Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 261716
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1016 AM MST Sat Nov 26 2016

.SHORT TERM...Saturday through Monday night

It looks like one more day of dry weather before things take a more
active turn. One problem will be the continued gusty winds across
the southwestern wind corridor. There could be a few gusts above 55
mph today. However, they should be only a few and most areas will
not blow that strong. So for now, we will go with a special weather
statement and not a high wind warning. Temperatures should be
similar to yesterday or perhaps a couple of degrees warmer.

The next weather maker will move in from the south and west in the
form of a trough and weak cold front.The trough does look to be
going negatively tilted and has a decent amount of upper level
divergence associated with it. However, there is not a ton of upper
level forcing except for a brief period late tonight. There could be
a period of moderate snow late tonight. As for amounts, at this time
they look to be sub advisory and since it will be a quick hitter we
will hold off from any advisories.

The steadier snow should end in the west Sunday morning as the jet
dynamics and divergence move away from the area. However, the area
will continue to be under an area for cyclonic curvature with a
couple of shortwaves that will keep unstable northwest flow going
over the area. As a result, there will be showers around much of the
day. Some of these will likely jump East of the Divide in the
afternoon and nighttime hours. We will also have the potential of
some snow bands setting up. However, the models have backed off on
the idea of some northerly upslope flow setting up. So we have kept
POPS across much of the area. The models have been waffling on the
placement of them and they are difficult to pinpoint to begin with.
We should have a better idea tomorrow night. In addition, it will
become blustery across much of the area as mid level winds
strengthen.

On Monday another wave will move into the west around the base of
the longwave trough. At this point, the main effects should remain
west of the divide with continued snow showers. East of the divide
should be mainly dry. One fly in the ointment though could be an
upper level low that could stall over the northern Plains and may
bring some wrap around precipiation to eastern portions of the county
warning area, especially Monday night. In addition, 700 millibar
winds will be becoming quite strong Monday night and areas that area
favored by north to northwest flow like the northern Johnson County
and the northern Big Horn Basin may begin to see stronger winds at
that time.

.LONG TERM...Tuesday through Saturday

Synopsis...A slow-moving upper level low pressure system over the
northern plains will continue to bring gusty northwest wind and
some wraparound snow showers across eastern Johnson County on
Tuesday. Another low pressure system will dive south across the
western U.S. late Wednesday through Friday. The main impact on
west and central Wyoming will be keeping temperatures cooler than
average with some light mountain snow showers.

Discussion...Synoptic pattern at Tuesday morning consists of stacked
low near the North Dakota-Minnesota border on leading edge of broad
longwave trough extending west of the Continental Divide, upper
ridge along 130W, and potent shortwave just upstream,  ECMWF is
slower to eject upper low over the northern plains northeastward than
GFS. ECMWF is also further east with next upper low digging
across the western U.S. Thursday and Friday than GFS. Increased
distance between the GFS between the two systems allows for some
ridging to build in Wednesday and Thursday for dry conditions
while ECMWF shows a more unsettled pattern over area with a SW-NE
oriented trough stretching from the west coast to the Great Lakes
region by Thursday night. Forecast is weighted toward ECMWF
keeping some chances of snow showers mainly in the mountains
Wednesday and Thursday before drying things out Friday as upper
low over the west sinks into NW Mexico. Highs through the extended
period will be on the cool side with mostly low to mid 30s across
the central basins and 20s in the western valleys. Lows will be in
the single digits and teens.

&&

.AVIATION.../18Z ISSUANCE/

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

VFR conditions to prevail through 06Z Sunday. Clouds will be on the
increase after 00Z with a few rain or snow showers developing in SW
WY toward 06Z Sunday. Snow will increase in coverage after 06Z
Sunday across Western and Southwest WY with MVFR to IFR conditions
in reduced VIS from -SN and low CIGS prevailing after 09Z Sunday.
LLWS is expected to continue periodically at or near most terminal
through the end of the forecast period. See the latest terminal
forecasts for details.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR conditions will prevail through the forecast period for most
terminal sites...with KCOD and KCPR seeing near MVFR increases in
cloud cover to nearly MVFR sometime after 12Z. KCPR airport will
continue a gusty southwest surface wind through 18Z Sunday...but may
decrease some in strength between 06Z and 12Z Sunday. LLWS is
expected to continue periodically at most terminal sites except KWRL
through the forecast period. See the latest terminal forecasts for
details.

&&

.FIRE WEATHER...

A ridge will dominate the weather across the area through this
evening with mainly dry weather. Some valley inversions and patchy
fog will be possible this morning. Moisture will move in from the
south beginning later this evening with the next chance of snow,
especially across southern portions of the area. The heaviest snow
is expected from midnight through around 8 am on Sunday morning.
There will be further chances of snow showers through Sunday and
Monday although pinpointing the area of heaviest snow is very
difficult at this time.
&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Hattings
LONG TERM...AEM
AVIATION...Braun
FIRE WEATHER...Hattings



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