Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 170531
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1031 PM MST Sat Feb 16 2019

.SHORT TERM...(This evening through Sunday)
Issued at 341 PM MST Sat Feb 16 2019

Two hazards and resultant impacts to focus on next 24 hours:

1) Localized moderate snow bands and snow squalls this afternoon
to early evening along with scattered snow showers overnight into
early Sunday. Impacts could be difficult driving conditions at
times, especially in localized heavier snow bands/squalls and in
the higher terrain along I-80.

2) Cold wind chills of negative 5F to negative 15 degrees will
occur tonight into early Sunday and even colder wind chills are
expected Sunday night into Monday morning of negative 15 to
negative 25 degrees for a larger portions of the area. A Wind
Chill Advisory will likely be needed for Sunday night into Monday.

Weather Details: Modest divergence aloft with localized near-
surface convergence is ongoing underneath a shortwave trough
passage this afternoon across southeast Wyoming and Nebraska
Panhandle. A localized boundary was noted on satellite imagery
this early afternoon and this is the location of a now developing
narrow snow band across west Laramie County into Kimball County,
Nebraska. NAM and HRRR soundings indicate 50-100 J/Kg of low-level
CAPE with steep lapse rates present. In combination with elevated
snow squall parameter values, hi-res guidance indicates a
favorable environment for localized banding of snow showers that
could reduce visibility quickly across short distances. This
appears to be ongoing at this time near Kimball, NE. Additional
scattered snow showers are shifting southeast across the northern
Laramie Mountains and additional local bands and squalls will need
to be monitored for through the early evening hours. Low-level
lapse rates and instability will decrease through the mid evening
with localized banding likely to decrease with the shortwave
trough passage to the east. Meanwhile, the Sierra Madre and Snowy
Mountain Ranges will pick up an additional 3 to 6 inches of snow
through this evening where a Winter Weather Advisory remains in
effect until 11pm tonight. Some additional light snow showers will
linter tonight and Sunday but overall intensity will be reduced.

Following the passage of the trough to the east tonight, cold air
advection will shift over the region tonight and early Sunday.
Much colder temperatures expected tomorrow and even more so early
next week. Wind chill values will fall below zero Sunday night and
even further on Monday. Wind Chill advisories will likely be
needed Sunday into Monday for a large portion of the area.
Temperatures will remain below normal through all of the short
term and much of the long term as well.

.LONG TERM...(Sunday through Friday)
Issued at 300 AM MST Sat Feb 16 2019

A series of short waves will rotate through the base of the long
wave upper trough over the western CONUS through much of next
week. This pattern favors much below normal temperatures through
Tuesday with daytime highs in the teens and 20s and nighttime lows
from 5 to -10 degrees. Could be dealing with wind chill headlines
Sunday night and Monday night with wind chills from -15 to -25
degrees. Temperatures will moderate closer to normal Wednesday
through Friday with highs in the 20s and 30s. Windy Wednesday,
especially the I-25 corridor between Wheatland and Chugwater with
700mb winds around 40 kt and CAG-BRX 850mb gradients 55-65mtrs.
Snow showers will be confined to the southeast WY mountains and
high plains into parts of western NE Sunday through Tuesday, and
again Thursday through Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1027 PM MST Sat Feb 16 2019

Wyoming TAFS...VFR, except MVFR at Laramie and Cheyenne after
00Z. Wind gusts to 22 knots at Cheyenne until 00Z.

Nebraska TAFS...IFR or MVFR at Chadron and Alliance until 12Z,
then VFR. VFR at Scottsbluff and Sidney. Wind gusts to 30 knots
from 11Z to 01Z.

&&

.FIRE WEATHER...
Issued at 341 PM MST Sat Feb 16 2019

Scattered snow showers will move across the High Plains
and the higher terrain this afternoon and evening. Snow will taper down
Sunday but winds will remain elevated at 20 to 30 mph across southeast
Wyoming. Fire weather concerns will be minimal over the next several days
as below normal temperatures will hold on through the weekend into
early next week. Relative humidities will stay above critical values.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 11 PM MST this evening for WYZ112-
     114.

NE...None.
&&

$$

SHORT TERM...JSA
LONG TERM...MAJ
AVIATION...RUBIN
FIRE WEATHER...JSA


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