Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 300842

Area Forecast Discussion
National Weather Service Cheyenne WY
242 AM MDT Thu Mar 30 2017

.SHORT TERM...(Today through Saturday)
Issued at 242 AM MDT Thu Mar 30 2017

High clouds now spreading into the western parts of the CWA ahead
of the next upper system digging over the far western CONUS.
Warmer today across the CWA as an upper ridge departs to the east
and the upper flow backs to southwesterly. Should see some widely
scattered showers develop this afternoon as weak impulses move by
in a diffluent upper flow. A couple weak storms not out of the
question out west this afternoon though instabilities will be low.
Much cooler and wetter conditions return tonight through Friday
night as an upper low cuts off over southern Utah then drifts
slowly east along the Colorado/New Mexico border...similar in
track to the previous system.  Falling surface pressures over
Colorado will induce a cooler wind flow over the CWA Friday
allowing temperatures to fall. This system looks a little colder
than the last so snow should spread into the plains adjacent to
the mtns especially late Friday into Friday night. Heaviest snow
looks like it will be over the southern Laramie Range where over 6
inches is possible by Saturday morning. Winds not looking too
strong though so will hold off on a watch though at least an
advisory may be needed eventually.

Should see a slow improvement in conditions Saturday as an upper
shortwave moving across southern Canada weakens and opens up the
upper low over the southern high plains with short ridging moving
towards the CWA.

.LONG TERM...(Saturday night through Wednesday)
Issued at 242 AM MDT Thu Mar 30 2017

The upper low looks to push south and east of our forecast area
Saturday night through Sunday, although GFS and ECMWF handle the
departure of this system differently. The ECMWF keeps a closed low
over TX while the GFS shears the upper low apart with an open trough
moving quickly to the east. This will impact a secondary shortwave
trough that is expected to jet east across the plains on Sunday. GFS
is slower and further south with this shortwave than the ECMWF due
to the open trough to the south. Therefore, a few showers are not
out of the question on Sunday if the GFS pans out. Low amplitude
ridging will move over the Rockies on Sunday night and Monday in
advance of yet another strong Pacific storm system approaching the
cwa on Monday. The track of this storm is further north that the
recent storms with the upper low center progged to move across WY/CO
Monday and Monday night. The attendant sfc trough will deepen to the
lee of the mountains, with models developing a low over eastern
Colorado Monday evening. Llvl convergence resulting from the leeside
trough/low combined with plentiful QG dynamics will bring a good
chance for precip starting Monday morning then increasing in
coverage and intensity through Monday night. Rain and high elevation
snow will start in the high country early Monday morning, with rain
and isolated mountain storms expected through the afternoon. Rain
should change to snow in the high country Monday evening, with rain
spreading east over the plains through Monday night. Temperatures
may not get all that cold across the plains on Monday night as 700mb
temps look only to drop to -6C, so we may once again struggle to get
snow below roughly 6000ft.

The system will become stacked on Tuesday as it treks across the
central plains, with rain and high elevation snow continuing through
much of Tuesday in northerly wrap around flow. Northwesterly sfc
winds could become quite strong as the system reaches the central
plains, and with temperatures progged to remain in the 40s, could be
a very unpleasant day. Breezy and cool conditions will continue for
Wednesday as we remain in northwest flow on the backside of the
strong upper low. Rain/snow will steadily push off to the east by
Wednesday morning.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1146 PM MDT Wed Mar 29 2017

VFR conditions are expected to prevail through the period,
although MVFR conditions are possible at KRWL early Thursday
morning. Breezy southwest winds will continue across southeast WY
thought Thursday afternoon, then winds will lighten and shift to
the east-northeast as low pressure system approaches from the
west. Isolated showers are possible in the afternoon mainly across
southeast WY.


Issued at 242 AM MDT Thu Mar 30 2017

A generally cool and unsettled weather pattern will continue over
the area into early next week with periodic wetting rains and
higher elevation snow keeping fire weather concerns low.




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