Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 231046
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
346 AM MST Thu Feb 23 2017

.SHORT TERM...(Today Through Friday Night)
Issued at 346 AM MST Thu Feb 23 2017

Upper Level analysis shows large scale trough over the Pacific NW
and the intermountain west, with low pressure over northern UT,
moving to the east southeast. Strong shortwave and jet energy is
rotating around the low and moving northeast across northwest CO,
southern WY, and now into southwestern portions of our area.
Current surface analysis shows low pressure over western CO, with
secondary low pressure developing over southeast CO. This
secondary low will become the primary one as it strengthens and
moves into KS later today. Colder air is in place now, with temps
in the upper 20s and lower 30s. Regional radars show light
snowfall has moved into southern portions of northeast WY and
southwest SD, with the heaviest snowfall still across southeast WY
and western Neb. The heavier snow will move into southern
portions of northeast WY and southwest SD over the next few hours.

00Z model runs are in decent agreement on the upper level system
moving across the region over the next 24 hrs. They have now come in
with the upper low a bit weaker, faster, and further south as it
crosses the region later today and tonight. This would shift the
heavier snowfall a bit further south across the southern CWA and
push the heaviest snow to near the Nebraska border and points to the
south across northern Neb. The adjustments are relatively minor to
the downward side, but the northern edge of the warning area would
likely not see quite as much snow as was previously expected, but
still several inches expected at this point from Spearfish, eastward
across much of southern Meade County and into Haakon County. There
still looks to be a sharp cutoff in snowfall across northwest SD,
with Harding and Perkins counties seeing little or no snowfall,
especially toward the ND border. Will keep current warning and
advisory coverage as is, but have trimmed back the ending times
across northern portions of the headline area to late tonight as
snow ends earlier and conditions should improve significantly by
morning. Also pushed back the end timing for south central SD to
midday Friday.

Snow will be heaviest in most areas during the daytime hours, into
the evening across south central SD. Snow will be heavy at times
across far southern SD today and far southern portions of northeast
WY this morning as best lift moves across these areas, with 1"+/hr
rates expected at times. Snow will decrease in intensity tonight,
especially overnight, with most of the accumulating snow done by
daybreak in most areas. With the surface low forecast to track a
little further south and east across the Central Plains into the
upper Midwest, winds do not look to be quite as strong, though
likely strong enough to produce at least some patchy blowing and
drifting snow, especially to the south and east of the Black Hills
later today into Friday.

Projected snowfall totals at this time generally range from 0 to 2
inches across most of northwest SD, 2 to 4 inches across far
northeast WY, 4 to 8 inches across most of the Black Hills, and 8 to
15 inches across far southern SD, with portions of northeast WY
south of Wright and Clareton receiving close to a foot. The heaviest
snowfall will likely end up being across the Pine Ridge, as well as
over any banded areas that develop over far southern SD. Along the
Interstate 90 corridor, amounts of 2 to 5 inches are forecast across
northeast WY, with mostly 4 to 7 inches from Spearfish to
Chamberlain.

.LONG TERM...(Saturday Through Wednesday)
Issued at 346 AM MST Thu Feb 23 2017

Mostly dry weather is expected over the weekend and early next
week as drier northwest flow is in place. Weak disturbances will
bring clouds and the possibility for snow showers at times, mainly
across far northeast WY, the Black Hills, and northwest SD. Best
chances at this time look to be Saturday afternoon and evening and
then again Monday night into Tuesday. Temperatures will be
slightly below average over the weekend, with highs in the mid 20s
to mid 30s, then near average temperatures for much of next week.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 346 AM MST Thu Feb 23 2017

Snow with IFR/LIFR conditions will overspread northeast WY, along
with the southern 2/3rds of western SD this morning. These
conditions will continue through the evening hours, with snow
heavy at times today across far southern portions of northeast WY
and far southern SD. Conditions will gradually improve late
tonight and Friday morning from north to south as snow tapers off
and moves out of the forecast area.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Warning until 11 AM MST Friday for SDZ027-029-030-
     041-042-044-074.

     Winter Storm Warning until 11 AM MST /noon CST/ Friday for
     SDZ032-043-046-047-049.

     Winter Storm Warning until 5 AM MST Friday for SDZ024>026-028-
     031-072-073.

WY...Winter Weather Advisory until 5 AM MST Friday for WYZ054-056-057.

     Winter Storm Warning until 11 AM MST Friday for WYZ055-058.

&&

$$

SHORT TERM...26
LONG TERM...26
AVIATION...26


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