Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 211733 CCA
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1127 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
storms.

.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
time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday morning)
Issued at 1127 AM MDT Sun May 21 2017

A passing disturbance will bring some showers and a few tstms to the
area mainly this afternoon with clearing conditions this evening.
VFR expected to prevail though some patchy MVFR cigs around KRWL
early this afternoon.

&&

.FIRE WEATHER...
Issued at 315 AM MDT Sun May 21 2017

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

&&

.HYDROLOGY...
Issued at 215 PM MDT Sat May 20 2017

Concerns late 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 this 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.

&&

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

$$

SHORT TERM...CLH
LONG TERM...RJM
AVIATION...RE
FIRE WEATHER...CLH
HYDROLOGY...MAJ



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