Weather Service Report

FXUS65 KRIW 191941

Area Forecast Discussion
National Weather Service Riverton WY
141 PM MDT Mon Mar 19 2018

.SHORT TERM...This afternoon through Thursday
Issued at 1243 PM MDT Mon Mar 19 2018

Isolated to scattered showers are expected this afternoon into the
evening across northern portions, as a weak trough moves over
western/southern MT. Some of this will also be driven by diabatic
heating, as the CU field develops over the area this afternoon.
Snow will mainly be confined to the higher elevations, before
temperatures fall tonight in the lower elevations. There will
be a chance to slight chance of snow showers to continue over the
western and northern mountains Tuesday, as weak upslope flow
continues. Another weak shortwave will also help produce these
showers over the west. 

Otherwise, the period will be marked by a warming trend as a ridge
of high pressure builds over the area. Precipitation chances will
remain confined to the west/northwest, as moist upslope flow
continues. Any rain Tuesday afternoon is expected to change back
over to snow overnight Tuesday, before changing back to rain by
midday Wednesday. This is expected to lead to rain on snow to
those low elevation locations in the Jackson/Star Valleys and
Upper Green River Basin that still have snow on the ground. This 
will continue Thursday and increase any low land flooding risk, as
precipitation amounts will be greater compared to Wednesday. This
will also affect the mountainous areas, as snow levels will range
between 7500 to 8500 feet on Wednesday, possibly increasing to
9000 feet on Thursday (especially for the Salt/Wyoming Ranges). 

.LONG TERM...Thursday night through Monday night
Issued at 1243 PM MDT Mon Mar 19 2018

Beginning of forecast: Trough/ridge/trough pattern in place across 
the CONUS with passing ridge axis just to the east of the forecast 
area roughly along the eastern border of Wyoming. Upper level flow 
has transitioned to southwest with the nose of a broad strong jet 
and associated embedded shortwave moving into/over western WY along 
with what looks to be decent Spring moisture from the EPAC and then 
across the southwestern CONUS. In reality, will have to see just how 
much actually makes it to the CWA after bumping into/over the Sierra 
Mountain range. Regardless, it will be raining/snowing west of the 
Divide in Wyoming. 

Overall, MR models are in decent agreement through the day Saturday 
before more significant differences begin to show. Regardless of 
differences, however, the region does stay under the influence of 
the western CONUS trough through the end of the forecast period with 
the best chance for precipitation (overall) occurring during this 
period of the forecast. (Particularly between Thursday night and 
Sunday morning). Sunday and beyond, the main difference between the 
EC and GFS occur within the trof as the EC evolves a closed low 
while the GFS remains open. Both are progressive, however, and the 
model solutions with respect to precipitation areas and amounts 
actually are quite close (the EC is somewhat more expansive with 
precipitation due to the closed system's area of influence). Sunday 
night through the end of the forecast, models differ somewhat in 
their respective exit strategies, but all stick with the idea of 
finally pushing the main upper trough east/northeast and out of the 

Possible impacts during the Thursday night through Saturday period 
will include: 1. Potential periods of moderate to occasionally heavy 
rain/snowfall (convective) with possible low end flooding concerns 
for portions of Lincoln County due to increased/added snowmelt 
leading up to/through these periods. 2. Advisory to possible Warning 
level snowfall across the western mountains. 3. Brisk, potentially 
high, winds across portions of the Wind Corridor Friday and/or 
Saturday. 4. A few isolated Thunderstorms possible Friday...mainly 
across the west/southwest portion of Wyoming. 


.AVIATION...For the 00Z TAFS through 00Z Wednesday
Issued at 1243 PM MDT Mon Mar 19 2018

The main aviation concern will be along and west of the Divide in 
addition to portions of northern Wyoming where periodic light snow 
shower activity, some mountain obscuration, and occasional MVFR 
conditions (KJAC) cannot be ruled out. Breezy winds are expected to 
continue early this evening and then again Tuesday afternoon across 
portions of west, central, south and southwest Wyoming. Much of the 
rest of the forecast area will see relatively light winds. 


Issued AT 1243 PM MDT Mon Mar 19 2018

Isolated to scattered snow showers will redevelop over the 
northwestern and northern mountains this afternoon into this 
evening. Precipitation will be in the form of rain (along the Cody
Foothills) or mixed with snow (along the foothills of the 
Absarokas and Bighorns). Elsewhere, conditions will mainly be dry 
across the area, with seasonal temperatures and gusty winds across
the south. A warming trend will begin Tuesday and continue 
through the week. Gusty winds will also return across wind prone 
locations (mainly during the afternoon) from Tuesday through 
Thursday. At the same time, mixing heights will also continue to 
increase through the week. Smoke dispersal will also be fair to 





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