Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 010953

Area Forecast Discussion
National Weather Service Cheyenne WY
353 AM MDT Sat Oct 1 2016

.SHORT TERM...(Today through Monday)
Issued at 300 AM MDT Sat Oct 1 2016

Weak ridging in place across the central rockies today as
upstream trough of low pressure carves onto the west coast.
Morning satellite images point to a sunny start to the day as
sub-tropical moisture plume that brought weak precip yesterday
continues shifting east. Models prog weak destabilization by
afternoon (SBCAPES of 200-400 j/kg) which will be sufficient for
weak convection in and around the southeast Wyoming mountains
after 3-4 PM. In the absence of an organized disturbance, coverage
will be limited. This activity dissipates quickly with loss of
daytime heating.

Ridge axis ever so slowly continues to shift east on Sunday, with
southwest flow moving into the area by afternoon. Although high
temperatures slightly cool on Sunday, falling heights ahead of low
pressure swinging thru the Great Basin will yield another day of
afternoon destabilization. Progd instabilities will be more
favorable on Sunday (SBCAPES of 400-800 j/kg) and with the
approach of increasingly diffluent flow and leading shortwave,
expect convective coverage to expand mainly for areas east of the
Laramie Range especially by evening. This convection will likely
linger into the overnight hours Sunday night, especially across
east-central Wyoming and the northern Nebraska Panhandle.

Low pressure are lifts northeast from the Great Basin into NW
Wyoming on Monday. A strong surface cold front will accompany this
feature moving west-east on Monday. Models prog this front near the
WY/NE stateline or slightly farther east by late Monday.
Instability pooling out ahead of this cold front could set the
stage for potentially thunderstorm development across the eastern
plains mid-late afternoon Monday. Timing will be everything with
placement and strength of storms, but something that will need to
be watched. Strong winds will be the other side of the story with
and behind the front with as H7 winds increase to 40-50 knots by
late Monday. These winds increase further in the following
periods. Temperatures will be cooler especially across western
zones where CAA associated with the cold front will be felt

.LONG TERM...(Monday Night through Friday)
Issued at 350 AM MDT Sat Oct 1 2016

Medium range models in better agreement with the strong upper
level low forecast to move across Wyoming and then stall somewhere
in the Dakotas or far eastern Montana on Tuesday. Although run to
run consistency has been poor...all models and associated ensemble
forecasts have trended towards the northern solution similar to
the yesterday`s 00z ECMWF. With the track of the low across
northern Wyoming and eastern Montana...continued to trend the
forecast towards more wind and less precipitation. Still believe
it will get quite chilly with high temperatures 10 to 15 degrees
below normal...and highs in the upper 40`s to upper 50`s across
most of the area. May see our first widespread freeze Wednesday
night and early Thursday as skies clear and good radiational
cooling takes place. The mountains may still see some snow...and
can not rule out some light snow flurries even across the lower
elevations Tuesday night and Wednesday...but impacts should be
minimal. The main story may be the wind...with models showing the
potential of a strong bora after the front moves east of the area
late Monday through early Tuesday. The wind prone locations
appear to have the best chance to receive winds over 60
mph...with the valleys and high plains of southeast Wyoming likely
over 50 mph. May need High Wind headlines over the next 48 hours
if this trend continues. Otherwise...started lowering POP from
south to north through Tuesday. Models do indicate a secondary
disturbance pushing east on the backside of this upper level low
on continued chances for rain/snow showers into
Wednesday night.

By Thursday and Friday...all models show the upper level low
lifting northeast into Canada...with improving conditions across
southeast Wyoming and most of western Nebraska. A slight warming
trend is expected with highs returning to the 60`s across the
eastern plains...but with northwest flow aloft daytime
temperatures will struggle to increase much until Friday
afternoon. Kept POP below 10 percent as the next Pacific system
will likely remain well north of the forecast area.


.AVIATION...(For the 12Z TAFS through tonight)
Issued at 330 AM MDT Fri Sep 30 2016

VFR conditions are expected to continue today and through late
this evening. A few thunderstorms and showers are possible late
this afternoon and early this evening across the
mountains...potentially impacting KCYS and KLAR. Should remain dry
elsewhere with south to southwest winds between 10 to 15 knots
during the afternoon.


Issued at 300 AM MDT Sat Oct 1 2016

Mild conditions will continue over the districts into early next
week with periodic low chances of showers and thunderstorms. Any
fire weather concerns will be low. A strong area of low pressure
will usher in cooler temperatures after Monday along with a period
of strong winds. Latest forecast information points to lessening
chances of significant precipitation from this event, but some
shower activity especially over the mountains will be a good bet
on Tuesday. Cool temperatures will continue for the rest of the





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