Area Forecast Discussion
Issued by NWS Rapid City, SD

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490
FXUS63 KUNR 221727
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1127 AM MDT Sat Jul 22 2017

.DISCUSSION...(Today Through Friday)
Issued at 234 AM MDT Sat Jul 22 2017

08z surface analysis showed cold front south of the CWA with weak
high pressure settling in. Water vapour showed upper low spinning
over south central Canada with main shortwave trough east of the
CWA. Some high level moisture streaming over CWA from the
southwest US. Isolated ACCAS/TS over the far southwest will end by
12z.

Today through Sunday, upper ridge will build over the western US,
slowly moving into the northern Plains as it flattens somewhat.
Temperatures will be a few degrees above normal given forecast
soundings. This will be near guidance, although smoke from wildfires
in MT may keep readings from reaching full potential. Few breezy
spots over northwest SD this afternoon. Modest low level jet Sunday
night as return flow sets up may create a bit of elevated convection.

Monday, upper and thermal ridge peaks over the CWA ahead of a
cold front. Readings near 100F likely, especially if southwest
downslope develops in the afternoon. As cold front moves through,
some TSRA possible as a shortwave flattens upper ridge Monday
night.

Rest of next week, progressive flow expected over the CWA with a
series of shortwaves and frontal boundaries meandering through.
Long term guidance appears to be targeting Wednesday for the best
chance of TSRA. Temperatures will be noticeably cooler mid-week
given cloud cover and higher PoPs.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1126 AM MDT Sat Jul 22 2017

Isolated showers will continue to cross south central SD this
afternoon before dissipating or moving out of the area. Smoke
from fires in central Montana may result in periods of MVFR
visibility at times. Otherwise VFR conditions are expected.

&&

.FIRE WEATHER...
Issued At 234 AM MDT Sat Jul 22 2017

Deep mixing is again expected today over northwest SD with very
dry minimum relative humidities. Breezy winds expected at times.
Combination of minRH around 15% and frequent gusts to 25 MPH
indicate need to convert Fire Weather Watch to Red Flag Warning.
Wild card will be effect of smoke on temperatures and mixing. Rest
of area will see 15-20% minRH`es, but winds will be more gentle.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning until 7 PM MDT this evening for SDZ261-266.

WY...None.
&&

$$

DISCUSSION...Helgeson
AVIATION...13
FIRE WEATHER...Helgeson



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