Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 180459

Area Forecast Discussion
National Weather Service Cheyenne WY
1055 PM MDT Mon Jul 17 2017

.SHORT TERM...(This evening through Wednesday night)
Issued at 300 PM MDT Mon Jul 17 2017

Cold front laying along a line from Rapid City to Wright to Cody
this afternoon. Southeast surface winds out across western
Nebraska, northeastern Colorado and northwestern Kansas this
afternoon with dewpoint temperatures in the low 60s. So far,
latest SPC mesoanalysis showing surface based CAPE over the
southern Panhandle around 2000 J/KG with 1500 J/KG over the
northern Panhandle with no capping inversion. Weak upper shortwave
seen on latest water vapor in southwestern Wyoming this afternoon.
Seeing some convection forming over southwestern Wyoming to near
Rock Springs with this shortwave. So far, not a whole lot being
observed in the Cheyenne CWFA.

Latest HRRR guidance definitely showing an increase in convection
late this afternoon and into the evening hours with the approach
of the upper shortwave. Convection blossoms out across Carbon
County and spreads into Converse and Niobrara Counties this
evening. Believe the northern Panhandle stands the best chance at
seeing severe thunderstorms late this afternoon/evening as this
area closest to the northern front and is under the track of the
upper shortwave. SPC`s Marginal Risk area looks pretty good. HRRR
is also some convection developing across the southern Panhandle
after 00Z, which would have better instability, but less forcing.
Need to watching this area this evening as well.

Tuesday may be a little drier as the front looks to be south
across northern Colorado and much of the CWFA under dry northerly
flow. That begins to change Wednesday as southeasterly winds
return and increasing PWs return to eastern Wyoming and Nebraska
Panhandle. By Wednesday evening, PWs back to 1.2" across the
southern Panhandle. That boundary to the south looks to begin
shifting northward once again as a warm front which could serve as
a forcing mechanism for showers/storms to develop. Should begin
to see an increase in PoPs across the area Wednesday afternoon and
evening as this happens.

.LONG TERM...(Thursday through Monday)
Issued at 300 PM MDT Mon Jul 17 2017

Thursday...A slow moving shortwave trough aloft progged to move
northeast across our counties in the afternoon, and combined with
adequate low and mid level moisture, we expect scattered showers and
thunderstorms to develop, most numerous south of a Rawlins to Lusk
line. Temperatures a bit cooler with the additional clouds and
precipitation compared to Wednesday.

Friday...Drier zonal, west to east flow, develops, which will help
dry out the airmass and limit thunderstorm development somewhat,
mainly over the mountains.

Saturday...Zonal flow continues. With progged low and mid level
moisture, expect primarily isolated afternoon and evening showers
and thunderstorms, mainly east of I-25.

Sunday...Flow aloft becomes northwest. With the deeper moisture over
our eastern counties, that location expected to see the greatest
coverage of late day showers and thunderstorms.

Monday...Flow aloft is northwest, with low level southeast upslope
winds prevailing. Enough moisture for at least isolated showers and
thunderstorms to develop in the afternoon east of I-25. After a
cooler Saturday and Sunday, this day will be slightly warmer with
more sunshine and a moderating airmass.


.AVIATION...(For the 06Z TAFS through Tuesday evening)

VFR conditions will prevail tonight with widely scattered rain
showers possible, mainly north of Interstate 80. Another round of
showers and thunderstorms are possible Tuesday afternoon, mainly
from KLAR to KSNY near the Colorado border. Winds should remain
light out of the northwest in the morning, with winds shifting into
the northeast or east by the afternoon.


Issued at 300 PM MDT Mon Jul 17 2017

Daily chances for showers and thunderstorms mainly over the
mountains the next few days. Upper high pressure currently over
the 4 corners area will drift east the next few days allowing
more monsoonal moisture to mover into southeast Wyoming and
Nebraska Panhandle. Increasing chances for afternoon and evening
showers and thunderstorms each day, peaking out on Thursday where
most locations should see chances for wetting rains. The high then
shifts back west, cutting off monsoonal moisture, resulting in
decreasing chances for precipitation. Afternoon humidity through
Wednesday poor in our northern and western fire weather zones, but
winds should remain light.




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