Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 191117
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
417 AM MST Tue Feb 19 2019

.DISCUSSION...(Today Through Monday)
Issued at 310 AM MST Tue Feb 19 2019

Current surface analysis shows Canadian high pressure to the east
of the region, with very cold air remaining in place across the
northern Plains. Upper level analysis still shows large scale
trough over the western US, with a couple of lows within in the
trough. One is located over the Four Corners region and the other
is over central MT. Shortwave energy in southwest flow aloft over
the high plains is bringing increasing cloudiness to the area.
Regional radars show some areas of light snow over southeast WY
and NE. Temps are below zero across much of the area. Temps have
risen a bit where clouds have moved in, above zero in parts of
northeast WY and southwest SD. Winds are relatively light across
the area, though they have picked up a bit from the south across
Campbell County. Wind chill values are as low as around 25 below
over parts of far northwest SD. Some fog has also developed in the
valleys across parts of northwest into south central SD.

The system over the southwest US will move quickly northeast into
the Plains today and tonight, with the moisture starved upper low
over MT moving slowly eastward and helping to keep most of the pcpn
with the southern system south and east of the region. However,
shortwave energy ahead of the MT low will bring some light snowfall
today into tonight, especially to the south and east of the Black
Hills, Accumulations will be very light in most areas from the Black
Hills eastward, less than an inch. An inch or two of accumulation is
possible over far south central SD later today and tonight as some
moisture front the southern system clips the area. Highs today will
be a bit warmer with southerly flow, teens to lower 20s, with
considerable cloud cover.

Wednesday into Thursday will be relatively quiet between systems,
but temperatures will remain well below average. Highs will mostly
be in the mid teens to mid 20s, though it will be a bit warmer
across far southern areas each day, especially where less snow cover
is in place. Medium range models continue to have a hard time with
track and speed of systems late this week into the weekend. Looks
like another system will dig south across the western US Thursday
and then move east-northeast into the Plains Friday and Saturday.
How this system organizes as it moves across the Rockies and into
the Plains is the main question. Latest runs have the main low
tracking south of the region Saturday, with weaker shortwave energy
moving across the Northern Plains Friday into Saturday. Latest EC
and Canadian models show weaker systems and relatively light
snowfall potential across our area, while the GFS is stronger with
northern stream energy and allows more moisture to make it into the
forecast area, especially southwest into central SD. Will keep
higher pops in those areas for Thursday night through Friday night.

The weekend looks relatively dry for most areas, especially for
western areas, but will have to see what happens with the central
Plains system early in the weekend. Highs will still be below
average, mostly in the upper teens and 20s. Some unsettled weather
could return by early next week with the cold temperatures
persisting through the end of the month.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Wednesday Morning)
Issued At 412 AM MST Tue Feb 19 2019

Areas of fog will persist over northwest South Dakota early this
morning, with local LIFR conditions. MVFR ceilings over portions
of northeast Wyoming into southwest South Dakota will continue to
push northward through this afternoon. Light snow will spread into
the area this morning with areas of IFR visibility, especially
across southwest and south central South Dakota.

&&

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

$$

DISCUSSION...26
AVIATION...7


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