564
FXUS63 KUNR 272246
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
446 PM MDT Sat Apr 27 2024

.KEY MESSAGES...

- Chances of rain showers return late tonight into Sunday; best
  chance for measurable precipitation east of Rapid City into
  south-central SD.

- Temperatures trend warmer to near-normal levels Monday into next
  week with active flow --> near daily chances of rain showers
  through the week.

- Elevated fire weather conditions Monday and Tuesday; cold front
  arrives with strong winds and dry air behind it for Tuesday
  afternoon.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 135 PM MDT Sat Apr 27 2024

Water vapor imagery shows strong upper level closed low centered
over SW CO/northern NM this afternoon with a 80-100 knot jet
rounding the base of the trough axis. Our (KUNR) 12z RAOB sampled
dry air aloft, with driest layer from ~700mb-500mb; this dry air at
mid-levels is well identified by the low-and-mid-level WV bands.
Surface high pressure is situated to our north, centered over
northern Manitoba, with lee cyclogenesis ongoing across the
southern/central Plains. Northeasterly surface flow is ongoing with
temperatures in the 40s to mid 50s this afternoon.

As the closed upper low continues to eject into the Central and
Northern Plains tonight, broad upper level ascent will slowly
overspread the forecast area with chances of showers returning
later this evening into the overnight hours. Recent trends continue
to push the surface and mid-level low slightly eastward, with best
synoptic and mesoscale forcing remaining south and east of the
forecast area along with drier air quickly filtering in across NE
WY/far western SD Sunday. As such, both HREF and LREF
(GEFS/EPS/GEPS) ensembles have placed the axis of heaviest
precipitation south and east of Rapid City, with best chances of QPF
>0.25" across south-central SD and areas southeast. Total QPF
amounts taper off quickly along the foothills into NW SD and NE
WY, where most areas will remain dry.

After this system lifts into the Great Lakes, we will see a return
to seasonable temperatures Monday through the upcoming week. Active
upper level flow will remain in place with near daily chances of
rain showers; thunderstorm chances remain low through at least
Thursday/Friday. Of particular note, a quick moving shortwave
and cold front will clip the forecast area early Tuesday. Winds
will shift NW and ample mixing will result in potential for
advisory level wind gusts Tuesday afternoon across NW SD. Moisture
will be limited with very dry boundary layer during peak heating
-> elevated fire weather potential across much of the forecast
 area.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 444 PM MDT Sat Apr 27 2024

CIGS over most of western SD will become IFR tonight as upslope
flow lowers CIGS and patchy fog develops. Widespread rain will
develop east of the Black Hills later tonight, esp toward
scentral SD. Over northeastern WY, expect mainly VFR conditions.

&&

.FIRE WEATHER...
Issued At 135 PM MDT Sat Apr 27 2024

Temperatures will trend back toward seasonable levels by Monday
through the week. Winds will shift southwesterly for Monday with
breezy conditions and RH falling into the teens to near 20% across
NE WY and portions of SW SD Monday afternoon. A quick moving cold
front will arrive early Tuesday morning. While a few spotty
showers are possible through the late morning/early afternoon
hours, most areas will remain dry. Drier air and gusty NW winds
will push in behind the front. Daytime minimum RH from ~12-30%
(driest NE WY into the Black Hills and western SD plains) coupled
with sustained NW winds 15-20+ mph with gusts 35-50 mph will
support near- critical fire weather conditions Tuesday afternoon
and evening. Will continue to monitor Tuesday for possible fire
weather headlines.

&&

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

$$

DISCUSSION/KEY MESSAGES...SE
AVIATION...JC
FIRE WEATHER...SE