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Area forecast discussion 
National Weather Service Cheyenne Wyoming
542 PM MDT Wednesday Sep 17 2014

Short term...(this evening through Friday night)
issued at 400 PM MDT Wednesday Sep 17 2014

Scattered showers with a few embedded thunderstorms continue over
portions of the County Warning Area this afternoon...mainly along the Interstate 80
and 25 corridors. The main outflow boundary with the initial burst
of activity extends from western Kimball County...south into
Colorado...then back up into southeast Albany County. Observed winds
with this feature were as high as 45 miles per hour earlier on...with the
strongest activity currently located at the eastern and western
extents of the boundary. Could still see gusty winds and brief
moderate rain with this activity...which will shift southeast over
the next few hours. Otherwise...isolated light rain showers with a
few claps of thunder will be the rule elsewhere through sunset.
Winds across the plains are still expected to become a more
southeasterly upslope component overnight...with increasing low level
moisture in this pattern enough to keep mention of patchy fog in the
easternmost zones of Nebraska.

The upper level ridge axis will move overhead on Thursday as a deep
trough digs into the West Coast. Temperatures will increase a few degrees
from today...with 90s more widespread in the lower elevation of the
Nebraska Panhandle. Winds will continue to be out of the south but
will be light for the most part. A weak disturbance in the flow
could generate a few showers over the high peaks...but likely will
be just some vigorous cumulus over the mountains. The upper trough
looks to split through Thursday and night...with the northern
piece moving across the northern rockies on Friday. The
associated cold front looks to move across the County Warning Area early Friday
afternoon once again...with increasing chances for showers and
thunderstorms expected through the day along with cooler

Long term...(saturday through Wednesday )
issued at 400 PM MDT Wednesday Sep 17 2014

Medium range model guidance is in good agreement with a closed upper
low over Southern California early in the period. This feature is nestled in
behind a high amplitude upper ridge anchored over the Rocky Mountain
region...likely slowing its progress. Saturday afternoon should be a
pleasant day in the Post frontal air with seasonal temperatures and precipitation
chances confined to the mountains. The GFS/European model (ecmwf) both move the upper
low northeast across the Great Basin on Sun afternoon. Moisture increases
in the 700-500 millibar layer after 00z owing to diffluent southwest
flow aloft. Chances for precipitation should increase from SW to NE through
Monday only changes to the inherited grids were to increase
probability of precipitation slightly. Coolest day of the period should be Monday. Low level upslope
flow is prognosticated to ramp up as well which should keep clouds and precipitation
going through the day east of the Laramie range...much like we saw
earlier this month. GFS 700 mb temperatures are only in the single digits c and
ecm MOS suggests highs only in the lower 60s for southeast Wyoming. We
lowered temperatures by a couple of degrees with the expected slow progress
of the system. Warming and drying trend ensues through midweek with
precipitation ending by Tuesday morning beneath upper-level ridging.


Aviation...(for the 00z tafs through 00z Thursday afternoon)
issued at 534 PM MDT Wednesday Sep 17 2014

Shower activity will continue to diminish through sunset with VFR
conditions prevailing through much of the night. Light winds and
lower level moist upslope flow will promote the development of fog
and/or low stratus over the NE Panhandle after 09z. IFR ceilings
and visibilities are especially possible at kbff with upvalley
winds out of the southeast. Kaia and ksny may see visibilities
between 1 and 5sm along with IFR ceilings. The IFR conditions
should gradually improve around 15z. It is possible that aia may
remain at least MVFR for most of the morning as high- resolution
models are slow to dry out the boundary layer.


Fire weather...
issued at 400 PM MDT Wednesday Sep 17 2014

Scattered showers with a few embedded thunderstorms will continue
through early this evening for much of southeast Wyoming. Light
rain...gusty winds to 40 miles per hour...and occasional lightning is expected
with the strongest activity which will occur across southern Albany
County and Laramie County. Warm and dry conditions will occur on
Thursday...with humidities looking to drop to 15-25 percent in the
afternoon. Wind gusts will generally be 20 miles per hour or less through
this time. The next chance for showers and thunderstorms will
occur Friday...with temperatures cooling to more normal values
for this time of year through the weekend.


Cys watches/warnings/advisories...


Short term...rjm
long term...hammer
fire weather...rjm

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