Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 212120

Area Forecast Discussion
National Weather Service Riverton WY
320 PM MDT Sun Apr 21 2019

.SHORT TERM...This afternoon through Monday

Rain showers will be common across the forecast area today and
tonight. Most of the activity so far has been confined to central
portions. This will continue through the afternoon, as precipitation
chances increase over southern and western portions. The focus
for the precipitation will shift to southern and southwestern
portions tonight, along with the east slopes of the Wind River
Mountains. This will be due to a surge of moisture, that is
currently moving northward from E UT. Locally heavy rain remains
possible over southern and southwestern portions, with 0.50" to
0.75" possible over the Salt and Wyoming Ranges. Any thunderstorms
today will also be confined to these areas. Otherwise, rainfall
amounts around 0.25" will be common. Eastern portions of the
Bighorn Basin and Johnson and Natrona counties will only receive
0.05" to 0.15". The rest of the forecast area will have scattered
to numerous showers through the overnight hours. Snow levels will
continue to range between 7500 to 8500 feet over much of the area
today, dropping to 6000 feet to 7500 feet through the overnight
hours. As a result, snowfall amounts will be highly variable. But,
3 to 6 inches are generally expected.

Shower activity will gradually decrease by Monday morning, with
isolated to scattered showers continuing across the forecast area
through the day. This will be due to the upper low, that is
currently over the Great Basin, moving southward over the Four
Corners area. Temperatures will remain similar to Sunday, as skies
stay overcast. Winds will be light over much of the area as well,
with gusty northeast to east winds occurring over southern portions.

.LONG TERM...Monday night through Sunday

The slow moving upper level system will finally lose its grip on
the forecast area by Monday afternoon, as the system will shift
southeast and weaken with time. A ridge of high pressure in the
mid to upper levels will move int central/western Wyoming by
Tuesday with lower level southwest winds picking up. Abundant
sunshine and the low level southwest flow will result in decent
warm advection, as temps should warm through the 60s to around 70
degrees or so across portions of the region, especially east of
the Divide. High temps on Tuesdays and through the rest of the
extended forecast period will be 10 to 15 degrees above normal
across the region.

The next upper level short wave is still progged by the extended
forecast models to move across Montana between Wednesday and
Wednesday night. Will continue with a chance of showers and
isolated thunderstorms over the north and northwest with lesser
coverage in the central sections. A mid to upper level zonal flow
will ensue across the area through Friday with another weak system
expected to move through the west on Thursday afternoon/night with
isolated afternoon and evening showers or storms over and near
the mountains are expected. Rain showers may increase late
Thursday night in the west with snow at the higher elevations.

This moist westerly zonal flow is progged by the models to move
through the west on Friday into Friday night. A good chance of
rain showers and isolated storms are possible with higher
elevation snow showers in the west through this time period.
Another two systems will move toward and into the western counties
between Saturday and the end of the extended forecast period, so
will continue with precip chances to round out the extended
forecast time frame with an unsettled pattern continuing. Temps
should be slightly cooler in the west by next weekend with more
clouds and precip possible.


.AVIATION...For the 00Z TAFS through 00Z Monday evening

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

The slow moving cold front is expected to remain nearly stationary
overnight tonight. Will continue with at least MVFR to IFR
ceilings until between 15Z-18Z Monday at all TAF sites east of the
Divide. Until the conditions improve, scattered showers and lower
ceilings will continue. Will trend toward VFR conditions after 18Z
Monday through the end of the forecast period.

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

Scattered to numerous showers are expected and isolated
thunderstorms are expected through around 03Z at KRKS with
borderline MVFR ceilings expected through the balance of the
forecast. Snow levels will lower to near valley floors 06z-12z
Monday but precipitation intensity and coverage will be on the
decrease by after 18Z Monday, with improving ceilings toward the
end of the forecast period.



Rain showers with isolated thunderstorms will be prevalent across
the area through the rest of the day and tonight. Thunderstorm
activity will be confined to southern portions. Precipitation
amounts will vary, with 0.25" to 0.50" for most areas west of the
Divide, including zones 283 and 289. Gusty north to northeast
winds will subside this evening, but will continue over zone 279
tonight. Isolated to scattered showers will continue across the
area Monday, with precipitation amounts much lower compared to




LONG TERM...Troutman
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