Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 170912
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
212 AM MST Fri Nov 17 2017

.DISCUSSION...(Today Through Thursday)
Issued at 210 AM MST Fri Nov 17 2017

09z surface analysis had low pressure over eastern SD with
initial cold front into east central WY. Water vapour showed
region under influence of left exit region of 130kt jet streak
which is combining with weak 850-700mb frontogenesis behind front
to produce some radar returns across northwest half of CWA. Lots
of dry air in place, but some precipitation reaching the ground.
This initial forcing will continue this morning as cold front
exits the CWA to the south. Secondary cold front will push through
CWA this afternoon/early this evening with moderate frontogenesis
under main shortwave trough moving into the CWA. Additional
RASN will develop with mainly SN over the higher elevations.
Accumulations by this evening will be an inch or less on the
plains where it snows and 1 to locally 3 inches over the northern
Black Hills. Froude numbers don`t become favorable for upslope
until 03z, but by that time drier boundary layer air will be in
place. Upslope enhancement should be minimal. Temperatures today
and tonight will be near guidance.

Saturday through Monday, CWA under the influence of upper ridge with
a warming trend. Shortwave drops a cold front through the CWA for
Tuesday with a brief cooldown before upper ridge builds back for the
end of next week. Still significant spreads for Thursday/Friday for
temperatures, but consensus continues to be 10-15F above normal
temperatures and mainly dry weather.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1009 PM MST Thu Nov 16 2017

A cold front will continue to slip southward tonight bringing
with it gusty winds and winds shifting to the north. Once the
front has passed winds should die down. MVFR ceilings will spread
into northeast Wyoming and northwest South Dakota tonight and
continue into Friday. Local IFR ceilings will be found near the
Black Hills. Scattered rain/snow showers will also develop across
northeast Wyoming into northwest South Dakota tonight and continue
into Friday. MVFR visibility with the rain showers and IFR
visibility with the snow showers.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...Foscato



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