Area Forecast Discussion
Issued by NWS Cheyenne, WY

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128
FXUS65 KCYS 290529
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1130 PM MDT Tue Mar 28 2017

.UPDATE...
Issued at 904 PM MDT Tue Mar 28 2017

Evening water vapor loop showed the slow-moving upper low centered
over New Mexico. Upper diffluent flow aloft and isentropic lift
continued to generate mainly light precipitation. Snow levels were
steadily falling, areas along and west of the Laramie Range above
7000 feet reporting light snow. The changeover from rain to snow
will occur later this evening for elevations between 5500 and 6500
feet, including Cheyenne. Have lowered nighttime snow accumulations
to 2-4 inches above 8000 feet, 1-2 inches down to 6000 feet, and
little or no snow elsewhere. Outside the mountains, most of the
precipitation has diminished across Carbon County, and have trimmed
PoPs here. Adjusted low temperatures in a few areas. Black ice will
be a traveler`s concern tonight as sub- freezing temperatures cause
slick roadways, especially for elevations above 5000 feet.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 250 PM MDT Tue Mar 28 2017

Widespread rain continues for areas east of the Laramie Range as the
midlevel vort max approaches from the south, especially for areas
along the sfc boundary situated roughly along the WY/NE border and
the Cheyenne Ridge. The upper jet is readily apparent on GOES-16
imagery across eastern Colorado into southwest Nebraska with the
deformation zone stretching northeast-southwest across Wyoming into
northwest Colorado. The deformation zone is likely producing rain
and high elevation snow over the western zones, although it`s very
difficult to tell due to lack of radar coverage out that way. As
expected, near sfc air temperatures are proving difficult for snow
to reach the surface below about 7500ft, and warm ground temps
hovering in the mid to upper 30s along I-80 will continue to make
snow accumulations hard to come by at least until later this
afternoon and evening.

Road condition reports up at the I-80 Summit are mainly of slushy
but slick roads early this afternoon, and air temperatures are right
around freezing. As precip continues to expand in coverage with the
approach of the vort max in combination with strengthening upper jet
to our east, still thinking temperatures may cool a few degrees with
stronger northerly flow out west of the Laramie Range, so some snow
accumulation is possible. However, not much snow has been observed
for northern and western portions of Carbon County today, so even
additional light snow will bring minimal impact to these areas.
Therefore, cancelled the Winter Weather Advisory for areas from
Rawlins, to Muddy Gap, to the Ferris/Seminoe Mountains. Also,
downgraded the Snowy Range to an Advisory as obs are showing minimal
snow so far with only a few additional inches expected through
tonight, mainly above 9500 ft. Elsewhere, will hold onto the Winter
Weather Advisories for now as there are some areas with snow
accumulation observed and the fact that roads could remain very
slick as temperatures drop into the upper 20s tonight. Overnight
lows are expected to drop into the low 30s roughly above 4500ft
across the plains, so rain should change to snow at these locations
with little to no accumulation anticipated. For areas near Cheyenne
proper and along and west of the Laramie Range, roads could get
pretty icy tonight as temperatures drop below freezing and wet roads
freeze over.

Rain/snow will steadily end through Wednesday morning, with perhaps
a light shower or two in the southern Panhandle Wednesday afternoon
in wraparound moisture. Temperatures will rebound back into the 40s
and 50s across the forecast area.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 250 PM MDT Tue Mar 28 2017

After a short dry period Wednesday night through Thursday, the
active pattern ramps back up with another deepening and slow
moving upper low passing to our south late in the week. The next
round of precipitation comes in Thursday night as the upper flow
goes southwesterly and the first in a prolonged series of
shortwaves moves through. With a continued lack of significantly
cold air, we expect snow in the higher elevations and rain or a
snow mix in the lower elevations for the period Friday through
Saturday as the slow moving upper trough moves across. The pattern
does suggest a prolonged period of snow Friday through Saturday
across the higher elevations of the Snowy and Sierra Madre Ranges
with not much for elevations below 8500 ft. We could see an
additional 1 to 2 feet of snow above 10000 ft elevation in the
Snowy Range Thursday Night through early Saturday evening...so be
on the lookout for potential Winter Storm Watches for the
mountains later this week. Precipitation should taper off
Saturday night as the upper system moves east.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday evening)
Issued at 1130 PM MDT Tue Mar 28 2017

IFR-LIFR cigs with some fog will affect KLAR and KCYS into Weds
morning with more MVFR cigs elsewhere. Cigs will improve slowly to
MVFR-VFR through the late morning and afternoon for southeast
Wyoming and the Nebraska Panhandle terminals.

&&

.FIRE WEATHER...
Issued at 250 PM MDT Tue Mar 28 2017

No fire weather concerns through this week with widespread
precipitation expected across the district along with cooler
temperatures. Weather systems are expected to move through the area
every 2-3 days that will drop wetting rains and mountain snows
through the middle of next week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 6 AM MDT Wednesday for WYZ103-110-
     112-114-116.

NE...None.
&&

$$

UPDATE...MAJ
SHORT TERM...RJM
LONG TERM...JG
AVIATION...RE
FIRE WEATHER...RJM



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