Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 240540 AAA

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
1140 PM MDT TUE AUG 23 2016

.SHORT TERM...(This evening through Thursday night)
Issued at 300 PM MDT Tue Aug 23 2016

Fire weather concerns today followed by PoPs in the short term as
the forecast challenges.

Currently...Cold front currently bisecting the CWFA along a line
from Chadron to Torrington to Rawlins out to Salt Lake City. South
of the front, west to northwest winds have been really strong,
gusting to 40 MPH at many locations. Humidities have been very
low, currently 11 percent here at Cheyenne, down to 7 percent out
by Rawlins. Behind the front, winds have eased and humidities have
begun to rise. Still getting close to red Flag criteria at Lusk in
FWZ 301 this afternoon, so am reluctant to drop the warning we
have out for Converse/Niobrara Counties. May be a last minute
decision based on what the observation does at Lusk.

Winds shift to the east this evening and begin easing. Fire
weather concerns should come to an end early this evening.

Chances for showers and thunderstorms begin to increase Wednesday
with low level southeast upslope winds and an upper disturbance
moves across the front. Did increase PoPs across the mountains,
especially near the Colorado/Wyoming border where both the GFS and
ECMWF shows the highest QPF.

Cool temperatures in store for the next couple days as 700mb
temperatures fall into the single digits C. 60s and 70s look to be
pretty common across the CWFA both days.

.LONG TERM...(Friday through Tuesday)
Issued at 300 PM MDT Tue Aug 23 2016

Medium range models are in good agreement with a broad upper-level
trough over the central/northern Rockies on Friday. The GFS and EC
both show excellent low-level convergence along with numerous mid-
level disturbances embedded within the flow, so expect coverage of
precipitation to become scattered to numerous with virtually every
model showing QPF over one tenth of an inch across mainly southern
and eastern portions of the CWA. Precipitation chances and low-lvl
upslope flow should yield enough cloud cover to limit possible sfc
heating, so expect Friday to be fairly cool w/ widespread highs in
the low/mid 70s. Models begin to diverge somewhat beyond Friday w/
respect to the timing of individual waves, but the consensus would
favor a weak cutoff low over central CO this weekend before larger
scale ridging begins to take shape by Monday. That said, we cannot
rule out a few high elevation showers or thunderstorms on Saturday
or Sunday but coverage will not be nearly to the extent of what is
expected on Friday. The GFS/ECMWF suggest varying degrees of upper
level ridging on Monday and Tuesday, but both model solutions will
promote warmer/drier conditions at the tail end of the period. The
overall model differences become much more significant into mid to
late next week, but would continue to give the nod to the ECMWF as
it has been much more consistent with its solutions and makes much
more sense with an active jet along the Canadian border and little
opportunity for even a stronger wave to penetrate the southwestern
US ridge.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1133 PM MDT Tue Aug 23 2016

VFR will prevail overnight with occasional ceilings between 10000
and 15000 ft agl. Winds will be south-southwest 8-15 kt for the
southeast WY terminals and light/variable for western NE terminals.
Widely scattered convection will develop over the mountains around
midday Wednesday and spread east-northeast across southeast WY and
southern NE panhandle, including KLAR, KCYS and KSNY between 19Z
and 00Z. Brief periods of MVFR in heavier showers and gusty outflow
winds will be possible.


Issued at 722 PM MDT Tue Aug 23 2016



.CYS Watches/Warnings/Advisories...


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