Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 222354 AAA

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
554 PM MDT Sat Sep 22 2018

.SHORT TERM...(This evening through Sunday)
Issued at 259 PM MDT Sat Sep 22 2018

Latest surface analysis was showing red flag conditions affecting
much of southeast Wyoming. Meanwhile, we are starting to see wind
speeds starting to pick up a bit in the northern panhandle as
well. It looks a bit marginal, but we may need to consider a last
minute Red Flag Warning in that region as well. Otherwise, the
Ryan Fire is really evident today on Satellite and even Radar with
plenty of wind and low humidity providing a high plume. It should
be a mostly quiet night across the area with rather cool
conditions. The upper level trof is expected to gradually approach
the region tomorrow and cause the wind speeds aloft to increase.
This combined with good mixing especially west of the Laramie
Range will favor another Red Flag Warning day with the potential
for even higher wind speeds. We did hold off on issuing a Red
Flag Warning east of the Laramie Range tomorrow afternoon, due to
the slight potential for some standing mountain wave clouds
(similar to what is happening in the Big Horn mountains this
afternoon) which may reduce mixing somewhat.

A Frontal boundary is expected to push through the area tomorrow
night and bring a good chance of showers and isolated
thunderstorms. In fact, there may be a few snow showers on the
highest peaks of the Snowy Range. After the front, pushes through
we may also see some low clouds and patchy fog develop late.

.LONG TERM...(Monday - Friday)
Issued at 410 AM MDT Sat Sep 22 2018

A cyclonic flow pattern will develop Monday/Tuesday in the wake of
the aforementioned disturbance. The associated mid-lvl instability
should help support shower chances through at least Late Monday if
not into early Tuesday. By Tuesday morning, the models show 700 mb
temperatures falling to -2 to -4 deg C over northern/eastern zones
with areas of light precipitation possibly still ongoing. No doubt
it will turn considerably cooler by mid-week, but current thinking
is for cloud cover to keep overnight lows warm enough for rain and
not snow on Tuesday morning. The ECMWF/GFS have come into somewhat
better agreement w/ precipitation coverage and intensity, but some
differences still exist w/ the ECMWF considerably more robust than
the GFS. Regardless, no winter impacts are expected right now, but
later shifts will certainly want to monitor. We continued to trend
cooler for highs on Tuesday, w/ highs likely struggling to get out
of the 50s. These cooler temperatures should not last for long, as
flow aloft becomes more zonal through mid/late week, giving way to
near normal temperatures for late September.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 547 PM MDT Sat Sep 22 2018

VFR conditions prevail across the region but smoke continues to be
an issue near and over KLAR and points southwest due to the
growing Ryan Wildfire in the Sierra Madre Mountains. Have added
smoke directly to the KLAR TAF through the evening hours.
Elsewhere, no aviation impacts are expected as the west winds
decrease through evening and overnight. Winds will increase again
late-morning Sunday from the west to southwest sustained near 15
kt with higher gusts to 30 kt for KRWL. Wind gusts will be lower
for the NE Panhandle in the 20 kt range.


Issued at 259 PM MDT Sat Sep 22 2018

There will be limited recovery in the relative humidity values
tonight especially in the higher terrain. Meanwhile, Red Flag
conditions look favorable across areas mainly along and west of
the Laramie Range tomorrow as wind speeds increase ahead of the
upper level trof moving through the northern Rockies. Another
Red Flag day is possible on Monday mainly along and west of the
Laramie Range as a dry slot develops behind the front due to good


WY...Fire Weather Watch from Sunday afternoon through Sunday evening
     for WYZ310.

     Red Flag Warning until 8 PM MDT this evening for WYZ301>310.

     Red Flag Warning from noon to 8 PM MDT Sunday for WYZ301>309.

NE...Fire Weather Watch from Sunday afternoon through Sunday evening
     for NEZ311-312.



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