707 
FXUS63 KUNR 021051
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
351 AM MST Sat Jan 2 2021

.DISCUSSION...(Today Through Friday)
Issued at 232 AM MST Sat Jan 2 2021

09z surface analysis had low over central AB with trough into 
eastern WY. 2-3mb/3hr pressure falls along trough supporting 
increasing southwest winds over part of northeast WY. Water 
vapour loop had upper trough moving into the northwest CONUS with 
shortwave ridge over the Rockies. Thin cirrus spilling into the 
northern Plains.

Today/tonight, upper trough zips across the northern Rockies into 
the northern Plains. Surface trough moves through late this 
afternoon/evening. Synoptic forcing/moisture fairly weak, but 
sufficient to keep low pops across the northwest third of the CWA. 
Gusty early morning southwest winds ahead of surface trough over 
northeast WY/Black Hills will become gusty northwest behind it later 
this afternoon/early evening mainly over northwest SD. Temperatures 
will be similar to yesterday, but perhaps a bit warmer over areas 
that lose their snowcover.

Sunday, another fast-moving shortwave trough will move across the
US/Canadian border pushing dry front through the area Sunday 
evening. 30-50kt 850mb winds, but timing of front not ideal and 
cold air advection not that strong. However, 2-3mb/3hr pressure 
rises will support a few hour period of stronger gusty northwest 
winds especially along the northeast/east slopes of the Black 
Hills where boundary layer winds forecast around 35kts.

Next week, west/northwest progressive flow aloft will continue. A
series of moisture-starved disturbances will drop by. Pops 
continue to be painted for the wave late Tuesday in association 
with a splitting upper trough. Ensemble probabilities of 
impactful precipitation virtually zero. Interesting fact, the 
chance of 1"+ of snow through January 18 is only 50-60% on the SD 
plains per GEFS/EC.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 348 AM MST Sat Jan 2 2021

VFR conditions are expected this morning and early afternoon. 
Breezy south to southwest winds will continue across northeast WY 
and the Black Hills overnight. Winds will shift NW behind a low 
pressure trough this afternoon. This system may bring some light 
rain or snow showers to NE WY and through NW SD this afternoon and
evening. MVFR conditions are possible...even dropping to IFR with
any heavier showers. VFR conditions will return tonight.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...13