Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 240820
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
220 AM MDT Tue Oct 24 2017

.SHORT TERM...(Today through Wednesday night)
Issued at 220 AM MDT Tue Oct 24 2017

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

Currently...High pressure dominates Wyoming as a 1043mb surface
high is centered over the Idaho Panhandle with surface ridging
extending southeast through Wyoming to the Texas Panhandle this
morning. Skies are cloud free across the CWFA today and winds are
fairly light.

A pretty nice day today with sunny skies, light winds and
temperatures in the mid 50s west of the Laramie Range/low 60s east
for highs. No weather impacts expected today.

That changes Wednesday as a cold front currently over British
Columbia moves southeast. Guidance has been very consistent on the
timing of this front and increasing winds over the past three
days, so confidence is high that winds will be on the increase.
Latest GFS high wind guidance showing Craig to Casper 850/700mb
height gradients increasing to above 60mtrs by 15Z Wednesday. NAM
guidance shows this increase as well, just a little lighter, but
still in the mid to upper 50 mtr range. Timing identical to GFS.

GFS 700mb winds increase through the day Wednesday, hitting
50-55kts Wednesday afternoon across southeast Wyoming. Wind prone
areas (Arlington, Bordeaux, south Laramie Range) should see main
effects of these strengthening gradients. Went ahead with a High
Wind Watch for Wednesday for these wind prone areas. Have the
Watch running from 9AM through 9PM. Only question I can see is
maybe a little later start to the winds as GFS 700mb winds don`t
increase above 50kts til around 21Z. Will let the dayshift take
another look before issuing the warnings.

Critical fire day for tomorrow as very warm temperatures and
increasing winds combine with the dry airmass (afternoon humidity
down to 10%) for critical fire weather conditions to develop. A
Fire Weather Watch has been issued as well for areas along/east of
the Laramie Range into the Panhandle.

.LONG TERM...(Thursday through Monday)
Issued at 220 AM MDT Tue Oct 24 2017

Much colder across the CWA Thursday behind a cold front that will
clear the CWA by Thursday morning. Temperatures likely falling
during the afternoon as clouds increase. A shortwave will swing
across the area Thursday and bring a shot of rain and snow
showers across much of the CWA Thursday morning into the afternoon
before ending by evening.  Dry and cool Friday then warming
Saturday and Sunday under northerly upper flow. Next upper trough
drops out of Canada Sunday night into Monday and drives the next
cold front across the CWA Monday with rain and snow showers
developing across much of the CWA behind the front.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 220 AM MDT Tue Oct 24 2017

VFR conditions through the period under nnw upper flow. Gusty
northwesterly winds over the Neb Panhandle this afternoon with
some gusts around 30 kts.

&&

.FIRE WEATHER...
Issued at 220 AM MDT Tue Oct 24 2017

Fairly light winds expected today with afternoon humidities
staying above critical thresholds. That changes Wednesday as a
strong cold front moves into northwest Wyoming and eventually
through southeast WYoming and Nebraska Panhandle Wednesday night
and Thursday morning. Ahead of the front westerly winds are
expected to become strong. A very warm day expected Wednesday with
very dry air in place. Afternoon humidities expected to fall to 10
percent across a large swath of southeast Wyoming east of the
Laramie Range into the Nebraska Panhandle. A Fire Weather Watch
has been issued for strong winds and low humidity Wednesday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Fire Weather Watch Wednesday afternoon for WYZ301-306-309-310.

     High Wind Watch from Wednesday morning through Wednesday evening
     for WYZ106-110-116-117.

NE...Fire Weather Watch Wednesday afternoon for NEZ311>313.

&&

$$

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


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