Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 211123 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Grand Junction CO
423 AM MST Sat Jan 21 2017

.SHORT TERM...(Today through Sunday)
Issued at 233 AM MST Sat Jan 21 2017

As predicted by previous forecasters, snow increased in coverage
and intensity over southeast Utah and southwest Colorado early
this morning. Models indicated broad ascent responsible for snow
was provided by combined jet divergence, a passing 7H trough,
steep lapse rates and favorable south to southwest orographic
lift. Models further suggest that these favorable conditions will
perist through sunrise assuring additional snowfall across the
Four Corners region along with the San Juan, Abajo and La Sal
mountains. Meanwhile, the central and northern mountains remained
in a bit of a lull overnight.

Expect this will change during the afternoon when flow shifts to
the northwest and lapse rates steepen further in response to
cooling aloft. Instability, lingering moisture and orographic lift
will keep snow going in the mountains tonight. Consequently, given
all that was discussed previously will continue current
highlights, though will cancel the WW.Y for CO zone 8 where snow
hasn`t fallen since yesterday afternoon.

The third in a series of storms to move through the the area
stretching back to Thursday will begin to impact the area as early
as Sunday afternoon. Eastern Utah and the San Juan mountains
appeared favored during the early phase of the storm and PoP
fields have been adjusted to reflect this potential.

.LONG TERM...(Sunday night through Friday)
Issued at 233 AM MST Sat Jan 21 2017

The extended forecast will begin with the last storm in this trio
beginning to move through 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. During the latter part of the week
amplified ridging will dominate the West Coast with a deep trough
blocking downstream over the eastern states.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1000 PM MST Fri Jan 20 2017

As a storm spreads across the area expect ceilings to fall
steadily and snowfall to become more widespread. KDRO will remain
IFR through 12z then improve to MVFR and ILS breakpoints by 18z.
Elsewhere VFR conditions will transition to MVFR and scattered
IFR before sunrise, with mountains obscured. VIS will also slowly
decline as light to moderate snow overspreads most all valley
terminal locations. Expect MVFR conditions to continue through the
mid morning hours on Saturday with gradual improvement after 18z.
Winds will remain generally out of the west-southwest through the



CO...Winter Weather Advisory until midnight MST tonight for COZ003-

     Winter Weather Advisory until 2 PM MST this afternoon for COZ020.

     Winter Storm Warning until 5 PM MST this afternoon for

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

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

     Winter Weather Advisory until 6 AM MST Sunday for COZ004.

UT...Winter Weather Advisory until midnight MST tonight for UTZ025.

     Winter Weather Advisory until 2 PM MST this afternoon for

     Winter Storm Warning until 5 PM MST this afternoon for UTZ022-

     Winter Weather Advisory until 5 PM MST this afternoon for UTZ028.



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