Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 230421
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
921 PM MST Wed Feb 22 2017

.UPDATE...
Issued at 921 PM MST Wed Feb 22 2017

Not much to update here for tonight as the forecast seems to be
in good shape for now. 00Z models are showing a slight shift south
and west with the inverted trough, which opens the door for
stronger upslope forcing across the plains and the east/northeast
facing slopes of the mountains. QPF output seems to be wetter as a
result, so bumped up snow for tonight a bit in the areas favorable
for the stronger upslope component. Otherwise, Winter Storm
Warnings are on track for widespread heavy snow and wind.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 230 PM MST Wed Feb 22 2017

No real big changes in the 12Z guidance with regard to the
upcoming winter storm. The largest uncertainty with snow amounts
continues to be in areas along Interstate 80 where the models
depict an inverted sfc trough and relative minimum in QPF through
18Z Thurs. The deterministic and ensemble guidance continue to
show the axis of best forcing and ascent generally over the
northern half of the CWA. Did not change snow amounts all that
much across northern Carbon county eastward into the northern
Nebraska Panhandle, where widespread 12-16 inches is expected to
fall. With frontogenesis shifting northward through the night and
good elevated instability, would not be surprised to see a few
heavy snow bands develop within the larger snow shield.

As mentioned earlier, the snowfall amounts continue to be
uncertain along Interstate 80. Would like to see the midlvl low
track a little further south to be more confident about higher
amounts across the southern half of the CWA. The models continue
to indicate an inverted sfc trough stretching from Rawlins
southeastward into northern Colorado. Went ahead and lowered
amounts a few inches along Interstate 80 from Rawlins to
Cheyenne, but still have widespread 6-9 inches over lower
elevations. East to northeast winds will be strongest across
northern Platte and Converse counties through the morning, so will
likely see some blowing snow up there. Snow will gradually come
to an end by late Thursday evening into Thursday night. Lows on
Thursday night will be cold, dropping into the single digits and
low teens.

.LONG TERM...(Friday through Wednesday)
Issued at 230 PM MST Wed Feb 22 2017

Snow will taper off to light snow/flurries during the day Friday
as the sfc/upper lows move farther away from the area. It will be
a rather cold day with high likely holding in the 20s for the
most part. Cold Friday night especially if skies clear with some
below zero mins possible especially in areas such as the Laramie
Valley. The overall pattern over the weekend into early next week
will feature broad cyclonic upper flow across much of the country
with a couple of upper systems dropping initially south along the
west coast then turning east across the central and southern
Rockys...just brushing the southern parts of the CWA. This will
keep temperatures below average across the CWA with periods of
snow showers mainly over the higher mtns as the aforementioned
system pass mostly south of the area.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 447 PM MST Wed Feb 22 2017

Snow is steadily becoming more prevalent across southeast Wyoming
late this afternoon, with IFR conditions observed at times. Expect
this trend to continue through the evening, with the current band
of snow shifting north to span from KRWL to KDGW to KCDR by
midnight. Snow will then re-intensify across the entire forecast
area from north to south as sunrise approaches, with snow expected
to continue through Thursday night. IFR/LIFR conditions are
likely in moderate to heavy rates at times, especially near the
Laramie Range and also from KDGW to KBFF to KAIA and areas north.


&&

.FIRE WEATHER...
Issued at 230 PM MST Wed Feb 22 2017

No fire weather concerns with widespread snow falling through
Friday morning and colder temperatures persisting into next week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Warning until 11 AM MST Friday for WYZ101-102-107-
     108-118-119.

     Winter Storm Warning until 11 AM MST Friday for WYZ103>106-
     109>117.

NE...Winter Storm Warning until 11 AM MST Friday for NEZ002-003-019-
     020-095-096.

     Winter Storm Warning from 5 AM Thursday to 11 AM MST Friday for
     NEZ021-054-055.

&&

$$

UPDATE...RJM
SHORT TERM...ZF
LONG TERM...RE
AVIATION...RJM
FIRE WEATHER...ZF



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