Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 230926
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
326 AM MDT FRI SEP 23 2016

.SHORT TERM...(Today through Saturday)
Issued at 310 AM MDT Fri Sep 23 2016

Widespread low clouds continue across areas along and east of the
Laramie Range. WYDOT obs from Cheyenne to the I-80 summit show vis
remaining mostly below a quarter mile so the dense fog advisory is
working out well. Will keep it going for central Laramie county
even though the fog has not developed at CYS yet. HRRR guidance
shows much quicker clearing through the morning compared to
yesterday. Models show the closed upper low currently near Salt
Lake City lifting northward into central WY by this evening. The
warm front will lift northward across the plains through the day
with southerly winds strengthening from I-25 eastward. Did
increase wind speeds over the Panhandle with the southern
Panhandle getting close to advisory level (fcst gusts to 35 kts)
by the late aftn.

Cold front is progged to be near the Laramie Range by the aftn,
and this will be focus for shower/tstm development. Went with
40-60 POPs over much of the plains of southeast WY during the aftn
as the HRRR/NCAR ensembles are in good agreement with the global
models. There will be a marginal risk of svr storms across the
plains and especially north of the warm front. This is due to CAPE
values of 500-1000 J/kg and excellent bulk shear. Storm activity
over the plains should begin to die down by the late evening with
the cold front pushing across the Panhandle by 06Z.

The other story with this storm system will be the orographic snow
over the Sierra Madre and Snowy Ranges by late tonight into
Saturday morning. Wet bulb zero heights are around 8500 ft MSL.
Moist westerly 700-500 mb flow on the backside of the upper low
will create favorable orographics, especially over the Sierra
Madre Range. Currently have 1-4 inches of snow over much of the
western mtns, which would be welcome news for the fires that have
been ongoing near the Sierra Madre Range. It will be breezy to
windy on Saturday with highs struggling to get above the mid 60s.

.LONG TERM...(Saturday night through Thursday)
Issued at 310 AM MDT Fri Sep 23 2016

Upper trough moves through the area Saturday night into Sunday.
Going to be cold as 700mb temperatures fall to -4C Sunday into
Monday.

Warmer and drier weather for the rest of the upcoming week as
ridge of high pressure builds back over the area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1105 PM MDT Thu Sep 22 2016

Challenging forecast for the overnight hours. HRRR guidance
showing IFR/LIFR lifting across the southern Panhandle early this
morning as a trough of low pressure moves out of northeast
Colorado. Generally followed the HRRR guidance on timing/clearing
of stratus and fog. Strong winds this afternoon and evening as a
cold front moves through the area. Could see gusts to 45kts out at
KSNY, KAIA and KBFF, first from the southwest and then from the
northwest when the front moves through.

&&

.FIRE WEATHER...
Issued at 310 AM MDT Fri Sep 23 2016

No fire weather concerns through the weekend.  Temperatures will
cool across the entire area after today behind a cold front. Minimum
afternoon humidity values will mostly be above 25 percent through
the weekend. There will be a chance of showers and thunderstorms
through tonight across the region.  A few inches of snow will be
possible tonight through Saturday morning over the Sierra Madre and
Snowy Ranges.

&&

.CYS Watches/Warnings/Advisories...
WY...Dense Fog Advisory until 7 AM MDT this morning for WYZ116>118.

NE...None.
&&

$$

SHORT TERM...ZF
LONG TERM...GCC
AVIATION...GCC
FIRE WEATHER...ZF



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