Area Forecast Discussion
Issued by NWS Cheyenne, WY

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204
FXUS65 KCYS 262318
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
518 PM MDT FRI AUG 26 2016

.SHORT TERM...(This evening through Saturday)
Issued at 218 PM MDT Fri Aug 26 2016

As expected, scattered thunderstorms are now developing across the
southern half of the CWA in response to a weak shortwave currently
tracking from west to east across southeast Wyoming. Convection is
expected to remain intact through early/mid evening before dynamic
support weakens as the wave moves east of the area. Small hail was
observed earlier at the WFO, which is no surprise given CAPES near
1500 J/kg and around 30 knots of 0-6 km shear. A few strong, maybe
marginally severe storms are possible, and most of our high plains
zones are still highlighted in a MRGL risk from SPC per the latest
convective outlook. This threat should quickly diminish after 3-6z
as all model guidance shows the leading edge of much drier mid-lvl
air sweeping across the CWA by that time. Light winds along with a
divergent flow pattern expected over east central Wyoming into the
northern Panhandle after 06z, along w/good boundary layer moisture
so we may see some fog development overnight once convection moves
east or dissipates.

Much drier air is expected for Saturday with the GFS/NAM/ECMWF all
in excellent agreement with H7-H3 humidities under 25 percent, and
at least modest mid-level subsidence associated with the departing
wave. Dry westerly flow through the column would suggest consensus
guidance for dew points is at least 5-10 degrees too high. In fact
the raw GFS/NAM models are much drier than the SuperBlend. Trended
warmer and drier which pushes afternoon RH values under 15 percent
and raises some fire weather concerns. Winds should be marginal on
Saturday but forecast soundings show a deep layer of 12-18 kt flow
which could easily yield a few gusts over 25 mph, especially given
subsidence aloft. Issued a Fire Weather Watch for FWZ 301, 303 and
308 for these reasons. Believe the main area of concern will be in
northern Carbon, northern Albany, and western Converse counties w/
the main belt of stronger flow aloft. Even warmer/drier for Sunday
with additional fire weather concerns.

.LONG TERM...(Saturday night through Friday)
Issued at 218 PM MDT Fri Aug 26 2016

A warm and dry weather pattern expected to prevail across the CWA
this period. A narrow upper ridge is initially expected to nose
northeastward from the desert southwest on Monday then build over
the Rocky mountains into the southern plains by midweek. Majority
of the moisture looks to remain suppressed south of the CWA
through Wednesday before possibly moving more up the Rocky
Mountain chain by late in the week as the upper ridge axis shifts
eastward over the plains...allowing for some convection mainly
around the mountains at that time. Temperatures expected to be
above seasonal norms for the week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 516 PM MDT Fri Aug 26 2016

Mainly VFR for our southeast Wyoming and Nebraska Panhandle
airports. Did continue the MVFR forecast for KBFF and KSNY for
early saturday morning, but confidence is not that high in this
happening. Will try to make a determination on the 06Z TAFs after
seeing what this evenings convect6ion does. If it dies out after
sunset, then stratus will probably not occur.

&&

.FIRE WEATHER...
Issued at 218 PM MDT Fri Aug 26 2016

Thunderstorms will continue over portions of southeast Wyoming and
the western Nebraska Panhandle through early evening. A few strong
storms are possible with small hail and gusty/erratic surface wind
along with heavy rain and cloud to ground lightning. Critical fire
weather conditions are possible over parts of FWZ 301, 303 and 308
on Saturday afternoon w/the arrival of a much warmer/drier airmass
and gusty winds. A Fire Weather Watch is in effect. Conditions are
expected to remain at least elevated through much of next week, if
not critical for areas mainly west of the Laramie Range.

&&

.CYS Watches/Warnings/Advisories...
WY...Fire Weather Watch from Saturday afternoon through Saturday
     evening for WYZ301-303-308.

NE...None.
&&

$$

SHORT TERM...CLH
LONG TERM...RE
AVIATION...GCC
FIRE WEATHER...CLH



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