Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 152303
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
403 PM MST Sun Jan 15 2017

.SHORT TERM...(Tonight through Monday night)
Issued at 403 PM MST Sun Jan 15 2017

The system responsible for clouds and showers over the past
couple of days was centered over the El Paso, TX area early this
afternoon. Though well south of the forecast area, mid-level
moisture and clouds continued to surge northward across the region
with light showers observed under a light band arcing from KDWX
to KCEZ . However, at the 7H level flow was light and from the
north. Rising temperatures have helped lift fog from valley
bottoms, though a persistent low stratus has caused fog to move up
the slopes of surrounding higher terrain, most notably around KGUC
and KSBS. Have done my best to properly represent the stratus
layer in the evening grids.

Persistent low level moisture indicated to be on the order of 3.5
to 4.0 g/kg at the 7H level favors formation and expansion of fog
across region during the night. Went ahead and added mention of
fog to all areas which have seen it over the past couple of
nights. Areas where fog was most dense had experienced some form
of precipitation late in the afternoon. Potential for a repeat
occurrence of late afternoon showers appears unlikely at this
point, so am not inclined to issue Dense Fog Advisories with this
package, but encourage the evening shift to reassess.

The low moves from El Paso to the Panhandle region overnight while
a second, shallow low pressure system dips into the Baja region
keeping the forecast area beneath the mean trough. Diffluent flow
and lingering moisture is expected to continue to bring light snow
to the San Juans and West Elk mountains tonight, though
accumulations will be light, generally ranging from 1 to 3 inches.
Adjacent lower elevations including Cortez, Durango have a chance
for rain showers this evening, transitioning to snow later
tonight. Pagosa Springs should transition earlier. In any event,
any snow accumulations at lower elevations will be light and
localized. Northeast Utah and northwest Colorado will remain
quiet tonight.

The low over the Panhandle region moves to the central Plains
tonight while the Baja low moves to the northwest Mexico mainland.
As a result, the mean trough remains aligned from southwest to
northeast from southeast Arizona to the central Plains. Weak lift
below the trough will keep chances for snow over the San Juans and
central mountains and adjacent valleys going into Monday night.
Moisture will slowly decrease during this period, so any
additional snowfall will continue to be light. Drying will be more
pronounced north of this area so looking for continued dry weather
elsewhere.

Temperatures were running cooler in all but the Uncompahgre and
Paradox valleys. Expect this will lead to colder overnight lows
for most areas. Monday`s afternoon highs will also be a bit cooler
due weak cold advection which should carry over into Monday night.

.LONG TERM...(Tuesday through Sunday)
Issued at 403 PM MST Sun Jan 15 2017

A deepening trough off the West Coast finally gets the mean trough
axis to shift east of the forecast area Tuesday. A positively
tilted ridge shifts over the area easing drier air already over
the north into south and bringing an end to shower chances. This
heralds a period of quiet weather which is expected to last into
Thursday morning. Fog is likely again Tuesday night, though drying
should limit its density.

Confidence in onset of showers not great on Thursday as ECMWF and
GFS a bit out of step. 12Z/EC was a bit shallower and more
progressive with the West Coast trough thereby generating the
first chances for precipitation across eastern Utah in the
morning, then portions of western Colorado during the afternoon.
GFS ensembles showing less than confidence inspiring spread and
CMC similar to EC solution. Therefore...am inclined to bring
snowfall chances for the mountains earlier than indicated by GFS.

Regardless of timing issues, models all indicated the trough will
bring rain and snow to the area through Friday. Another trough
ejecting from a closed low off the coast of British Columbia is
set to generate more unsettled conditions this weekend. Given
model spread, hesitate to mention snowfall amounts, snow levels
and other details at this point.

Temperatures are forecast to hover near or a little above normal
through the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1002 AM MST Sun Jan 15 2017

Primary aviation challenges this early afternoon will be how to
handle the low cloud decks across the region. Low stratus firmly
in place with MVFR to LIFR conditions in ASE, EGE and MTJ. Short-
term soundings do not show much hope for this cloud deck breaking
in any of these locations through the afternoon or Sunday evening.
Forecast will be status-quo with current ceilings remaining mostly
unchanged through 0z-6z tonight. In fact, with relatively little
flow at all to speak of, these low CIGs may last through the night
into Monday before flow finally turns around to the northwest and
clouds break. No wind issues to speak of for the next 6 hours, and
precip should not be an issue anywhere other than perhaps TEX as
rain/snow will stay mostly east of the divide today.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.

&&

$$

SHORT TERM...NL
LONG TERM...NL
AVIATION...MAC



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