Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 191124
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
524 AM MDT Fri May 19 2017

.SHORT TERM...(Today through Saturday night)
Issued at 524 AM MDT Fri May 19 2017

Radar returns early this morning continue to show widespread light
to moderate precip across the area. Snow has been observed for much
of southeast Wyoming above roughly 4500 ft, with rain in the lower
elevations of WY and western Nebraska. Uncertain as to whether
snow has been falling in Sioux County, NE due to lack of reports
from that area, but sfc temperatures up there have been cold
enough for snowfall and radar echoes were persistent earlier along
the Pine Ridge. Therefore, would expect some snow up in that
region.

Water vapor trends show at least two more shortwaves to rotate up
the eastern periphery of the upper low today, bringing another
round of moderate precip to the forecast area. The first wave will
focus enhanced snowfall across southeast Wyoming, In general,
looking at additional snowfall totals of 3 to 8" for the Laramie
Range and nearby portions of Albany, Platte, and Laramie Counties,
plus the Snowy and Sierra Madre Mountains this morning, with 1 to
3" elsewhere. The highest snowfall is expected in the Laramie
Range, southern Platte County and northwest Laramie County.
Temperatures are expected to hover around or slightly below
freezing this morning, so melting rates may not be as high as we
saw yesterday. However, as we head through the day and see some
warming with the high sun angle, do think snow will melt off a bit
especially on the paved/cement surfaces. The upper low will begin
to move eastward at a quicker pace this afternoon with subsidence
and drier air filtering in from the northwest. Isentropic lift
will weaken through the day as the system departs, so snow should
taper off significantly through the late afternoon and evening.
Will keep the current winter highlights in place for the expected
additional snowfall. The second shortwave will spark heavier
rainfall across northern Colorado which looks to sneak into the
southern panhandle this afternoon and evening. Rainfall amounts
up to a few tenths of an inch are possible through this afternoon
and evening.

Saturday will remain mostly dry as heights build aloft in the wake
of the departing system.  A shortwave will slide southeast across
our plains counties in the afternoon, so may see a few light rain
showers over this area. The main upper jet will move over the
mountains during this time, so can`t rule out a few high elevation
rain/snow showers and perhaps even a clap of thunder as well.
Temperatures will be on the steady rise but will be very dependent
on the rate of snow melt.

.LONG TERM...(Sunday through Thursday)
Issued at 524 AM MDT Fri May 19 2017

The models are in good agreement with cyclonic flow aloft remaining
in place over the CWA through Tues. This should result in continued
unsettled weather conditions w/daily chances for showers and storms
as multiple mid-level disturbances traverse the flow. The strongest
piece of energy is progged to move across northern/eastern areas by
Mon afternoon, likely bringing the most widespread precipitation of
the forecast period. Temperatures are expected to trend warmer thru
early next week, but more so after Tuesday with upper-level ridging
building eastward across the central Rockies. The overall potential
for high-impact weather this period appears low at this time.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 524 AM MDT Fri May 19 2017

A widespread swath of precipitation (snow above 5500 feet MSL) will
remain intact this morning. Rain/snow may be heavy at times, w/ IFR
or LIFR conditions likely mainly across southeast WY terminals with
the precipitation type predominantly snow. We also expect LIFR cigs
to persist at KSNY with periodic MVFR conditions across the rest of
the NE Panhandle. Precipitation is expected to decrease some during
the afternoon, but will persist w/ continued poor (IFR/LIFR) flying
conditions along I-80 between KCYS/KSNY. Those areas to the west of
the Laramie Range should see some improvement by 00z with VFR cigs/
vsbys slowly returning from west to east.

&&

.FIRE WEATHER...
Issued at 524 AM MDT Fri May 19 2017

No fire weather concerns through the weekend due to recent
precipitation, and as temperatures remain on the cool side with
humidities of 30 percent or higher.

&&

.HYDROLOGY...
Issued at 524 AM MDT Fri May 19 2017

Concern in the near term will be the influx of water into area
creeks, streams, and rivers as a result of yesterday and todays
heavy precipitation event. Expect high plains locations east of
the Laramie Range to see these rises first through the upcoming
weekend. Although flooding is not anticipated at this time, many
of these drainages will be running full thru this time. Fortunately,
cool conditions will continue for the next 1-2 weeks, which
should help slow the mountain snow melt and resultant flows into
the mainstem rivers. Will continue to watch these levels very
closely over the coming few weeks.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Warning until 3 PM MDT this afternoon for WYZ102-
     103-105>107-110-112-114>118.

     Winter Weather Advisory until 3 PM MDT this afternoon for WYZ101-
     104-108-109-111-113-119.

NE...Winter Storm Warning until 3 PM MDT this afternoon for NEZ095.

&&

$$

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



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