National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KUNR 240934
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
334 AM MDT Wed Apr 24 2024

.KEY MESSAGES...

- Mainly dry and warmer weather through Thursday morning.

- A couple of systems will bring showers and some thunderstorms late
 Thursday afternoon through the weekend.

- Warmer and drier weather quickly develops during the first half of
  next week.

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 333 AM MDT Wed Apr 24 2024

Current sfc analysis depicts broad area of high pressure centered
over western ON and extending down into the Northern Plains. 500
mb ridge is building over the region with some mid-level moisture
resulting in high cloud cover over southwestern SD. Winds at the
sfc are light and generally from the south - UDX VWP depicts
30-40kt southerly winds just above the sfc. We could see some of
those winds mixing down to the sfc after sunrise this morning.
Return flow on the back side of the high today will advect warm
temperatures into the region - highs will largely be in the upper
60s to mid 70s. Min RHs across northeastern WY may drop below 20%
but greening fuels and light winds preclude any elevated fire wx
concerns at this time.

Late Wednesday into early Thursday, shortwave progged to cross
the southwest and eject into the plains with lee cyclone
developing over the central plains late Thursday. This will be the
first of the two systems that will impact us this weekend. As for
weather on Thursday, limited moisture, weak forcing, and capping
over most of the western SD plains will preclude any widespread
chances for precip through Thursday afternoon. Chances for showers
and storms are better further west and over the Black Hills where
forcing will be stronger due to midlevel frontogenesis. While
CAPE will be 500- 1000 J/kg over far western SD into northeastern
WY Thursday afternoon - deep layer shear is expected to be
marginal at best. Any widespread severe weather risk isn`t
expected at this time but can`t rule out a strong to severe storm
or two forming over the Black Hills Thursday afternoon. Main
threats would be gusty winds and hail.

Low pressure will continue to deepen and track northeastward over
NE into southeastern SD and then into MN. NAEFS guidance depicts
PWATs approaching climatological maxes for this time of year -
indicating a moisture laden system and the potential for a decent
rainfall event over much of western and south central SD.
GEFS/EPS/GEPS grand ensemble output has 70-90% probs of total QPF
exceeding 0.25" by midnight Saturday across much of western SD.
The northern hills and south central SD look to see the most
amount of QPF from this first system with 40-60% probs of seeing
0.75" or greater total QPF by midnight Saturday. Pressure rises of
2-3 mb/3hr Friday night as the low exits the region will result
in some gusty winds, though gusts will likely remain below
advisory level. Temps will cool off this weekend as well - with
highs in the 40s to 50s by Saturday and Sunday. Lows Saturday and
Sunday night will dip into the 30s with the Black Hills
potentially seeing some snow mixing in with the rain Saturday and
Sunday night.

Another shortwave ejects over the central plains Saturday, so far
recent deterministic runs show this storm will track a little
further south which could mean less precip for us. Ensembles are
right now showing 20-40% chances of 24-hr QPF exceeding 0.5" over
southern SD by noon Sunday.

As this second system moves out of the region, upper flow becomes
quasi-zonal with drier weather and warmer temps. Upper ridge
starts building back into the region by midweek with mostly dry
(though can`t rule out a few afternoon showers or storms over the
Black Hills) and warm weather.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1002 PM MDT Tue Apr 23 2024

VFR conditions will continue through the TAF period. There is a
chance of showers, and possibly a thunderstorm, over the Black
Hills and parts of southwestern South Dakota from late Wednesday
afternoon into Wednesday evening.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...10