FXUS63 KUNR 180452
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1052 PM MDT Sun May 17 2026

.KEY MESSAGES...

- Another round of rain, with snow in Black Hills, is likely later
  tonight into Monday.

- Much colder to start the week but warmer temps return by late week.

- Low-end chances for rain return later this week.


&&

.DISCUSSION...(Tonight Through Sunday)
Issued at 1051 PM MDT Sun May 17 2026

Upper air analysis depicts upper trof digging into the 
Intermountain West with southwest flow across the Northern Plains.
Water vapor imagery shows moisture associated with our next 
system making its way into the area. Precip chances will increase 
overnight across northeastern WY, the Black Hills, and 
southwestern SD as this system approaches from the southwest. 
Precip will overspread the region Monday as band of 850-700mb FGEN
and plenty of available moisture sets up over much of the CWA. 
Expecting mainly rain over the western SD plains with snow over 
the Black Hills. Northeastern WY could see snow to start out with 
with a change over to rain in the afternoon as the day warms up. 

There's still some uncertainty as to where the strongest forcing 
(and therefore the highest precip amounts) will be, right now it 
looks like the greatest precip totals will be across the Northern 
Black Hills and southwestern SD into the western SD plains with 
total QPF amounts of up to 0.25 to 0.4 inches are likely. Froude 
numbers of around 1 and moist, northerly flow will support upslope
snow across the northern Black Hills. However, given the time of 
year and the fact that the snow is going to be falling during the 
day, snow accumulations (especially on roadways) may be limited by
melting. Therefore, anticipating slushy accumulations of up to 
3-5", mainly on grassy sfcs and in the higher elevations of the 
Black Hills. Northeastern WY could also see light snow 
accumulations with this system though, again, the time of year and
the fact that this will be occuring during the daytime will limit
overall snow totals. Expecting around a trace to up to 2 inches 
with the highest amounts across southern Campbell County. 
Regardless of final snow amounts, the main thing to note is that 
much of the area will receive some much needed moisture.

Below normal temps expected through early this week with lows 
tonight, Monday, and Tuesday nights dropping into the 20s to 30s. 
A Freeze Warning remains in effect for northeastern WY for early 
this morning as temps are expected to drop into the upper 20s. 
Additional Frost/Freeze headlines may be needed for Monday and 
Tuesday nights, but will hold off on issuance for now. Shortwave 
ridging develops by the mid-week and kick off a gradual warming 
trend for the rest of the week. Approaching upper trof then brings
precip chances back to the CWA for the late week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 523 PM MDT Sun May 17 2026

Leftover showers with local MVFR conditions over south-central SD
will wane this evening. VFR conditions over northeastern
WY/western SD will change after 18/06z as an area of rain (snow up
high) develops leading to widespread IFR/MVFR conditions after
18/12z across the entire area.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WY...Freeze Warning from 5 AM to 10 AM MDT Monday for WYZ054>056-
     058>060.
&&

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...Helgeson