Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 231207
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
507 AM MST Mon Jan 23 2017

.SHORT TERM...(Today and Tonight)
Issued at 451 AM MST Mon Jan 23 2017

Moisture arrived right on time with snow breaking out over eastern
Utah and much of southwest Colorado from late afternoon into the
evening. Isentropic upglide seemed the dominant lifting mechanism
across southwest Colorado where moderate snowfall began to fall
beginning right around 00Z from KBDG to KPSO. KGUC began receiving
snow around the same time and an area spotter recorded 2 inches
of new snow by 05Z. Meanwhile, the cold pool over the eastern
Uinta Basin of northeast Utah seemed to be largely responsible for
persistent snow there, though divergent left exit region of SW to
NE directed 160 kt jet also playing a role. Meanwhile, winds were
picking up over the mountains according to KGJX VWP which
indicated 35 to 40 kt sustained winds, while sensors above 10000
feet in the San Juan mountains were reporting gusts from 50 to 65
mph. Meanwhile, snow was slow to develop across northwest Colorado
and the central valleys overnight.

Snow over southwest Colorado has waned a bit during the latter
part of the night but expect it will pick up again this morning as
the jet sags southward in response to a shortwave ejected from a
broad low over the west. Warmer air flowing northeastward ahead
of the front associated with this storm will drive temperatures
above normal and will likely result in a change in precipitation
state to rain or a rain/snow mix across the Four Corners area.
This adds an element of uncertainty to expected accumulations from
KBDG to KPSO. Meanwhile, in the mountains, deep Pacific moisture
driven by strong southwest winds is all that is required to
provide lift for snowfall during the day. Appears snowfall will
soon break out across northwest Colorado as KGJX radar showing a
band of snow moving in that direction.

During the latter part of the day, the cold front with this storm
will move southeastward across northeast Utah, then across the
remainder of the forecast area during the night. The front,
combined with diurnal cooling will cause a shift in precipitation
phase back to snow. The northwest flow behind the front will
favor snow accumulations across northwest Colorado during the
latter part of the night. Until then, expect snow will continue
for most areas through midnight with some decrease in intensity
and coverage during the latter part of the night.

Highlights appeared to be in order for the most part. I did
upgrade the advisory for the Gunnison Basin to a warning based on
heavier than expected snowfall last evening and anticipation that
the cold pool over the area will continue to bring more snow than
models have indicated. Had some concerns about the advisory for
northwest Colorado as snow was slow to materialize. However, snow
band moving into the area has allayed concerns.

.LONG TERM...(Tuesday through Sunday)
Issued at 451 AM MST Mon Jan 23 2017

Models were in fairly good agreement taking the storm center
eastward to a position over Nebraska before closing off later in
the day Tuesday. The storm system will continue to move slowly
east through the remainder of the week. As result...expect snow
intensity will decrease and become less widespread in the
wraparound moisture with best focus over the northern mountains
and northern San Juan mountains Tuesday and Tuesday night. A
relatively weak east/west oriented shortwave will slowly drop
south across the Great Basin Wednesday into early Friday. This
system will bring an unsettled period of snow showers across
mainly mountain locations with light accumulations expected.
Confidence is lower with this storm system. Temperatures are
expected to remain below normal through the work week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 507 AM MST Mon Jan 23 2017

Prolonged periods of precipitation at area TAF sites will result
in persistent MVFR VSBY and CIGS below ILS breakpoints over the
next 24 hours. Stretches of IFR/LIFR conditions in moderate to
heavy snowfall can be expected.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory until 9 AM MST Tuesday for COZ001-002-
     005-020.

     Winter Storm Warning until 9 AM MST Tuesday for COZ009-012-014-
     017>019-021>023.

     Winter Weather Advisory until noon MST Tuesday for COZ003-004-
     010-013.

UT...Winter Weather Advisory until midnight MST tonight for
     UTZ022>025-029.

     Winter Storm Warning until midnight MST tonight for UTZ028.

&&

$$

SHORT TERM...NL
LONG TERM...TGJT
AVIATION...NL



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