Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 260807

Area Forecast Discussion
National Weather Service Cheyenne WY
207 AM MDT Wed Jul 26 2017

.SHORT TERM...(Today through Thursday night)
Issued at 133 AM MDT Wed Jul 26 2017

Today...Heights aloft rise slowly today as a weak ridge aloft builds
overhead. In the wake of a cold front, low level upslope east and
southeast winds will prevail. Plenty of low and mid level moisture
will remain in the atmosphere, though a more stable airmass will
reside along and east of Interstate 25, limiting areal coverage of
showers and thunderstorms. Greatest coverage of showers and
thunderstorms will be this afternoon west of I-25 in proximity to
the low and mid level theta-e ridge axis and instability axis.
Relatively cool with cloud cover.

Tonight...With the absence of a shortwave trough aloft or other
lifting mechanism, expect showers and thunderstorms to gradually
diminish and decrease in areal coverage as the night progresses. A
mild night with abundant low level moisture and cloud cover.

Thursday...Warmer temperatures as the airmass moderates and with
less cloud cover. With adequate low and mid level moisture
remaining, and low level southeast upslope remaining, will see
scattered to numerous showers and some thunderstorms develop in the
afternoon mainly from I-25 westward.

Thursday night...As is typical, will see areal coverage of showers
and thunderstorms decrease with loss of daytime heating and with the
absence of another lifting mechanism. Continued mild.

.LONG TERM...(Friday through Tuesday)
Issued at 133 AM MDT Wed Jul 26 2017

Weak shortwave will move slowly over the top of the persistent
upper ridge over the SW US on Friday. Models differ with the
timing of this wave but most have it somewhere in the vicinity of
the plains of SE WY and western NE during peak heating on Friday.
Airmass should be quite moist and unstable with SFC dewpoints well
into the 50s to low 60s. Low level SE flow will be topped by
modest W flow aloft which will produce bulk shear values around 35
kts or so. May see some strong storms especially east of the
Laramie Range where the best instability/shear overlap is located.
For Saturday through Tuesday, GFS and EC differ somewhat on the
position of the upper ridge. The GFS builds the ridge more
strongly over the Rockies while the EC tends to retrograde it
towards the US west coast. Either way, seasonable temps are
expected with at least some monsoonal moisture causing daily
chances for showers and thunderstorms. Convective details will
most likely be tied as usual to subtle waves which are
unpredictable at this time scale and/or previous days convection.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1122 PM MDT Tue Jul 25 2017

Latest short range models are not handling current precipitation
very well so confidence is a bit lower than normal in precip and
resultant ceiling/vis restrictions tonight. Expect the area of
showers over western Carbon County to continue to affect KRWL with
periods of MVFR in heavier showers through 10Z. Showers will
expand over the northern Panhandle into the early morning hours as
well. Elsewhere expect ceilings to lower into the early morning
hours with widespread MVFR to IFR ceilings developing in moist
upslope flow over the plains east of the Laramie Range. This low
stratus may persist into the late morning hours in the favored
locations such as along the Cheyenne Ridge near KCYS. Low ceilings
should eventually lift to VFR by Wednesday afternoon.


Issued at 133 AM MDT Wed Jul 26 2017

Minimal concerns based on projected winds and humidities.




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