Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 201946
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
145 PM MDT Sun Aug 20 2017

.SHORT TERM...(Today through Monday night)
Issued at 209 AM MDT Sun Aug 20 2017

Models show a weak front backing into the plains through the
morning, with sfc winds becoming light easterly by the aftn.  Temps
will be slightly cooler (5-10 degrees) today for areas to the east
of the Laramie Range.  Although afternoon RH values will drop to
near critical levels over Carbon/Albany counties, no fire weather
concerns are anticipated with winds weaker than yesterday.  The
HRRR/NCAR ensemble shows some storms developing along the southern
Laramie Range as convergence increases between 18-21Z.  The primary
threat from these storms will be gusty outflow winds with deep
boundary layers in place.  SREF low cloud probs suggest some patchy
stratus will be possible by late tonight over the Nebraska
Panhandle.  However, NAM/GFS soundings do not indicate much llvl
saturation, so confidence is not high that low clouds will be
widespread by late tonight into Monday morning.

Not much change with regard to cloud fcst on Monday (Eclipse
day). A shortwave will be moving from eastern Montana into the
northern Plains through the day. All models show the highest mid
to high lvl RH values through midday over the western Nebraska
Panhandle. Will continue with 50-65 percent sky cover in the
Panhandle, decreasing to 15-40 percent over southeast WY. A fropa
will occur through the day with northerly winds over southeast WY.
There will be a slight chance of tstms over the plains by the
aftn with overall weak forcing.

.LONG TERM...(Tuesday through Saturday)
Issued at 209 AM MDT Sun Aug 20 2017

A rather strong upper level ridge will build over the western CONUS
Tuesday and will slide east over the Rockies on Wednesday. An
upper low situated over the southeast Pacific will advect monsoon
energy and moisture up into the region on Wednesday and Thursday
within the ridge, so we should see at least some weak convection
both days. Focus looks to be in the west over the high country on
Wednesday, shifting east into the plains for Thursday as the ridge
shifts out into the central plains. For Friday, models show a
deep upper low moving across southern Canada with a cold front
moving south into the high and central plains sometime Friday and
stalling along the Front Range on Saturday. Therefore, expect
continued chances for showers/storms over portions of the
forecast area on Friday with Saturday highly dependent on the
stability of the post-frontal environment. Temperatures through
the period should start below normal, increasing to near normal
values through the end of the week.

&&

.AVIATION...(For the 18Z TAFS through Monday morning)

VFR conditions will prevail at most locations this evening through
midnight. Stratus is expected to spread from east to west after 06Z,
including KAIA, KSNY, and KBFF. But do not expect stratus to impact
the southeast WY terminals at this time. Periodic gusts of 20 to 25
kts are likely this afternoon and into this evening. A few
thunderstorms will develop in the afternoon over and near the
mountains as well.

&&

.FIRE WEATHER...
Issued at 209 AM MDT Sun Aug 20 2017

Minimal fire weather concerns through early next week.  Although
minimum humidity values will fall to 15-20 percent today over lower
elevations to the west of the Laramie Range, wind gusts will mostly
be below 20 mph.  Isolated thunderstorms with gusty outflow winds
will be possible in areas near the southern Laramie Range this
afternoon.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...ZF
LONG TERM...RJM
AVIATION...TJT
FIRE WEATHER...ZF



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