010 
FXUS65 KCYS 110502
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1002 PM MST Wed Mar 10 2021

.UPDATE...
Issued at 517 PM MST Wed Mar 10 2021

Let the Winter Storm Warnings and Winter Advisories expire this
evening as most of the snow has ended with the first shortwave
moving into the northern plains. Will send out updates to POP,
temperature, and winds over the next few hours once the snow
showers or flurries end shortly. Winter Storm Watch in effect for
Friday and this weekend with the most severe conditions likely
Saturday, Saturday night, and Sunday morning.   

&&

.SHORT TERM...(This evening through Friday) 
Issued at 300 PM MST Wed Mar 10 2021

...One winter event winding down this afternoon.
Another...potentially historic event taking shape for Friday
through Sunday....

Currently...Surface low near Wheatland this afternoon with cold
front extending southwest into northwestern Colorado. Snow band
continues across the northern Nebraska Panhandle westward to
Converse County. Still getting snow reported on mountain SNOTELS
in the SNowy and Sierra Madre Ranges as well as Metars up near
Douglas and Chadron. Decided to clear out most of the advisories
across the southern CWA with the exceptions of the Snowy and
Sierra Madre Ranges and Converse/Niobrara and northern Panhandle
where warnings will be allowed to continue through 5PM. Off to our
west across central California...our next low pressure system is 
moving on shore. 

Evening shift will need to monitor for fog development this
evening as the snow that fell today had quite a bit of moisture
content to it. Would say the lower elevations of the Panhandle and
maybe Laramie would be the prime areas for fog tonight.

Mainly dry Thursday for most of the day...but guidance begins to
hint at qpf developing across our southwestern counties late
Thursday afternoon. Upper low moves into southern Nevada and
northern Arizona Thursday evening with difluent upper level flow 
over southern Carbon and Albany Counties. NAM...SREF and GFS all 
showing widespread QPF Thursday evening into Friday morning in 
this diffluent flow. ECMWF showing similar placement...but much 
less QPF. Given the pretty good agreement from the GFS...NAM and 
SREF QPF...decided to start a Winter Storm Watch for our western 
counties after 00Z Friday...spreading east to the Panhandle by 12Z
Friday.

.LONG TERM...(Friday night through Wednesday)
Issued at 300 PM MST Wed Mar 10 2021

Key messages...Heavy snowfall is likely starting Friday afternoon.  
Prepare for impossible travel conditions starting Saturday morning into
Sunday evening. Protect livestock, people, property, and pets. 
IMPACTS...Whiteout conditions, low visibility levels, and possible
power outages. Blizzard conditions are possible starting Saturday
afternoon into Sunday evening for the Nebraska Panhandle and 
Albany, Laramie, Platte, and Goshen counties. 

Saturday and Sunday's snowfall will bring major impacts to the 
entire CWA across southeastern Wyoming and the western Nebraska 
Panhandle. Forecast confidence is medium with placement and duration 
of the low pressure system hovering in Colorado. The uncertainty 
continues for exact snowfall amounts and intensity of this system 
due to the forecast concerns of varying dynamics and the 
possibility of a barrier jet forming. Although it is still early, 
this system shows tight gradients and strong winds aloft will 
support strong surface gusts up to 35-40 MPH for the Nebraska 
Panhandle and southeastern Wyoming. A possible jet could develop 
along the Rocky mountain ranges which could enhance snowfall 
development especially with most models showing cold air aloft. 
Snowfall ratio were too high with the GFS so using a NBM/ECMWF 
blend, I created a sweet spot ratio across the CWA ranging from 
11:1-8:1. If this set up continues on track, this will lead to 
record-breaking snowfall across the region. Potential 3-day storm 
total snow forecasts are significantly above maximum 3-day records
for Cheyenne and Scottsbluff including the March 2003 snowfall 
event. 

In addition to snowfall and strong winds, temperatures continue below
freezing in southeastern Wyoming and hover in the upper 30s for 
the Nebraska Panhandle into next week. Skies will remain overcast 
into Tuesday afternoon. A piece of energy cuts off the same low 
pressure system from the weekend which may lead to light snowfall 
again Tuesday although upper level moisture is not present at this
time. Mild conditions are possible mid next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1002 PM MST Wed Mar 10 2021

Current radar imagery has indicated that the snow has finally 
shifted to the east, lifting the majority of terminals to VFR 
conditions. VFR and MVFR conditions expected to through the late 
afternoon tomorrow. Through the forecast period, winds are 
expected to remain light. Main concern for the remainder of this 
evening, into tomorrow morning, are the fog potentials for KCDR. 
Forecast soundings still look good for that terminal showing a low
level moisture layer below the inversion. Still some uncertainty 
with the cloud deck above, which will limit fog development.

Next shot for wide-spread snow is expected tomorrow evening. At this 
time the low pressure cell seems fairly disorganized, primarily 
bringing snow only for the KCYS, KLAR, and KBFF with some wrap- 
around moisture on the northern portion of the low. There is a 
chance that the snow will need to be included in the remaining 
terminals, depending on how this low develops over the next 12 to
18 hours.

&&

.FIRE WEATHER...
Issued at 300 PM MST Wed Mar 10 2021

Minimal fire weather concerns as we have seen widespread snow and
are looking at another widespread heavy snow event Friday through
the weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Watch from Thursday evening through late Sunday 
     night for WYZ101>103-106>108-116>119.

     Winter Storm Watch from Thursday afternoon through late Sunday 
     night for WYZ104-105-109-110-113>115.

NE...Winter Storm Watch from late Thursday night through late Sunday 
     night for NEZ002-003-019>021-054-055-095-096.

&&

$$

UPDATE...TJT
SHORT TERM...GCC
LONG TERM...AW
AVIATION...MD
FIRE WEATHER...GCC