing smaller hail for the most part. Various CAMS
show numerous storms continuing to develop through the afternoon
along and ahead of the front, trying to consolidate into at least a
broken line of storms along the front by late afternoon/early
evening. Marginally severe hail and strong winds would be the main
threats with stronger storms through at least late afternoon, with
gusty winds perhaps a threat into the early evening over portions of
the western SD plains if a more organized line of storms did
develop. With precipitable water values up to 150 percent of
average, heavy rain will accompany the stronger storms as well.
Initial activity with the cold front should shift east of the
forecast area toward midnight.

Upper low moves into the central Plains later tonight and somewhere
across central NE/eastern SD on Friday. Showers and some embedded
thunderstorms will wrap north-northwestward into the forecast area
late tonight and Friday, especially for the Black Hills area and
eastward. There appears to be at least a slightly further south and
east trend to the low track for Friday in the EC and now the latest
GFS, which would shift the heavier rainfall potential a bit further
east onto the western SD plains Friday. Right now, probabilities are
40 to 70 percent for an inch or more of rainfall Friday into Friday
night for the northern Black Hills and much of the west central to
south central SD plains. It will be breezy and cooler Friday, with
highs in the 50s and lower 60s. Lingering areas of lighter rainfall
can be expected Friday night into Saturday, especially for the Black
Hills area. Even cooler air pushes in for the weekend, with highs
only in the mid 40s to mid 50s, 40s over the Black Hills. As the
first upper low weakens and departs the region, a second one
develops over the central Rockies Saturday and moves northeast
across nearly the same areas as the first one Saturday night and
Sunday. This one looks to be somewhat quicker moving and its pcpn
shield not quite as big. Best chances for more significant rainfall
later Saturday night into Sunday will be across south central SD,
with mostly light rainfall elsewhere. Not much, if any, thunder
expected with the second system. There could be a little bit of snow
across the higher Black Hills Saturday night into Sunday, but any
accumulations look to be very minor. Breezy north to northeast winds
will persist through the weekend.

After this system exits the region Sunday night, near zonal flow is
expected to develop early next week. Above average temps will
quickly return to the area Monday and likely persist through the
week. Another low pressure system is progged to develop over the
northern Rockies and track north of the region Monday night and
Tuesday. There will be chances for showers and a few thunderstorms
late Monday into Tuesday, mainly across the Black Hills and northern
portions of the CWA. A building ridge behind this system should
bring mild and mainly dry conditions midweek, with the possibility
of a cold front passage in the Friday timeframe.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1115 AM MDT Thu Apr 25 2024

VFR conditions are expected through early afternoon. Showers and
thunderstorms will increase in coverage and intensity after 20Z.
MVFR/IFR conditions are expected with the heavier precipitation.
Widespread MVFR/local IFR conditions expected tonight with
expanding area of stratus and showers. Northerly winds will
increase to 15-25 kts with gusts around 35 kts Friday morning.

&&

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

$$

DISCUSSION/KEY MESSAGES...26
AVIATION...Pojorlie