Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 250625

Area Forecast Discussion
National Weather Service Cheyenne WY
1225 AM MDT THU AUG 25 2016

Issued at 915 PM MDT Wed Aug 24 2016

Bumped up PoPs in our northern zones for tonight as radar is
showing a fair amount of shower/t-storm activity over central
Wyoming at this hour, and this activity should move into our
northern zones overnight. Can also see additional development over
this area within a zone of strengthening isentropic lift
overnight. Lastly, added in patchy fog along and near the Laramie
Range as latest model guidance is showing a better fog signal for
after midnight.


.SHORT TERM...(This evening through Friday night)
Issued at 300 PM MDT Wed Aug 24 2016

Surface analysis showing frontal system that moved through last
evening currently laying along a line from southeast Colorado,
northwest to near Dixon and then west out to Evanston this
afternoon. Most of the CWFA in easterly flow with 1PM temperatures
in the 60s. Mosaic radar do show convection beginning to blossom
out over southern carbon County with cell movement to the east at
20-25MPH. Cloudy skies have kept temperatures in check and latest
SPC Mesoanalysis only showing roughly 500 J/Kg CAPE along the
Wyoming/Colorado border. Better instability south in central
Colorado with 1000-1200 J/Kg CAPE being observed.

For this afternoon, expect to see an increase in coverage of
showers and thunderstorms through the afternoon. CAPEs climb to
around 1000 J/Kg late this afternoon with peak heating. Am not
expecting thunderstorms to be severe today based on this lack of
instability. Storm motions on the low end though this afternoon,
generally under 10kts, so we could see some moderate to heavy rain
showers at some location. Best chances over the mountains and
adjacent eastern slopes as the storms move off and drift east.

NAM, ECMWF and SREF showing showers continuing over our northern
zones of Converse and Niobrara Counties through the night time
hours. This is due to an upper shortwave moving through northern
Wyoming tonight. So kept some low chance PoPs going across our
northern mountains and Converse/Niobrara Counties overnight. Did
consider fog here and along the east slopes of the Laramie Range
tonight as we stay in a southeast upslope flow. But forecast
soundings and latest HRRR output keeping stratus chances on the
low side.

Fairly widespread showers Thursday east of the Laramie Range and
more widespread Friday as a strong shortwave approaches and then
moves through Friday afternoon. Did go with Superblend PoPs which
puts us into Likely category for most areas along and east of
Laramie Range Thursday night into Friday.

.LONG TERM...(Saturday through Wednesday)
Issued at 300 PM MDT Wed Aug 24 2016

The extended forecast period appears to be fairly quiet overall w/
dry, quasi-zonal flow aloft in place over the CWA. The models show
a few disturbances traversing the flow, but modeled H7-H3 moisture
progs suggest minimal activity outside of maybe an isolated shower
or thunderstorm over the mountains. With an active jet well to the
north along the Canadian border, no major weather events appear to
be in the offing. Daytime high temperatures should be right around
normal for this time of year, generally in the 70s and 80s. Models
begin to diverge late in the period with the GFS showing continued
upper-level ridging through Wednesday, and the ECMWF becoming more
unsettled w/increasing southwest flow aloft ahead of an amplifying
upper trough over the western US.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1225 AM MDT Thu Aug 25 2016

Initial aviation concern will be the potential of low stratus
and/or fog developing KRWL-KLAR-KCYS by sunrise. Confidence is
highest of fog occurring at KLAR so trended the TAF into the MVFR
category 11-16z. Will continue to monitor trends for possible
inclusion later at KCYS. Otherwise, will need to watch once again
for the development of isolated thunderstorms at KLAR and KCYS
after 21z. Given uncertainty in timing and spatial extent of
convective activity...VCTS mention will suffice. Otherwise, expect
VFR conditions to prevail at other SE WY and W Nebraska Panhandle
terminals thru the period.


Issued at 124 PM MDT Wed Aug 24 2016

Minimal fire weather conditions the next few days with cool and
moist air over area from yesterdays frontal passage. Afternoon
humidities to stay well above critical levels with chances for
wetting rains for most of the area. Do begin to dry out this
weekend with westerly winds increasing. Could see critical fire
weather conditions return Saturday and Sunday for areas west of
the Laramie Range.


.CYS Watches/Warnings/Advisories...



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