Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 221121

Area Forecast Discussion
National Weather Service Cheyenne WY
421 AM MST Sun Jan 22 2017

.SHORT TERM...(Today through Monday)
Issued at 335 AM MST Sun Jan 22 2017

Winds overall are behaving early this morning. However, MSAS sfc
pressure change plots show some pressure falls across the region,
so expect winds in the wind prone areas to increase over the next
couple of hours. In fact, already seeing an uptick in wind speeds
at some observation sites. Gradient progs remain marginal tho as
there is no upper wave to initiate a significant deepening of the
leeside pressure trough. Thus, will maintain marginal gusts of 50
to 55 mph in the wind prone areas through mid-morning.

A dry slot evident on current water vapor imagery will move
overhead for today which should keep things dry through this
afternoon. The strong Pacific jet currently over CA/NV will move
over the area this afternoon advecting in a deeper plume of
moisture. Orographic snow will thus begin over the mountains
perhaps as early as late this afternoon/evening, with snow rates
increasing through Monday as a shortwave trough accompanies the
jet. Will likely see light snow spread to the nearby high valleys
late Sunday night through Monday in this pattern as well, along
with gusty southwest winds. Could be a messy travel situation out
in this area Monday afternoon with the wind and snow, so
definitely thinking highlights will be needed. Will hold off on
any highlights for now as agreed upon by surrounding offices since
there remains some time until impacts are felt. Further east
across the plains, added in light snow for the Pine Ridge area
Monday morning as convergence along a sfc boundary across this
region will combine with weak isentropic lift. Then, expect light
rain showers in the afternoon across the plains as the sfc low
over begins to deepen over eastern Colorado in advance of the
upper low pressure system, enhancing llvl convergence. As this
occurs, CAA will strengthen, thus beginning the transition from
rain to snow from northwest to southeast in the late afternoon.

.LONG TERM...(Monday Night through Saturday)
Issued at 335 AM MST Sun Jan 22 2017

Models and ensembles continue to advertise the broad upper trough
moving east across the central rockies through midweek with an
upper low deepening to our east Tuesday into early Wednesday. This
pattern will bring a cold front south across our area Monday night
with initially the best coverages of snow still occurring over
the Sierra Madre and Snowy mountains where the entrance region of
the stronger midlevel jet will still be in place. Snowfall rates
over the mountains will gradually taper off as we get into the day
Tuesday as the midlevel winds start to abate, with the low
pulling farther east and continuing to deepening over north
central Nebraska. Models are indicating a prolonged period of
light to moderate snowfall from east of Douglas across the
northern Nebraska Panhandle Tuesday into early Wednesday. Given
the pattern, there is a decent chance that we could see an
enhancement of snowfall rates along the Pine Ridge at this time
Tuesday into Tuesday night, and this is where we have anywhere
from 4 to 6 inches of storm total snowfall by Wednesday morning.
As we get into Wednesday we keep a chance of snow over the Sierra
Madre and Snowy Ranges, keeping areas farther east dry but cold
through Friday with a slight warmup going into the weekend east
onto the plains.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 421 AM MST Sun Jan 22 2017

Winds will become breezy from the west today across portions of
southeast Wyoming so have included higher winds in comparison to
last couple of days for Rawlins, Laramie and Cheyenne. VFR
expected at all airports except Rawlins where light to moderate
snow will move in from the west late tonight, so have dropped
visibilities down to IFR category after midnight at Rawlins.


Issued at 335 AM MST Sun Jan 22 2017

No Fire Weather concerns through next week with temperatures at or
below normal and chances for precipitation. Another round of snow
is expected Monday and Tuesday as storm system moves across the




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