FXUS65 KRIW 240435

Area Forecast Discussion
National Weather Service Riverton WY
1035 PM MDT Thu Mar 23 2017

.SHORT TERM...(This evening through Sunday) (Issued at 439 PM MDT)

A well defined circulation is evident over far Southwest Wyoming
along with an extensive thick elongated cloud mass oriented
northeast to southwest aligned with the asct frontogenesis.
Southeast Fremont, Eastern Sweetwater, and Southeast Natrona
Counties have been relatively mild ahead of the main area of
moisture with Casper Mountain well above freezing all day today.
The coldest air appears to have been closely linked to the mid
level cold core low over Southwest Wyoming today where 1 to 3
inches of snow has fallen today across the Upper Green River Basin
and the surrounding foothills. Many areas have received over one
half of an inch of precipitation along the aforementioned
northeast southwest oriented stream of moisture along with added
lift from the jet couplet/left front quad dynamics from the
southern stream jet, as well as QG forcing. Snowfall did occur
briefly in Lander thanks to adiabatic cooling from low level
upslope flow, otherwise rain fell all day there today. The trend
for tonight will be clearing from the northwest as cyclogenesis
takes place over Southeast Colorado with the energy quickly
propagating to the south as the trough splits with the blocking
mean ridge over the High Plains still in place. Friday will be a
dry day as a transitory positively tilted ridge builds into the
area. Then on Saturday, the next Pacific trough now out at 140W
will deliver more snowfall to far Western Wyoming beginning late
Friday night and continuing and increasing in intensity Saturday
with perhaps 3 to 7 inches of snow in the Western Mountains and 1
to 3 inches in the valleys along with at least a half of an inch
of precip over much of the area. There may be a little rain mixed
in with the snow in the valleys, but should be more snow than
rain. Then this trough will split, just like this evenings trough,
with cyclogenesis taking place once again over Southeast Co. As
this system also splits, precip will spread east of the divide as
an asct cold front gets pulled south over the area and the
northern stream energy tracks east. Areas east of the divide were
left with high pops, with the most significant qpf in the northern
zones east of the Divide Saturday night. Precip will exit east on

The flood warning remains in effect for Lincoln County with more
precip expected but at least temps will be cooling off.

.LONG TERM...(Sunday night through Thursday)

Active weather pattern continues into and through the medium-
range forecast period. Departing Sunday trough will leave
gradually improving and drier conditions Sunday night into Monday
morning with transient ridge sweeping east across the forecast
area. The next trough will already be moving into the Pacific
Northwest Monday with moisture spreading east across the
Intermountain West. As a result, expect scattered showers across
the far west by late Monday afternoon. Eastward push of this
moisture continues Monday night into Tuesday morning. Upper low
will form in the base of this trough and continue to dig into the
Desert Southwest Tuesday. Pieces of energy and associated moisture
are likely to hand around Tuesday with general troughiness
remaining across the forecast area. At this time, believe the best
chance for precipitation will be in areas east of the Continental
Divide, and especially the central basins and Johnson/Natrona.
This scenario could be similar to what we have seen in central
Wyoming today (Thursday). Split flow will again be the rule as we
head into Wednesday with upper low in the Desert Southwest and
northern stream kicker moving the precipitation east of Wyoming
with drier westerly flow aloft. Wednesday looks to be mainly dry
on both sides of the Continental Divide as the upper low sets up
shop in the southern Rockies and the next trough moves into the
Pacific Northwest. This next trough will serve to nudge the upper
low onto the southern Plains and the pattern may repeat itself all
over again. Moisture returns to the west Thursday as the Pacific
Northwest trough moves onshore. Temperatures will yo-yo during the
week with Tuesday and Thursday the coolest days, albeit still
close to normal. More sunshine and generally dry conditions in
warmer west to southwest flow will enable temperatures to be 5 to
8 degrees above normal Monday and Wednesday. Gusty southwest wind
will be found Monday in the Wind Corridor from Sweetwater to
Natrona County. Otherwise, nothing more than a typical Wyoming
breeze anticipated through the period. |


.AVIATION...(For the 06Z TAFS) (Issued at 1035 PM MDT)


VFR conditions will prevail through 06Z Saturday. Areas of fog
are possible through 16Z this morning with MVFR/IFR conditions.
Clouds will be increasing in the far west after 00Z Saturday
with isolated mountain snow showers by 06Z.


Areas of MVFR will occur through 12Z with isolated rain showers.
Areas of fog may form after 10Z with local MVFR/IFR conditions
until 16Z. After 16Z, VFR conditions will prevail through 06Z



Fire danger will be low through the weekend. Increasing moisture
will continue to spread across WY along with measurable
precipitation at many locations...both liquid and frozen. Friday
night through Saturday night the next spring/winter system will
move through the region with rain and snow most likely west of the
Divide...isolated to widely scattered east. Smoke dispersion will
be fair to good most afternoons.





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