Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 211125
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
525 AM MDT Fri Apr 21 2017

.UPDATE...
Issued at 522 AM MDT Fri Apr 21 2017

Looking at the WYDOT cameras along I-80 near the summit this
morning as well as the blossoming shield of heavy precipitation on
radar seems to necessitate an upgrade to a Winter Storm Warning
for the South Laramie Range. An estimated 3 inches of snow fell
yesterday evening and it is likely that an additional 3 to 4
inches will fall by late morning before the best forcing begins to
shift east.

&&

.SHORT TERM...(Today through Saturday night)
Issued at 300 AM MDT Fri Apr 21 2017

Strong shortwave over western CO will close off briefly over
northeastern CO early this morning before sliding quickly eastward
into KS during the afternoon. A second shortwave will dive
southeastward and across the area this evening.

Still expect a period of heavy precipitation rates early this
morning especially just north of the track of the mid level
circulation where the best deformation/frontogenesis and upslope
flow will be focused. Snow levels currently around 7200 ft or so
based on radar and these should lower some more as the low levels
cool and precip rates increase. Current advisories look good
although can probably drop the Sierra Madre Range once the wave
passes early this morning. Best snow accumulations still look to
be 7000 ft or above. Not out of the question for the Cheyenne area
to see a burst of snow early this morning as heavier rates and
melt cooling may try to drive the snow level lower. Warm ground
temps should preclude much accumulation but could see 1 to 2
inches in grassy areas if it comes down hard enough.

Showers continue through the afternoon and evening hours tonight
especially over the mountains as the second shortwave passes.
Added in some mention of patchy fog tonight along the Cheyenne
Ridge and over the South Laramie Range as the ground should be
moist and the winds will be light upslope from the south or
southeast.

Saturday and Saturday night should start a clearing and drying
trend. Winds should become westerly on Saturday but remain
relatively light.

.LONG TERM...(Sunday through Thursday)
Issued at 300 AM MDT Fri Apr 21 2017

Unsettled week ahead as the west coast is open for Pacific systems
to move into the Rockies. Much needed rainfall to continue.

Starting off Sunday, we have a transitory shortwave ridge overhead
that should keep things relatively dry. Next frontal system begins
impacting Carbon County as early as Sunday night. Most of the
energy with this system should track across northern Wyoming, with
the south staying dry.

Another system quick on the heels of the first system looks to
stall along the Colorado/Wyoming border area Monday afternoon into
Tuesday. ECMWF has widespread precip over the area, while the GFS
is showing precip further north. Went more with the ECMWF
solution as the front stays pretty much along the state line. This
front finally shifts south on Wednesday for a brief break in
shower activity.

Both the GFS and ECMWF in good agreement on the next system that
looks to impact the area Thursday evening. GFS showing well over
two inches of precip with this system. ECMWF about half that on
rainfall, but very similar on placement. 700mb temperatures -5 to
-7C, so there definitely looks like a chance of moderate/heavy
snow for some areas.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 509 AM MDT Fri Apr 21 2017

LIFR to IFR ceilings and visibility this morning for Cheyenne and
Laramie where stronger dynamic forcing for precipitation is
expected through mid morning in snow showers. Farther east onto
the plains rain is slowly making its way eastward across the
southern Panhandle with IFR ceilings and visibility expected at
Sidney by 13Z, and MVFR ceilings expected for Alliance,
Scottsbluff and Chadron by 14Z.


&&

.FIRE WEATHER...
Issued at 138 AM MDT Fri Apr 21 2017

Wetting rain should occur over much of the area through today.
This should keep any fire weather concerns at bay through the
weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 6 PM MDT this evening for WYZ112-
     114.

     Winter Storm Warning until 6 PM MDT this evening for WYZ116.

     Winter Weather Advisory until 3 PM MDT this afternoon for WYZ115.

NE...None.
&&

$$

UPDATE...DEL
SHORT TERM...GCC/DEL
LONG TERM...GCC
AVIATION...GCC
FIRE WEATHER...DEL



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