Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 161133
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
433 AM MST Thu Nov 16 2017

.SHORT TERM...(Today through Friday night)
Issued at 331 AM MST Thu Nov 16 2017

Lead shortwave emanating from the large scale upper trough off the
Washington coast early this morning will track quickly NE into
southern Alberta this afternoon. This wave, combined with increasingly
strong SW flow aloft will contribute to significant pressure falls
over southern Alberta and southward along the lee of higher
terrain this afternoon. Low level winds will respond with BUFKIT
soundings from the NAM and GFS continuing to indicate 50 to 55 kt
flow as low as 2-3 kft this afternoon. Only thin high cloud cover
expected so think mixing will be decent this afternoon. Went ahead
and upgraded the high wind watch to a warning for Converse County
and also extended it to the northern part of Carbon County given
winds already gusting to 50 mph at Camp Creek just outside the
Muddy Gap area as of this writing. The rest of Carbon County will
likely be quite windy as well but the strongest pressure falls and
best low level wind response will be just to the north and west.
CAG-CPR gradients remain elevated through today and given wind
gusts to 59 mph already at Elk Mountain, think the gap areas near
Arlington will continue to gust this afternoon.

Mountain snow will be another concern for tonight through Friday
evening. Very strong WSW`ly jet of 155kt will combine with steep
lapse rates, and strong dynamic forcing from the approaching upper
trough and associated cold front to produce significant snowfall.
Upgraded the mountain zones to a warning as 1+ inch per hour rates
are likely for a time especially on Friday. Some sort of headline
may eventually be needed for the Interstate 80 corridor near
Arlington for the combination of snow and strong winds during the
frontal passage on Friday.

Next in line for concern is the very strong cold front which will
cross the area from west to east late Friday and Friday evening.
Forecast soundings from both the NAM and GFS indicate that we will
remain well mixed in the lowest 5 kft through about 06z on
Saturday. This will be a bora type event with very strong
pressure rises behind the front as well as CAA related subsidence.
Potential for a period of 50kt gusts especially over the Wyoming
plains from the South Laramie Range eastward where NW flow is a
favored wind direction for high winds. With this in mind thought
it prudent to issue a High Wind Watch and this may need to be
extended into parts of the southern Panhandle if current trends
hold. Winds will slowly diminish late Friday evening as the
gradient relaxes.

.LONG TERM...(Saturday through Wednesday)
Issued at 331 AM MST Thu Nov 16 2017

Windy conditions can be expected almost everyday in the long term
as we stay in fast northwesterly flow. Fast moving shortwaves
tracking across northern Wyoming/southern Montana which is a
favorable windy pattern for us here in southeast Wyoming and
Nebraska Panhandle.

Could see wind headlines on an almost daily basis as GFS 850/700mb
Craig to Casper gradients stay right around or slightly above
60mtrs in this pattern through Thursday next week before gradients
ease. Dry conditions and above normal temperatures in this pattern
if there is a silver lining.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 431 AM MST Thu Nov 16 2017

Wind impacts today for airports along and west of Laramie Range.
Could see gusts close to 45kts at KRWL and 40kts at KLAR late this
morning through the afternoon hours. Front moves in tonight with
rain turning over to snow at KRWL tonight.

&&

.FIRE WEATHER...
Issued at 331 AM MST Thu Nov 16 2017

Dry and warm conditions will continue over the plains this
afternoon. Winds will remain on the light side where RH values
fall to around 20 percent however. Much cooler weather with better
chances for precipitation will follow for Friday and the cooler
weather will continue for Saturday which should minimize fire
weather concerns.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Warning from 11 PM this evening to 5 PM MST Friday
     for WYZ112-114.

     High Wind Warning until 6 PM MST this evening for WYZ110.

     High Wind Warning from 9 AM this morning to 6 PM MST this
     evening for WYZ101-104.

     High Wind Watch from Friday afternoon through Friday evening for
     WYZ116>119.

NE...None.
&&

$$

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



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