Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 200520

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1020 PM MST Sun Nov 19 2017

.DISCUSSION...(This Evening Through Sunday)
Issued at 256 PM MST Sun Nov 19 2017

Current surface analysis shows weak low pressure over south
central Canada, with warm front north and east of the area. Upper
level analysis shows large scale trough over the eastern US, with
broad ridge covering the western US. Warmer air has pushed into
the area, with temps in the 50s across the plains, 40s over the
Black Hills. High clouds are spilling over the ridge to the west,
with some filtered sun at times in most areas. Winds have mostly
turned to the southwest across the area, breezy over northeast WY.

A dry and mostly mild pattern will continue this week as general
pattern aloft remains in place across the region. The main weather
feature for the next several days will be a passing cold front
Monday afternoon and evening, bringing a chance of rain and snow
showers over parts of the area. The one cold day of the week will be
Tuesday, otherwise above average temps will persist through at least
Friday. Medium range models are in pretty good agreement through
much of the period.

Skies will be mostly clear to partly cloudy tonight into Monday
morning. Milder conditions can be expected tonight, with lows mostly
in the mid 20s to mid 30s. Monday highs will be in the mid 50s to
mid 60s, with increasing clouds by the afternoon as cold front
approaches. Breezy west-southwest winds can be expected tonight into
Monday across much of northeast WY. Winds will increase by late
Monday afternoon across northwest SD as cold front begins to push
through. There will be a chance for rain and snow showers Monday
night, mainly from northeast WY through the Black Hills area, as
post-frontal shortwave slides through western and southern portions
of the area. There could be a light snow accumulation across some of
the higher elevations, but should generally be less than an inch.
Breezy conditions can be expected late Monday into Tuesday as cold
front pushes through with strong cold advection. Tuesday will be a
chilly day, with highs in the 30s to mid 40s, warmest over northeast
WY and far southwest SD.

The colder air will be short-lived as ridge rebuilds over the
western states. Highs will be back in the 50s and 60s for Wednesday
through Friday, with highs possibly near 70 in a few spots south and
east of the Black Hills on Thanksgiving day. Another cold front is
progged to cross the area on Friday, dropping temps back to more
seasonable levels for the weekend. There are some differences
between the medium range models as far pcpn chances go Friday into
the weekend. GFS now mainly dry, while EC shows chances mostly with
the front. Will keep some pcpn chances on Friday for now.


.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1020 PM MST Sun Nov 19 2017

VFR conditions will continue through Monday afternoon. Gusty west
to northwest winds will be the main concern through the first half
of the TAF period as a cold front approaches and crosses the
region. Ceilings will begin to lower late Monday afternoon and
evening, with some MVFR ceilings possibly developing after 00z
Tuesday. A few showers may also occur 00-06z Tuesday at GCC, but
confidence is too low to include in the TAF at this time.


Issued At 256 PM MST Sun Nov 19 2017

Mild and dry conditions can be expected across the area Monday,
ahead of an approaching cold front. Relative humidities will drop
to around 20 percent Monday afternoon across southwest SD, with RH
values in the 20s elsewhere. West to northwest winds will
increase as the front moves into the area during the afternoon. A
period of elevated fire weather conditions is likely across a good
portion of the forecast area Monday afternoon, with high to very
high grassland fire danger across the western and south central SD




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