Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 202137 AAA
AFDRIW

Area Forecast Discussion...UPDATED
National Weather Service Riverton WY
337 PM MDT Fri Apr 20 2018

.SHORT TERM...(This evening through Monday) Issued at 1226 PM MDT
Fri Apr 20 2018

By Monday evening, the models all agree that the southern and
northern stream shortwaves will become congruent and track
southeast across the CWA around 00Z Tuesday. The rain and high
mountain snow showers along with isold thunder, mainly across the
northern half of Wyoming, will dissipate after 00Z Tuesday with
the troughpa. Showers will end during the course of Monday night.
Then on Tuesday, the Canadian/GFS have us under the northerly
steering flow with the Euro under a looser gradient. This brief
cool air advection from the north will knock temps down just a few
degrees for highs on Tuesday, along with dry weather. After a
ridge builds into the area Wednesday, along with high temps in the
upper 50s and 60s, the next upstream shortwave will approach from
the northwest during he middle of the week, with the
Euro/Canadian bringing it through around 00Z Thu, and the more
robust GFS around 12Z Thursday. The GFS still indicates some
shower activity asct with this feature, so, for now, we will keep
the idea of isold shower activity in the mtns mainly Wednesday
night. Expect slightly cooler and dry conditions in the wake of
this shortwave for Thursday but with temps still rather seasonal.
Then another amplified ridge builds in from the west resulting in
nicely warming temps for Friday with highs in the 70s at the lower
elevations east of the divide and 60s west.

.LONG TERM...(Monday night through Friday night) Issued at 1226
PM MDT Fri Apr 20 2018

By Monday evening, the models all agree that the southern and
northern stream shortwaves will become congruent and track
southeast across the CWA around 00Z Tuesday. The rain and high
mountain snow showers along with isold thunder, mainly across the
northern half of Wyoming, will dissipate after 00Z Tuesday with
the troughpa. Showers will end during the course of Monday night.
Then on Tuesday, the Canadian/GFS have us under the northerly
steering flow with the Euro under a looser gradient. This brief
cool air advection from the north will knock temps down just a few
degrees for highs on Tuesday, along with dry weather. After a
ridge builds into the area Wednesday, along with high temps in the
upper 50s and 60s, the next upstream shortwave will approach from
the northwest during the middle of the week, with the
Euro/Canadian bringing it through around 00Z Thu, and the more
robust GFS around 12Z Thursday. The GFS still indicates some
shower activity with this feature, so, for now, we will keep the
idea of isold shower activity in the mtns mainly Wednesday night.
Expect slightly cooler and dry conditions in the wake of this
shortwave for Thursday, but with temps still rather seasonal.
Then, another amplified ridge builds in from the west resulting in
nicely warming temps for Friday with highs in the 70s at the
lower elevations east of the divide and 60s west.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 335 PM MDT Fri Apr 20 2018

An upper level low pressure system will move across southern
Colorado through this evening. Widespread MVFR conditions, local
IFR conditions in rain and snow will occur south and east of a
KRKS-KLND-KRIW-KBYG line mid afternoon but will continue to retreat
toward the southeast during the rest of this afternoon and
evening. Snow levels will elevate to 8000 feet. Above 8000 feet
where snow is falling, conditions will become mostly obscured.
Precipitation will decrease NW- SE 03z- 09z Saturday but areas of
MVFR-IFR ceilings and patchy fog are likely to linger through 12z.

Further north and west, VFR conditions will prevail through the
period with scattered MVFR shrasn decreasing followed by clearing
00z- 06z Saturday.

Expect mainly VFR conditions after 15Z Saturday everywhere.

&&

.FIRE WEATHER...
Issued AT 1226 PM MDT Fri Apr 20 2018

Widely scattered showers will continue over southeast portions of
the forecast area this afternoon. Expect some of this activity to
fill in this evening to include eastern portions of Fremont
County. Some rain or rain and snow mixture and gusty northeast to
east wind will extend as far north as Fremont and Natrona Counties
today into tonight with a brief period up into Johnson County.
The northern zones will be dry with a period of gusty north wind
as the storm moves by. Dry and warmer conditions over the weekend,
with the next chance for precipitation arriving Monday and Monday
night.

&&

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

$$

SHORT TERM...LaVoie
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...LaVoie


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