Area Forecast Discussion
Issued by NWS Rapid City, SD

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043
FXUS63 KUNR 161102
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
402 AM MST Thu Nov 16 2017

.DISCUSSION...(Today Through Wednesday)
Issued at 231 AM MST Thu Nov 16 2017

09z surface analysis had weak low pressure over southeast MT with
a stationary boundary into southern SK and a warm front into
central NE. Pressure falls increasing along boundary as warm air
advection increases under upper ridge in place over the central
US. Upper trough digging across southwest Canada into northwest
US, which will be the main concern in the short term.

Today, thermal ridge peaks over the CWA with sustained pressure
falls across the region. Warm front will move slowly northeast today
as lee trough pushes into eastern WY. Mixing between these two
features will partially tap into 40-60kt 700mb winds over the far
southwest portions of the CWA. Latest guidance shows 25-35g50 MPH
likely across southern Campbell County and potentially into
southern Weston County. Strongest winds should remain southwest
of CWA. Rest of CWA will see breezy/windy spots, but lower mixing
heights north of boundary will bring lower wind potential along
with a tight temperatures gradient from northeast to southwest.

Tonight, upper trough moves into the Rockies with surface low over
western MT moving into SK. It will drag weak trough into the CWA.
Narrow band of weak frontogenesis behind trough will support low
pops especially late across northwest portions of the area as weak
shortwave moves across the CWA. Temperatures will be near guidance.

Friday, upper trough moves into the northern Plains as main cold
front is propelled through CWA in response to better defined
shortwave energy moves across eastern MT/WY into the CWA. Narrow
band of moderate 850-700mb frontogenesis forecast by models behind
cold front along with rapidly decreasing condensation pressure
deficits. Models continue to differ on placement of precipitation
band as well as amounts. Snow amounts range from 1-2" to several
inches or more across the far north, but consensus is around 1"
possible across northern half of CWA given mixed precipitation
possible. Later shifts will need to watch with sustained band
likely being all snow given wet bulb profiles.

Cooler temperatures Saturday will be replaced by above normal
temperatures Sunday and Monday. Then, substantial guidance
uncertainty develops for the rest of the upcoming Thanksgiving
Holiday. Consensus is near normal to above normal temperatures
with little precipitation, but confidence is low.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 355 AM MST Thu Nov 16 2017

VFR conditions are expected through the period. Low-level wind
shear will continue across parts of the area this morning. Look
for breezy SW winds across the SW half of the area today,
especially across northeastern WY. Winds will shift NW behind a
cold front this evening, and light rain/snow will begin moving
into the CWA after midnight.

&&

.FIRE WEATHER...
Issued At 231 AM MST Thu Nov 16 2017

Gusty south to west winds expected today with minimum relative
humidities dropping into the 20s creating elevated fire danger,
especially across northeast WY into southwest SD. Colder and
moister air settles in tonight into Friday as a cold front moves
through and precipitation chances increase.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...Pojorlie
FIRE WEATHER...Helgeson



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