Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 140351
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
951 PM MDT Wed Mar 13 2024

.KEY MESSAGES...

- Snow becomes widespread east of the Divide by the afternoon
  today with winds increasing, especially in parts of Fremont,
  Natrona, and Sweetwater Counties.

- Moderate to heavy snow is expected to develop by the evening
  and overnight hours. Travel is expected to be the most
  difficult at this time, due to the combination of gusty winds
  and heavy snow.

- Snow will gradually dissipate during the morning and early
  afternoon hours Thursday. A few scattered snow showers cannot
  be ruled out during the day Thursday with minimal impacts
  expected.

- The weekend looks dry with temperatures moderating back to
  near normal values. The start of next week looks to bring a
  taste of spring, with highs near to above 50 degrees across
  most of the state.

&&

.DISCUSSION...
Issued at 212 PM MDT Wed Mar 13 2024

March came in like a lion across western WY but did not bring the
same ferocity to places east of the Divide. That looks to change as
an intense winter system brings moderate to heavy snowfall over
parts of central WY. Precipitation has begun late this morning,
becoming widespread by the afternoon and evening. Temperatures will
be a key factor in determining how much snow can accumulate during
the day. Currently, temperatures are forecast to be near to slightly
above freezing for most areas east of the Divide. This likely means
initial snowfall will have difficulty accumulating on some surfaces
such as roadways. However, by the time the sun sets snow should
begin to accumulate creating hazardous travel conditions in some
locations. The forecast has not changed all too much with the places
seeing the greatest impacts being in favorable northeasterly upslope
flow, such as the Lander Foothills and Casper Mountain.

There are two key components of this system the potent upper level
low that digs south over the Great Basin, and the lee cyclogenesis
that develops over Colorado. Each component interacts with another
and together will create what is forecast to be an impactful weather
system for parts of the central Rockies. The setup for this system
is a strong upper level trough that has moved south to the Four
Corners Region. Due to this, lee cyclogenesis will occur over
Colorado with a low pressure center developing. By Wednesday evening
a potent closed low that developed within the trough will drop
south, moving over the Great Basin and begin to influence the
movement of the low that is over Colorado. These two disturbances
will help create well defined northeasterly flow across much of the
Cowboy State. 700 mb to 500 mb winds gradually shift to the
northeast/east, which will aid in funneling moisture into the area.
As mentioned before, places favored by this flow, such as the
eastern slopes of the Wind River Range, Lander Foothills, and Casper
Mountain are going to be the most effected. The heaviest snowfall is
expected to occur through much of Wednesday evening into Thursday
morning as flow will be the most favorable. As the Colorado low is
ushered east, precipitation begins to dissipate and is expected to
end by early Thursday afternoon.

This system still has many unknowns, especially for areas east of
the Divide. Current forecasts show the greatest snowfall occurring
over the high elevations of central Wyoming and northeasterly
favored upslope areas. Models still continue to have uncertainty in
the forecasted range of snow amounts but have somewhat narrowed this
range. An example of this would be Lander`s snowfall range where the
10th and 90th percentiles have slightly shifted from yesterday.
Current forecasts show snowfall amounts ranging from 3 to 13 inches
in Lander, which encompass a wide range of impacts from minimal to
significant. The Wind River Basin is still forecast to see light
snow accumulation, with amounts of 1 to 4 inches. However, amounts
may vary depending on the location of heavy snow banding that looks
to develop Wednesday night into Thursday. Sweetwater and Natrona
Counties have seen snowfall amounts increase overnight, ranging from
2 to 6 inches now. One thing to keep in mind when it comes to snow
accumulation is temperature of ground surfaces. Due to the recent
mild temperatures and strong March solar radiation, places east of
the Divide, may have difficulty accumulating snow on surfaces during
the day Wednesday. Winds increase from the north to south today
through Thursday, with gusts of 25 to 35 mph in much of Central WY.
South Pass, Sweetwater, and Natrona Counties may see gusts exceeding
45 mph at times. The combination of snow and gusty winds will likely
lead to difficult travel conditions over central basins, especially
for South Pass and I-80 through early Thursday afternoon.

Regarding winter highlights, Winter Storm Warnings continue for the
Lander Foothills, eastern slopes of the Wind River Range,
Rattlesnake/Green Mountain Ranges and Casper Mountain. The
combination of winds and moderate to heavy snowfall will create
difficult travel conditions, especially overnight Wednesday through
early Thursday afternoon. Additionally, Winter Weather Advisories
continue for most of Sweetwater, Fremont, and Natrona Counties due
to light to moderate snowfall combined with gusty winds. For more
information regarding snowfall amounts and probabilities, visit
weather.gov/riw/winter.

The end of this system looks to come by Thursday morning into
early Thursday afternoon. The majority of precipitation should
end by the morning but a few scattered showers cannot be ruled
out during the afternoon/evening. Overall, dry conditions return
by Friday, with temperatures on the cool side and highs near to
below normal values. The weekend looks to remain dry, as the
weak disturbance that might have brought some precipitation to
the state, has moved out of reach. Winds may become breezy in
parts of the Bighorn Basin and Johnson County over the weekend.
The start of next week is currently forecasted to see the return
of mild temperatures and dry conditions across the Cowboy
State. Early indications are showing a taste of spring with
highs near to above 50 degrees in many parts of the state.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 949 PM MDT Wed Mar 13 2024

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

VCSH and VFR conditions are expected through Thursday afternoon at
KBPI/KPNA/KJAC. Snow has begun at KRKS this evening and will
continue into Thursday morning. Conditions will be IFR for most of
tonight with -SN and low CIGS. Wind will increase greatly tonight as
a cold front passes through with northeasterly wind gusting to 40
knots, so have reductions in VIS through Thursday afternoon to
account for BLSN, but -SN should end around 15Z. Another period of -
SN is possible at KRKS Thursday evening, so expect conditions to
drop to IFR by 02Z/Fri Wind will increase late Thursday morning into
Thursday afternoon for KBPI/KPNA and earlier Thursday morning at
KJAC. Gusts of 15 to 25 knots are expected at KJAC. Mountaintop
obscuration will continue through Thursday morning, improving
Thursday afternoon.

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

Rain has changed over to snow for KCPR/KRIW/KLND, with IFR
conditions expected tonight. Conditions may improve briefly at times
tonight at KRIW as dry downsloping air mixes in. Improvement to MVFR
is expected early Thursday morning as snow begins to taper off, with
VFR conditions by Thursday afternoon. Expect mostly VFR conditions
at KCOD/KWRL as snow is less likely to occur there. Wind will remain
breezy through Thursday morning due to the effects of a cold frontal
passage. Gusts of 20 to 25 knots are expected at KRIW/KCPR. Mountain
obscuration will continue through Thursday morning, especially along
the eastern slope of the Wind River Mountains and northern slopes of
Casper Mountain.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MDT Thursday for WYZ008-009-
017-020.

Winter Storm Warning until noon MDT Thursday for WYZ015-018-
019-022.

Winter Weather Advisory until noon MDT Thursday for WYZ028>030.

&&

$$

DISCUSSION...Dziewaltowski
AVIATION...Rowe


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