Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 272100

Area Forecast Discussion
National Weather Service Cheyenne WY
300 PM MDT Sat May 27 2017

.SHORT TERM...(This evening through Monday night)
Issued at 237 PM MDT Sat May 27 2017

With weak instability in place, will continue to see scattered
showers and isolated tstms over the next few hours, before
activity decreases around 00Z with the loss of daytime heating.
Cannot rule out pea sized hail with the heavier showers with the
low freezing levels. The shortwave wave trough axis that is
currently overhead will move southeastward into Kansas by tonight.
Northwesterly flow aloft will dominate the pattern through early
next week. Highs will rise around 10 degrees on Sunday, back into
the 60s to low 70s for areas to the east of the Laramie Range.
There will be enough aftn instability (CAPE values of 100-200
J/kg) for at least isolated to scattered showers/tstms to develop,
although the activity looks less than today across the plains. A
weak front will push across the region on Sunday night, with llvl
winds becoming more easterly/upslope along the southern Laramie
Range. All models show more storm activity in Albany/Laramie
counties by Monday aftn in an area of enhanced sfc convergence.
Thus, will show higher PoPs 30-40 percent for Monday. Outside of
some breezy northerly winds through the remainder of the aftn,
winds will be rather light in the short term period.

.LONG TERM...(Tuesday through Saturday)
Issued at 237 PM MDT Sat May 27 2017

Upper ridge over the western US at the start of the period will
migrate very slowly eastward and be positioned roughly over the
central and northern Rockies by Thursday. Temps will be gradually
warming each afternoon through Thursday with Thursday likely being
the warmest day. Chance for afternoon showers and thunderstorms
will return by Wednesday mainly over the mountains and possibly
over the plains as some mositure return gets going in S`ly to
SE`ly boundary layer flow. GFS might be a little over aggressive
with the amount of precip generated in this environment especially
in the evening/overnight hours with only weak forcing from minor
shortwaves traveling through the mean ridge and weak flow aloft.
Should be a fairly robust cap in place with 700 mb temps progged
at 10-12 C on the GFS and EC. Trimmed POPs back to slight chance
Wednesday and Thursday over much of the area outside of the
mountains. Model difference become much larger after Thursday with
the EC maintaining significant ridging aloft and warm conditions
through Sat with only slight chances for afternoon convection. GFS
allows stronger shortwave energy to flatten the ridge with much
higher chances for storms along the front range.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1142 AM MDT Sat May 27 2017

VFR will prevail this afternoon through tonight across all
terminals. Scattered showers are currently developing along a
trough axis running roughly from the Black Hills southwest to the
Saratoga area. These showers will progress to the southeast
through the afternoon and will reduce ceilings/vis locally to MVFR
at times. Showers should exit the area to the southeast late this
afternoon/early this evening.


Issued at 225 AM MDT Sat May 27 2017

The cool and showery weather will continue today. Isolated afternoon
thunderstorms are also forecast, however strong storms are not
expected. Somewhat drier and milder weather returns Sunday and Monday,
with widely scattered afternoon thunderstorms, mainly over the higher
terrain of southeast Wyoming. Minimum humidities of 40 to 50 percent
today will decrease to 30 to 35 percent Sunday and Monday.


Issued at 237 PM MDT Sat May 27 2017

No fire weather concerns through early next week.  Temperatures will
warm to back around normal over the next few days.  However, minimum
afternoon humidity values will mostly remain above 25-30 percent.




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