461
FXUS63 KUNR 171718
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1018 AM MST Mon Nov 17 2025

.KEY MESSAGES...

- Soggy overcast day in store for today

- Surface trough passing through Thursday will bring next chance
  for pcpn

- Temps to remain seasonable to perhaps slightly above seasonable
  through the week

&&

.DISCUSSION...(Today Through Sunday)
Issued at 239 AM MST Mon Nov 17 2025

Latest water vapor imagery shows 500hpa negative tilted ridge
axis from gulf coast into eastern MT with closed 500hpa low
located in southwest WY with extensive cloud shield across WY and
western NE and lifting into southwest SD. At the surface, low
pressure is located across southwest SD with a warm front along
the NE/SD border and a trough dropping south through the panhandle
of NE. Latest radar imagery shows weak returns across southwest
SD. Webcams from the area are showing perhaps some dibble-dots on
camera lenses, but feel that most of this is just mid-level
cloudiness helping to moisten things up for later today.

The main fcst concern is the closed 500hpa low previously
mentioned that deepens slightly as it moves quickly across
northern NE. 700hpa theta-e warm advection (trowel) becomes
established during the day today as cold air at 850hpa filters in
behind quick moving system. Models are fairly adamant about a
banded pcpn event setting up with the trowel. Ensembles by 00z
Tuesday are showing 6-hourly probabilities of greater than 0.25
from 30-50% from the Black Hills to near Eagle Butte. 6-hourly
probabilities of greater than 0.10 range from 40 to 90% across
much of the CWA except for south central SD and Campbell Co, WY.
Have left the inherited slight pops for convection along the NE/SD
border for this afternoon as models cont to show weak MUCAPE
creeping along the NE/SD border this afternoon, and ensembles are
showing 15-20% probabilities of lightning across the southern
counties within 10km of a point. The coldest air attm appears to
stay off to the east, so have kept all the pcpn in the form of
light rain, even for the highest sections of the hills, although
somebody reporting a few flakes late in the day wouldnt be too
shocking. With the moisture advection and rapidly moistening
layers, have introduced some patchy fog into the grids as well,
although admit this may take the form of some patchy drizzle
versus fog. Pcpn should come to a fairly quick end this evening as
the upper low and associated surface systems slide quickly east.

Upper flow then becomes basically zonal Tuesday through Thursday
with little in the way of movement with 850hpa temps (they
basically stay in the 6-10 C range). Next 500hpa trough slips
through the upper plains during the day Thursday, dragging a
surface trough/cool front with it. This will be the next chance
for pcpn during the week, but the chances look weak at best.

Looking into the long range crystal ball, it still appears that
some of the coldest air yet of the season may be headed our way
during the week of Thanksgiving. Well dial that in as we get
closer.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1014 AM MST Mon Nov 17 2025

Low pressure will move along the NE/SD border today, bringing
widespread areas of light rain and low clouds to the area. A band
of heavier showers is slowly pushing northward from southwestern
SD into the Black Hills area. Look for MVFR to IFR ceilings and
visibility to develop across the Black HIlls and plains of
western SD after 19-21z. The rain will end from west to east aft
18/06Z with lingering MVFR/IFR ceilings overnight.

&&

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

$$

DISCUSSION/KEY MESSAGES...Hintz
AVIATION...SE