Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 221754

Area Forecast Discussion
National Weather Service Cheyenne WY
1154 AM MDT Tue Aug 22 2017

.SHORT TERM...(Today through Wednesday night)
Issued at 443 AM MDT Tue Aug 22 2017

Stratus has developed in southerly upslope flow along the
Cheyenne Ridge and southern Laramie Range, but so far no fog has
been observed in these areas. Dew point depressions in these areas
are not all that impressive, so will keep fog out of the forecast
for now. An upper level ridge will build over the western CONUS
today, and over the Rockies by Wednesday. Temperatures should
increase a few degrees each day as the ridge builds, and it looks
like precip chances will increase as well. For today, the dry
airmass evident on current water vapor imagery will remain
overhead, although some moisture to our southwest may reach the
higher mountain peaks of south-central WY. Maintained slight
chance for t-storms in this area, which includes the Snowy and
Sierra Madre Ranges. Further east, should remain relatively stable
and mostly dry in the post-frontal airmass although can`t rule
out a shower or storm over the Laramie Range in the late

Wednesday will see a marked increase in precip chances from
southwest to northeast as energetic southwest flow increases in
strength and carries with it subtropical moisture. Bulk shear
values are progged to be low so could see regeneration of
pop up showers/storms over the same areas, with moderate rainfall
possible. Maximum model QPF values are progged around one quarter
of an inch through Wednesday evening. Some of this activity may
last through Wednesday night as a slow moving shortwave trough
rounds the ridge and over our forecast area.

.LONG TERM...(Thursday through Monday)
Issued at 443 AM MDT Tue Aug 22 2017

The models continue to advertise a weak shortwave moving across
central WY on Thursday with a sfc trough along the Laramie Range.
Isolated/scattered storms will likely develop along this trough
during the aftn and progress eastward into the Panhandle.  Have
lower PoPs across the far western zones as drier air aloft works
into that area.  Friday is now looking drier behind the upper wave
and a morning fropa with PW values falling to 0.5-0.75 inches.  Sfc
winds become weak easterly by Saturday with some llvl moisture
advection toward the Laramie Range and better instability.  Could
see an isolated stronger storm across the plains on Saturday with
decent northwesterly flow aloft providing good bulk shear.  A drier
pattern will likely occur by Sunday into early next week as a strong
upper ridge develops over the Great Basin, cutting off any monsoonal
moisture.  Highs through early next week will be around normal for
late August.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1147 AM MDT Tue Aug 22 2017

Latest satellite loop was showing the stratus having a tough time
scouring out this morning. These clouds should continue to scour
out at KCYS during the next hour or so. The rest of the TAF sites
should see VFR conditions through the afternoon with mainly
southerly flow in the panhandle and west-northwest flow at
KLAR/KRWL. The wind speeds should begin to diminish after sunset
with these light wind speeds persisting through 18z tomorrow.


Issued at 443 AM MDT Tue Aug 22 2017

For today, afternoon humidities will fall to around 15 percent
across lower elevations of Carbon County, however winds will be
relatively light. Further east, minimum humidities will remain
above 20 percent, and southerly winds across the plains will be
breezy with gusts around 20 mph through early evening. Isolated
thunderstorms are possible this afternoon over the mountains as
well. Moisture will increase on Wednesday and will persist through
the end of the week as monsoonal flow from the southwest returns
to the district. Higher humidities and better chances of showers
and thunderstorms can be expected through this time.




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