Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 192125

Area Forecast Discussion
National Weather Service Cheyenne WY
325 PM MDT Sat Aug 19 2017

.SHORT TERM...(This evening through Monday)
Issued at 240 PM MDT Sat Aug 19 2017

Mainly dry conditions across most of southeast Wyoming and western
Nebraska this afternoon with dewpoints in the 20`s and 30`s. A few
showers and one lone thunderstorm have developed near the Colorado
border from south of Cheyenne to Sidney Nebraska. Increased POP
slightly in these areas since there is some weak convergence and
enough instability to initiate convection. Otherwise, kept POP
near zero through tonight further north and west.

Another pleasant day is expected on sunday with similar
temperatures and mostly sunny skies north of I-80. Further south,
models show a slightly more favorable environment for
thunderstorms along Interstate 80 from near Kimball Nebraska
westward towards Cheyenne and Laramie including the mountains.
Winds are expected to shift into the east with moisture advection
and upslope into the afternoon. Moisture will likely be limited
however, so kept POP 15 to 25 percent outside the mountains. Some
of this activity may make it into western Nebraska in the evening
hours. Will have to watch which locations do get rainfall, since
that may result in low stratus and/or fog for early Monday
morning across the High Plains.

Forecast for Monday, and specifically the eclipse, looks on track.
There are a few weather concerns which include afternoon
thunderstorms and low stratus clouds mainly across western
Nebraska. However, thunderstorm chances appear to be lower
compared to yesterday and may be later in the afternoon across
most of the area, so do not expect convection to play much of a
role other than slight impacts on afternoon travel. Low clouds
and patchy fog is more of a concern mainly for western Nebraska
but this could also include areas near Lusk and Torrington as
well. Models do show a frontal system moving across the area
Monday morning with winds shifting into the northwest behind the
front. This will allow a cooler and more stable airmass in the
area for the morning hours and may help with eclipse visibility
across most of southeast Wyoming. Starting to trend the forecast
for mostly cloudy across western Nebraska however as model
sounding show a saturated layer around 1000 feet AGL in upslope
southeast flow, which usually indicates broken to overcast skies.
Will continue to monitor this through the weekend, but for now
increase cloud cover between 50 to 70 percent across western
Nebraska through noon Monday with rapid clearing behind it as
northwest winds develop.

.LONG TERM...(Monday Night through Saturday)
Issued at 208 PM MDT Sat Aug 19 2017

A couple of showers/thunderstorms may be ongoing on Monday evening
over southern/eastern portions of the area given lingering mid-lvl
energy embedded within northwest flow aloft. By Tuesday, the GFS &
ECMWF both show an upper-level ridge beginning to build across the
central Rockies. This feature appears to remain intact through Thu
AM, effectively limiting precipitation chances through mid to late
week. A return to southwest flow aloft is expected on Thursday, so
expect to see better chances for convection late in week depending
on timing/placement of individual waves. Daytime high temperatures
will be near to slightly below normal w/many areas consistently in
the 75-85 degree range, coolest along/west of the Laramie Range.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 208 PM MDT Sat Aug 19 2017

VFR prevails. There is some risk for an isolated thunderstorm near
KCYS or KSNY through early this evening, but overall coverages are
expected to be very low. The main aviation hazard with any t-storm
activity would be gusty and erratic surface winds.


Issued at 208 PM MDT Sat Aug 19 2017

Red Flag Warning for zones 303 and 306 will continue into this
evening for critical Fire Weather conditions as winds have gusted
up to 35 MPH earlier this afternoon. Further east, conditions are
above criteria or marginal this afternoon even though humidities
will be around 15 percent along I-25. Slightly cooler temperatures
and higher humidities are expected Sunday and Monday, but
conditions west of the Laramie Range may continue to be elevated
into early next week.



WY...Red Flag Warning until 8 PM MDT this evening for WYZ303-306.



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