782 
FXUS63 KUNR 312312
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
412 PM MST Thu Dec 31 2020

.DISCUSSION...(This Evening Through Thursday)
Issued at 222 PM MST Thu Dec 31 2020

Shield of AC continues to stream over the area this aftn as a weak 
shortwave and attendant upper jet streak move thru the n cntrl 
CONUS. More substantive features evident on CONUS WV imagery include 
a robust cyclone taking shape across the srn Plains/Lower MS Valley 
and another upper low digging thru the desert SW. Farther west, an 
upper ridge axis is shifting from the ern Pacific toward the West 
Coast. Closer to home, winds generally contain a westerly component 
aside from some locations in the immediate vicinity of the Black 
Hills, which are dominated by upslope. Temperatures are mild for the 
end of the year, with near to above readings area-wide and the 
coolest temps in areas with continued snowpack.

Aforementioned upper ridge will flatten as it shifts ewd toward the 
Rockies/Plains thru the end of the week. This will promote fairly 
progressive upper flow over the region, with several weak shortwaves 
crossing the nrn High Plains from now thru the beginning of next 
week. However, given that none of these disturbances are associated 
with substantial deep moisture or appreciably cooler air, main 
impact of each will be a period of breezy conditions. In particular, 
pressure gradient tightens considerably across portions of southern 
Campbell County during both Friday night and Saturday night as trofs 
approach, which could lead to some gusts in excess of 40 kt both 
nights into the following mornings. Additionally, strong winds look 
possible across nwrn SD late Sunday/early Monday as a more robust 
cyclone passes to our north. Low-level thermal ridging will 
generally build thru Sunday, allowing above normal temps to continue 
thru at least the end of the weekend. 

Differences in pattern evolution continue in guidance beyond Monday. 
Regardless, ensemble probabilities of measurable precip increase in 
the Tuesday-Wednesday time frame across all model suites, especially 
across the Black Hills and nern WY. That said, probabilities of over 
0.1 of an inch of precip remain very low for much of the area thru 
the middle of next week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 411 PM MST Thu Dec 31 2020

VFR conditions will continue through the TAF forecast period.

&&

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

$$

DISCUSSION...Sherburn
AVIATION...JC