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Area forecast discussion 
National Weather Service Cheyenne Wyoming
401 am MDT Tuesday Jul 29 2014

Short term...(today through Thursday night)
issued at 400 am MDT Tuesday Jul 29 2014

Morning water vapor satellite imagery shows a well organized
upper-level low developing over southern Nevada/Utah within a general
weakness in a larger scale ridging pattern. Abundant monsoonal
moisture continues to spread northward into the central rockies
in advance of this feature with isolated showers now developing
over southeast Wyoming and the northern Panhandle. Convection should
only increase in coverage with time as large scale ascent spreads
across the area. Moist low level upslope strengthens dramatically by
18z beneath strong divergence aloft associated with a 100 knots jet
streak over the northern plains. Excellent moisture is in place
with precipitable water values around 1.5 inches and widespread surface dewpoints
in the 50s to near 60f per recent observation. Believe convection should
become quite numerous by middle afternoon. Introduced categorical probability of precipitation
after 21z along and just east of the Laramie range with the
upslope enhancement.

GFS k-index values of 35 to 40 c and strong upward vertical velocities point to heavy
rain potential this afternoon and evening. GFS and NAM BUFKIT soundings
support efficient rain production with tall/skinny cape profiles
and deep saturation after 21z. While the residence time of
favorable dynamics may not support a significant flooding
risk...storms will be slow moving with average 700-300 millibar
winds only around 10 knots. Plus the GFS/NAM/ECMWF models all agree
with quantitative precipitation forecast values between 1 and 2 inches along and on either side of
the Laramie range. Wpc still paints a MDT risk for excessive
rainfall in our southern zones. Went ahead and hoisted a Flash
Flood Watch for the mountains and some of the adjacent valleys/High
Plains. Not too confident that areas farther east will see higher
amounts as convection may be largely terrain driven. Left those
areas out of the watch for the time being...but the day shift may
wish to revisit.

Convection should decrease in coverage and intensity by sunrise
Wednesday as stronger dynamics shift south and east. European model (ecmwf) and NAM are
slower to move things out with some higher quantitative precipitation forecast carrying over into
the 18z to 00z time frame on Wednesday will need to monitor
for a temporal extention of the flash flood threat. Otherwise...
temperatures today and Wednesday will rather cool with widespread clouds
and precipitation. 700 mb temperatures only around 5-7c on Wednesday suggests cooler than
consensus MOS indicates...only looking at a high around 65f here
in cys. Warmer and drier for Thursday as ridging re-establishes itself
over the Rocky Mountain region. Precipitation chances will be confined to
the mountains.

Long term...(friday through tuesday)
issued at 400 am MDT Tuesday Jul 29 2014

A very typical early August pattern taking shape during the extended upper-level ridge axis over the intermountain west is
periodically infiltrated by shortwave energy and associated pockets
of monsoonal moisture. It becomes more difficult this time of year
to feel confident in removing diurnally driven convective chances.

The first shortwave will move into western Wyoming Friday morning
reaching western zones for Friday afternoon. Best chances for convection
will be for areas in closest proximity of this wave west of
Interstate 25. Forecasts sbcapes of 200-400 j/kg suggest any
thunderstorm development would be non-severe. Weak steering flow
will only move this shortwave to northeast Wyoming/western South Dakota
by late Saturday. Instability axis will remain parked along the
Front Range and adjacent eastern plains. Convective chances again have
been confined generally west of Interstate 25 on Saturday.

Medium range guidance is consistent in slinging another piece of
shortwave energy through The Four Corners towards the cowboy state on
Sunday. The GFS is quickest and strongest with this energy while the
European model (ecmwf) offers a slightly slower and weaker solution. In either case
its effects really wont be felt until late Sunday and more so on
Monday as cold front slips south through the County warning forecast area. This will bring the
next chance for shower and thunderstorm activity. Depending upon the
timing of this may linger and/or have the most impact on
Tuesday. For now...have been fairly Liberal with convective chances
for Monday/Tuesday with the expectations that these will be refined as
solutions converge.

Temperatures will be the warmest on Sunday as highs climb back into
the 80s at all locations. Cooler temperatures anticipated behind the
cold frontal passage Mon/Tue...with highs falling back into the 70s for most


Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1139 PM MDT Tuesday Jul 29 2014

Nebraska aerodromes...through 15z isolated slow moving
thunderstorms possible...south of a Scottsbluff to Bridgeport line
producing locally heavy rain...erratic wind gusts to 40 knots and
turbulence with localized MVFR...otherwise VFR. Areas of fog late
tonight through early morning.

After 15z...scattered to numerous showers developing in the
afternoon...most numerous south of a Scottsbluff to Alliance
line...with isolated to scattered thunderstorms. MVFR in showers
and thunderstorms...with thunderstorms producing gusty and erratic
winds and localized turbulence.

Wyoming aerodromes...through 15z isolated slow moving thunderstorms
possible. A few thunderstorms producing locally heavy
rain...erratic wind gusts to 40 knots and turbulence with
localized MVFR...otherwise VFR.

After 15z...scattered to numerous showers developing in the
afternoon...most numerous east of a Laramie to Wheatland line...
with mountains obscured. Isolated to scattered afternoon
thunderstorms...producing gusty and erratic winds and localized


Fire weather...
issued at 400 am MDT Tuesday Jul 29 2014

A strong storm system combined with monsoon moisture will give
way to widespread showers and thunderstorms on Tuesday and
Wednesday. The greatest coverage will be along and on either side
of the Laramie range where a general 1 to 2 inches of rain can be
expected. Cooler temperatures and new moisture will mitigate any
fire weather concerns through middle week.


Cys watches/warnings/advisories...
Wyoming...Flash Flood Watch from noon MDT today through late tonight for



Short term...hammer
long term...Hahn
fire weather...hammer

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