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Area forecast discussion 
National Weather Service Cheyenne Wyoming
613 am MDT Wednesday Oct 1 2014

Short term...(today through friday)
issued at 206 am MDT Wednesday Oct 1 2014

Current infrared satellite loop shows mostly clear to partly cloudy
skies across most of southeast Wyoming and western Nebraska early
this morning as the low pressure system which brought heavy rain
to the area yesterday is now entering southern Saskatchewan and
Manitoba. However...the next upper level trough is currently digging
south across the eastern Great Basin region...with showers and
thunderstorms developing over Utah and entering western Colorado at this
hour. This will be our next precipitation producer today as the
upper level system continues to dig southeast this morning and
eventually pushes eastward this afternoon. Not much dynamic lift
at the surface with this system...but models indicate strong upper
level divergence as a 100 knots jet lift northeast into the High
Plains today. The GFS and European model (ecmwf) do indicate strong 700mb
convergence across northeast Colorado and extreme southeast Wyoming as a
700mb low tries to develop across the High Plains this evening.
This middle to upper level couplet will allow for some substantial
lift in addition to any low level instability. Continued to increase
pop between 70 to 90 percent this afternoon through late this
evening. This system will move rather quick across the
only expect perhaps 3 to 6 hours of precipitation. In the
mountains and locations above 7500 feet...rain will mix with and
change to snow. This includes the southern Laramie range and the
i80 Summit which may receive 1 to 3 inches of snow by late this
afternoon. The snowy and Sierra Madre ranges may see a little
more...but no more than 3 to 5 inches is expected into this
evening. Will hold off on any winter weather advisories due to the
progressive nature of the trough. For the lower elevations...the
heaviest rainfall amounts will generally be along the i80 corridor
from Laramie...eastward to Cheyenne and Sidney Nebraska. Can not
rule out some rain/snow mix as the precipitation comes to an end across
the Laramie valley this afternoon with snow levels lowering
between 7000 to 7500 feet. Tonight will be much cooler with lows
in the 20s to low 30s across southeast Wyoming due to clearing
skies and good radiational cooling.

Models are struggling with an Alberta clipper potentially
impacting the area for late Thursday. Current watervapor loop shows
this broad trough digging south into western Canada early this
morning...with an intensifying shortwave and associated cold front
as it moves southward into Montana. Models were not showing this
feature 24 to 48 hours ago...and are generally trending colder
with more precipitation. The main concern is freezing temperatures
Thursday night after rain/snow mix or even a quick burst of snow
as the front moves across the area. This may create problems on
the roadways due to black ice and slick conditions. Increased pop
to 20 percent...and started adding a mix of rain/snow for areas
between 6000 to 7000 feet. Will have to closely monitor this
clipper...due to potential impacts to travel across the area.
Otherwise...a drying trend and slow warming trend will begin on
Friday as an upper level ridge along the West Coast strengthens
and drifts eastward.

Long term...(friday night through Tuesday night)
issued at 301 am MDT Wednesday Oct 1 2014

The extended period will be dry and mild under persistent northwest
flow aloft. The main jet core will remain over the Central
Plains...separating a deep long wave trough over the eastern Continental U.S.
And a broad ridge over the western states/eastern Pacific. The
position of the jet will keep the forecast area on the dry side of
the flow pattern and on the southwestern edge of any clipper
systems. Thus...not expecting any precipitation through the period. A somewhat
stronger shortwave moving within the northwest flow on Sunday could
deepen the longwave trough enough to bring some moisture and energy
over eastern portions of the County Warning Area...but will just maintain
increasing clouds through the afternoon as this seems a more
likely scenario right now. Temperatures through the period will remain at or
slightly above normal for this time of year...with maximum temperatures of
60s/70s expected for the eastern plains and 50s/60s out west in
the high valleys and mountains. Winds will be quite similar each
day as well with breezy west-northwest winds developing each
afternoon and evening for the majority of the County Warning Area. These breezy
conditions will persist through the overnight hours in the wind prone
areas along and west of the Laramie range.


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 613 am MDT Wednesday Oct 1 2014

A weak surface front will continue to slowly move south across the
forecast area this morning...with winds shifting to the north to
northwest and becoming breezy at times this afternoon. Showers
will move from west to east this morning with T-storms developing
in the afternoon and evening as an upper level disturbance moves
over The Rockies. The best coverage for storms still looks to be
focused towards areas near the Colorado border where the strongest
upslope flow will be in place. Looking at mainly MVFR conditions
with this activity...with scattered-broken MVFR ceilings lingering through most
of the night within the cool and moist Post-storm environment.


Fire weather...
issued at 206 am MDT Wednesday Oct 1 2014

No fire weather concerns through this weekend due to recent heavy
rainfall and cool temperatures. An upper level disturbance will
quickly move across Wyoming and Colorado today resulting in more
rain and isolated thunderstorms...mainly along the Interstate 80
corridor near the Colorado border. Wetting rains appear likely in
this area as the system will quickly move into the Great Plains
tonight. A drying trend is expected for late this week and into
this weekend with slightly warmer temperatures and daytime
humidities trending lower each day...but remaining above 20
percent through the weekend.


Cys watches/warnings/advisories...


Short term...tjt
long term...rjm
fire weather...tjt

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