Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 200446
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
946 PM MST Thu Jan 19 2017

.UPDATE...
Issued at 917 PM MST Thu Jan 19 2017

A few stronger bands of snowfall moved through central CO this
evening and will continue to do so through about midnight,
followed be a short break in the action before the next small wave
moves in late tonight. Updated the forecast to include a bit more
snow accumulation at lower elevations over central CO and east-
central UT this evening and overnight.

&&

.SHORT TERM...(Tonight through Friday night)
Issued at 341 PM MST Thu Jan 19 2017

Large scale ascent is increasing under the upper jet moving over
western Colorado this afternoon. Upstream webcams...observations
are verifying that snow is falling under the enhanced radar echos
and cooling cloud tops. The colder air arriving with the jet
shifting eastward overnight is bringing in less stable conditions
which is influencing model QPF output to some extent. Did have to
tweak the forecast some to lower some extreme snow amounts over
the some of the higher peaks but overall the spirit of the
forecast remains unchanged for the passage of the systems tonight
and again for early weekend period. Cold air is now trapped in the
Gunnison Basin and will try and outwit many of the model solutions
with light snow amounts. This atmospheric river event should again
push moist air over the cold dome and produce some decent snow
amounts so have added winter headlines there. Some concern about
the Aspen areas in this pattern but the top of the Elks should do
quite will and the instability should allow some snow to spread
downstream of the main ridgelines. Snow will also persist over the
busy interstate corridor in ski country so added an advisory here
as well. Lastly the low confidence area is usually the far
northern mountains in southwest flow. However behind the passing
waves and eventually northerly flow late in the storm should keep
some decent snow going at elevation over Routt County so upgraded
the watch there. Moderate to heavy snow still expected through
sunrise on Friday and especially Saturday morning over the
southern valleys where again snow rates will be accentuated by mid
level instability and low level forcing. There will unfortunately
be some lulls in the action during the daylight hours on Friday as
the precipitation takes on a strong convective signature. These
showers however will be capable of putting out some decent snow in
a short amount of time.

.LONG TERM...(Saturday through Thursday)
Issued at 341 PM MST Thu Jan 19 2017

Transitory short wave ridging Friday night leads to another strong
push of moisture and lift in a strongly phased trough moving
across the Utah/Colorado line by mid morning Saturday. Another
push of colder air aloft will keep the atmosphere conditionally
unstable and keep snow rates moderate to heavy in many of the
showers through late Saturday. We will also be transitioning from
southwest flow dominating to the westerlies then northwesterlies
by early Sunday as this trough moves into the plains and a more
defined ridge moves over the Great Basin. This ridge gives us a
decent break for much of Sunday before the last in this series of
storms begins to track across the intermountain west and Rockies
early next week. Again moisture and cold air is plentiful with
this storm which should bring another good shot of snow to much of
our region. Not many folks will miss out it will still just be a
matter of defining where the main precipitation shield will be
moving under this closed system. Plenty of details yet to work out
after this event begins to wind down. Cold unstable flow will
continue to bring snow shower chances to the region through mid
week though amounts looks to be much lighter with no direct tap to
the Pacific. Instead any moisture will have to traverse the
amplifying ridge forming over the left coast. This means a split
flow pattern and most likely a more defined drying period over our
CWA to end out the month.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 945 PM MST Thu Jan 19 2017

Aviation forecast remains a challenge this evening as IFR
conditions are in place at all terminals as of 0445 UTC. CIGs
will bounce up and down over IFR/MVFR levels at all sites through
12z as snow moves west to east. VIS will also varry, dropping to
under a mile at times in the heaviest snow but generally not
getting above 3mi in the lighter precipitation. Precipitation type
will remain all snow through 12z at all terminal locations.
Conditions should improve into MVFR by Friday mid-morning in
valley locations however mountains will see snow linger into the
afternoon hours.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until midnight MST Saturday night for
     COZ003-008-014.

     Winter Storm Warning until 5 PM MST Saturday for COZ021>023.

     Winter Storm Warning until 6 AM MST Sunday for COZ009-010-012-
     013.

     Winter Storm Warning until midnight MST Saturday night for
     COZ017-018.

     Winter Storm Warning until 8 PM MST Saturday for COZ019.

     Winter Weather Advisory until 6 AM MST Sunday for COZ004.

UT...Winter Weather Advisory until midnight MST Saturday night for
     UTZ025.

     Winter Storm Warning until 5 PM MST Saturday for UTZ022.

     Winter Weather Advisory until 5 PM MST Saturday for UTZ028.

&&

$$

UPDATE...CC
SHORT TERM...15
LONG TERM...15
AVIATION...MAC


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