Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 191004

Area Forecast Discussion
National Weather Service Cheyenne WY
404 AM MDT Wed Apr 19 2017

.SHORT TERM...(Today through Friday)
Issued at 353 AM MDT Wed Apr 19 2017

Strong shortwave trough seen on WV imagery early this morning over
western WY will move quickly eastward and amplify over the Dakotas
through this evening.  Gradients will increase rapidly this morning
in the wind prone areas, first in Arlington and then later this
morning for the I-80 summit/Bordeaux/Cheyenne areas.  CAG/CPR
gradients peak at 50 to 55 m on the GFS and 45 to 50 m on the NAM
for a brief period between 12 and 15z this morning.  It is quite
possible that we could see some high wind gusts for a period this
morning as the shortwave passes.  Should not be a long duration
event so kept gusts just below high wind criteria for now but will
definitely need to be monitored through the morning.

Brief and transient ridging will pass overhead tonight and early
Thursday ahead of the next vigorous trough which will dig into the
central Rockies Thursday night and Friday. Models have come into
better agreement with the track of this feature.  An elongated,
negatively tilted trough will evolve over WY on Thursday night
before closing off over northern CO early Friday.  Favorable
position of the mid level wave, combined with strong low level moist
upslope flow of 35 to 45 kt at 700 mb will provide ample lift for a
significant amount of precipitation especially in the favored
upslope areas along and east of the Laramie Range. Model soundings
show a warm boundary layer persisting outside of the mountains until
very early Friday morning as the mid level center closes off and
forces the sfc winds into a more E or NE direction.  Think most
snowfall outside of the mountains will most likely occur on Friday
morning.  Warm ground temps and increased solar radiation from the
high April sun angle will likely limit snowfall amounts but areas
such as the I-80 summit are concerning given the amount of qpf and
the likelihood that they will be able to maintain cooler
temperatures. Elected not to issue headlines for the higher
elevations at this time as there is enough time for later shifts to
monitor model trends, especially given model track records on winter
storms this spring.

.LONG TERM...(Friday Night through Tuesday)
Issued at 353 AM MDT Wed Apr 19 2017

Weaker second shortwave should keep some showers going mainly
around the mtns Friday night into Saturday. While temps will
moderate some on Saturday, better warming will occur by Sunday as
the upper ridge axis moves overhead and 700 mb temps increase to
around 6C. Continued mild and dry Monday under a generally zonal
flow. Another shortwave moves quickly by to the north on Sunday
night into Monday, with main effect being some enhanced wind. The
GFS shows stronger low level gradients and winds aloft, suggesting
some high wind potential across the wind prone areas of southeast
WY. A few showers could return to the area by late Tuesday as the
next upper trough begins digging over the western CONUS.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1157 PM MDT Tue Apr 18 2017

IFR/MVFR cigs will be possible at several of the sites through mid
morning. The lowest cigs are expected at CYS/SNY. Showers and
isolated thunderstorms will continue across the northern Panhandle
through around 12Z. A cold front will push across the region
between 12-18Z with gusty west to northwest winds through the


Issued at 353 AM MDT Wed Apr 19 2017

No fire weather concerns through the end of the week. Although it
will be breezy to windy through this afternoon behind a cold front,
minimum humidity values will mostly be above 25 percent.  A storm
system will move across the region late Thursday into Friday
bringing cooler temperatures and widespread precipitation.




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