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278
FXUS65 KCYS 270527
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1127 PM MDT Fri May 26 2017

.UPDATE...
Issued at 807 PM MDT Fri May 26 2017

Severe thunderstorm watch will be allowed to expire. Only one
storm along the CO/WY border currently being warned on but this
one is showing a weakening trend on the last few radar scans.
Scattered to numerous showers and thunderstorms are expected to
continue through the late evening hours, but the stabilizing
effect of previous convective overturning and loss of daytime
heating will preclude any severe threat.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 232 PM MDT Fri May 26 2017

Active convective situation still underway currently. Severe
storm currently in Carbon County has produced reports of funnel
clouds and a wind gust to 64 mph at the Rawlins airport. Storms
will continue to develop along the leading edge of a plume of
steep mid level lapse rates over south-central Wyoming and spread
eastward through the evening hours. Short range convective models
still indicating 1000 to 1500 J/kg of MLCAPE developing late this
afternoon east of the Laramie Range. Deep layer shear of around 50
kt will remain supportive of supercell structures with large hail
and damaging winds being the main threat. A low end tornado
threat cannot be ruled out due to locally backed surface flow just
north of the Cheyenne Ridge. There is some concern however, that
the area of showers and weaker thunderstorms currently moving off
the Laramie Range will keep these areas from realizing the
instability that was earlier expected and thus reduce the overall
severe threat. Severe Thunderstorm Watch remains in effect for
southeast WY and western NE along and south of highway 26 through
8 pm.

Storms may tend to congeal into one or more clusters later this
evening in the strengthening warm advection regime ahead of an
elongated mid-level shortwave.  This activity should exit the area
to the east late tonight.

Saturday should be cooler with breezy northwest to north winds. With
the upper trough passing overhead during peak heating, expect
scattered shower activity especially over the higher terrain.  Some
thunder cannot be ruled out but the severe threat should be minimal.

.LONG TERM...(Sunday through Thursday)
Issued at 355 AM MDT Fri May 26 2017

Medium range models/ensembles are in general agreement with a
northwest flow aloft between a upper ridge over the Intermountain
West and upper low south of Hudson Bay Canada Sunday and Monday.
The western CONUS upper ridge weakens Tuesday and Wednesday as a
upper trough digs southeast across the Pacific coast states.
Consequently, winds aloft become more westerly. The upper ridge
rebuilds over the High Plains Thursday as trough moves toward the
Four Corners, and winds aloft back to the southwest.

Convection for the most part will be widely scattered, diurnally
driven, and generally confined to the higher terrain. Any convection
that manages to spread onto the plains will be more isolated.
Convective coverage increases somewhat Thursday with increasing
moisture in the southwest flow aloft. Daily temperatures gradually
moderate to seasonal normals by Thursday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday evening)
Issued at 1127 PM MDT Fri May 26 2017

Some lingering showers early in the period mainly over the Neb
Panhandle.  Sctd IFR cigs early in the period but improving during
the morning.  Sctd showers and a few tstms again later this morning
through the afternoon.

&&

.FIRE WEATHER...
Issued at 232 PM MDT Fri May 26 2017

A cool and unsettled weather pattern will persist through the
weekend with humidity values remaining well above critical
thresholds, and good chances of wetting rain across all of
southeast WY and the western NE Panhandle. There is potential for
a few strong to severe storms this afternoon and evening.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

UPDATE...DEL
SHORT TERM...DEL
LONG TERM...MAJ
AVIATION...ZF
FIRE WEATHER...JG