Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 151117

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
517 AM MDT Sun Sep 15 2019

.DISCUSSION...(Today Through Saturday)
Issued at 133 AM MDT Sun Sep 15 2019

The latest surface analysis has a lee trough/weak warm front over
eastern WY. Water vapor images and the RAP analysis showed a
dirty, low-amplitude ridge over the northern Rockies. Some high
clouds were sweeping across the CWA.

Today through Monday night, upper ridge builds over the MO River
Valley in response to deepening upper trough over the West Coast.
Strong thermal ridge builds over the CWA bringing high temperatures
around 10F above average. The HRRR-smoke suggests smoke will move
over parts of the CWA today from western CONUS wildfires. A weak
short-wave trough with limited forcing and moisture moves through
tonight with some clouds. Another slightly stronger short-wave
trough moves through Monday night, with low-level jet/850-700mb
theta-e advection expected. Some storms may form just east of the

Tuesday will be a transition day as a stronger short-wave trough
ejects northeast from the West Coast upper low. Moisture will be
limited ahead of the wave, but synoptic forcing, frontogenesis, and
midlevel moisture should be sufficient for scattered TSRA Tuesday
afternoon and evening. The main threat appears to be gusty winds
given unidirectional hodographs, a linear storm mode, and a dry
boundary layer. A strong cold front then moves through with gusty
west/northwest winds Tuesday evening lingering into Wednesday

Wednesday through Saturday, southwest flow aloft transitions to a
large upper trough moving through the northern Plains later Friday
into Saturday. A cooling trend is expected, especially Friday and
Saturday, along with increased precipitation chances at the end of
the week.


.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 516 AM MDT Sun Sep 15 2019

VFR conditions can be expected through Monday morning.


Issued At 133 AM MDT Sun Sep 15 2019

Relative humidities will drop into the teens over northeastern
WY/far southwestern SD this afternoon. Forecast soundings show
deep mixing with potential gusts of 20-25 MPH, just short of Red
Flag criteria.




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