Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 220641
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1141 PM MST Tue Feb 21 2017

.UPDATE...
Issued at 900 PM MST Tue Feb 21 2017

Have updated the Winter Weather Advisory for the Park and Elkhead
Mountains to begin at 6:00 AM MST Wednesday morning. The rational
for this update is a cold front currently located over western
Wyoming is expected to dive south overnight tonight bringing
sufficient lift and moisture to the area to produce rapid snow
accumulations. Both the 0000Z Nam12 and GFS20 show a quick 5
inches of accumulation for the Park and Elkhead mountains by
sunrise.

&&

.SHORT TERM...(Tonight through Wednesday night)
Issued at 257 PM MST Tue Feb 21 2017

A tricky forecast coming up thanks to the ongoing warm
temperatures, an approaching boundary, and then stronger cold
front. First though, high clouds are on the increase this
afternoon thanks to the jet stream that is oriented from the
southwest to northeast causing some cirrus to form. Southwest flow
also continues allowing warm temperatures to advect in with many
areas reporting well above normal temperatures. Some gusty winds
of 20 to 30 mph are also being felt across the region in response
to the jet and a tightening pressure gradient.

As far as the big picture is concerned, an upper level trough
currently situated along the west cost will slowly dig south and
deepen some tonight and into tomorrow. Ahead of this trough, a
weak boundary has set up and is also dropping south. For the
remainder of today and tonight, variable cloudiness is expected
with a few snow showers possible for the highest elevations of the
eastern Uintah and northern mountains as the boundary just makes
the Colorado/Wyoming border after midnight.

This is where things get tricky. Latest guidance now shows the
boundary stalling out a little bit south of the border with
precipitation focused generally north of the I-70 corridor. The
eastern Uintas still look good for accumulating snow so the Winter
Storm Watch has been upgraded to an advisory through Thursday
night. As the boundary stalls, showery activity will continue north
of I-70 Wednesday morning but at this time, it doesn`t look `too
impressive`. However, it is the start of a long stretch of
unsettled weather and with that in mind, upgraded the watches to
advisories for the northern mountains, Flat Tops, and Book Cliffs
as the higher elevations look favored for snowfall through Friday
morning. We will need to keep an eye on the boundary and adjust
timing as necessary since models do seem to be having a bit of
trouble.

The trough that is just off the west coast will be just over
Nevada Wednesday afternoon and this trough will support a cold
front at the surface. The front looks to push through late
Wednesday night into Thursday morning. The heaviest precipitation
will accompany frontal passage and again, areas north of I-70 look
to be favored. Did have some concern about the central mountains
possibly needing an advisory and though they`ll see some
accumulating snow, didn`t look widespread or prolonged enough to
warrant any advisories. Something else later shifts will need to
keep an eye on.

.LONG TERM...(Thursday through Tuesday)
Issued at 257 PM MST Tue Feb 21 2017

By daybreak Thursday, the cold front will be moving across
western Colorado causing a noticeable drop in temperatures with
some snow and rainshowers possible for much of the area. By noon,
the front will have moved through while a closed low forms over
the plains. Showery activity still remains possible for most areas
though as the upper level trough moves through. As that occurs,
cold air aloft will cause an uptick in instability allowing snow
showers, some heavy, to continue through Friday afternoon for the
northern and central mountains.

By late Friday, precipitation will end as another low pressure
drops down the west coast almost exactly like this last system
did. This low will eject a short wave, just like the last one did,
and bring some light precip to the eastern Uintahs and northern
and central mountains Saturday evening through noon Sunday.

By Sunday evening, the low pressure will have tapped into Pacific
moisture and widespread showers will form ahead of the system.
This system will influence our weather through Wednesday and
beyond. Winter isn`t done with us yet!

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1150 PM MST Tue Feb 21 2017

Southwesterly winds are expected to increase overnight as a storm
system approaches from the northwest. Otherwise VFR conditions are
anticipated to prevail through the forecast period.

Forecast confidence is moderate to high.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory from 6 AM Wednesday to 9 AM MST Friday
     for COZ004.

     Winter Weather Advisory from 6 PM Wednesday to 9 AM MST Friday
     for COZ003-013.

UT...Winter Weather Advisory from 6 AM Wednesday to 6 PM MST Thursday
     for UTZ023.

&&

$$

UPDATE...Larry
SHORT TERM...TGR
LONG TERM...TGR
AVIATION...Larry



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