Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 232138
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
338 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 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1207 PM MDT Tue Aug 23 2016

VFR conditions are expected today with gusty winds continuing thru
early to mid afternoon, especially across southeast Wyoming. Light
and variable winds expected overnight with generally SCT-BKN skies
above 10k feet AGL.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Tue Aug 23 2016

Critical fire weather conditions once again today along and south
of a cold front pushing south into the area. Front moves through
southern Wyoming this evening, with cooler air and higher
humidities behind the front. Will keep the current Red Flag
Warnings going through the afternoon as winds are pretty strong
out west with humidities in the single digits. We finally get a
break in the winds Wednesday and humidities should be higher
behind the front for the entire forecast area of southeast
Wyoming. Should stay good on winds and humidities through at
least Friday when southwest winds return and we start to dry out.

&&

.CYS Watches/Warnings/Advisories...
WY...Red Flag Warning until 8 PM MDT this evening for WYZ301>304-306-
     308>310.

NE...None.
&&

$$

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



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