349
FXUS63 KUNR 181745
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1045 AM MST Tue Nov 18 2025

.KEY MESSAGES...

- Patchy/Areas of fog this morning, some locally dense

- Weak wave may bring isolated showers to northwest SD tonight

- Temperatures still on track to remain seasonable to slightly
  above seasonable through the week

&&

.DISCUSSION...(Today Through Monday) Issued at 226 AM MST Tue Nov
18 2025

Latest analysis shows closed 500hpa low located over NW Iowa with
associated cloud shield pushing east out of the CWA. Upper
ridging is seen along the Rockies, with another 500hpa closed low
spinning off of CA coast. There is another 500hpa low spinning
along the WA/BC border. Water vapor imagery is also showing minor
500hpa wave ejecting out of CA low into western UT, which this
will become a player in the forecast for tonight. At the surface,
surface low located in northwest MO with high pressure trying to
build into region from northeast ND into northern CO. At 09Z
satellite imagery is also showing skies trying to clear across
northeast WY and parts of northwest SD.

First forecast concern is the probabilities for fog this morning,
how widespread and how dense? Forecast model soundings are showing
low level saturation hanging on until the 15Z-18Z time frame, and
ensembles are showing probabilities of visibilities < 0.5 mile
ranging from 20% on the plains, to around 40% along the foothills
of the Black Hills. For now, will keep the patchy/areas of fog
wording going in the grids and monitor for fog headlines as we get
closer to sunrise when temps will bottom out and see how
widespread clearing skies are. Highs today will be fully dependent
on how long the low clouds/fog stick around. For now, have opted
to lower highs roughly a category due to anticipated cloud cover
and lack of mixing.

Next attention getter deals with aforementioned wave ejecting out
of CA closed low. This doesnt really begin to generate any
rainfall until aft 03Z Wednesday, and then across southeast MT.
Models show 700hpa theta-e downglide pushing in across the Black
Hills and nosing into northwest SD, and deterministic pcpn
forecast keeps all of the rain in an area from southeast MT into
southwest ND, keeping our northern counties dry. However,
ensembles do paint probabilities of 20-40% of seeing at least
0.03 rainfall across the northern counties. Ended up pushing pops
a bit further north during the overnight period tonight.

The remainder of the week appears to be mainly dry. The next
surface trough will drop through Wednesday night which may (key
word) bring some isolated sprinkles/flurries to the higher
elevations of the Black Hills, but not overly confident as
moisture is a limiting factor. Cold air advection follows this
trough, setting forecast highs back a notch on Thursday, but for
mid-November, still not bad. Considering that normal highs for
this time of year are in the mid 40s to near 50 on the plains, and
mid 30s to lower 40s in the hills, highs this week will still be
above seasonal norms.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1041 AM MST Tue Nov 18 2025

Areas of MVFR/IFR/LIFR conditions will persist across portions of
western South Dakota this afternoon as low clouds linger. Some
improvement to transient MVFR/VFR conditions is expected after
19/06-08z tonight. Another low probability (<30%) of IFR
conditions again at KRAP after 12z Wednesday morning, but have
kept mention out of the TAF with this forecast update.

&&

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

$$

DISCUSSION/KEY MESSAGES...Smith
AVIATION...SE