Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 190839

Area Forecast Discussion
National Weather Service Cheyenne WY
239 AM MDT Sat Aug 19 2017

.SHORT TERM...(Today through Sunday night)
Issued at 239 AM MDT Sat Aug 19 2017

It will be a warm and dry day across the region with westerly
boundary layer flow.  With 700mb temps rising to 14-16C, highs will
be above normal in the mid 80s to mid 90s over lower elevations. The
models show dry midlvls, so should get some pretty low RH values
(dropping to around 15 percent) as deep mixing occurs from late
morning through the afternoon.  Winds aloft appear marginal for a
widespread critical fire weather day, however cannot rule out a few
gusts to 25-30 mph, particularly from Arlington to Rawlins.  Will
maintain an elevated fire weather threat for now and let the day
shift monitor trends.  Not much change in the pattern for Sunday,
except the gradient will weaken so expect winds to be weaker over
the CWA.  Winds become easterly over the plains by the aftn, so
cannot rule an isolated storm along the southern Laramie Range. With
weak instability and dry boundary layers, the main threat would be
gusty downdraft winds.

.LONG TERM...(Monday through Friday)
Issued at 239 AM MDT Sat Aug 19 2017

An upper level shortwave trough looks to track east into the
northern high plains on Monday, dragging a cold front south
through the forecast area later in the afternoon/evening
timeframe. Ahead of the trough, do anticipate some mid level
moisture to move overhead through the morning and early afternoon,
although models show an upper level dry slot moving over WY
around the noon hour. If this trend persists, could see even less
cloud cover with roughly 25-40% cloud cover possible along the
northwest-southeast eclipse path in WY, but up to 55% as you head
further east into the Nebraska Panhandle ahead of the dry slot.
As the upper wave and cold front move through the forecast area
later in the afternoon, we`ll see increasing clouds and chances
for showers and thunderstorms late afternoon/evening. Once this
trough passes to the east, an upper level blocking pattern is
progged to set up over the western CONUS through midweek. The
ECMWF is stronger with the upper ridge than the GFS on Tuesday and
keeps our forecast area to the east of the monsoon track. The GFS
brings a piece of energy over WY late Tuesday with mainly
isolated mountain storms possible, so kept in some chance for
convection on Tuesday afternoon/evening. Both models then bring a
stronger shortwave through on Wednesday and also develop a leeside
trough. The combination of both features should bring a better
coverage of showers and thunderstorms to the area. Thursday looks
very similar to Wednesday at this point except for a deeper plume
of monsoonal moisture advecting up from the southwest. That will
contribute to a better chance for convection Thursday and Thursday
night. The upper wave will shift to the east on Friday with a
weaker disturbance moving overhead in wsw flow.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1003 PM MDT Fri Aug 18 2017

VFR. Wind gusting 22 to 26 knots at Cheyenne, Laramie and Rawlins
from 15Z to 01Z.


Issued at 239 AM MDT Sat Aug 19 2017

There will be an elevated fire weather threat across portions of
southeast WY this afternoon.  Minimum relative humidity values will
drop to 12-15 percent over much of the region.  West winds will also
gust to 20-25 mph for mainly areas along and west of the Laramie
Range. Winds will be weaker on Sunday with relative humidity
slightly higher.




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