Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 140530

Area Forecast Discussion
National Weather Service Cheyenne WY
1130 PM MDT Sun Aug 13 2017

Issued at 853 PM MDT Sun Aug 13 2017

No further concerns for strong/severe convection this evening with
the loss of solar heating, and the resultant increase in sfc-based
inhibition. The latest radar trends indicate showers/thunderstorms
have decreased considerably in coverage/intensity, w/most activity
confined to areas along/west of the Laramie Range and parts of the
northern Nebraska Panhandle. Gusty winds around 40 MPH could still
accompany any remaining activity with T/Td spreads still some-what
high, but this threat should diminish soon as well. No real change
to the inherited forecast, other than to adjust precip chances and
weather to better reflect current trends.


.SHORT TERM...(This evening through Tuesday night)
Issued at 142 PM MDT Sun Aug 13 2017

Forecast challenges deal with severe thunderstorm potential today
and Monday.

Currently...Water vapor imagery showing upper level ridge over
western Wyoming this afternoon with another shortwave moving in
behind it over central Idaho. Latest SPC Mesoanalysis page
showing fairly weak instability over our western zones and up over
Converse/Niobrara Counties at 1PM. Radar is showing some
convection beginning to develop across southern Converse and
northern Platte Counties, but nothing widespread as of yet.

For remainder of today...SPC Mesoanalysis not showing a whole lot
of instability this afternoon, getting up to 2000-2500J/KG late
this afternoon on surface based CAPE. Convective inhibition
remains fairly high at -100 J/KG with north to northeast flow
across the eastern plains. Not feeling at all confident in seeing
severe thunderstorms today. Model soundings showing long/skinny
Cape profiles this afternoon across the Panhandle, so do believe
most of our storms today will be heavy rain producers with no much

Think conditions are better for Monday to see some severe
thunderstorms. Upper level ridge moves off to our east by noon
tomorrow and the upstream shortwave approaches from the west and
northwest. Coming through during peak heating Monday. NAM MUCAPE
running 2500-3000 J/KG out in the Panhandle with favorable shear
profiles. Didn`t add severe thunderstorms in the forecast, but do
feel we could see a few tomorrow afternoon. Night shift may want
to add depending on what the new guidance shows.

Upper shortwave moves through the area late Monday night into
Tuesday. Should see fairly widespread convection Tuesday afternoon
into the evening hours as the upper shortwave moves through the

.LONG TERM...(Wednesday through Sunday)
Issued at 142 PM MDT Sun Aug 13 2017

The models continue to advertise a transition to a drier pattern
occurring, especially after Thursday.  Fropa on Wednesday morning
will result in a cool and relatively stable airmass across much of
the region for Wednesday.  Isolated storms will be possible along
the Laramie Range.  A slightly better chance of storms will exist on
Thursday for areas to the east of the Laramie Range as a weak
shortwave trough moves overhead.   Increasing west to northwest flow
aloft will usher in lower PW values Friday into next weekend.  This
will keep any chance of aftn/evening storms mostly confined to the
mountains.  Could see elevated fire weather conditions impact areas
to the west of the Laramie Range from Friday onward.  After a cool
start to August, temps will rise into next weekend back to near


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1130 PM MDT Sun Aug 13 2017

Last of the evening showers have dissipated or moved east of the
aviation service areas, with VFR expected overnight under mainly
midlevel or high level cloudiness. We expect to see more scattered
showers and thunderstorms tomorrow developing initially along the
higher terrain west of Interstate 25 during the late morning and
early afternoon hours...spreading east in a scattered to widely
scattered fashion across the plains. Have a mention of showers or
thunderstorms in the vicinity starting 18-21Z for Monday for
Rawlins, Laramie, Cheyenne and Scottsbluff but no mention yet
given late timing and more isolated coverage expected farther east
into the Chadron, Alliance and Sidney areas.


Issued at 142 PM MDT Sun Aug 13 2017

Unsettled weather will keep fire weather concerns at bay. Looking
at daily chances for afternoon and evening showers/thunderstorms
through at least mid week. Afternoon humidities could get close to
critical from Thursday on into the weekend, but strong winds are
not expected.




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