Weather Service Report


616 
FXUS65 KRIW 230807
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
207 AM MDT Thu Sep 23 2021

.SHORT TERM...(Today through Friday)
Issued at 200 AM MDT Thu Sep 23 2021

A mid-level small trough over Idaho is expected to push southeast
into northern Utah between noon and 6 PM today. Some light 
showers over eastern Idaho early this morning are expected to 
push into far west-central Wyoming between 4 AM and 6 AM. Isolated
showers are expected to impact mainly northwest, west, and 
southwest through this afternoon possibly pushing east of the 
Divide this afternoon. Due to very limited instability and overall
weak forcing, and the Storm Prediction Center's convective 
outlook, have decided not to include any thunderstorms in the 
forecast. Very little or no rainfall is expected from this 
activity, with the main hazard being gusty winds due to a 
relatively large temp/dewpt spread. There could be even be brief 
light snow or graupel above 10,500 ft msl.

A cold front associated with a trough/upper low in south-central
Canada will push into northern Wyoming by around 6 AM, and sweep
southward, east of the Divide this morning. Breezy to windy
northerly winds will occur in wake of the front. The windiest area
will be across Johnson County, followed by northern Bighorn Basin.  
The breezy winds over the north will weaken by mid-afternoon. The
cold front is expected to reach the Divide by 10 AM and Noon, 
then continue southwest across the rest of the area this afternoon.
High temperatures over the north will be about 10 to 15 degrees 
cooler than yesterday.

Any lingering showers will dissipate or exit the area early to 
mid-evening. Dry conditions are then expected for the remainder 
of night and Friday. A relatively chilly northwest flow for 
September will keep highs temperatures about the same as what 
occurs today.

.LONG TERM...(Friday night through Wednesday)
Issued at 200 AM MDT Thu Sep 23 2021

For the long-term discussion, above normal temperatures are 
anticipated throughout the period and dry conditions until at least 
into Tuesday are anticipated.  To start looking more in detail, the 
00Z Saturday charts show northwesterly flow over Wyoming with a 
ridge axis extending from around San Francisco Bay through the 
Great Basin and into New Mexico and a smaller ridge over ID. A 
deep trough is showing over the middle of the CONUS. Progressing 
in time to 00Z Sunday, the trough continues its eastward movement 
plunging into the eastern CONUS. The ridge axis flattens and the 
flow becomes more zonal with jet support well to the north over 
Alberta and Saskatchewan. Models start to pick up on a tropical 
system near Baja California by 00Z Sunday as well. Zonal flow and 
dry weather continues for Sunday. With the dry weather over the 
weekend, some elevated fire conditions are possible. As the next 
deep trough starts approaching the West Coast on Monday, a ridge 
sets up over the state. The GFS and EC differ as far as the 
strength and placement of features by 12Z Tuesday, but overall are
in agreement with a trough coming onshore and a ridge axis 
stretching from North Dakota southward. By Tuesday evening, the EC
has a more amplified pattern than the GFS and a south- 
southwesterly flow over WY. The EC starts introducing some spotty 
precipitation by 00Z Wednesday. For Wednesday, models really are 
divergent with the EC having a high pressure center over MN a weak
trough over WY and the GFS with a closed low near the ID/UT 
border. Both models have some precipitation for Wednesday with 
moisture pulling in from the south.
 
Temperatures look to be above normal throughout the period. 
Wednesday looks to be the coolest day of the period, but still 
remaining several degrees above normal in many locations.  Highs on 
Wednesday looks to be mainly in the 50s and 60s across the west, the 
60s to near 70 over the south and the 70s to near 80 in the central 
basins and across the east.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1057 PM MDT Wed Sep 22 2021

Light winds and clear skies continue through Thursday morning.
During the late morning into the afternoon, winds shift to
northerly or northwesterly. Mid to high clouds increase as a weak
weather system moves through. It currently looks unlikely that 
any particular terminal will get wet from the isolated afternoon
mountain-based showers, but some scattered to broken high cloud 
decks have been added to TAFs where appropriate to hint at the 
possibility of a sprinkle. Showers end around sunset with winds 
remaining light and clearing skies into Friday morning.

&&

.FIRE WEATHER...
Issued AT 200 AM MDT Thu Sep 23 2021

A cold front will push south, east of the Divide this morning, and
then across the rest of the area this afternoon. Breezy northerly
winds will occur in wake of the front, mainly across the Bighorn 
Basin and Johnson County. Cooler temperatures and higher humidity
will also occur today. Isolated light showers are expected over 
the west beginning this morning, and lasting through the 
afternoon. Some of this activity could spread east of the Divide 
in the afternoon. This activity is expected to end by early to 
mid-evening. On Friday, expect dry and seasonable temperatures 
and mainly light winds.

Elevated fire weather conditions look to return Saturday and 
Sunday especially over central and southern areas.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Murrell
LONG TERM...Clayton
AVIATION...VandenBoogart
FIRE WEATHER...Murrell

Return to Home page


Western Regional Climate Center, wrcc@dri.edu