Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 272119

Area Forecast Discussion
National Weather Service Cheyenne WY
319 PM MDT Thu Oct 27 2016

.SHORT TERM...(Today - Saturday Night)
Issued at 228 PM MDT Thu Oct 27 2016

Quiet weather prevails this afternoon w/ broad upper-level ridging
in place across much of the central CONUS. Breezy conditions exist
to the west of the Laramie Range with Rawlins currently gusting to
40 MPH as of 20z. Lee troughing over the high plains has kept wind
speeds considerably lower to the east. An increase in mid and high
level cloud cover is expected tonight as a weak disturbance tracks
across the area. Subsidence associated with this feature is likely
to result in gusty winds over our wind corridors in the 06z to 12z
time frame tonight and early Friday. Winds will be slower to climb
at BRX as the surface trough will need to advance slightly further
to the east before gusts become more significant. 700-800 hpa flow
generally less than 45 knots, and an H85 CAG-CPR gradient at/below
40 meters per the GFS/NAM precludes the issuance of a warning over
the wind corridors at this time.

There is a chance for rain showers over our western/northern zones
on Friday afternoon and evening with mid-level PVA and strong low-
level convergence. Less-than-impressive moisture availability will
limit precipitation coverage and intensity. In fact, the NAM keeps
most of the QPF over central Wyoming in RIW territory. More in the
way of cloud cover on Friday, so believe temperatures will be some
what cooler than today. Dry and generally cooler for most areas on
Saturday post-fropa, warmer along the I80 corridor between CYS-SNY
with more sunshine.

.LONG TERM...(Sunday - Thursday)
Issued at 228 PM MDT Thu Oct 27 2016

The main forecast issue in the long term is a shortwave and associated
cold front moving through Central Wyoming on Monday. The GFS and
the ECMWF are coming into agreement that the incoming shortwave
will produce a widespread high wind event across southeast Wyoming
and western Nebraska. The 850 mb Craig to Casper gradient are
producing increasing values beginning midnight on Monday and
peaking at 85 meters at noon on Monday. The winds will begin to
pick up overnight on Sunday out west along the I 80 corridor from
Rawlins to Laramie. During the day on Monday a strong bora event
will produce strong winds over the high plains of Wyoming and
Nebraska. Wind gusts currently are looking to be between 50 to 60
kts along and west of the Laramie Range and 40 to 50 kts over the
high plains, although, depending on the path of the shortwave the
wind gusts could increase beyond that. Widespread wind gusts of
50+ kts are a very real possibility on Monday morning and early
afternoon across much of the high plains.

Precipitation chances will be limited with the frontal passage. Lack
of low to mid level moisture will keep any shower chances confined
to the Sierra Madre and Snowy Ranges on Monday. The wind will
decrease Monday night leading into a cooler and dry pattern.

GFS and ECMWF diverge after Tuesday leading to a lot of
uncertainty about possibly another shortwave moving through on
Wednesday and Thursday. The GFS is showing an increase in moisture
over Wyoming and Nebraska while the ECMWF shows a drier solution.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1127 AM MDT Thu Oct 27 2016

VFR conditions will prevail today. Gusty winds across the
southeast Wyoming will develop after 18Z today through 0Z. Wind
gusts between 20 and 30 knots will be common.


Issued at 228 PM MDT Thu Oct 27 2016

Near-critical fire weather conditions will persist over some parts
of southeast Wyoming through late this afternoon with RH values at
or slightly below 15 percent and wind gusts approaching 25 kts. No
Red Flag Warnings are in effect as overall conditions remain below
RFW criteria. A cold front will yield slightly cooler temperatures
and higher humidities for the weekend.




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