Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 132327
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
527 PM MDT Wed Mar 13 2024

.KEY MESSAGES...

1) Winter Storm Warnings are in effect starting Wednesday
morning for the Snowy and South Laramie Ranges, including the
I-80 Summit between Cheyenne and Laramie.

2) Light to moderate snowfall accumulations will be likely
across the lower elevations of Carbon and Albany counties and
across the I-80 corridor from Cheyenne to Sidney, with the
higher totals occurring over Cheyenne with less amounts further
east.

3) Normal temperatures at the end of the weekend will giveaway
to well above normal temperatures to begin next week.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 126 PM MDT Wed Mar 13 2024

Main focus for the short term forecast remains this incoming
winter storm that should bring widespread valley snowfall and
heavy mountain snow accumulations, especially for the Snowy
Mountain range.

Multiple runs of HI-RES models this afternoon show widespread
QPF fields but totals are unimpressive and comparing these runs
to local observations, areas that have received precipitation
this afternoon have been reporting .05" or less. Latest radar
trends over the past few hours has a large area of light
precipitation beginning to fill in across much of SE Wyoming and
portions of the southern Nebraska Panhandle. This is the
initial surge of the incoming storm system with the arrival of
the weak frontal boundary. The one thing that has remained
consistent is all models are in agreement of bringing this
system as a weaker and fragmented, coupled with both the lower
QPF fields and weaker upslope flow, snow accumulations were
trimmed down slightly from the previous forecast package.

Timing the rest of the system out, the best forcing is still on
track to arrive this evening with a now 2hr later arrival than
the previous runs, now looking at the heaviest snowfall for the
I-25 corridor will be around 9pm, with the arrival of upper
level jet support and the low level winds shifting toward a
better upslope flow regime. During this time, HI-RES models
still hint at some embedded heavier bands developing in the
broad precipitation shield but pinpointing where these bands
occur is a low confidence forecast. Any location that is
impacted by one of these heavier bands could see and additional
2-3" of snow from what the current forecast shows, which is why
the Winter Weather Advisory for Laramie County is for 3-9"!. The
main concern will be the Thursday morning commute where
overnight snow and the arrival of gusty winds may create some
blowing issues through the morning hours. With snow
accumulations expected on the roads these factors may create a
hazardous morning commute. When these gusty arrives these will
be westerly downslope which should end all precipitation chances
for areas east of the Laramie Range. Post storm, temperatures
will remain on the cooler side and these temperatures may need
to be adjusted downward if we get more robust clearing and keep
the snowpack around.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 126 PM MDT Wed Mar 13 2024

Minimal changes made to the long term forecast. The 12Z HREF
soundings show conditions conducive for producing freezing fog
or even freezing drizzle. Soundings show a shallow layer of east
to southeasterly upslope winds into the Cheyenne Ridge with Td
depressions of 0 to 2 degrees at -3 to -8 C temperatures, and a
dry layer aloft near to above 700 mb. While light snow showers
may stick around the South Laramie Range and Foothills Friday
morning, areas below 6500 feet have the potential for freezing
drizzle or at the least freezing fog through mid- morning.

By Friday evening, southeast Wyoming and western Nebraska are in a
col or saddle point with high pressure systems to the NW and SE and
low pressure systems to the SW and NE. This pattern will bring
warmer temperatures Saturday with highs near 5 degrees above-
average. Sunday, models show the low pressure over the Great Lakes
drifting southeast, dropping a backdoor cold front into the Nebraska
panhandle and far east Wyoming. Due to this, temperatures Sunday are
a few degrees cooler than they were Saturday, especially in the
northern panhandle and east-central Wyoming. Overall this is
expected to be a dry cold front, mainly turning winds to the
east/northeast with wind gusts 30 to 40 mph possible. The ridge over
the western CONUS then moves east and takes over with much warmer
temperatures, dry conditions, and generally light winds.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 522 PM MDT Wed Mar 13 2024

Active weather for aviation assets the next 24 hours. Looks like
lowering conditions this evening as rain turns over to snow.
Northeast upsloping winds expected to bring IFR and below
conditions here at KCYS. Out west...short term mesoscale
guidance showing snow becoming more widespread with KRWL and
KLAR going down in snow in the next few hours. Panhandle
airports may stay VFR/MVFR overnight as temperatures stay fairly
warm with rain not turning over to snow. Will continue to
monitor...and adjust TAFs as needed this evening.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 6 AM MDT Friday for WYZ101-
     103>105-109-115.
     Winter Weather Advisory until 6 AM MDT Friday for WYZ106-
     117>119.
     Winter Storm Warning until 6 AM MDT Friday for WYZ110-114-116.
     Winter Weather Advisory until 3 PM MDT Thursday for WYZ111-113.
     Winter Weather Advisory until 6 PM MDT Thursday for WYZ112.
NE...None.

&&

$$

SHORT TERM...AW
LONG TERM...LEG
AVIATION...GCC


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