Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 230545

Area Forecast Discussion
National Weather Service Cheyenne WY
1035 PM MST Thu Feb 22 2018

.SHORT TERM...(This evening through Friday)
Issued at 320 PM MST Thu Feb 22 2018

The main area of light snow is moving east from the Nebraska
panhandle at this time. There is still a little instability
upstream that will move across the southeast corner of Wyoming and
the southern panhandle through mid evening, but a little drying
below this layer means this will be mainly virga. High clouds will
quickly spread back over the area ahead of the next shortwave, so
cooling tonight will be limited. Tough call on fog and low clouds
for the panhandle, as there will initially be a little bit of
drying trying to work in from the northwest behind this
afternoon`s shortwave. However, low level winds are light so there
won`t really be much change in the surface moisture. Expect that a
little clearing will allow low clouds and fog to redevelop if they
do break up a little.

By Friday morning the mid and high level clouds will be thickening
from the west as lift moves in again. Plains winds will be
trending southeast in response, which will advect low clouds
westward during the day. This should all come together to produce
an area of light snow that spreads across southeast Wyoming in the
evening across the panhandle overnight. While lift is modest and
there`s not a lot of moisture to work with, it should not take
much to produce light snow. There are two questions with this
system. First is whether the snow skips over Cheyenne and areas
just east of the mountains due to drier low level air and a
quicker start of downsloping. These factors will inhibit snow
amounts, but there is a pretty good chance of getting a dusting as
the lift moves over in the evening. The other question is whether
precipitation begins as freezing drizzle in areas east of Cheyenne
in the late afternoon or early evening. There is some potential
for the lift to begin before the deeper moisture arrives. Again,
if there is any precipitation at this time it should be quite
light. We will mention the chance of freezing drizzle but do not
believe it is a big threat for travel impacts due to a quick
changeover to snow in the evening if it does occur. Any more
significant snow amounts should be southeast of our area, though
there is some chance that Sidney could get a little more than the
2 inches we`re advertising should the system trend a bit more

.LONG TERM...(Friday night through Thursday)
Issued at 320 PM MST Thu Feb 22 2018

The story for the extended period is warmer and windier as a
broad trough develops near the west coast. The winds should come
up quickly behind the shortwave Saturday morning. This could cause
problems in the wind prone areas if there is much fresh snow, but
it does not look like there will be much new snow in the wind
areas. Saturday afternoon looks close to high wind warning
guidance for the windiest places, while Sunday looks like there
should be a bit more widespread windy conditions and maybe a bit
more of a high wind threat for the wind prone areas. After that,
the flow becomes more southwest for warmer temperatures and a bit
less wind. There is pretty good agreement on a trough about
Wednesday. At this point it looks to be fast moving and probably
sheared apart. Model blend gives a quick chance of showers and a
bit more wind Wednesday, which looks good. Then a trend back to
southwest flow with less agreement about the details of an
upstream trough that would not arrive until next weekend.


.AVIATION...(For the 06Z TAFS through Friday evening)

Low confidence forecast for most of the area.  Low clouds and fog
have developed further to the west than earlier anticipated, near
KCYS and KLAR, and even KRWL, but conditions have been mostly
variable as intervals of midlevel clouds have pushed over the area,
limiting surface cooling. In addition, periods of downslope winds
have produced VFR conditions in these areas off/on this evening as
well as some flurries and light snow which has complicated things
further around KCYS and KLAR.  Given radar trends, will continue
with periods of fog/snow for KLAR, and to a lesser extent KCYS,
tonight and keep western Nebraska VFR into early Friday morning.

For Friday, expect a band of snow to develop and push across the
eastern plains by Friday evening. There is a good chance of
widespread IFR conditions in light snow between 21z Friday through
06z Saturday.

Issued at 320 PM MST Thu Feb 22 2018

No issues due to snow cover and cool temperatures. Windy
conditions are expected Saturday and Sunday, then less wind early
next week.




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