Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 241740

Area Forecast Discussion
National Weather Service Cheyenne WY
1140 AM MDT Sun Sep 24 2017

Issued at 912 AM MDT Sun Sep 24 2017

WYDOT sensors and webcam images suggest that areas of dense fog
continue and the models indicate that fog will likely continue
well into the afternoon, so we have extended the dense fog
advisory until 3 pm for the southern Laramie Range and its


.SHORT TERM...(Today through Tuesday)
Issued at 400 AM MDT Sun Sep 24 2017

Well-defined upper low was spinning over southern UT. Diffluent
flow aloft and fast upper level jet max induced precipitation band
extends from the southern High Plains to the Dakotas. The western
edge of this precipitation was along a Chadron-Sidney line, moving
slowly to the east. More shower activity extended from eastern UT
into central and northern WY. Areas of dense fog continued between
Cheyenne and Laramie overnight, with WYDOT webcams indicating
visibilities a 1/4 mile or less. Patchy fog will develop along I-80
from Cheyenne to Sidney, and Laramie to Rawlins and linger through
at least mid-morning.

Good short range model/ensemble consensus with the northeast
track of the UT upper low into central WY by Monday morning, and
western ND Monday night.

Diffluent flow in the mid/upper levels ahead of upper low will
maintain the wet and unseasonably cool weather through Monday.
Colder air aloft will spread east to the Laramie Range with 700mb
temperatures 0 to -2C. Snow levels will lower to 9000 ft this
afternoon and 8000 ft this evening. Snow shower coverage and
intensity will increase this afternoon west of the Laramie Range
this afternoon, spreading east to the Laramie Range this evening.
Isolated afternoon t-storms are possible over southern Carbon and
southwest Albany counties with lifted indices near 0C. Periods
of moderate snowfall will occur with the heavier showers over the
higher mountain peaks, especially the Snowy Range. The higher
mountain passes will become snow-covered with poor visibilities.
Issued a Winter Weather Advisory for the Snowy Range from noon
through midnight tonight for 6 to 8 inches of snow above 9000 ft.
High temperatures today will average 20-25 degrees below normal
with upper 30s to lower 50s.

Monday will be the transition day as the upper trough to the west
weakens. Some lift from shortwave energy aloft and lingering
moisture/instability will produce isolated to scattered showers.
It will not be as cool with high temperatures moderating into
the 40s and 50s. The flow aloft backs from northwest to southwest
Tuesday, resulting in warmer temperatures and dry conditions.
High temperatures Tuesday will average about 5 degrees below

.LONG TERM...(Tuesday night through Saturday)
Issued at 330 AM MDT Sun Sep 24 2017

Mild and mainly dry weather expected to prevail through the period
with the area under a generally northwesterly upper flow. An upper
trough over the western CONUS Tuesday night is depicted to cut off
an upper low over the Desert Southwest Weds with models then drifting
this system slowly northwest through the end of the week. Differences
on how much if any associated pcpn moves into southern Wy. GFS brings
some into southern Wy late Thursday through Friday while the EC holds
it south of the area. Otherwise, a minor push of cooler air arrives
for Thursday before warming again to close out the week.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1135 AM MDT Sun Sep 24 2017

Widespread IFR/MVFR conditions will occur through the taf period.
IFR cigs will be most prevalent at the southeast WY sites through
00Z, with MVFR cigs in the western Nebraska Panhandle. Light rain
will become more widespread over southeast WY by the late
afternoon. Winds will mostly be below 12 kts, except at RWL/LAR.


Issued at 300 AM MDT Sun Sep 24 2017

A slow moving Pacific storm system will bring unseasonably cool
temperatures and widespread rain and high elevation snow showers
through Monday. Light to moderate snowfall will occur over the
higher mountain peaks of southeast Wyoming this afternoon and
evening. Warmer and drier conditions will return to the districts
Tuesday and persist through the end of the week.


WY...Dense Fog Advisory until 3 PM MDT this afternoon for WYZ116-117.

     Winter Weather Advisory until midnight MDT tonight for WYZ114.



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