Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 302040
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
240 PM MDT TUE AUG 30 2016

.SHORT TERM...(This evening through Thursday night)
Issued at 240 PM MDT Tue Aug 30 2016

Some isolated convection has fired along a weak convergence zone
around the southeast Wyoming/northern Colorado border this
afternoon...on the northern periphery of an elongated upper low
over Colorado. This will persist through late in the afternoon
with some instability but will dissipate early in the evening with
loss of heating. Moist flow on southerly winds may be enough for
some low clouds and fog mainly from far southeast Wyoming across
the southern Nebraska Panhandle later tonight into Weds morning.

An upper high will build over the region Wednesday into Thursday
boding for warm and mainly dry weather across the CWA. Surface
winds will increase especially over the plains Tuesday afternoon
and again Weds as the gradient steepens between a surface high
over the northern and central plains and falling pressures over
the northern Rockys. Atmosphere should be sufficiently capped so
convection should be held off into Thursday. On Thursday the
upper ridge axis will shift east of the area leaving swly flow
aloft. A weak impulse will approach the area and should set off
at least isolated convection Thursday afternoon and
evening...mainly around the mtns.

.LONG TERM...(Friday through Monday night)
Issued at 240 PM MDT Tue Aug 30 2016

Southwest flow will strengthen overhead Friday and on through the
weekend in advance of the upper low moving across the PacNW and
northern Rockies. Models remain fairly consistent showing a number
of weather disturbances moving over the Rockies as the upper trough
stalls over the western CONUS, however differences do exist with
strength and timing of the individual systems. Confidence remains
relatively  high though that gusty south-southwest winds and
showers/storms will occur nearly each day within this flow pattern.
To start, a leeside surface pressure trough will develop in
advance of the system on Friday, shifting to the east on
Saturday. ECMWF/GFS do show some differences in timing of this
feature, but still expect fire weather concerns out to the west
due to gusty southwest winds and dry humidities both Friday and
Saturday. Looking at widely scattered convection in the afternoon
over much of the area as well, with a few strong storms possible
east of the sfc trough. The main cold front associated with this
system doesn`t look to move across the forecast area until
Saturday night or Sunday, and in the wake of the leeside trough.
Will remain active for convection for Sunday and Monday, with some
strong to severe storms possible across the plains on Monday in
the postfrontal, upslope environment. Temperatures will slowly
but steadily cool off through the period, with Monday looking to
be the coolest day as temps should be in the 60s/70s. Stratus and
fog chances will be high Friday night with strong southerly flow
in place, and again on Monday night in strengthening upslope flow.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1159 AM MDT Tue Aug 30 2016

Added mention for thunder at KCYS for this afternoon as a cluster
of storms fired along the WY/CO border just southeast of the
terminal, and this activity is slowly moving west. May also see
t-storms at KSNY later this afternoon per current trends and model
guidance. Otherwise, moist upslope flow will continue tonight,
likely bring a period of IFR/LIFR fog and stratus to many eastern
terminals. Maintained such conditions at KAIA, KSNY, and KBFF, but
also added in KCYS to the mix due to a better fog/stratus signal
in the boundary layer profile that is progged for tonight. Gusty
southerly winds in excess of 20kts will develop Wednesday morning
mainly across the plains of southeast Wyoming and Nebraska
panhandle.


&&

.FIRE WEATHER...
Issued at 240 PM MDT Tue Aug 30 2016

Breezy to windy conditions expected to develop over the plains
Weds through Thursday but humidities look to stay well above
critical levels. Concerns increase out west late in the week as
winds there increase and humidities get rather low.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...None.
&&

$$

SHORT TERM...RE
LONG TERM...RJM
AVIATION...RJM
FIRE WEATHER...RE


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