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Area forecast discussion
National Weather Service Grand Junction Colorado
250 am MDT Tue Oct 17 2017

Short term...(today through wednesday)
issued at 231 am MDT Tue Oct 17 2017

A ridge of high pressure centered over Baja California will ride southeast
and flatten through Wednesday as the next series of Pacific storms
rides east along the US and Canadian border. The lower atmosphere
is very dry, with precipitable water less than 0.2 inches. Zonal
flow Wednesday will increase a bit causing west winds to increase
a bit over the area Wednesday.



Long term...(wednesday night through monday)
issued at 231 am MDT Tue Oct 17 2017

The latest models continued to show a shift in the pattern
beginning Wednesday night as a low amplitude shortwave trough
moves across the southwest. In response, clouds will begin filling
in over southeast Utah and southwest Colorado toward morning
Thursday. As the shortwave-trough moves northeastward across the
forecast area on Thursday clouds will thicken and light showers
will develop. The San Juan Mountains appear favored, though both
NAM and GFS indicated light quantitative precipitation forecast was possible over the eastern
Uinta Mountains as well. With 7h temperatures running near 8
degrees c, expect most precipitation will fall as rain, with snow
at and above 11,000 feet. The dry subcloud layer in place ahead of
this system will limit precipitation accumulations to less than
0.1 of an inch. Showers will linger into the evening and possibly
longer with snow levels lowering a bit in response to diurnal
cooling.

A deeper, long-wave trough sweeps eastward across the Great Basin
on Friday bringing breezy southwest winds ahead of cold front
associated with the system. The GFS solution was a bit more
progressive driving the cold front to northeast Utah late Friday
afternoon while generating some light scattered precipitation in
the warm sector over northeast Utah and portions of northwest
Colorado. Precipitation holds off until Friday night in the European model (ecmwf)
solution. Despite timing differences, it appears Friday night will
be the active period with snow levels lowering to mountain bases
late Friday night across the northern and central Colorado
mountains. This is a pretty quick hitting system which will be
moving out of the area late Friday night (gfs) or Saturday morning
(ecmwf) so accumulations not expected to reach advisory criteria
at this point, but light accumulations are likely.

Back to dry weather Saturday afternoon through Sunday. Ec and GFS
in poor agreement Sunday night and Monday. The European model (ecmwf) builds a
ridge over the area and keeps the dry weather going. In contrast,
a shallow short-wave in northwest flow may bring additional
showers to the northern mountains Sunday night and early Monday.

Before the weather shifts highs will continue to run around 5
degrees above normal Thursday and Friday. However, once the cold
front sweeps through Friday night, highs will fall to between 5
and 10 degrees below normal Saturday, moderating a few degrees on
Sunday then close in on near normal levels Monday.

&&

Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 231 am MDT Tue Oct 17 2017

VFR conditions will prevail across the area under mostly clear
skies and light diurnal winds.

&&

Gjt watches/warnings/advisories...
Colorado...none.
Utah...none.
&&

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