Area Forecast Discussion
Issued by NWS Grand Junction, CO

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251
FXUS65 KGJT 221853
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1153 AM MST Sun Jan 22 2017

.UPDATE...
Issued at 1153 AM MST Sun Jan 22 2017

Have upgraded the Winter Storm Watches for the southern valleys to
Winter Storm Warnings and upgraded the Watches for the northern
and central Colorado mountains to Winter Weather Advisories.
Showers will begin this evening and become numerous to widespread
on Monday. Periods of rain mixed with snow will fall throughout
the day tomorrow but this is not expected to significantly impact
overall accumulations for the southern valleys. An exception is
near the Four Corners, where the Warning was hoisted for
elevations above 5500` due to the abundance of warm air advection.
Impacts to travel will begin tonight and continue through at least
midweek with this storm.

&&

.SHORT TERM...(Today through Monday)
Issued at 442 AM MST Sun Jan 22 2017

A weak short-wave trough working eastward across western Colorado
continued to bring light snow to portions of the northern and
central mountains early this morning according to radar and
surface observations. This activity will linger along the Divide
this morning before largely diminishing by noon. Any additional
accumulations will be light and localized. Meanwhile, to the west
most areas will experience some sunshine ahead of the next system
which will impact the area through Tuesday.

Clouds will be increasing ahead the next surge of Pacific moisture
delivered on the nose of a 160+ kt jet moving through the base of
a low centered off the coast of the Pacific Northwest from late
morning onward. This system will force the short-lived ridge east
of the Continental Divide during the afternoon. Large scale ascent
provided by overrunning and increasing orographic lift provided by
a freshening southwest flow will cause precipitation to develop
over eastern Utah and the southern two-thirds of western Colorado.
Mild temperatures at lower elevations favors rain or a rain/snow
mix this afternoon.

Moisture deepens during the night raising 7h specific humidity
from a modest 2.5 g/kg to 3.5 g/kg with greatest levels across
the south. Overrunning and orographic lift remain the primary
components for ascent, but increased moisture favors more
widespread precipitation with snow becoming heavy at times.
Meanwhile, the jet will shift over the area bringing an increase
in winds, especially across the higher terrain which will result
in areas of blowing snow. Continued warm air advection (WAA) will
prevent a shift to frozen precipitation in the lower elevations of
southeast Utah.

The overall pattern Monday will shift from the warm advection
overrunning early in the day. This will be followed by cold
advection through all levels. An embedded shortwave trough will
move overhead about midday Monday, starting the transition to the
next phase of the storm, then a somewhat weak cold front is
projected to slowly drag through the area during the afternoon.
Cold advection behind the front should kick in about 3 pm Monday
afternoon behind the front. 700 mb temps in the GFS drop from
around -4 to -6 C in the Morning to -8 to -10 at sunset.
Concurrently, deep moisture continues to sweep across the area
generating continued mountain snow. However, ahead of the front
temperatures will be quite mild and valleys will see either rain
or a mix. For this reason, left watch in place for the lower
elevations of southwest Colorado where rain or mixed precipitation
could cut into snowfall accumulations. This won`t be a problem for
the southern and central mountains where snow will continue to
pile up and, for this reason, upgraded watches to warnings. Snow
accumulations across the north less clear at this time and latest
model output has these areas between warning and advisory
criteria and for this reason, let watches ride for now.

.LONG TERM...(Monday night through Saturday)
Issued at 442 AM MST Sun Jan 22 2017

The cold front should clear the forecast area to the east Monday
night, then another trough will dive into the northern Great Basin
from the north Tuesday. A cold and snowy pattern with 700 mb temps
below -15 Thru Wednesday.

The overall pattern from Wednesday night through Saturday will
include a longwave trough over the midwest and eastern U.S. and a
strong ridge over the west coast and the Rockies for a period of
more quiescent conditions.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1130 AM MST Sun Jan 22 2017

Low clouds and patchy fog will remain trapped within the Uinta
Basin this afternoon, resulting in IFR/MVFR CIGS and VSBYS.
Elsewhere, VFR conditions will stick around through 23Z this
afternoon, before CIGS start dropping again as the next round of
rain and snow moves in to the area. Expect a rapid drop in CIGS
overnight at all sites with rain and snow showers developing.
Mountains will become obscured in cloud cover and showers. Expect
ILS cigs after 00Z/Mon at all sites and a return of MVFR and IFR
conds. This system will impact through region through Tuesday.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Storm Warning from 6 PM this evening to 9 AM MST Tuesday
     for COZ009-012-017>019-021>023.

     Winter Weather Advisory from 6 PM this evening to noon MST
     Tuesday for COZ003-004-010-013.

UT...Winter Weather Advisory from 3 PM this afternoon to midnight MST
     Monday night for UTZ023-025.

     Winter Storm Warning from 3 PM this afternoon to midnight MST
     Monday night for UTZ028.

&&

$$

UPDATE...MMS
SHORT TERM...NL/CC
LONG TERM...TGJT
AVIATION...JDC



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