Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 222111
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
311 PM MDT Mon May 22 2017

.SHORT TERM...(Late this afternoon through Wednesday night)
Issued at 310 PM MDT Mon May 22 2017

The early afternoon GOES water vapor loop showed a upper low
spinning north of MN and a stout upper ridge from the eastern
Pacific into southwest Canada. Active cyclonic flow aloft was
transporting shortwave energy southeast across the Dakotas, WY
and NE. Colder air aloft resulted in steep lapse rates and
around 500 J/Kg SBCAPE. Scattered to numerous showers and
isolated tstorms wil continue late afternoon. The threat for small
hail is present given the low-topped convection and fairly low
wet-bulb heights. A cold front was moving southeast across the
Interstate 80 corridor. Gusty northerly winds up to 40 mph
accompanied the fropa. Temperatures peaked in the 50s to lower 60s
around midday, and were falling into the 30s and 40s behind the
front.

The shortwave responsible for the convection will push southeast
of the CWA tonight, with showers and isolated thunderstorms
diminishing later this evening. The upper ridge to the west will
make a slow trek to the east across the Intermountain West and
northern Rockies Tuesday. The majority of the short range models
continue to prog weak moisture convergence/lift over western NE.
Maintained low /15-20 percent/ PoPs for the western NE Panhandle.
Drier and milder weather will prevail for southeast WY Tuesday.
It will be breezy along and east of the Laramie Range with
northwest winds gusting to 30 mph.

The upper ridge axis shifts further east across the Rockies and
high plains Tuesday night and Wednesday. Dry conditions and much
warmer temperatures are forecast Wednesday as 700mb temperatures
rise to 10-13 degrees Celsius. Expect high temperatures in the
70s and lower 80s for the valleys and plains, with 50s and 60s
for higher elevations. Westerly winds will become quite breezy
west of the Laramie Range Wednesday afternoon with gusts near 40
mph.

An intense low pressure system over Alberta Canada will move east
into Manitoba Wednesday night. A cold front will be moving into
southeast WY late Wednesday night, with scattered showers developing
from the northeast plains into south central WY.

.LONG TERM...(Thursday through Monday)
Issued at 230 PM MDT Mon May 22 2017

Unsettled weather will be over the CWA this period with temperatures
below seasonal averages. An upper low over south-central Canada will
drift slowly northeast Thursday through Saturday with an upper trough
extending southwestward from this low across the northwest part of
the country. Several weak impulses will rotate through this trough
and across the region and produce mainly afternoon and evening showers
and a few storms through Saturday. The upper trough axis should move
east of the area by Sunday leaving a drier northwesterly flow in its
wake, so expect precipitation to decrease at that time with temperatures
becoming a little warmer.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday morning)
Issued at 1120 AM MDT Mon May 22 2017

A cold front will move southeast across the area through this
afternoon. Scattered showers and a few thunderstorms will develop
with the front and move southeast with associated brief periods of
MVFR cigs and vsbys. Pcpn should end early this evening.

&&

.FIRE WEATHER...
Issued at 230 PM MDT Mon May 22 2017

No fire weather concerns this week. Scattered showers and isolated
thunderstorms accompanying a cold front and upper level disturbance
will end tonight. A warmer and drier weather pattern will prevail
Tuesday and Wednesday with the passage of a upper ridge. It will
be breezy across the plains Tuesday and west of the Laramie Range
Wednesday. Another cold front and upper level disturbance will
move through the districts Wednesday night, with scattered showers
and cooler temperatures.

&&

.HYDROLOGY...
Issued at 230 PM MDT Mon May 22 2017

Concerns through the middle of this week will focus on runoff from
the recent heavy precipitation into area creeks and streams east of
the Laramie Range. Although flooding is not anticipated, many of the
creeks and streams may reach bankfull by the middle of the week.
High temperatures Wednesday in the 50s and 60s above 8000 feet will
result in snow melt and runoff. Cooler temperatures over higher
elevations after mid-week should slow the snow melt and resultant
runoff into the mainstem rivers. Routine monitoring of water levels
will continue over the next few weeks.

&&

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

$$

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



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