Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 220351

Area Forecast Discussion
National Weather Service Cheyenne WY
951 PM MDT Fri Apr 21 2017

Issued at 942 PM MDT Fri Apr 21 2017

Evening water vapor loop showed a mid/upper level low circulation
located over central Wyoming. An inverted surface trough extended
south across west central CO into northern NM. Moist upslope
southeasterly flow and weak forcing aloft still producing light
rain and snow showers across much of southeast WY into far western
NE this evening. Snow levels are expected to fall to near 5500
ft tonight with changeover to all snow. Additional accumulations
up to an inch expected, mainly for higher elevations of southeast
WY. Areas of fog, dense in spots, will likely form late tonight
from the Laramie Valley east into Laramie County. Also concerned
about very slick roadways as temperatures fall into the 20s,
especially along the I-80 corridor between Cheyenne and Laramie.
The Winter Weather Advisory remains in effect for the southern
Laramie Range and foothills through 8 AM Saturday.


.SHORT TERM...(This evening through Sunday)
Issued at 411 PM MDT Fri Apr 21 2017

Rain and snow continuing to diminish very slowly this afternoon
with the most concentrated area holding over the far southwest
Panhandle into far southeast Wyoming. Radar showing a small
circulation center over far northern Colorado southeast of
Cheyenne...which has only drifted slowly southeast this afternoon
and helped to keep somewhat enhanced pcpn going.

Models continue to show a slowly diminishing area of pcpn over
mainly southeast Wyoming overnight as a secondary shortwave drops
southeast across the area. Additional snowfall amounts should be
light but given rather cold temperatures overnight and the
potential for freezing of water and additional snowfall between
Cheyenne and Laramie have opted to post a winter wx advy for that
area into Saturday morning. Some fog...possibly dense...also a
likelihood over far southeast Wyoming overnight.

The weekend will see warming temperatures with any lingering pcpn
ending Saturday morning and upper ridging nosing into the region.
Skies expected to clear out during the day Saturday with max temps
rebounding into the 50s to mid 60s...and in the 60s and the 70s
over lower elevations Sunday as the upper ridge slides by.

.LONG TERM...(Sunday night through Thursday night)
Issued at 411 PM MDT Fri Apr 21 2017

A fast zonal flow pattern will be overhead through the middle part
of the week with embedded midlevel disturbances moving through the
flow. Expect chances for showers and afternoon t-storms through
this time. Temperatures look to be warm enough to keep precip type
mainly rain, except for the mountains and Laramie Valley where we
may see temps drop below freezing during the overnight hours to
support snow. Westerly winds will be on the breezy side as well
in this pattern. A deeper upper low is progged to dig into the
Rockies on Wednesday and Thursday although GFS/ECMWF differ quite
a bit at timing and strength of this system. Will keep it simple
and just maintain chances for precip through this time, along
with a trend towards cooler temperatures.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 530 PM MDT Fri Apr 21 2017

VFR CIGS will prevail tonight, except invof KCYS where IFR-LIFR
CIG/VIS in fog develops 03Z-04Z. HRRR model introduces MVFR-IFR at
KLAR and KSNY, and MVFR at KRWL by 09Z tonight. These low conditions
will likely persist through late Saturday morning. Winds will be
variable less than 10 kt through the TAF period.


Issued at 411 PM MDT Fri Apr 21 2017

Concerns look to remain low through the weekend into early next
week given wetting pcpn over much of the area today and min RHs
remaining above critical levels.


WY...Winter Weather Advisory until 8 AM MDT Saturday for WYZ116-117.



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