Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 231700

Area Forecast Discussion
National Weather Service Grand Junction CO
1000 AM MST Mon Jan 23 2017

Issued at 1000 AM MST Mon Jan 23 2017

Main part of storm is organizing over the northern NV/UT this
morning with a bit of a break in the significant snow this
morning. All eyes will be on the cold front nearing the Wasatch
attm which will be swinging through the afternoon and evening. Do
expect snow to increase across NW Colorado the remainder of the
morning ahead of the main system to the west. Instability is
increasing ahead of the storm/front so do expect an isolated
thunderstorm is also possible through mid evening. Have adjusted
some of the snow totals with this mornings reports and the lull in
action this morning. Likely less snow in southern valleys with
temperatures mixing to near or above freezing ahead of the front
so snow ratios will suffer. Snow is likely to continue across the
northern mountains and foothills well into Tuesday and probably
into mid week so will be looking at that as well this afternoon.


.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 right944 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 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1000 AM MST Mon Jan 23 2017

Temporary break in the heavier snow this morning will be filling
in with precipitation through the late morning and afternoon hours
as a cold front approaches and moved through the region. This will
keep snow and lower clouds in the forecast for much the forecast
the next 24 hours with prolonged periods of mvfr or below
conditions. Mountain top winds are 50kt or higher which is aiding
llws and turbulence over the RIDGETOPS. The stronger winds slide
east late this evening with improvement in these areas expected.


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

     Winter Storm Warning until 9 AM MST Tuesday for COZ009-012-014-

     Winter Weather Advisory until noon MST Tuesday for COZ003-004-

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

     Winter Storm Warning until midnight MST tonight for UTZ028.



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