Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 190515

Area Forecast Discussion
National Weather Service Riverton WY
1115 PM MDT Sun Mar 18 2018

.SHORT TERM...This afternoon through Wednesday
Issued at 112 PM MDT Sun Mar 18 2018

Low clouds/fog from this morning over Johnson/Natrona counties
have lifted, but remain overcast this afternoon. The rest of the
pattern remains messy, with the remnant lows circulating over the
region. The main low continues to undergo leeside circulation
along the Front Range. The forming deformation band from this low
is rotating over the I-80 corridor, with light snow. This has kept
temperatures from rising above freezing and staying in the mid to
upper 20s. The other weak, mid-level circulation is located over
east-central WY and formed an isolated convergence band of snow
over western Natrona County earlier this afternoon. This trend is
likely to continue, before the band of snow shifts eastward by
this evening. Snowfall amounts will remain low, as drier air
from the west quickly follows behind the snow band. Most of the
precipitation will end by midnight, with only isolated lingering
showers possible over SE Natrona County and S Sweetwater County.

Otherwise, weak NW flow aloft will develop tonight into Monday.
This will allow weak troughs to brings enough moister to NW
portions. Have kept isolated to scattered chances through Tuesday.
Apart from this area, conditions are expected to be dry with
seasonal temperatures. Gusty afternoon winds will return to wind
prone locations by Monday. A ridge of high pressure will begin to
build over the region Tuesday into Wednesday. Moisture and clouds
will be picked up by the southern stream of the jet, with
increasing chances for rain and snow across the west on Wednesday.
With this ridge will also be a slight warming trend. Lower
elevations across western portions will once again see afternoon
temperatures in the lower to middle 40s. Rain showers on existing
snow will be possible for these areas, exacerbating any snow melt.

.LONG TERM...Wednesday night through Sunday night
Issued at 112 PM MDT Sun Mar 18 2018

All long range models show a moist southwest flow aloft across west
and southwest WY Thursday into Thurs night. Rain and higher
elevation snow is likely in these locations. Liquid amounts of a
quarter to one half inch may well occur in some locations. Some of
this moisture looks to cross east of the divide late Thurs afternoon
into Thurs night with scattered rain showers for the most part.
Temps to be mild on Thurs with 50s to lower 60s and mainly 40s in
the west and southwest. Will have to monitor lower elevation
snowmelt in portions of the west Thurs night into Fri. The GFS
model wants to dry things out Friday for the area, while the
ECMWF and Canadian models keep some light precip over the region
through Fri evening. Seems the GFS has been fast with this drying
over the past few model runs. Will leave some rain and snow
showers in the west and southwest Fri with light liquid amounts.
Saturday and Sunday a trough of low pressure swings into the Rocky
mountain region. Each model has its own way of moving this trough
across the area. The ECMWF is the wettest model, the Canadian the
driest, and the GFS in the mid range. Confidence is low this far
out. Will have low pops Saturday and Sunday with better chances in
the mountains. Temps will still be colder in the west Friday and
still mild east on Friday. Cooler highs Saturday and next Sunday.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1114 PM MDT Sun Mar 18 2018

The main aviation concern will be across northern Johnson County
where IFR conditions in low clouds and/or fog are expected through
about 15Z Monday. Snow showers with localized IFR/MVFR conditions
south and east of a line from KRKS-KRIW-KCPR will gradually come to
an end by 12Z Monday. Otherwise a mainly dry conditions through
Monday morning is expected, except perhaps the far west where
some snow shower activity cannot be ruled out. This afternoon
isolated to locally scattered mountain snow showers are expected
to develop over northern/and perhaps central mountains spreading
east into parts of the lower elevations through the evening hours.
This snow shower activity should rapidly dissipate with loss of
daytime heating. Breezy west to northwest wind are expected across
the south and southwest part of the area, while most of the other
areas will be relatively light.


Issued AT 215 PM MDT Sun Mar 18 2018

Snow showers will continue this afternoon across portions of
Natrona and Sweetwater counties into the Bighorns. Precipitation
will end over this area tonight, as isolated to scattered snow
showers redevelop over the northwest. 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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