Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 121158

Area Forecast Discussion
National Weather Service Cheyenne WY
458 AM MST Thu Jan 12 2017

.SHORT TERM...(Today - Saturday)
Issued at 232 AM MST Thu Jan 12 2017

Active weather pattern of recent will become more tranquil across
the CWA over the next few days. The CWA will lie generally under
a zone of confluence in the upper atmosphere between the northern
streamflow with a departing upper low along the US/Canadian
border and the southern streamflow...wrapping around an upper low
that will sink along the California coast through Friday before
moving over the Baja region of far northwest Mexico Saturday. Some
moisture in the mid/upper levels will still advect across the area
and interact with orographics to produce continued snow showers
over the higher mtns today into Friday though amounts less. Have
gone ahead and cancelled the Winter Storm Warning a bit early as
snow has tapered off. A weak impulse lifting northeast across the
region may spread some snow showers over the plains for a time
tonight before a mainly dry weather pattern settles over the area
Friday through Saturday. Rather cold temperatures will hold today
east of the mtns as a cold surface high moves into the northern
plains. This high will slip eastward tonight and Friday allowing
for warmer downslope air to spread east back over the plains.

.LONG TERM...(Saturday Night - Wednesday)
Issued at 232 AM MST Thu Jan 12 2017

We continue to pay close attention a potential winter storm system
which may impact portions of the area early in the period. The GFS
and ECMWF are in reasonable agreement at 00z Saturday evening with
a vigorous upper-level low over northwest Mexico, although the ECM
shows the low centered considerably farther north. The models then
lift this system across eastern NM on Sunday and eventually across
central Kansas by 12z Monday. In general, there appears to be good
agreement with the storm track through Monday, but there are major
differences with dynamics that could be the difference between the
potential for significant snowfall or none at all. The ECMWF shows
a weaker 4 corners low developing on the heels of the main wave on
Sunday as mid-level energy dives into western California. This may
slow the system down and force the surface low to curve back a bit
further west than the GFS would suggest. This would be a much more
favorable scenario for a high-impact snow event while the GFS soln
would offer little QPF period. Continued to focus higher PoPs over
southeastern portions of the CWA on Sunday night, and avoid higher
values than about 40 percent given significant uncertainty. After-
wards, dry-quasi zonal flow aloft is expected through much of next
week with strong winds possible in the wind corridors on Tue night
or Wed as the GFS shows a strong H85 CAG-CPR gradient. The biggest
change to temperatures this period was to lower highs on Monday w/
potential for snow early combined w/good cold air advection aloft.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 446 AM MST Thu Jan 12 2017

VFR conditions are expected this morning, with areas of fog and/or
low ceilings developing this afternoon. IFR conditions may develop
at KCYS/KLAR by 20z, spreading across the rest of southeast WY and
the western NE Panhandle by 00z. Visibilities should range from 2-
4 miles with ceilings generally between 1k-2k feet AGL w/ isolated
lower values. Most terminals should see some improvement in flying
conditions by 06z or so, but MVFR could prevail through the end of
the TAF period. Light snow showers are likely late this afternoon/
this evening across much of area, which may also reduce visibility
for some terminals. Did not include any TEMPO groups at this time.


Issued at 232 AM MST Thu Jan 12 2017

No concerns seen through the upcoming weekend with cold to cool
conditions continuing with non-critical fuels across the area.




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