Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS65 KRIW 211743

Area Forecast Discussion
National Weather Service Riverton WY
1143 AM MDT Fri Apr 21 2017

.SHORT TERM...Friday through Sunday night

Another day of mashing of teeth with the uncertainty in the
forecast. Much like a couple of weeks ago, the key phrase of the day
will be 1 or 2 degrees; or in a similar vain, 100 or 200 feet. This
is all it will take in many areas to make the difference between
just a cold front and a heavy, wet snow. The radar continues to fill
in as low pressure moves across the area. What we do know is that it
will be a cloudy, cool and wet day for many areas East of the
Divide. However, since the precipitation looks to be banded in
nature for many areas, pinpointing the exact locations of the
heaviest QPF is difficult at best. As for the highlights, they look
reasonable so we will continue them as is. This will be the same
situation for the Special Weather Statements as well. 700 millibar
temperatures will be in that critical minus 5 to minus 7 range as
well. A lot may depend on precipitation rate with any possible
dynamic cooling. Complicating matters even further today will be the
high late April sun angle. This could be a situation in some areas
where there is several inches of snow on the grass and very little
on paved surfaces. To sum it up, we made very few changes to
continuity as this may be a situation where we are reacting to
heavier bands of snow that pop up, stay tuned. Meanwhile, out west
the steadier precipitation will end, although with the atmosphere
becoming unstable with daytime heating, snow showers will remain

As low pressure moves away tonight, there should be a lessening in
intensity and coverage from west to east, although rain and snow
should linger in the east much of the night. Transitory ridging
building across the area should then bring a return to dry weather
for all areas by noon Saturday along with a good deal of sunshine.
High temperatures could be a bit tricky though, depending on any
snow cover and heating going toward melting snow rather than heating
the air.

On Sunday, the next system will approach the west. However, the
models have trended a bit further north with the best energy. For
now, any showers during the day should be confined to areas West of
the Divide. Meanwhile, areas East of the Divide should see a nice
end to the weekend with mild temperatures and light to moderate
wind with sunshine mixing with high clouds. Some showers may spread
East of the Divide Sunday night although at this point it does not
look like a big event.

.LONG TERM...(Monday through Friday)
Issued at 154 AM MDT Fri Apr 21 2017

The GFS and ECMWF models are painting an unsettled weather pattern
for the last week of April. Differences in the pattern show up Wed
night and continue through Friday with respect to the timing of
weather systems in the westerly flow aloft. Areas along and west
of the continental divide look to see periods of rain and snow Mon
through Fri with mainly snow in the mountains above 7500 feet. The
potential exists for significant snow accumulations above 8500
feet in the western mountains which could lead to travel issues
over the passes. Will be keeping an eye on this pattern in the
coming days to better time the heavier snowfall events. Meanwhile,
east of the divide, the weather pattern looks to be showery at
times on any given day or night. Some places may be totally dry on
a given day while other locations could see some precipitation
each day. Again, will adjust the forecast as needed based on model
consistency. High temps will be on the cool side Mon through Fri
with near to below normal readings. Expect breezy to windy
conditions at times in the favored wind corridors.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1126 AM MDT Fri Apr 21 2017


VFR ceilings at or above 4KFT are expected to linger through the
afternoon at the TAF sites. Left in mention of VCSH conditions at
KJAC and KPNA until around 01z based upon latest observations and
radar trending into the afternoon. Have slightly upped the wind
forecast for KPNA due to recent trending. After 01Z tonight,
expect generally mostly clear/clear conditions through the end of
the forecast period with lighter and variable winds especially
after 06z.


Widespread MVFR/IFR conditions will continue at most TAF sites
until around 00Z with a -RASN mixture expected at KLND and MVFR
visibilities expected at times at KCOD,KRIW and KWRL through the
same time frame. The precipitation is expected to gradually end
from the west to east this evening, but wukk jeeo ub a VCSH
mention at KCPR due to trending until around 15z Saturday. Also
expect gradually improving ceilings with KWRL expected to become
VFR by around 06z, KCOD by 09z and KCPR by around 15z Saturday.
Mountains will be obscured much of the time with IFR or LIFR
conditions expected.



Low pressure moving through the area will bring rain and snow
showers to most areas today with the exception of the far southwest.
As a result, a wetting rain is likely for many areas. Snow levels
may reach valley and basin floors at times although pinpointing the
heaviest rain or snow is difficult. Mixing and smoke dispersal will
be generally fair to poor but except in southern Sweetwater county
where it will be fair to good. A gusty north wind will also blow at
times. Mainly dry weather will return Saturday as high pressure
builds across the state.


Winter Weather Advisory until midnight MDT tonight for WYZ002-

Winter Storm Warning until 6 AM MDT Saturday for WYZ008-009.



SHORT TERM...Hattings
FIRE WEATHER...Hattings is the U.S. government's official web portal to all federal, state and local government web resources and services.