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Area forecast discussion 
National Weather Service Cheyenne Wyoming
611 PM MDT Tuesday Apr 21 2015

Short term...(this evening through friday)
issued at 209 PM MDT Tuesday Apr 21 2015

Tonight...relatively weak shortwave trough aloft and a wind
shift...or weak cold frontal passage will help spark isolated to
widely scattered evening showers...and isolated thunderstorms this
evening along and west of Interstate 25...well depicted by the GFS
quantitative precipitation forecast with localized enhanced areal coverage over our snowy and Sierra
Madre ranges due to differential heating. Low level moisture fuel
provided by the melting snowpack over the Laramie valley. Expect
showers to dissipate with loss of solar insulation and daytime
heating with lack of other lifting mechanisms.

Wednesday...well pronounced 850/700 mb Theta-E ridge axis develops
north to south in the afternoon along the Laramie valley with a nice
convergence axis setting up centered over the Laramie valley. With
decent amounts of low level moisture...fuel...available from the
melting snowpack over the Laramie valley...daytime heating...expect
isolated to scattered afternoon and evening showers and isolated
thunderstorms to spark again...along and west of Interstate 25.
Areal coverage will be minimized by ridging aloft.

Wednesday night...again...showers and thunderstorms will dissipate
and cessate in the evening with loss of daytime heating...in the
absence of other lifting mechanisms.

Thursday...in contrast to Wednesday...the 850/700 mb Theta-E ridge
axis will translate eastward to the Wyoming and Nebraska state line
in the afternoon with a decent low level convergence axis setting up
along a surface trough which will parallel Interstate 25. This
combined with a passing weak shortwave trough embedded in the
southwest flow aloft at peak heating...will spark scattered to
numerous showers and isolated thunderstorms along Interstate 25 from
Douglas and Lusk southward to Wheatland and Cheyenne...with lesser
coverage elsewhere...though rain lovers will enjoy some beneficial
rainfall...especially with much of the Laramie valley and mountain
snowpack providing low level moisture...fuel...for showers and
thunderstorms.

Thursday night...isolated to scattered showers will translate east
of Interstate 25 overnight along the eastward propagating surface
trough...with areal coverage decreasing due to loss of daytime
heating...though a passing shortwave trough aloft will keep enough
lift to keep showers ongoing even after midnight east of Interstate
25.

Friday...slow moving trough aloft moves into central Nebraska and
central Kansas by supper time...though with our atmosphere well
stocked with decent low and middle level moisture...much of it provided
by the melting Laramie valley and mountain snowpack...will again see
isolated to scattered afternoon showers...and isolated thunderstorms
erupt again...most numerous along the surface trough and low level
convergence axis over western Nebraska.

Long term...(friday through tuesday)
issued at 209 PM MDT Tuesday Apr 21 2015

Unsettled weather in the extended as a slow moving low pressure
system moves through the area. Afternoon lifted indices quite low
Friday afternoon -3 to -5c...so would think there is a good chance
for thunderstorms Friday afternoon.

Upper low tracks into the central Kansas/Nebraska area Friday
night into Saturday and we get wrap around moisture for Saturday.
European model (ecmwf) much more bullish on quantitative precipitation forecast for Saturday with a surface low
developing along the Front Range and good easterly upsloping winds
into the Panhandle and over to the east slopes of the Laramie
range. Did go higher on probability of precipitation over guidance as GFS does show
scattered showers as well.

Sunday through Tuesday looks dry as upper level ridging builds
back into the area. Gradually warming temperatures as the ridge
builds in with 700mb temperatures climb to +4c by Monday night.

&&

Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 611 PM MDT Tuesday Apr 21 2015

VFR conditions will prevail for most areas through the period.
Winds will shift to the south-southeast tonight and will gust to
around 20 kts for the Panhandle sites Wednesday afternoon. Am
concerned that kcys and klar may see conditions deteriorate for a
period tonight as moist southerly upslope flow strengthens up the
Cheyenne Ridge...and possibly spills into the Laramie valley.
Kept prevailing VFR at these sites for now...but will reassess
for next taf cycle. Showers and T-storms will increase in coverage
Wednesday afternoon along and west of I-25.

&&

Fire weather...
issued at 209 PM MDT Tuesday Apr 21 2015

No concerns due to recent rainfall and snowfall
event...relatively wet ground...and prognosticated humidities and winds.

&&

Cys watches/warnings/advisories...
Wyoming...none.
NE...none.
&&

$$

Short term...Rubin
long term...gcc
aviation...rjm
fire weather...Rubin

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