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Area forecast discussion...updated 
National Weather Service Cheyenne Wyoming
546 PM MDT Wednesday Jul 29 2015

Update...for the early evening aviation forecast package release.


Short term...(this evening through Friday night)
issued at 245 PM MDT Wednesday Jul 29 2015

A few patches of low level cumulus are developing along and east of the
Laramie range at this hour while some thin high clouds are moving
overhead. Winds overall are lighter than yesterday with generally
south-southeasterly winds over the plains and southwest winds out
west. Observation show gusts in the 15 to 25 miles per hour range early this
afternoon...and think that will persist through the early evening.
Right now kept the forecast dry for this afternoon/evening...however
a thin axis of instability is moving up from the south and across
Laramie County in southerly surface flow while some enhancement is
evident on water vapor imagery from west-central Colorado into
extreme southern Nebraska Panhandle. So will have to watch for
towering cumulus development and potential shower activity within these
regions. Otherwise...looking at a dry forecast tonight through early

The deepest portion of the monsoon plume will remain south of the
forecast area although some midlevel moisture does look to clip the
area both Thursday and Friday. In addition...south-southeasterly
flow in the llvls will maintain dew points in the 40s-50s across the
plains so could see a couple showers/storms develop over the
southern Laramie range and push east tomorrow afternoon...with a
more isolated coverage possible over the higher terrain and across
the eastern plains on Friday. Warm air advection over the next few days will keep
this activity weak...while temperatures will steadily increase a few
degrees each day.

Long term...(saturday through tuesday)
issued at 245 PM MDT Wednesday Jul 29 2015

With the subtropical high to the southwest of the region through
the weekend...monsoonal moisture will be limited with the west to
northwest flow aloft. Precipitable water values will remain low and mostly below
0.5 inches...thus convection will be really limited and the string
of dry days will continue. With 700mb temperatures of 17-18c...highs will
be about 5 degrees above normal. The biggest disagreement between
the longer range models arrives by early next week and especially
Tuesday. Whereas the GFS shows the ridge remaining strong...the European model (ecmwf)
indicates a weak shortwave moving into Wyoming with a
corresponding increase in subtropical moisture. Will keep probability of precipitation low
for now as the Canadian model is more in line with the GFS.
There will be minimal fire weather although min relative humidity
values will drop to near critical levels each afternoon to the west of
the Laramie range...winds will remain weak.


Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 546 PM MDT Wednesday Jul 29 2015

Breezy early evening winds will decouple for all forecast sites by
03z...except for a few high based cumulus Cheyenne to Scottsbluff
and Alliance...clear skies expected overnight with light winds.
Expect similar conditions tomorrow with a slight chance of
thunderstorms from Cheyenne to Sidney...but chances so low at this
point didn't feel confident enough to include a mention that far
out in the tafs even for a vicinity mention.


Fire weather...
issued at 245 PM MDT Wednesday Jul 29 2015

Very dry conditions will prevail west of the Laramie range through
the end of the week with humidities dropping into the low teens each
afternoon. Winds will generally be light for these areas...with
gusts averaging 15 to 20 miles per hour and an occasional gust to 25 miles per hour.
Across the Wyoming plains...expect afternoon humidities in the middle
to upper teens with 20 percent readings in the Nebraska Panhandle
through the end of the week. A few showers and thunderstorms are
possible along and east of the Laramie on Thursday...and for the
high country and plains on Friday. However...not much rainfall is
expected from this activity.


Cys watches/warnings/advisories...


Short term...rjm
long term...zf
fire weather...rjm

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