Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 170531
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1030 PM MST Fri Feb 16 2018

.SHORT TERM...(Tonight - Saturday Night)
Issued at 246 PM MST Fri Feb 16 2018

A widespread & potentially significant episode of strong winds now
appears likely across much of southeast Wyoming this weekend. Late
this evening, a surface low will track across east central Wyoming
into the western Nebraska Panhandle. This is expected to result in
strong low-level gradients, with an H7 CAG-CPR gradient around 65-
75 meters from 00z this evening through 12z Saturday. Overall flow
aloft is not super impressive overnight, but still peaks at around
55 knots at H7-H8 across much of southeast Wyo. Deep subsidence in
association with the RFQ of a 120+ knot H25 jet, combined w/ steep
low-level lapse rates should easily support downward momentum xfer
over many areas. Downward omega fields also support high winds for
both Laramie and Cheyenne. A little more marginal for the Rawlins/
Saratoga areas tonight, but certainly cannot rule it out. Pressure
rises on Saturday should yield a lull in high winds, then a strong
surface low along the WY/MT border yields impressive low-level CAG
to CPR gradients of 80 to 90 meters Saturday night/early Sunday w/
even stronger flow aloft on the order of 55-65 knots (75 kts at H7
over the North Laramie Range). This should yield round 2 of strong
winds for most areas, this time possibly affecting Converse county
as well.

Concerning the Blizzard warning, not much blowing snow to speak of
outside of some very localized areas near ARL despite gusts of 50-
55 MPH. There is also quite a bit of brown on several web-cams, so
some question marks with how much snow is blowable. Still think we
will see some significant blowing snow overnight, but highs of 35-
40 degrees on Saturday afternoon should effectively end the threat
for blowing snow. Adjusted the timing of the BZW to end at 21z Sat
instead of 12z Sun based on this reasoning. Opted to issue a High-
Wind Warning from 21z Sat through 12z Sun.

All inherited High Wind Warnings remain in effect, w/minor changes
to timing. We added Saratoga starting late tonight, even though it
appears the best chance will actually be on Saturday night for SAA
and RWL. A High Wind Watch was issued for the N. Laramie Range and
lower elevations of Converse county from 21z Sat - 12z Sun. We may
see some pretty impressive gusts over the mountains, possibly near
90 MPH.

.LONG TERM...(Sunday - Friday)
Issued at 313 AM MST Fri Feb 16 2018

Edit 246 PM MST Fri Feb 16 2018:
Issued a Winter Storm Watch for Converse/Niobrara counties w/ high
confidence in snow rates picking up by Sunday mid-morning with the
front dropping down. Later shifts will want to look into expansion
of this headline to the south and east.

Arctic front begins to impact the area Sunday afternoon as it
moves into Converse County. Very slow movement of the front will
create a widespread and prolonged snow event across the area.
Areas impacted the most will be along and north of a line from
Alliance to Guernsey to maybe Rawlins where the potential for 10
to 12 inches of snow is possible. Southern Panhandle and over to
Cheyenne may get shadowed by the Laramie Range as westerly winds
create downsloping conditions here.

Front finally clears the area Tuesday morning with snow ending
from north to south. We will definitely need some winter headlines
with this event once we get through the wind event.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday evening)
Issued at 1030 PM MST Fri Feb 16 2018

VFR. Primary concern for aviation operations wil be strong westerly
winds with gusts of 35-50 kt at the southeast Wyoming terminals
during the TAF period. Moderate to severe mountain wave turbulence
can be expected. The Nebraska Panhandle terminals, except Chadron,
will experience west to northwest winds gusting 25-35 kt tonight and
Saturday. There will be occasional mountain obscurations from snow
showers.
&&

.FIRE WEATHER...
Issued at 313 AM MST Fri Feb 16 2018

Widespread strong wind event to begin late this afternoon and
continue into Sunday morning. Much of southeast Wyoming expected to
see wind gusts in excess of 65 mph. An arctic front is approaching
from the north and is set to move into Converse County Sunday
afternoon as moves southeast. Along and behind the front, we are
looking at widespread moderate snow and very cold temperatures
through Tuesday morning.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 8 PM this evening to 5 AM MST Sunday for
     WYZ104>106-116-117.

     Blizzard Warning until 2 PM MST Saturday for WYZ110.

     High Wind Warning from 2 PM Saturday to 5 AM MST Sunday for
     WYZ110.

     High Wind Watch from Saturday afternoon through Sunday morning
     for WYZ101-103.

     Winter Storm Watch from Sunday morning through Monday afternoon
     for WYZ101-102.

     High Wind Warning from midnight tonight to noon MST Saturday for
     WYZ118.

     High Wind Warning from midnight tonight to 5 AM MST Sunday for
     WYZ107-109-113.

     High Wind Warning from 11 PM this evening to 5 AM MST Sunday for
     WYZ115.

NE...None.
&&

$$

SHORT TERM...CLH
LONG TERM...CAH/CLH
AVIATION...MAJ
FIRE WEATHER...GCC



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