Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 220514

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1114 PM MDT Tue Mar 21 2017

Issued at 1008 PM MDT Tue Mar 21 2017

Widespread dense freezing fog and freezing drizzle is ending
across the area and visibilities continue to increase. Therefore
have cancelled the Freezing Fog Advisory that was in effect.


.SHORT TERM...(This Evening Through Wednesday Night)
Issued at 218 PM MDT Tue Mar 21 2017

20z surface analysis had 1042mb high over southern MB with east
to southeast flow over the CWA. Upslope flow sustaining dreary
day over much of the CWA. Frontal boundary on southwest edge of
high from southeast WY into western MT. Latest water vapour loop
had upper ridge heading into the plains with a couple of weak
shortwaves over ID and NV. These waves heading in our direction
for tonight.

Tonight, upslope flow continues with strengthening warm air advection
from 850-700mb in response to shortwave energy passing through. At
least through this evening, expect upslope fog mixed with drizzle or
freezing drizzle (depending on ground temperatures) to continue,
especially on the SD plains and eastern slopes of the Black Hills.
Gradient tightens considerably with low level jet developing. This
will cause gusty winds over northeast WY and the higher Black Hills
as well as the frontal boundary to move northeast as a warm front.
Synoptic support for precipitation is there with forecast soundings
suggesting a wintry mix at times. Ice accumulations should be light,
but will need to be watched if sustained -FZRA develops.

Wednesday, upper ridge builds into the CWA with much warmer
temperatures and precipitation ending early. Temperatures will be
near guidance.

Wednesday night, upper low pulls into the southwest US with impulse
laden southwest flow across the CWA which will support a chance of
mainly rain, possibly mixed with snow over the higher elevations.
Lows will be near guidance.

.LONG TERM...(Thursday Through Tuesday)
Issued at 218 PM MDT Tue Mar 21 2017

Upper low moves from the four corners area Thursday to the
southern plains by Saturday morning with good model consistency.
Several pulses of energy will move through the CWA with decent
waves for the far northwest Thursday and then the southwest
Thursday night, where some convection may occur. Thermal profiles
show mostly a rain event at this point, but some snow could sneak
in over the higher elevations at night and possibly near the NE
border if dynamic cooling extends far enough north from main upper
low. Temperatures will be seasonal.

Sunday and Monday, progressive flow expected with PoPs warranted at
times, although timing confidence low given fast flow. Temperatures
will remain seasonal with cold air bottled up north of the CWA.


.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1109 PM MDT Tue Mar 21 2017

IFR CIGS will local LIFR conditions in low stratus and fog will
occur over the Black Hills and parts of far western South Dakota
until 11Z-15Z on Wednesday morning. VFR conditions will then
prevail on Wednesday and Wednesday evening. Isolated rain showers
or showers of light freezing rain are possible during the rest of
the night.




SHORT TERM...Helgeson
LONG TERM...Helgeson
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