FXUS63 KUNR 190455
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1055 PM MDT Mon May 18 2026

.KEY MESSAGES...

- Cold temperatures overnight with freeze/frost headlines

- Gradual warmup mid-week with increasing precipitation chances
  for Thursday/Friday

- Sharp warmup for the weekend into early next week

&&

.UPDATE...
Issued at 919 PM MDT Mon May 18 2026

Going forecast in pretty good shape. Clouds are starting to 
breakup as leftover diurnal showers wane per shortwave moving 
into the upper Midwest. This will allow temperatures to drop into 
the upper 20s to lower 30s over much of the CWA overnight, covered
by Freeze/Frost headlines.

A warming trend begins tomorrow and peaks over the weekend. Weak 
disturbance and a bit of buoyancy may pop weak convection 
Wednesday with better chances Thursday/Friday as stronger 
disturbances rotate through the northern Rockies into the northern
Plains. Ensemble spreads tight, but then diverge a little for the
weekend into early next week, but most paint a sharp warmup in 
line with flat upper ridge/westerly downslope flow.

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 128 PM MDT Mon May 18 2026

Current Water Vapor and upper air models show troughing just east
of the Rockies running through the northern and central plains,
with upper ridges over the New England region and off the west
coast. 19Z surface analysis depicts a surface low to our east over
MN, surface high over central MT. Radar shows widespread
precipitation across the forecast area, with some of the higher
elevations receiving light accumulations of snow today. Winds are
currently breezy out of the northwest to north, with temperatures
in the 30s to low 40s. 

Precipitation will taper off from west to east late afternoon
through the evening, as trough slides eastward today. Cool
temperatures continue tonight as clouds clear up and light
northwest winds continue. Much of the area is expected to reach
near or below freezing overnight. HREF probability for temps to
reach at or below freezing sit at 80-100% for areas from the Black
Hills and west. Further east will be a bit trickier as cloud cover
will linger into tonight as the trough slowly shifts eastward. A 
Freeze warning has been issued for most of our plains areas, with 
a frost advisory in effect for part of south-central SD for 
Tuesday morning. 

Brief and weak ridge sets over the region mid-week, resulting in
drier conditions and a warming trend towards near seasonable.
Another wave rides southeast from western Canada towards the
northern plains later in the week, increasing chances for
precipitation late Thursday into Friday. Shortwave ridging moves
over the weekend, bringing warmer temps back in as well. By
Sunday/Monday the region should see highs climb back into the 80s
to low 90s. 

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1055 PM MDT Mon May 18 2026

Some low clouds remain in the area tonight as the earlier
precipitation moves out. Ceilings will slowly improve through the
night. For KRAP, cloud base will be around 5kft at the start of
the forecast period (06Z) and lifting. Relatively calm winds and
IFR conditions are expected for Tuesday.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Freeze Warning until 9 AM MDT Tuesday for SDZ001-002-012>014-
     025>027-030>032-041>044-072>078.
     Frost Advisory until 10 AM CDT Tuesday for SDZ046-047.
WY...Freeze Warning until 9 AM MDT Tuesday for WYZ054>056-058>060.
&&

$$

UPDATE...Helgeson
DISCUSSION/KEY MESSAGES...Dye
AVIATION...Schweigert