Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 140540

Area Forecast Discussion
National Weather Service Grand Junction CO
1040 PM MST Mon Feb 13 2017

Issued at 919 PM MST Mon Feb 13 2017

Dense fog has formed in the Steamboat Springs area with the
airport reporting visibilities of a quarter mile. Added that area
to the dense fog advisory through tomorrow morning. Will be
keeping an eye on the Hayden and Craig areas for some fog. For
now, some low ceilings showing up but wouldn`t surprised if they
go down too.

Some light snow showers will continue over the San Juans but
significant accumulations look to have ended. With that, the
advisories have been allowed to expire.

UPDATE Issued at 648 PM MST Mon Feb 13 2017

Temperature and dewpoint spread for our southern valleys is close
to zero meaning a saturated atmosphere. Spotter reports have also
indicated dense fog forming down south so went ahead and issued a
dense fog advisory for all Colorado southern zones through
tomorrow morning. Take extra care if driving down south overnight
and give yourself some room. Advisory remains in effect.


.SHORT TERM...(Tonight through Tuesday night)
Issued at 220 PM MST Mon Feb 13 2017

As of Monday afternoon, a cutoff low pressure system continues to
spin over the southwestern CONUS. The center of this low pressure
system will slowly drift east through New Mexico this evening.
Mesoscale analysis reveals a substantial area of 250mb to 850mb
differential divergence, stretching from the Four Corners eastward
through southern Colorado. This feature has been co-located with
colder cloud tops on IR satellite imagery and precipitation at the
surface during the afternoon hours today. This divergence aloft,
along with light easterly upslope flow in the 850-500mb layer,
will help to sustain precipitation in southwest Colorado through
the early evening hours. Subsidence to the north of this band will
allow for continued clearing and drying along and to the north of
Interstate 70 through this evening.

By midnight low pressure will transition eastward, with the best
dynamic support for snow and mid-level moisture content shifting
east into the high plains as well. Light northerly flow and
lingering low level moisture below 650mb will result in the chance
for a few snow showers in the San Juan mountains. Otherwise, a
mostly clear night is expected in the north with mostly cloudy
skies slowly clearing in the south. Some patchy fog is possible in
the northern valleys around sunrise. A dry day is expected area
wide on Tuesday with high temperatures running around 10 degrees
above average.

.LONG TERM...(Wednesday through Monday)
Issued at 220 PM MST Mon Feb 13 2017

A ridge of high pressure will continue to build in from the west
on Wednesday. This high pressure system will last through Thursday
afternoon, with dry weather expected on both days. Once again,
afternoon highs will run around 10 degrees above normal. Mostly
clear nights on Tuesday, Wednesday, and Thursday morning will
allow for some high- altitude valley inversions to set up in
places such as Craig and Gunnison where snow cover lingers.
Overnight low temperatures have been lowered in this forecast
package as a result, and run at or slightly below the lowest
available MAV guidance.

By Thursday afternoon, clouds will be on the increase over eastern
Utah and Western Colorado as the overall weather pattern shifts
from ridging to troughing in the western CONUS. A series of weak storm
systems will pass through the Rockies from Friday through early
next week as a result of this change. The first system to affect
the central Rockies will arrive on the west coast on Thursday,
with a weakening shortwave trough quickly scooting through the
central Rockies by early Friday morning. This system will spread a
few showers across the northern half of eastern Utah and western
Colorado before midnight on Friday. With plenty of warm air in
place, rain is expected in the valleys with light to moderate
snowfall from the central mountains northward. Overall
precipitation totals are expected to be light with this fast-
moving event, with total liquid equivalent around one to two
tenths of an inch even in the northern Park range before snow
showers taper off on Saturday afternoon.

Following this first event, forecast guidance diverges rather
significantly for the remainder of the weekend. The GFS shows a
lengthy break in precipitation from Saturday afternoon through
Sunday morning, while the ECMWF keeps light rain and snow over
much of the Four Corners region during this timeframe. Both models
do indicate a more significant trough diving southward through the
southwestern CONUS from Saturday into Sunday with warm southerly
flow firmly in place. Confidence is high on unsettled weather and
mild temperatures this weekend. However, confidence in details
regarding precipitation timing from Saturday evening through
Sunday night is very low...for now.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1037 PM MST Mon Feb 13 2017

Clouds will continue to lift overnight though plenty of moisture
will allow fog to form, some of it dense, bringing some low clouds
to TAF sites. For now, Telluride, Durango, and Steamboat Springs are
reporting VLIFR conditions and expect these conditions to persist
through the overnight. Other areas of concern will be Hayden and
Craig up north and Cortez down south. Most fog and low ceilings
will burn off between 16 to 17Z tomorrow. After that, plenty of
sun returns with no aviation concerns noted.


CO...Dense Fog Advisory until 9 AM MST Tuesday for COZ005-021>023.



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