Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 261119 AAA

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
519 AM MDT TUE JUL 26 2016

.UPDATE...for the early morning aviation forecast update.


.SHORT TERM...(Today through Wednesday night)
Issued at 304 AM MDT Tue Jul 26 2016

Main forecast concerns Today and Wednesday will be the threat of
thunderstorm activity and the position/speed of a surface cold
front forecast to push into the forecast area. A broad upper level
high pressure south of Wyoming will continue to retrograde
westward into the eastern Great Basin region today. This will
allow some jet energy and a weak frontal boundary to drift a bit
further south across central Wyoming today. Surface trough
currently extends from north of Douglas near Gillette...southward
along the Front Range of the Rockys. This surface trough will
serve as a weak dryline with a high moisture gradient along the
boundary. LAPS surface analysis shows a surface low over northeast
Wyoming. This low will slowly drift southeast across the area
today and will aid the development of thunderstorms. A few strong
to marginally severe thunderstorms are expected east of a line
from Lusk to Scottsbluff Nebraska where the highest instability
will be along with the most favorable shear profiles. Strong
winds/hail/frequent lightning are the main concerns into this
evening. Further south...just a general risk of thunderstorms is
expected along the dryline-like boundary as it gradually moves
eastward through the afternoon. Activity is expected to move east
of the forecast area while another round of showers and isolated
thunder is possible further west tonight as a 700KT jet max and
surface cold front begins to move south into east central Wyoming
and the northern Nebraska panhandle. Kept POP around 15 to 20
percent after midnight...mainly well north of I80.

For Wednesday...Models all show the surface cold front pushing
southward and eventually stalling along the Laramie Range
Wednesday night. With cooler air aloft moving into the area under
northwest flow and some jet energy...expect a pretty good chance
of widely scattered or scattered thunderstorms along and east of
the Laramie Range/I-25 corridor Wednesday afternoon through late
Wednesday evening. Strong to severe thunderstorms are also
possible in these areas as well...especially if there is limited
cloud cover. Kept POP between 25 to 40 percent across the eastern
plains into western Nebraska with a better chance at organized
sustained convection through Wednesday evening. Temperatures will
begin to lower a few degrees on Wednesday...but highs will remain
in the mid to upper 80`s before lowering late in the afternoon.

.LONG TERM...(Thursday through Tuesday)
Issued at 304 AM MDT Tue Jul 26 2016

The upper ridge sets up shop over the desert southwest through
Tuesday with periodic shortwave energy moving east across Wyoming
and western Nebraska. With the upper high over central Nevada on
Thursday we see a shortwave driving southeast across Wyoming and
western Nebraska Thursday afternoon producing scattered showers
and thunderstorms during the afternoon and evening hours.
Weak shortwave ridging Friday results in lower PoPs in the
isolated category through the weekend for afternoon convection,
then we see the upper ridge start to move east with southwesterly
upper flow returning by Tuesday as a stronger shortwave starts to
drive east from Idaho possibly resulting in eventual higher PoPs
by early next week.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 519 AM MDT Tue Jul 26 2016

HRRR and NAM still showing isolated thunderstorm development near
Cheyenne...Sidney and Scottsbluff in the mid to late afternoon
hours with a little higher coverage for Alliance and Chadron
through early evening. For now didn`t go with a prevailing period
of thunder those areas but did put in a vicinity thunderstorm
mention leaving them VFR. No mention of thunder for Laramie or
Rawlins as chances much lower those areas based on the latest


Issued at 304 AM MDT Tue Jul 26 2016

Fire weather concerns will be low across the majority of the area
today...but near critical conditions are possible across portions
of FWZ 301 and western 303 and 304 due to low humidities and west
to northwest winds gusting between 20 to 25 MPH at times. Coverage
of showers and thunderstorms will increase over the next few days
through Friday with minimal concerns for the rest of the week.


.CYS Watches/Warnings/Advisories...


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