Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 210606 CCA
AFDCYS

Area Forecast Discussion...Corrected Aviation
National Weather Service Cheyenne WY
1204 AM MDT Tue Mar 21 2017

.SHORT TERM...(This evening through Wednesday night)
Issued at 230 PM MDT Mon Mar 20 2017

Forecast challenges deal with precip chances through the short
term.

Currently...Frontal boundary lays across the southern CWFA,
generally from Cheyenne to Shirley Basin to just north of Rawlins
this afternoon. AFternoon humidities have been fairly high
compared to recent days north and east of the front. Looking at RH
values ranging in the mid to upper 30 percent for these areas.
South and west of the front, upper teens to low 20 percent reports
were common. Radar not showing a whole lot of activity at this
time, but short range guidance shows this ramping up later this
afternoon. Water vapor imagery showing a pretty strong low off the
coast of northern California around 40N 138W that we need to be
watching in the long term.

Latest run of the HRRR shows a band of showers and isolated
thunderstorms developing towards 00Z this afternoon. This looks to
be basically along the front from Alliance to Wheatland to maybe
Casper. Convection stays north of Cheyenne through the overnight
hours, so kept the city fairly dry for tonight. Front continues to
slowly lift north through the overnight hours. Though I did not
add fog into the forecast for the northern Panhandle and Niobrara
County, the evening and mid shift will need to monitor conditions
overnight. Forecast soundings showing more of a stratus event
than a fog event.

Front does south southwest again Tuesday afternoon, so think
Cheyenne`s best chance looks to be the tomorrow afternoon.
Westerly mid level flow returns Tuesday night into Wednesday,
which will force the surface front eastward into the Panhandle.
700mb winds increase to 35-40kts Wednesday afternoon, leading to
breezy to locally windy conditions across southeast WYoming.

.LONG TERM...(Thursday through Monday)
Issued at 230 PM MDT Mon Mar 20 2017

Main focus this period will be with the system that will be moving
across the central Rockys late Thursday through Friday. Models
have shifted the track a bit farther south thus the main effects
from this system look to be over the southeast part of the CWA.
main problem will be where pcpn transitions to snow...and how
much. Not much cold air associated with the system so snow looks
like it will be highly elevation dependent. Snow should fall over
the mtns by late Thursday then reach out into the adjacent higher
plains Thursday night into Friday morning. Right now looks like
several inches of snowfall over the mtns with lesser amounts over
the adjacent higher plains of southeast Wyoming. Have undercut
guidance temps as they look too warm especially on Friday given
clouds and pcpn. Rather windy as well Friday. Clearing friday
night with dry and warmer conditions Saturday as an upper ridge
slides across the area. Progressive pattern brings the next system
to the CWA Sunday with rain and snow showers. Short break early
Monday before the next upper system approaches.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1203 AM MDT Tue Mar 21 2017

Scattered light rain showers will move east across the forecast
area through 09Z or so. Winds across the plains are generally out
of the east behind the cold front that moved through earlier.
Cigs may drop to MVFR/IFR across the plains in shower activity
overnight, and as easterly upslope flow persists through Tuesday
morning. Southwest winds look to gust to 25-30kts at KLAR and KRWL
Tuesday afternoon.

&&

.FIRE WEATHER...
Issued at 230 PM MDT Mon Mar 20 2017

A more unsettled and wetter weather pattern setting up for
southeast Wyoming and Nebraska Panhandle. Showers and isolated
thunderstorms are possible this afternoon and this evening as a
stalled out front interacts with upper disturbances to produce
increased chances for wetting rains. This front will stay in the
area east of the Laramie Range through Wednesday before being
shifted east. For late in the week, a Pacific low pressure system
is forecast to track through Colorado, bringing at least a
heightened threat for mountain snow and widespread rain to areas
along and east of the Laramie Range. In the meantime, afternoon
humidities are expected to fall to the low 20 percent range east
of the Laramie Range for Tuesday and Wednesday with fair to good
overnight recoveries. Fire weather concerns are therefore low
through the upcoming week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...GCC
LONG TERM...RE
AVIATION...RJM/CLH
FIRE WEATHER...GCC



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