Area Forecast Discussion
Issued by NWS Rapid City, SD

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700
FXUS63 KUNR 210938
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
238 AM MST Tue Nov 21 2017

.DISCUSSION...(Today Through Monday)
Issued at 216 AM MST Tue Nov 21 2017

Water vapor shows trof axis moving from the Dakotas into the upper
Midwest, and upper ridge over the western CONUS. Short wave at the
base of trof resulting in band of light snow shifting southward
through the cwfa. At the surface, high pressure building into the
Northern Plains early this morning with brisk northwest winds and
much colder temps.

Light snow will quickly shift south of the region around daybreak,
with clearing skies as much drier air works in from the north.
Temps today will be much colder than yesterday, but still very
close to average. Gusty northwest winds will diminish later this
afternoon with Canadian high moving into the central Dakotas.

Warm advection will return in earnest tonight as lee trof quickly
advances into eastern MT/WY. Much warmer temps and dry conditions
then expected Wednesday and Thanksgiving as upper ridge axis
shifts eastward across the Northern Rockies/Plains. Temps well
into the 60s expected Wednesday, with some lower 70s on
Thanksgiving day. Will probably see some record highs set on
Thanksgiving.

Next upper trof will arrive on Friday, bringing gusty northwest
winds and cooler temps, along with some light pcpn. Have trended
winds upward from guidance give the strength of upper trof and
cold advection.

Upper ridge then rebuilds for the weekend into early next week
for more dry and very mild conditions. Would not be surprised to
see more record highs by next Sunday or Monday as thermal ridge
axis passes overhead.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1033 PM MST Mon Nov 20 2017

VFR conditions continue across TAF sites for now. However, IFR
CIGS and/or VSBYS are ongoing across northeast WY and the northern
Black Hills and should continue through most of the overnight.
Expect GCC to fall to MVFR by 06z as lower CIGS upstream
approach. Should also begin to see sufficient moistening for snow
to reach the ground around this time. Not currently expecting IFR
CIGS/VSBYS at GCC, but it is plausible that IFR conditions could
briefly occur through 10z. Snow should end by 12z as mid and upper
levels dry rapidly, but low CIGS will continue into Tuesday
afternoon. Western SD (outside of the Black Hills) may temporarily
drop to MVFR CIGS/VSBYS with light rain/snow showers tonight, but
conditions should improve to VFR for most of Tuesday.

&&

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

$$

DISCUSSION...Johnson
AVIATION...Calderon



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