Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 131733
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1133 AM MDT Thu Jul 13 2017

.DISCUSSION...(Today Through Wednesday)
Issued at 345 AM MDT Thu Jul 13 2017

Current surface analysis shows frontal boundary well south and
west of the area, with high pressure centered over ND and south
central Canada. Upper level analysis shows ridge has begun to
build over the intermountain west, with west-northwest flow over
the Northern Plains. Water vapor imagery shows that shortwave
energy that brought showers and storms yesterday afternoon and
evening has moved south and east of the area, with clearing skies
over much of the area. Temps are pleasantly cool across the area
compared to previous nights, mid 50s to lower 60s. Winds are
mostly light and variable.

Temperatures will be on the rise over the next several days,
especially from Friday onward, as the ridge builds to the west and
then slides east across the Rockies and into the Plains through
early next week. Today will be a little warmer than yesterday, with
highs in the mid 80s to lower 90s under mostly sunny skies. Chances
for storms this afternoon should mainly be limited to the Black
Hills as warmer air aloft caps much of the plains. If storms do
develop over the Black Hills, they could be strong to severe, with
forecast CAPE values around 1000 j/kg and moderate shear. Stronger
storms would likely track south-southeast across the Black Hills
with larger hail likely the main threat. Any activity should
dissipate by early evening, with clear skies and lows mostly in the
60s tonight.

Warmer conditions Friday as boundary shifts back northeast across
the area as a warm front, with highs in the 90s to around 100 across
the plains, some 80s across the higher Black Hills. We will see a
better chance for thunderstorms late Friday into Friday evening as a
weak shortwave and surface trough help to trigger storms, mainly
from northeast WY to northwest SD. The best instability is forecast
to be from far northeast WY to northwest SD and into ND. Strong to
severe storms are possible across these areas with strong wind gusts
likely the main threat and some hail also possible.

Hot and mainly dry conditions then expected for the weekend, with
highs well into the 90s and some triple digits across the SD plains.
Upper 80s and lower 90s can be expected across the Black Hills. As
ridge and upper high shift east into the plains early next week, the
hot conditions will continue but chances for thunderstorms will
increase. Ridge will eventually weaken and shift east of the region
midweek, bringing some cooler air into the region. Active zonal flow
should bring continued chances for thunderstorms to much of the area
during the middle of next week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1132 AM MDT Thu Jul 13 2017

Isolated to scattered thunderstorms are possible across portions
of the Black Hills area this afternoon. Otherwise VFR conditions
expected through the period.

&&

.FIRE WEATHER...
Issued At 345 AM MDT Thu Jul 13 2017

Hot conditions will return to the area Friday and persist into
early next week. Relative humidities will drop to the upper teens
and lower 20s across much of the area each afternoon. Winds do not
look strong over the next few days, but periods of elevated fire
weather conditions are possible, especially later in the weekend
into early next week if humidities are lower.

&&

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

$$

DISCUSSION...26
AVIATION...13
FIRE WEATHER...26



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