Area Forecast Discussion
Issued by NWS Rapid City, SD

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757
FXUS63 KUNR 171255
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
555 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 12Z TAFS Through 12Z Saturday Morning)
Issued At 553 AM MST Fri Nov 17 2017

MVFR and IFR conditions are expected across parts of the area
today as rain and snow affects northeast Wyoming and western South
Dakota. IFR conditions are especially possible across the Black
Hills area as snow falls over the area. Conditions will improve to
VFR tonight as drier air moves in.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...13



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