Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 190005
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
555 PM MDT SUN SEP 18 2016

.SHORT TERM...(This evening through Tuesday Night)
Issued at 200 PM MDT Sun Sep 18 2016

Zonal flow early in the period will gradually back to the
southwest ahead of an upper trough digging into the Pacific
Northwest. Winds and critical fire conditions have been and will
continue to be the primary challenge for the first half of the
work-week. Winds have been higher than anticipated thus far today
with gusts of 45-55 mph common from Arlington through Cheyenne. In
fact some of the most wind prone spots saw localized winds in
excess of 60 mph for a short time earlier this morning. These were
very short in duration (10 mins or less) and in only a handful of
spots, so opted to handle with an SPS. Low-level gradients were at
their max at 12-15z, with slow decline anticipated thru the rest
of the day. These winds and warm temps have led to critical fire
weather conditions across much of the area today. Humidities have
been a bit marginal west of the Laramie Range, but close enough to
warrant continuation of Red Flag Warning. Humidity recoveries will
be poor overnight, especially across southeast Wyoming and with
another day of critical conditions expected, opted to just extend
the Red Flag Warning for fire weather zones 303-310 through 8 PM
Monday. More details in the fire weather section. Otherwise,
expect dry conditions to prevail through the period with
temperatures running 10-15 degrees above normal.

.LONG TERM...(Wednesday through Sunday)
Issued at 122 PM MDT Sun Sep 18 2016

We are looking at a fairly active extended forecast period with an
organizing upper-level low over the western US during the mid-late
week time frame. Medium range model guidance appears to be in good
agreement with a closed low over the Pacific Northwest late in the
day on Wednesday. This system digs into the Great Basin on Thu/Fri
and pushes eastward into the Central Rockies, giving way to fairly
persistent moist south-to-southwest flow aloft w/daily chances for
convective activity. Severe weather appears unlikely, but there is
potential for stronger storms on Thursday with excellent speed and
directional shear (50+ knots in the 0-6 km layer) along w/ cooling
temperatures aloft, and moist low-level upslope. Model differences
exist with the exact placement/evolution of the low, but GFS/ECMWF
both suggest the mid-level cold core moving across the area during
the Fri night/Sat time frame with H7 temperatures plunging to near
-2 deg C along/west of the Laramie Range. A minimum of a mix of RA
and SN is quite possible with this system, mainly with wrap-around
on the back side. Forecast highs for Saturday/Sunday are likely to
trend lower over the next several days.

&&

.AVIATION...(For the 00Z TAFS through Monday afternoon)

VFR conditions expected through tonight and into Monday. Gusty winds
will continue into the evening hours with gusts between 30 and 35
knots. Winds will slowly subside after 02Z...but periods of gusty
winds are expected from KRWL to KCYS through tonight as winds
will remain strong just above the surface.

&&

.FIRE WEATHER...
Issued at 121 PM MDT Sun Sep 18 2016

Critical conditions to continue into early evening across all
districts in southeast Wyoming and the western Nebraska Panhandle.
Winds have been strong with gusts of 30 to 50 mph common.
Humidities have been more marginal however, with the only sites
reaching critical thresholds as of 1 PM located in areas east of
the mountains. Most areas should see an additional 1-4 percent
decrease thru the rest of the afternoon. Humidity recoveries will
be poor overnight across most of southeast Wyoming. Looking ahead
to tomorrow, the air mass actually dries some, but winds also
decrease across the eastern plains. The main chances with this
forecast was to extend the Red Flag Warning through 8 PM Monday
for FWZ 303-310. Conditions will improve above critical thresholds
overnight, but with a recurrence of critical conditions again on
MOnday afternoon, opted to just extend the Red Flag Warning thru
the night. Tuesday looks just as dry, but winds should be less
compared to Monday.

&&

.CYS Watches/Warnings/Advisories...
WY...Red Flag Warning until 8 PM MDT this evening for WYZ301-302.

     Red Flag Warning until 8 PM MDT Monday for WYZ303>310.

NE...Red Flag Warning until 8 PM MDT this evening for NEZ311>313.

&&

$$

SHORT TERM...CAH
LONG TERM...CLH
AVIATION...TJT
FIRE WEATHER...CAH



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