Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 211211

Area Forecast Discussion
National Weather Service Cheyenne WY
511 AM MST Sat Jan 21 2017

.SHORT TERM...(Today through Monday)
Issued at 304 AM MST Sat Jan 21 2017

CWA currently between systems with an upper low drifting north
over North Dakota and a negatively-tilted upper trough moving over
the southwestern CONUS. Narrow area of clear skies currently over
the CWA but mid/high clouds starting to increase from the
southwest in association with the southwestern upper trough.
Expect the clouds to continue spreading across the CWA today with
snow showers returning to the higher mtns this afternoon as some
shortwave energy passes by mainly to the south. Mainly dry
conditions return for a time later tonight through Sunday as an
upper ridge amplifies and moves across the Rocky mtns. Snow
showers will then increase over the far western parts of the CWA
Sunday night as the upper ridge axis moves east over the plains
and increasingly moist southwesterly flow sets up. Similar pattern
for Monday with rain and snow gradually spreading east but still
looking to remain over and west of the mountains...though some
showers may reach the se Wy plains Monday afternoon. Winds will
increase especially out west Sunday through Monday in the
favorable southwesterly upper flow.

.LONG TERM...(Monday night through Friday)
Issued at 304 AM MST Sat Jan 21 2017

The forecast remains on track for accumulating snow to impact much
of southeast Wyoming and western Nebraska Monday night through
Tuesday. The question remains though, just how much snow will
we see. Models still are latching onto the idea that a strong
PV anomaly and jet streak will eject northeast from the
desert southwest into the central plains on Tuesday, with an
upper low deepening within the left exit region of the jet. The
position and speed of the low is such that the most favorable
dynamic lift for heavy snow should remain just north and east of
our forecast area. However, enough lift will remain overhead to
bring us some snow accumulation, especially on Tuesday as the low
strengthens fairly rapidly. Still not anticipating significant
amounts overall due to the speed of the system, but could see a
few inches of snow near the Douglas-Lusk-Chadron-Alliance region
and the mountains, with less elsewhere. North to northwest sfc
winds will be gusty during this time as well, so we are still
expecting some impacts to travel as a result of blowing snow.
Once again, made very few changes to the ongoing forecast due to
consistent trends in the overall pattern, but much uncertainty
still inherently remains in the details with this storm system.

The system will quickly move to the northeast Tuesday night
and Wednesday, with the longwave trough taking over most of the
CONUS through Friday. Colder conditions and perhaps some light
snow showers will persist through this time within energetic
north-northwest flow.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 511 AM MST Sat Jan 21 2017

Stratus pushed southward into the northern Nebraska panhandle
early this morning, so added it into the TAF thru 14Z. Cigs should
lift thereafter, but may return again late tonight as guidance
hints at another southward push of llvl moisture. Still on track
to see snow showers develop over the mountains this afternoon and
evening, obscuring the peaks at times. Latest guidance indicates
KRWL may see some snow as well, so added MVFR cigs/vsbys in snow
after 20Z. Can`t rule out a brief shower near KLAR as well, so
added VCSH for this evening. VFR conditions are expected
elsewhere. Winds should remain light today, but will begin to
increase out of the northwest late tonight. Gusts around 20 kts
are likely across southeast Wyoming.


Issued at 304 AM MST Sat Jan 21 2017

No concerns expected into at least early next week with cool
temperatures and generally moist fuels. There will be some gusty
winds over western areas Sunday and Monday. Snow should also
increase over the districts Monday and continue into Tuesday as a
storm system passes by the region.




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