Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 130528

Area Forecast Discussion
National Weather Service Cheyenne WY
1128 PM MDT Tue Sep 12 2017

.SHORT TERM...(This afternoon through Thursday night)
Issued at 215 PM MDT Tue Sep 12 2017

Current Visible and Watervapor satellite loop shows the upper
level disturbance from this morning beginning to push eastward
into the western Dakotas and NW Nebraska panhandle this afternoon.
Isolated thunderstorms are developing along and ahead of this
disturbance with thunder near Chadron early this afternoon.
Increased POP between 15 to 20 percent across the western
Nebraska panhandle through this evening. Once the disturbance
moves eastward, increased subsidence aloft should result in
decreased convection outside of the mountains. Skies will clear
overnight with relatively mild temperatures for this time of the

For Wednesday and Thursday, the upper level ridge which has been
over the area for the last week will begin to weaken as a Pacific
upper level trough moves into Calif and eventually into the Great
Basin region. Meanwhile, a stronger Pacific system will dig
southward across the Pacific northwest associated with the Polar
jet steam. The upper level ridge will likely weaken and translate
eastward into the plains by Thursday as the flow aloft becomes
southwesterly. Expect a gradual increase in convection Wednesday
afternoon in response to this as the jet stream and overall
pattern starts to become more active. Kept POP between 20 to 40
percent on Wednesday, mainly across southeast Wyoming for some
high based thunderstorms. Temperatures will likely be the warmest
of the week Wednesday afternoon with highs in the 80`s to mid
90`s, coolest west of the Laramie Range due to cloud cover. Expect
a higher coverage of showers and thunderstorms for Thursday as the
first cold front makes its way through southeast Wyoming, so
increased POP between 30 to 60 percent over most locations with
values below 25 percent for the lower valleys of Carbon county.
Temperatures on Thursday will begin to lower in response to the
Pacific upper level trough, with highs likely in the 70`s west of
I-25 and 80`s east of I-25 with temperatures lowering through the

.LONG TERM...(Friday through Monday)
Issued at 117 PM MDT Tue Sep 12 2017

A transition to a cooler and more unsettled pattern is still
forecasted on Friday into the first half of the weekend.  Shortwave
is progged to be over western Colorado on Thursday night and will
swing rapidly northeastward over the CWA through Friday morning.
Best chance of precip through Friday afternoon will be over western
zones.  The models are in rather good agreement at showing the main
upper trough moving over Wyoming on Saturday with the sfc fropa on
Friday evening/night.  Highs on Saturday will be quite cool, around
10-15 degrees below normal with 700 mb temps dropping to 0-3C.  Will
show mostly chance PoPs spreading to areas east of the Laramie Range
by Friday night through Saturday morning as llvl forcing along the
front combines with upper level divergence in advance of the upper
trough.  Cannot rule out some snow showers above 10000 ft in the
Sierra Madre and Snowy Ranges by Saturday as the colder air aloft
moves overhead.  Sunday and Monday look like rather pleasant days as
heights aloft rise and temps moderate back toward normal.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1125 PM MDT Tue Sep 12 2017

VFR prevails through the TAF period. Scattered thunderstorms are
expected to develop over the mountains and affect KLAR, KCYS, and
KSNY through 00z this afternoon. Any of these storms are capable
of gusty downdrafts to 40kt. Storms should weaken with the loss of
heating after 00z.


Issued at 200 PM MDT Tue Sep 12 2017

Very warm temperatures are expected this afternoon and Wednesday
afternoon before a series of Pacific storm systems impact the area
late this week and into next weekend. Elevated Fire Weather
conditions are possible Wednesday afternoon due to minimum
relative humidities around 15 to 20 percent and gusty winds,
mainly along and west of I-25. Otherwise, concerns will trend
lower late this week through the weekend due to higher humidities
and cooler temperatures.




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