Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 141652

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
952 AM MST Wed Feb 14 2018

Issued at 946 AM MST Wed Feb 14 2018

Updated to extend the Dense Fog Advisory for the I-70 Corridor in
the vicinity of Rifle. Spotter reports indicated that the fog was
not lifting, and in fact had become more dense in some areas over
the past hour. In addition, forecast winds were increased over
the higher terrain to be more reflective of the strong winds aloft
indicated in model data. Finally, snow amounts were reduced a bit
over the Grand Mesa for the coming storm as models have
backtracked on precipitation output.

UPDATE Issued at 448 AM MST Wed Feb 14 2018

Local obs and webcams showing some very dense fog in and around
Rifle. Issued dense fog advisory through 11AM to account for


.SHORT TERM...(Today through Thursday)
Issued at 404 AM MST Wed Feb 14 2018

IR Satellite showing plenty of clouds to our south moving into our
area thanks to the 105kt subtropical jet located overhead.
Meanwhile over the Pacific Northwest, an upper level trough can be
seen dropping southeastward which is supported by the 100kt polar
front jet. This trough is what we`re keeping an eye on for the
overnight hours and tomorrow. Before that though, weak impulses of
energy will bring some light precip to the Continental Divide and
higher elevations of western Colorado for much of the day. A few
inches of snow not out of the question thanks to these waves and
favorable orographics.

By this evening, the upper level trough will be just to our west
as precipitation begins to pick up. The left entrance region of
the subtropical jet will start humming along at 140kts, and along
with favorable orographics continuing, plenty of lift will provide
the impetus to get snow going for higher elevations and rain or a
rain/snow mix for the lower elevations. The jet aloft will also
allow some gusty winds to reach the surface with gusts of 30 to 40
mph being common over the mountains. This will create some
hazardous conditions as blowing and drifting snow can be
expected. Models continue to show anywhere from 8 to 16 inches of
snow for the northern and central mountains with a few spots
seeing higher amounts so warnings have been posted for those
areas. As the trough approaches and the sun sets, a rain or
rain/snow mix for the Yampa River Basin will switch to snow as
well as the Steamboat Springs area and anticipate advisory levels
of snow there so advisories issued for those areas. Finally, the
San Juans will see some of the action and this area posed the most
problems as far as amounts were concerned. Went with advisory for
now but they`ll need to be monitored for possible upgrade. The
highest amounts of snow will be east of Pagosa Springs up to Wolf
Creek Pass under favorable southwesterly flow. All highlights will
run through midnight, early Friday morning. Did not include any
southern valleys either but this area will also need to be
watched as temperatures drop overnight possibly bringing snow,
especially to the higher elevations west of Durango.

.LONG TERM...(Thursday night through Tuesday)
Issued at 404 AM MST Wed Feb 14 2018

Snow showers will be hanging around the northern mountains
Thursday night in cold northwest flow. Pattern starts to dry out
over the rest of the forecast area with the dry conditions
reaching the northern mountains on Friday. This is now looking
rather short-lived as a few shots of energy kick southeast across
Idaho and Wyoming reaching our northern mountains Friday night.
This drags a few more snow showers through the area through
Saturday. Looks like piddly amounts at this time compared to
recent storms.

Models are reloading for another stronger storm pushing into the
western U.S. early next week. This looks like a cold and
potentially impressive storm although there are still timing
questions. The GFS is running about 12 hours slower and is more
focused on our northern zones, while the ECMWF drives the system a
bit farther west and south. Strong jet will be rotating around the
based of this long wave trough and position will play a roll in
who gets what and how much they get. Bulk of precip is expected to
fall in the Monday and Tuesday timeframe. So the recent streak of
unsettled weather will continue. Temperatures will remain near
to slight above normal through the period.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 404 AM MST Wed Feb 14 2018

Broken to overcast skies will be the norm today though ceilings,
for the most part, will remain VFR. Cloud heights will vary from
5K to 12K feet at times though KGJT, KRIL, KASE, KEGE, and KTEX
will likely see the lowest ceilings. Some showers will be
possible throughout the day with increasing chances from 21Z
onwards as the next system begins to move in. ILS breakpoints will
likely be met for the mountain TAF sites though they may hover
just at or below these values for much of the day. Conditions will
deteriorate after 00Z as snow moves in dropping ceilings and
visibilities for the overnight hours.



CO...Winter Weather Advisory from 6 PM this evening to midnight MST
     Thursday night for COZ002-005-018-019.

     Winter Storm Warning from 6 PM this evening to midnight MST
     Thursday night for COZ004-009-010-012-013.

     Dense Fog Advisory until noon MST today for COZ007.




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