Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 242250
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
450 PM MDT Sat Oct 24 2020

.DISCUSSION...(This Evening Through Saturday)
Issued at 151 PM MDT Sat Oct 24 2020

Upper level analysis and water vapor imagery depict largely zonal
flow across the northern half of the US with 100+ knot jet slowly
lifting northeastward. The lead shortwave is pushing east of the
forecast area through the area. In its wake, broad large-scale
ascent ahead of another approaching trough and mid-level
frontogenesis is supporting widespread light snow this afternoon.
Could see areas of banding/enhanced snowfall through the afternoon
across the northern half of the forecast area as this area of
frontogenesis strengthens and moves eastward. Second wave is
quickly pivoting through NW WY and will continue to push eastward
this afternoon and evening. Additionally, strong frontogenesis,
especially along and south of the SD/NE border will drive areas of
heavier snow late tonight into the overnight hours as this upper
trough pivots through the region. As winds turn more northerly
later today, upslope enhancement is likely across the northern
Black Hills through Sunday morning, where locally heavy snow is
possible. Overall, current headlines are on track for a relatively
prolonged light- to-moderate snowfall event.

Breezy winds of 10 to 20 mph with gusts up to 30-35 mph will result
in some blowing and drifting snow, especially across the plains.
These winds coupled with snow will result in reduced visibility
through at least Sunday morning. Conditions will then gradually
improve from north to south on Sunday as winds decrease and snowfall
wanes.

Once the arctic front surges southward late tonight, much colder air
will quickly filter into the Northern Plains. Temperatures tonight
through Tuesday morning will likely be at or near record highs/lows
as 850 mb and 700 mb temperatures plummet to around -14 to -16C and
-16 to -20C, respectively. These temperatures would rank at or
 very near the bottom of the NAEFS/EPS climatological minimums.
 Wind chills will fall to around zero tonight and again on Monday
 night, but will bottom out as low as 20 below Sunday night.
 Conditions then turn warmer and dry Tuesday through the rest of
 the week. Warm air advection and more zonal flow/weak ridging
 will allow for temperatures to warm to near normal temperatures
 by mid-week through next weekend; however, fresh snow cover will
 likely result in a more gradual return to normal temperatures as
 the snow cover slowly erodes.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 448 PM MDT Sat Oct 24 2020

Widespread IFR/LIFR conditions will persist through early Sunday
morning due to snow and gusty north winds. Conditions will
improve Sunday morning through Sunday afternoon as the snow ends.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Warning until noon MDT Sunday for SDZ024-025-072.

     Winter Storm Warning until 6 PM MDT /7 PM CDT/ Sunday for
     SDZ042>044-046-047-049.

     Winter Weather Advisory until noon MDT Sunday for SDZ026>031-041-
     073-074.

     Winter Weather Advisory until 6 AM MDT Sunday for SDZ001-012-013.

     Winter Storm Warning until 6 AM MDT Sunday for SDZ002-014-032.

WY...Winter Storm Warning until noon MDT Sunday for WYZ057.

     Winter Weather Advisory until noon MDT Sunday for WYZ054>056-058.

     Winter Weather Advisory until 6 AM MDT Sunday for WYZ071.

&&

$$

DISCUSSION...Eagan
AVIATION...7



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