Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 212332

Area Forecast Discussion
National Weather Service Cheyenne WY
532 PM MDT Fri Jul 21 2017

.SHORT TERM...(This evening through Sunday)
Issued at 314 PM MDT Fri Jul 21 2017

Water vapor imagery shows the monsoonal plume overhead with
thunderstorms popping up over the higher mountains this
afternoon. The cold front has passed south through our eastern
plains counties, and a more northeast upslope fetch along the
Laramie Range should aide in storm development along these
mountains. Additional development along the Cheyenne Ridge (I-80
corridor) is still progged by most models through later this
afternoon and evening. This activity will likely be associated
with a weak shortwave moving along the CO/WY border. As can be
expected, instability is meager in the post frontal environment
according to mesoanalysis so not anticipating strong activity.
Main threat will once again be moderate to locally heavy rain
resulting from the monsoonal moisture and energy, and relatively
slow storm motions. Showers and storms could linger through the
early morning hours as the shortwave is slow to move to the east.

Another shortwave approaching from the northwest on Saturday late
morning/afternoon should bring another chance for showers and
storms in the afternoon, however this wave will also push the
monsoonal moisture to the south and east. High temperatures will
be roughly 5-10 degrees cooler in the post-frontal environment,
and temps aloft will cool a couple of degrees as well. Moist
southeasterly return flow will aide in destabilizing the
atmosphere some through the afternoon, especially along the
eastern side of the Laramie Range and the Cheyenne Ridge. Not
expecting much in terms of convection, but can`t rule out a couple
storms developing in these areas with increasing llvl moisture
and some energy overhead. Sunday looks to be quite similar but
with a little less moisture through the column as the monsoonal
plume will be to our south. Will keep chances for storms confined
to the higher mountains for now.

.LONG TERM...(Sunday night through Friday)
Issued at 314 PM MDT Fri Jul 21 2017

The models continue to advertise a dry start to next week with the
midlvl ridge center located near northern Colorado Monday . and
Tuesday.  Overall, will keep PoPs rather low with PW values mostly
in the 0.5-0.75 inch range.  Highs will be around 5-10 degrees above
normal through Tuesday.  A transition to a wetter pattern may occur
by Wednesday into Thursday as the ridge aloft flattens and better
monsoonal moisture is transported into the region.  A look at GEFS
mean PW values show a rise to around 1.0-1.2 inches by the middle of
next week.  Thus, have better storm chances then, along with
slightly cooler temps.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 529 PM MDT Fri Jul 21 2017

Broken line of showers and embedded thunderstorms progressing
southeastward across the Snowy and North Laramie Ranges early
this evening. Wind gusts to 40 mph and brief heavy rain lowering
visibility to MVFR possible near KLAR before these storms die as
the move east into a more stable airmass east of the Laramie
Range. Elsewhere VFR should prevail with just scattered showers
near KCYS early this evening. Tomorrow should feature generally
clear skies with light winds and much lower chances of afternoon


Issued at 314 PM MDT Fri Jul 21 2017

Showers and thunderstorms will continue along and west of the Laramie
Range this afternoon, with some storms expected to expand to the east
along the I-80 corridor through the evening. A few showers may continue
overnight as well. Generally cooler and drier conditions will occur
through the weekend, with more isolated coverage for storms possible
over the mountains and along the I-80 corridor over the plains. Winds
on the whole will be be on the lighter side.




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