Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 150937

Area Forecast Discussion
National Weather Service Cheyenne WY
237 AM MST Wed Feb 15 2017

.SHORT TERM...(Today through Friday)
Issued at 236 AM MST Wed Feb 15 2017

Forecast challenges in the short term deal with winds and elevated
fire weather concerns.

Currently...1032mb surface high stretches from southern Idaho
through southwestern Wyoming into western Colorado this morning.
Increasing surface gradient developing across our western CWFA.
Winds are fairly light right now, but am seeing an increase in
speeds at Bordeaux already this morning with gusts to 35 MPH.

For today...Local High Wind forecast guidance showing a strong
850mb Craig to Casper gradient developing after 12Z this morning.
By 15Z 850mb gradients up around 54 mtrs, peaking out at 58mtrs by
18Z. Taking a look at forecast soundings though, winds are fairly
light, generally under 35kts. Thinking Bordeaux could get close to
warning criteria, but with mixing down lesser wind, decided to
hold off on any wind headlines. Did increase winds at both
Arlington and Bordeaux over guidance. Dayshift will need to watch
closely. Other area of concern is downsloping winds off the
Laramie Range will create very dry conditions across Laramie,
Platte Counties in southeast Wyoming and the southern Nebraska
Panhandle counties (FWZs 310 and 313). Afternoon humidities down
in the low to mid teens this afternoon. With very warm
temperatures, gusty winds and low humidities, could see any grass
fires that develop spreading rapidly.

Warmest/windiest day will be Thursday as upper ridge axis moves
east of the CWFA. 700mb temperatures up near +7C Thursday and
700mb winds increasing out west to around 30kts. Continued going
over guidance on high temperatures Thursday and getting low to mid
70s for highs east of the Laramie Range out into the Panhandle.
Resultant afternoon humidities under 15 percent for most areas
east of the Laramie Range Thursday afternoon. Grass fire threat
going to be highest Thursday.

Later shifts need to be on the lookout for high winds Friday as
GFS 700mb winds increase above 50kts ahead of an approaching
shortwave. Did increase winds at Arlington and Bordeaux with this,
though High Wind Guidance suggesting Craig to Casper gradients
fairly weak. Not so sure that will be the case.

.LONG TERM...(Friday night through Tuesday night)
Issued at 236 AM MST Wed Feb 15 2017

A very sharp trough will move into the western CONUS on Saturday and
will split into two systems on Sunday. A deep upper low will
characterize the southern system, with southwesterly flow advecting
a weak shortwave across our forecast area Friday night through
Saturday. Should see some light snow showers over the high country
in this pattern but moisture looks to be meager so not anticipating
much accumulation. Winds along and west of the Laramie Range will be
breezy on Saturday as the shortwave passes overhead, but not
expecting high winds at this time. A weaker, northern stream
shortwave moving across the PacNW and northern Rockies will act to
deepen the leeside pressure trough Saturday night into Sunday and
could bring a period of stronger winds through this time. However,
this split flow pattern is still not favorable for high winds. A
few rain and high elevation snow showers are possible on Sunday
night as a Pacific front moves across the forecast area, but again
the split flow pattern should keep amounts light as deepest
moisture will remain well north and south of our area. A much
stronger upper low pressure system moving into the PacNW Monday
and Tuesday could bring a period of high winds to our wind prone
areas on Monday night and Tuesday.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 236 AM MST Wed Feb 15 2017

VFR conditions are expected through the TAF period with just some
high clouds moving in from the north. Westerly winds will increase
late this morning with gusts to 20-30 knots at all terminals
through the afternoon, with the exception of KCDR. Winds should
ease with sunset this evening except for KCYS where breezy
conditions will persist through tonight.


Issued at 236 AM MST Wed Feb 15 2017

High pressure will bring another dry and sunny day across
southeast Wyoming and Nebraska Panhandle. Very warm temperatures
today with increasing westerly winds will create elevated fire
weather concerns for areas along and east of the Laramie Range.
Afternoon humidity down in the low teens for FWZ 310 and 313.
Warmer temperatures Thursday with more widespread low humidities.
Wind gusts of 25 to 35 MPH will create another elevated fire
weather day. Grass fires, if started will spread rapidly under
these conditions. Cool down begins Friday with afternoon
humidities back above critical.




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