Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 142058

Area Forecast Discussion
National Weather Service Cheyenne WY
258 PM MDT Mon Aug 14 2017

.SHORT TERM...(This Evening through Wednesday)
Issued at 300 PM MDT Mon Aug 14 2017

Scattered showers and thunderstorms have developed in the past few
hours across southeast WY.  Current thinking is the main threat from
these storms will be gusty downdrafts with deep boundary layers and
large DCAPE values in place.  Also cannot rule out small hail as the
SPC mesoanalysis shows SBCAPE of 500-750 J/kg and decent bulk shear
of 30-40 kts across northern zones.  Chance of showers and isolated
thunder will continue into the early night.  Shortwave trough
currently across the Great Basin will move eastward into central WY
by Tuesday.  Temps will be around 5-10 degrees cooler for tomorrow
behind a weak fropa overnight.  Expect another round of aftn/evening
storms to develop, with the coverage highest for areas to the east
of the Laramie Range.  There will be a better chance of strong
storms mainly over the Nebraska Panhandle during the aftn with CAPE
of 1000-1250 J/kg and good deep layer shear.  Shortwave trough axis
will move into northeast Colorado by late Tuesday night into
Wednesday morning.  Wednesday will be coolest day with a more stable
airmass in place and only isolated storms possible along the Laramie

.LONG TERM...(Wednesday night through Monday)
Issued at 300 PM MDT Mon Aug 14 2017

Somewhat active northwest flow on Thursday will gradually become
westerly by week`s end and southwesterly for the weekend and into
early next week. The latest GFS and to a lesser extent the ECMWF
show shortwave energy diving southeast towards the Dakotas on
Thursday. The associated sfc frontal boundary to be the focus for
at least weak afternoon/evening convection. Progd SBCAPE`s are at
most 500 j/kg across our eastern portion of the Panhandle, so
would not expect much organization to the convection. Dry, stable
air mass will yield a dry day on Friday. Flow turns more
southwest as the weekend wears on, which should advect moisture
back northeast into the CWA. Have added afternoon precip chances
to the Snowy/Sierra Madres on Saturday/Sunday as a result. This
pattern would be conducive to afternoon/evening
shower/thunderstorm chances lingering on Monday afternoon as well.
For now, have confined these to areas in east-central Wyoming
after 18z.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1225 PM MDT Mon Aug 14 2017

Main concerns for aviation ops will be the timing and location of
afternoon and nighttime convection that will develop and move
across the region. Latest info suggests thunderstorms will
continue developing near KCYS/KLAR after 19z. KRWL will likely see
some convective development as well, though the drier air mass
will likely only yield high-based showers capable of producing
gusty outflow winds. This area of -TSRA/-SHRA will lift northeast
towards western Nebraska Panhandle sites 21-23Z. The bulk of the
activity will likely depart by around 05Z, with perhaps a second
round of showers and/or weak thunderstorms lingering overnight.
For now have kept VCTS confined to the location and timing above.
May need to linger convection a bit longer on the 00z/06z TAF


Issued at 200 PM MDT Mon Aug 14 2017

Minimal fire weather concerns through midweek.  We expect good
chances for showers and thunderstorms this afternoon through
Tuesday.  Some of the storms will produce wetting rains.  Afternoon
humidities could drop down to 15-20 percent across portions of
southeast Wyoming by this weekend.





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