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Latest ZFP from WFO RIW

		
National Weather Service Local Forecast for Star Valley Ranch
Updated: 21 Sep 16:09 pm MDT

This Afternoon... Sunny, with a high near 62. West wind 3 to 5
mph. 

Tonight... Mostly clear, with a low around 35. West northwest
wind around 6 mph becoming east southeast in the evening. 

Wednesday... Sunny, with a high near 70. Southeast wind 5 to 10
mph becoming west in the afternoon. 

Wednesday Night... Partly cloudy, with a low around 37. West
wind 5 to 10 mph becoming east southeast after midnight. 

Thursday... Sunny, with a high near 68. East southeast wind 5
to 10 mph becoming west northwest in the afternoon. 

Thursday Night... Mostly clear, with a low around 36. Northwest
wind 5 to 10 mph becoming east southeast after midnight. 

Friday... Sunny, with a high near 69. East southeast wind 5 to
7 mph becoming west northwest in the afternoon. 

Friday Night... Mostly clear, with a low around 38.

Saturday... Sunny, with a high near 73.

Saturday Night... Mostly clear, with a low around 41.

Sunday... Sunny, with a high near 74.

Sunday Night... Mostly clear, with a low around 41.

Monday... Sunny, with a high near 74.

		

Latest AFD from WFO RIW

		
315 
FXUS65 KRIW 211950
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
150 PM MDT Tue Sep 21 2021

.SHORT TERM...(This Afternoon through Wednesday Night)
Issued at 150 PM MDT Tue Sep 21 2021

Morning fog has given way to cumulus clouds across Yellowstone 
National Park early this afternoon. Otherwise, a clear sky prevails 
in dry northwest flow aloft. Good radiational cooling will enable 
western valleys to go well below freezing again tonight. As a 
result, have made minor adjustments to drop overnight lows in the  
lower valleys west of the Continental Divide. Shortwave ridge 
transits the forecast area Wednesday ahead of a quick-moving 
trough. Dry and warmer air advects into southwest Wyoming 
Wednesday ahead of this trough. Above normal temperatures in store
along with dew points in the upper teens and lower 20s over the 
southwest. Similar to recent few weeks, 700mb winds are not that 
impressive, hovering around 20 kts. However, that has been enough 
to meet minimum red flag criteria. Have gone ahead and upgraded 
the fire weather watch to red flag warnings as relative humidity 
falls into the lower teens and the west to southwest wind gusts 
25 to 30 mph. The best chance for meeting criteria is likely to 
occur between 2 and 6 PM. Winds will decrease around sunset with 
another clear evening on tap. Mid- and high-level cloud cover 
begins to spread across the region later Wednesday night ahead of 
the approaching trough. Temperatures will moderate somewhat as a 
result of the cloud cover.

.LONG TERM...(Thursday through Tuesday)
Issued at 150 PM MDT Tue Sep 21 2021

The trough moves through the forecast area Thursday nudging a cold 
front south through areas east of the Continental Divide. Slightly 
cooler temperatures and a 10-20 mph north wind follow the front, 
which eventually slides into Sweetwater County Thursday evening. 
Moisture is limited with the trough and dynamics are not impressive. 
Nose of a northern stream jet streak may provide enough impetus for 
weak convection and it is difficult to trust moisture in northwest 
flow. So, cannot rule out a few light showers over the northern 
mountains Thursday afternoon and perhaps in the eastern zones 
heading into the evening.

Friday finds the cooler, yet seasonal temperatures, lingering as the 
trough deepens to our east and the pattern amplifies. This slows the 
eastward progression of the trough and leaves us in dry northwest 
flow aloft for Friday. Temperatures then rebound heading into the 
weekend as 700mb temperatures warm to 10C to 12C as a ridge builds
to our west. These temperatures translate to lower elevation 
daytime highs in the mid 70s to lower 80s. The ridge flattens 
somewhat over the weekend leading to breezy west winds in the high
basins and wind prone areas. Sunday appears to be the better of 
the two weekend days as far as potential fire weather highlights 
are concerned given wind, low relative humidity, and temperatures 
5F to 8F above normal. The ridge amplifies again to begin the work
week ahead of a developing trough in the Pacific Northwest. This 
leads to even warmer temperatures Monday and Tuesday as dry 
conditions persist.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday)
Issued at 1130 AM MDT Tue Sep 21 2021

VFR at all terminals through midday Wednesday as a ridge builds into 
western Wyoming. Southwest wind at KCPR will decrease around 
00Z/Wednesday before picking up again around 15Z/Wednesday. 

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for 
the latest information on smoke, icing, and turbulence forecasts.

&&

.FIRE WEATHER...
Issued at 150 PM MDT Tue Sep 21 2021

A transient shortwave ridge crosses the state Wednesday with dry and 
warmer temperatures in store through the end of the day. A weak 
weather system approaches from the west allowing for increasing 
southwest to west wind for Wednesday. This will be most prevalent 
across zones 277, 279, 280, and 289. Drier air advects into 
southwest Wyoming from the Great Basin and temperatures climb to 
above normal. This combination creates low relative humidity, and 
coupled with the wind, will produce red flag conditions in these 
zones Wednesday afternoon. The prime hours will be from 2 to 6 PM.

The weak weather system to our west sweeps across the forecast area 
Thursday. A cold front slides south through areas east of the 
Continental Divide dropping daytime highs from those seen Wednesday. 
Northerly wind 10-20 mph follows the front, while areas west of the 
Divide continue to see a westerly wind 10-20 mph. Other than a few 
light showers over the northern mountains, most areas will see dry 
conditions and increasing cloud cover. With the departure of this 
system, a ridge rebuilds over the western U.S. This leads to above 
normal temperatures and dry conditions through the weekend and even 
into next week. An afternoon, seasonal westerly breeze returns for 
the weekend. Possible elevated to critical fire weather conditions 
possible in the central and south both days.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 8 PM MDT Wednesday for WYZ277-279-
280-289.

&&

$$

SHORT TERM...CNJ
LONG TERM...CNJ
AVIATION...CNJ
FIRE WEATHER...CNJ

		

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