Area Forecast Discussion
Issued by NWS Grand Junction, CO

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436
FXUS65 KGJT 202245
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
345 PM MST Fri Jan 20 2017

.SHORT TERM...(Tonight through Saturday night)
Issued at 345 PM MST Fri Jan 20 2017

Radar mosaic and satellite imagery showing an impressive amount of
precipitation upstream of the 4 Corners across the Desert
Southwest into Southern California. PWAT in this region is 150 to
200 of normal and a signal this is another good AR event. Snotels
in the southeast Utah mountains continue to climb well so decided
to hoist them to a warning. Convection definitely helping boost
snow rates and also forming a continuous band of snow downstream
of the la sals that extends across the end of the Uncompahgre
to the western end of the Grand Valley. This is also evident over
the portions of the Central mountains. The current lull in
activity will be ending overnight as large scale ascent increases
over the southwest and moisture advection increases significantly
on the 300k theta surface. Again a complex situation for the
southwest CWA with low level warm advection moving in with the
moisture. This will keep the snow to liquid ratios very low and
there may be areas near the 4 Corners that stay all rain as this
pseudo warm front lifts to the north through the early morning
hours. Models continue to paint this region into the foothills of
the San Juans with high QPF and warnings should be on track. Did
introduce additional advisories for the remaining valley locations
in the SW CWA. The southern mountains that do especially well in
southwest flow should also do well overnight...only held back from
some really impressive amounts by the high liquid content. Much of
the central and northern mountains will stay relatively quiet
overnight with the focus to the south under the better QG forcing.
This region will do better into the day Saturday as the main
trough passes through and instability boosts snow rates. Even on
the back side the cold advective north flow should keep some
decent snow going over the Park Range down to the upper Elk
Range. Increasing heights and decreasing stability will be eating
away at the snow showers through Saturday night and we much of
this storm will be over by sunrise on Sunday.

.LONG TERM...(Sunday through Friday)
Issued at 345 PM MST Fri Jan 20 2017

The extended forecast will be dominated by the last storm of this
trio to move through beginning as early as Sunday evening in the
west. There will be a decent break on Sunday as a more substantial
ridge moves over the Rockies. Ensembles indicate another strong
tap to the deep Pacific moisture source and anomalously high PWAT
is once again directed across the 4 Corners as the main system
moves into Great Basin. Strong ascent from the upper jet and
approaching system will combine with the moisture and increasing
instability will likely produce decent snow banding in the Monday
into Tuesday portion of this storm. Cold advection and strong
orographics take over Tuesday night into Wednesday night as the
back side of this storm slowly works through. This will likely be
another really good storm for the area. Beyond this amplified
ridging will be dominating the western coast with a deep trough
blocking downstream over the eastern states.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1047 AM MST Fri Jan 20 2017

Scattered light snow showers will continue for many of the
terminals this afternoon with more isolated coverage north of
I-70. Another surge of moisture will infiltrate the area after
06Z, resulting in increased coverage and intensity of showers
through Saturday. The southern mountains will be favored in the
southwesterly storm track. The persistence of showers, plus the
development of fog in valleys overnight, will result in periods
of reduced VIS/CIGS for nearly all TAF sites.

Overall forecast confidence is moderate.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until midnight MST Saturday night for
     COZ003-008-014.

     Winter Weather Advisory until 2 PM MST Saturday for COZ020.

     Winter Storm Warning until 5 PM MST Saturday for COZ021>023.

     Winter Storm Warning until 6 AM MST Sunday for COZ009-010-012-
     013.

     Winter Storm Warning until 8 PM MST Saturday for COZ017>019.

     Winter Weather Advisory until 6 AM MST Sunday for COZ004.

UT...Winter Weather Advisory until midnight MST Saturday night for
     UTZ025.

     Winter Weather Advisory until 2 PM MST Saturday for UTZ022-027-
     029.

     Winter Storm Warning until 5 PM MST Saturday for UTZ022-028.

     Winter Weather Advisory until 5 PM MST Saturday for UTZ028.

&&

$$

SHORT TERM...15
LONG TERM...15
AVIATION...MMS



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