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fxus65 kcys 201751 
afdcys

Area forecast discussion
National Weather Service Cheyenne Wyoming
1151 am MDT Wed Sep 20 2017

Update...
issued at 1134 am MDT Wed Sep 20 2017

Issued a red flag warning for fire weather zones 301 and 311 based
on relative humidity values falling already to 15-20 percent and west winds
gusting to 30-35 mph over Niobrara County eastward into the
northern Nebraska Panhandle. Relative humidity values will fall to around 15
percent from 18-21z. Dewpoints will come up some by late aftn,
with relative humidity values rising slightly.

&&

Short term...(today through friday)
issued at 255 am MDT Wed Sep 20 2017

High winds have subsided across the County Warning Area this morning as a result of
weakening low-level gradients. Precipitation chances will end today
with significant mid-level drying beneath strong west-SW flow aloft on
the southern side of a deep low over the Pacific northwest. It will likely
be another windy day with excellent mixing after 15z and 25-35 knot
flow at 700 mb-800 mb over much of the area. However, overall gradients are
not expected to support significant wind gusts that would warrant a
High Wind Warning. Some fire weather concerns today, mainly for the
east central Wyoming and northern NE Panhandle zones (fwz 301, 311) with
the expected strong winds. Early mixing may force relative humidity values near or
below 15 percent, yielding a brief period of red flag conditions by
early afternoon. However, the models suggest increasing moisture in
the mid-levels after 18z which would help moderate dew points, plus
we would expect to see some increase in low-level moisture with sfc
winds turning to the south and southeast, especially across the neb
Panhandle. That said, our confidence in a sustained period (3 hour)
period of red flag conditions is too low to warrant the issuance of
a headline at this time.

No weather impacts for this County Warning Area on Thursday as an upper-trough digs
into the Great Basin. Southwest flow aloft will increase during the
day, with comfortable temperatures for many areas as 700 mb temps climb
to around +10 to +12 deg c. Thursday will be one day this period to
enjoy, because Friday Marks the beginning of a dramatic change to a
much colder and wetter pattern. Upper-level troughing advances from
west to east with strongly difluent flow overhead. Scattered shower
and isolated thunderstorm activity will return. Highs will be quite
tricky, with a range from the low/mid 50s northwest to around 80 in
the far southeast portion of the County Warning Area.

Long term...(friday night through tuesday)
issued at 340 am MDT Wed Sep 20 2017

All models continue to show a cool and unsettled weather pattern
for the weekend and well into next week. Medium to long range
models are in good agreement with the position of the strong
Pacific upper level trough as it moves eastward into the eastern
Great Basin region and stalls as it moves into the Rocky Mountain
area. A potent 110 to 130 knot jet will set up and extent
northward out of central Colorado. Models indicate numerous jet
streaks and vorticity maximum moving northward ahead of the
trough axis. With upslope flow and periods of diffluent flow
aloft, expect light to moderate rainfall with periods of heavy
rainfall, especially Saturday afternoon and Saturday night as the
second vigorous jet Max moves across the High Plains. Continued to
increase pop due to good model agreement even though they don't
agree on the exact position of the heavier rainfall. These
conditions should continue into late Sunday as another jet Max
lifts northward after a brief lull in the precip early Sunday.
High temperatures will struggle to reach 50 degrees across most of
southeast Wyoming, with mid to upper 50's across western Nebraska.
Periods of fog and drizzle are also possible during this period
due to moist llvls and upslope flow near the surface. Snowlevels
will gradually lower to between 7500 to 9000 feet from north to
south. Some snow is possible in the higher valleys of Carbon and
Albany County, but timing and location are uncertain at this time.
Will likely need winter headlines for the Sierra Madre and snowy
ranges since this will likely be their first heavy snowfall of the
season.

For early next week, the storm system will move very little with a
position somewhere near The Four Corners area. This is the portion
of the forecast that is a little more uncertain as some model and
ensemble runs want to form a closed low near The Four Corners
region while others keep an open wave trough over the rockys and
progress it eastward through Tuesday. One thing all models agree
on is another round of moderate rainfall on Monday as the trough
axis/upper level low moves towards the area. Based on model
soundings, this will likely be the most favorable time period for
rain to mix with snow down to the valley floors and adjacent
plains down to 6500 feet east of the Laramie range. Monday may
actually end up being the coolest day in the extended with highs
in the 40s along and west of I-25. By Tuesday, the trough axis
should be over the region with slightly improving conditions.
However, the Canadian model as well as a few ensemble forecasts
show the trough becoming a stalled upper level low near the
Colorado and Wyoming border, which would further enhance
precipitation rates and bring even colder air into the southeast
Wyoming. Kept pop between 10 to 20 percent for now through Tuesday
night due to considerable uncertainty.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1134 am MDT Wed Sep 20 2017

VFR prevails through the taf period. Gusty SW winds will develop
this afternoon and affect areas from krwl and klar to kcdr. Gusts
of 30 to 35kt are possible. Elsewhere winds will become more
southerly through the afternoon with 15 to 25kt likely. Gusts will
ease somewhat after sunset.

&&

Fire weather...
issued at 255 am MDT Wed Sep 20 2017

Elevated to near-critical fire weather conditions are likely across
east central Wyoming and the northern NE Panhandle today, with relative humidity values
falling to near 15 percent and wind gusts over 25 miles per hour. Fwzs 301 and
311 are the most likely areas to experience this in the hours right
around noon MDT today. Conditions should quickly improve by mid, to
late afternoon. A transition to a much colder weather pattern along
with good chances for precipitation by this weekend suggests little
or no fire weather concerns after today.

&&

Cys watches/warnings/advisories...
Wyoming...red flag warning until 7 PM MDT this evening for wyz301.

NE...red flag warning until 7 PM MDT this evening for nez311.

&&

$$

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