Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 160541

Area Forecast Discussion
National Weather Service Cheyenne WY
1141 PM MDT Sun Oct 15 2017

Issued at 834 PM MDT Sun Oct 15 2017

We are sending out a quick update to upgrade the Fire Weather
Watch to a Red Flag Warning for fire weather zones 309 and 310 due
to gusty downslope winds developing tomorrow afternoon.

Latest water vapor loop was showing some shortwave energy moving
through western Wyoming. This shortwave energy will move through
the area tonight. However, very little moisture will be associated
with this feature. Behind this shortwave, we will see good mixing
develop by noon along foothills of the Laramie Range. This deep
mixing is then expected to spread into the Wyoming Plains during
the early afternoon. This should result in gusty wind speeds of 25
to 30kts and low relative humidities. This rather deep mixing
could also spread into the southern Nebraska panhandle late in the
afternoon, but there is some uncertainty if this will meet the
3hr Red Flag Criteria. We have also left the Fire Weather Watch
in effect for Fire Weather Zone 301 due to the potential for
shallower mixing in that region.


.SHORT TERM...(This evening through Monday)
Issued at 140 PM MDT Sun Oct 15 2017

Ridging will build over the intermountain west through Monday with
the main northern stream jet shifting north into Canada. As
heights rise, a strong warming trend is expected to continue with
high temperatures reaching the mid to upper 60s west of the
Laramie Range and low to mid 70s east of the range Monday
afternoon. Moderately strong WNW flow aloft present over the area
on Monday and thus expect breezy conditions to develop west of the
surface trough roughly from I-25 west. GFS indicates low level
CAG-CPR gradients of 45-50 meters Monday morning so could see some
wind gusts of 40 to 50 mph near Arlington during this time.

.LONG TERM...(Monday night through Sunday)
Issued at 140 PM MDT Sun Oct 15 2017

Modest ridging will continue to shift eastward through the period
and emerge out over the plains by Thursday as troughing develops
along the US west coast. Warm, very dry, and breezy conditions can
be expected through mid week with the potential for fire weather
concerns each day. Models continue to struggle a bit with the
evolution of the west coast trough over the weekend with the GFS
now attempting to close off a low over the desert SW while the
EC/Canadian show a much more progressive and less amplified
feature. Still looks like a rather quick cold frontal passage
Saturday morning with little in the way of measurable precip with
the exception of some mountain snow. Ensembles indicate strong
ridging developing over the west early next week which would
indicate the return of warm and dry conditions.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1135 PM MDT Sun Oct 15 2017

A weak upper level trof is expected to pass through the area late
tonight into tomorrow. After this trof passes through, we will see
an increase in wind speeds around 18z. Wind speeds could be gusty
at times near 30kts especially at KRWL, KLAR, and KCYS. Could see
have some cirrus on Monday, but VFR conditions will prevail.


Issued at 140 PM MDT Sun Oct 15 2017

Sunny skies and breezy west winds will allow for excellent mixing
of dry air aloft on Monday and Tuesday afternoons.  Widespread critical
fire weather conditions are possible both afternoons so went with a Fire
Weather Watch for zones along and in the lee of the Laramie Range Monday
where fuels have been marked as ready.  Would also be concerned about
portions of the Laramie Valley and Carbon County where criteria will also
likely be met but fuel status is a no in these areas.  Some elevated
conditions are also possible into the Nebraska Panhandle Monday but
think the winds and humidity are too marginal right now to warrant
highlights.  Another watch or warning will likely become necessary for
parts of the same region by Tuesday afternoon as well.


WY...Fire Weather Watch from 11 AM MDT Monday through Monday
     afternoon for WYZ301.

     Red Flag Warning from 11 AM to 6 PM MDT Monday for WYZ309-310.



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