Area Forecast Discussion
Issued by NWS Rapid City, SD

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035
FXUS63 KUNR 130928
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
228 AM MST Sat Jan 13 2018

.DISCUSSION...(Today Through Friday)
Issued at 228 AM MST Sat Jan 13 2018

Near Omega block setup over NOAM will eventually breakdown in the
period as massive ridging over the western Atlantic subsides.
Arctic trough over the eastern CONUS will linger a few more days
with backside impulses supporting a wavering baroclinic zone over
the region. Two decent impulses will advect through the flow the
next couple days in NW flow supporting chances for snow over much
of the FA, esp the northern Black Hills where a moderate upslope
component will sustain. WAA wing of the advancing impulse is
already supporting snow across portions of NE WY and far western
SD this morning. Snow will continue to spread SE across the FA
this morning, with generally light accums expected outside of the
northern Black Hills. Favored NW flow upslope areas in the
northern Black Hills can expect 2-4 inches of snow today, with the
higher amounts generally above 6 kft. Linked flow under a jet
streak will support decent upslope enhancement in moist NW flow,
with steep LL lapse rates supporting deeper snow production layer
into the DGZ at times. Outside of the northern BH expect a half
inch or less accums. Upper wave and associated precip will wind
down this evening, with upslope forcing lingering through much of
the evening. As the upper wave exits and ice prod layer is lost
aloft, upslope forcing may support a period of freezing drizzle
over parts of the northern BH late tonight into Sunday morning,
esp as WAA revs up ahead of the next wave. Temps will vary sig
across the FA today as WAA spreads into and remains confined to
the higher terrain of NE WY and BH. Look for highs around 40 NE WY
to teens on the SD plains.

The next impulse will arrive Sunday afternoon, supporting another
round of snow across the region into Sun night. Snow is expected
to be more widespread as this wave will shift the arctic front
back west, with most places seeing at least a few tenths to an
inch of snow. The northern Black Hills will again see the most
snow as another round of upslope enhancement will be in place.
Current forecast amounts are for 2-4 inches there. Snow should end
most places in the evening, with perhaps lingering flurries in
vicinity of the front overnight into Monday. Temps will rise into
the 30s and 40s ahead of the arctic front Sunday, warmest in the
lee of the Black Hills. Expect temps to fall back below zero most
places by Monday morning.

Flow will become progressive across the western CONUS mid week
with a warm up on track for the rest of the week as fast PAC flow
becomes est. Highs into the 40s and 50s look probable by the end
of the work week as westerly flow spreads into the region and
arctic air remains confined to Canada for the time being. Forecast
models do support semi-amplified flow with a few fast moving
systems likely in the flow toward the weekend. However, given the
pattern and storm track, any precip looks to be minimal attm.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 1017 PM MST Fri Jan 12 2018

Areas of MVFR conditions will continue through tonight, with some
IFR conditions redeveloping especially across the Black Hills
area. Expect Areas of light snow and flurries tonight into
Saturday morning from far northeast WY to the northern Black Hills
area, spreading east onto the SD plains Saturday afternoon.

&&

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

$$

DISCUSSION...JC
AVIATION...Johnson



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