Area Forecast Discussion
Issued by NWS Rapid City, SD

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655
FXUS63 KUNR 212021
AFDUNR

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

.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 18Z TAFS Through 18Z Wednesday)
Issued At 218 PM MDT Tue Mar 21 2017

Widespread IFR/local LIFR conditions will continue over western
SD through this evening with some improvement late, and especially
Wednesday morning. Areas of -FZDZ/FZFG/BR will be present. Later
tonight, some -FZRASN are expected over western SD. Areas
IFR/local LIFR conditions due to stratus/BR over northeast WY
will slowly improve this evening with rapid improvement overnight.

&&

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

$$

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



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