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Area forecast discussion...updated 
National Weather Service Grand Junction Colorado
1147 am MDT Monday Sep 22 2014

issued at 1114 am MDT Monday Sep 22 2014

Upper trough is working through the northern rockies and its
associated jet streak is pushing through western Colorado this
afternoon and early evening. Drier air is working into eastern
Utah with only isolated mountains storms expected there this
afternoon. Western Colorado storms are moving at 30-35 miles per hour to the
east threatening strong outflow winds up to 40 miles per hour for brief
periods. Storms of 50 dbz or greater are producing small hail.
Some heavy rainfall occurred in Archuleta County this morning.
Emergency manager there has not reported problems so far. Some
storms will continue in the eastern mountains beyond midnight tonight.


Short term...(today through tuesday)
issued at 506 am MDT Monday Sep 22 2014

Today...showers and thunderstorms will continue moving across
much of the area this morning. A brief clearing band will move
over western Colorado early this morning followed by another band of
showers and thunderstorms in the late morning. This second band is
associated with 2 shortwave troughs ahead of the main upper
trough...and a jet streak passing over NE Utah and northwest Colorado. These
features will move over northwest Colorado before 10 am...then the main 500 mb
trough will move through between 18z and about 22z. With gradually
clearing skies this afternoon over the northwest part of the County Warning Area...and
the upper features moving through...believe clear areas will
form...but resultant surface heating will allow showers and
thunderstorms to continue developing through middle to late
afternoon. Thus have kept the chance of rain and cloud cover on the
high side for most of northwest and central Colorado.

Over SW Colorado this morning the last of monsoon related moisture will
affect the San Juan Mountains and the lower elevations of The
Four Corners until about 9 am MDT...then as winds aloft shift to
the west...clearer conditions currently over southeast Utah will move
into the area. Have continued the Flash Flood Watch...along with 2
areal flood advisories...through middle morning.

Tonight and Tuesday...the upper low will be arcing from the northern
rockies to the High Plains overnight. Energy rotating through the
backside of the low will brush northern Colorado during the late
evening hours. Isolated to scattered showers will persist across
this portion of our County Warning Area before drier and more stable air works in
the flow veering more to the northwest. The NAM wants to keep some
showers in the southeast mountains due to moist upglide but seems to
be the odd man out so have low probability of precipitation and mostly clear skies by
sunrise Tuesday. Subsident flow behind the wave promises dry and
mostly sunny conditions for Tuesday with a warming trend as ridging
begins to amplify northward out of the southwest deserts. Highs
should push back to or exceed normals.

Long term...(after midnight Tuesday night through sunday)
issued at 506 am MDT Monday Sep 22 2014

Tuesday night into Wednesday...low pressure deepens along the
offshore waters of the northwest Continental U.S.. the high pressure ridge axis
extends across our County Warning Area and again expect a quiet period with mainly
clear skies. This should bring a larger diurnal swing in temperature
with lows dropping a few degrees from days past and highs on
Wednesday pushing up a few degrees over Tuesday.

Wednesday night...Thursday and Friday should continue dry but the
upper ridge will weaken considerably as the Pacific trough moves
inland over Washington...or...and northern California. The midrange models show
disagreement on how quickly this strong Pacific storm moves across
the western U.S. The GFS continues to be considerably
it keeps this storm as an open wave at 500 mb until it reaches
Boise on Sat at 18z. The GFS pushes the surface cold front
through the forecast area late Sat morning through Sat
afternoon...with a good line of precipitation accompanying it. The European model (ecmwf)
is much slower as it develops a deeper closed low along the northern California
coast Sat morning...and stalls the system over northern California through Sat
night. The ec's cold front doesn't push through the forecast area
until Sunday afternoon... 24 hours behind the GFS projection.

This all leads to great uncertainty in timing the system through
the area late this week...though through the diversity of
solutions there is consensus the a significant Pacific storm will
affect the western U.S. In the Sat through Monday time frame.

Aviation...(for the 18z tafs through 18z Tuesday morning)
issued at 1114 am MDT Monday Sep 22 2014

Widespread precipitation across the forecast area will bring rain showers
and occasional thunderstorms to kege kase this afternoon. MVFR
ceilings and visibility...and in some cases...brief IFR conditions are
possible in heavy rain. Mountains will be obscured at times east
of kege and gusty and unpredictable outflow winds to 45 miles per hour will
occur with the stronger cells. Skies will gradually clear and
conditions improve this evening with only isolated storms along
the Continental Divide beyond midnight. VFR conditions are
expected for all taf sites after 03z this evening.

Gjt watches/warnings/advisories...



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