Area Forecast Discussion
Issued by NWS Cheyenne, WY

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

FXUS65 KCYS 211151

Area Forecast Discussion
National Weather Service Cheyenne WY
551 AM MDT Sun May 21 2017

.SHORT TERM...(Today - Tuesday Night)
Issued at 315 AM MDT Sun May 21 2017

A broad area of cyclonic flow aloft associated with a robust upper
low centered over northern MN will likely give way to a fairly un-
settled period of weather over the next several days with numerous
mid-level disturbances embedded within the flow. The morning Water
Vapor satellite loop was already indicative of the first such wave
moving southward across MT. Do not expect to see much of an impact
from this with a lack of substantial dynamics, but would expect to
have minimal inhibition with cold air aloft, so even weak lift may
be sufficient for at least isolated/widely scattered showers. CAPE
values of 300-600 J/Kg suggest enough instability for thunderstorm
activity as well. Sounding profiles suggest weak flow aloft, which
should limit potential for anything organized. Convection may very
well produce gusty winds though. The most significant wave of this
forecast period is still set to affect the area on Monday morning/
afternoon with strong mid-level PVA and increasingly difluent flow
aloft in the exit region of a 80+ knot H25 jet. This should result
in scattered to numerous coverage of convection across much of the
CWA on Monday. Breezy conditions are likely for Monday across much
of southeast WY and the western NE Panhandle w/ the passage of the
cold front. The presence of 30+ knot flow aloft suggests potential
for wind gusts in the 35-45 MPH range on Monday afternoon. Believe
temperatures will finally rebound some on Tue as ridging begins to
build eastward, but fast northerly flow will more than likely keep
it cooler (upper 50s/near 60) w/ lingering chances for showers and

.LONG TERM...(Wednesday - Saturday)
Issued at 315 AM MDT Sun May 21 2017

An upper level ridge will be overhead on Wednesday, bringing
temperatures back into the 60s and 70s. Dry but breezy conditions
will prevail as well. The upper ridge will shift east on Thursday
while a trough digs into the PacNW. This trough looks to park itself
over the PacNW and will remain quasi-stationary through the end of
the week with active southwest flow over Wyoming. Temperatures will
stay in the 60s and 70s in this pattern with chances for showers and
afternoon thunderstorms expected each day. The upper trough then
looks to eject eastward Friday and Saturday, although models show
some differences with its evolution through this time. Timing and
placement of individual shortwaves rounding the base of the trough
in WNW flow may be different between models, but the general pattern
will be wet and stormy Friday and Saturday. Therefore maintained
slight chance to chance PoPs across the forecast area through this


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 551 AM MDT Sun May 21 2017

Showers continue early this morning west of the Laramie Range.
Models are keying in on the development across Carbon County and
another area off the Snowy Range mountains, which should move
southeast toward KLAR and KCYS roughly between 14Z and 16Z. Cigs
could drop to MVFR. Showers and t-storms will redevelop late
morning through this afternoon over much of the forecast area as
an upper level disturbance moves overhead. This activity looks to
be high based, but cannot rule out MVFR conditions with the
t-storms. Northwest winds look to gust around 20 kts at the
Nebraska Panhandle sites in the afternoon. Conditions tonight will
generally be VFR, but may see some valley fog develop near KLAR.


Issued at 315 AM MDT Sun May 21 2017

No fire weather concerns due to recent, widespread heavy rain/snow
and cooler temperatures.


Issued at 215 PM MDT Sat May 20 2017

Concerns this weekend into early next week will focus on runoff from
recent heavy rain and snow melt into area creeks, streams, and mainstem
rivers east of the Laramie Range. Although flooding is not expected,
many of the streams and creeks may reach bankfull by early next week.
Fortunately, cooler than normal temperatures will continue for the
next week, which should help slow the mountain snow melt and resultant
runoff into the mainstem rivers. Will continue to monitor these water
levels very closely over the next few weeks.




HYDROLOGY...MAJ is the U.S. government's official web portal to all federal, state and local government web resources and services.