Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 172345
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
445 PM MST Sun Feb 17 2019

.SHORT TERM...(Tonight through Monday night)
Issued at 1237 PM MST Sun Feb 17 2019

Convective cloud cover has developed over much of southwest
Colorado and southeast Utah this afternoon ahead of our next storm
system. GOES satellite imagery depicts the first piece of this
system well - a trough with cooler cloud tops draped from
northwest to southeast over Utah. The main event with this system
still remains well to the west, currently located over central
California and moving to the east into the Great Basin. While a
few isolated snow showers may fall in the higher terrain of the
San Juans this afternoon, any precipitation will remain light and
accumulations are not expected until after 6pm.

Forecast guidance remains on track throughout the short term and
forecast confidence is high. A long-duration, light to moderate
snowfall rate event is in the works for central and southern
Colorado and Utah. While first wave of this system is not
expected to produce heavy snowfall tonight into Monday morning,
the story changes a bit on Monday afternoon. As the second, main
trough spirals into the Four Corners region, diffluent flow aloft
will support a period of better snowfall rates, arriving around
3pm Monday in southwest Colorado. Unlike some of our recent
storms, this event lacks a strong Pacific moisture
connection...however a period of favorable dynamics aloft combined
with upslope flow will overcome the lackluster moisture feed.
Additionally, cold temperatures in place throughout the entire
Four Corners region will support an all-snow event in all
locations. Snow-to-liquid ratios are expected to be nearly double
what was seen in the last event, somewhere in the 15:1 range or
higher, especially above 8000 feet. With all that being said, no
changes were made to expected snowfall accumulations or current
headlines this afternoon. A foot or more of snow is expected in
the San Juans, with 6-12 inches likely in the southern valleys
form Durango to Pagosa Springs. The La Sal and Abajo ranges in
southeast Utah should see 10 or more inches as well - especially
given the comparatively lighter southwest flow aloft that usually
results in better totals in these ranges. Farther north, there is
slightly less confidence in the snowfall forecast. The Grand Mesa,
Elk, Sawatch and Gore ranges will be downrange of the San Juans
for much of the event with regard to wind and moisture flow. The
San Juans will likely ring out much of the available liquid, and
keep snow totals around 6 inches or less on average in these
central mountain zones. Therefore, highlights were not issued for
this event here.

By Monday night into Tuesday morning, the best support for lift
and higher snow rates moves east of the Continental Divide. Snow
will begin to taper off in intensity after midnight, however light
snow accumulations will still be seen throughout western Colorado.

.LONG TERM...(Tuesday through Sunday)
Issued at 1237 PM MST Sun Feb 17 2019

The ongoing winter storm will slowly move east of the Rockies on
Tuesday. Light upslope westerly flow will result in continued snow
showers throughout the day, and with cold air in place (700mb
temps in the -14 to -16 range), excellent dendritic growth will
likely result in additional accumulations. This will be especially
true where cloud cover remains thicker and surfaces can avoid
heating from the mid-February sun angle. However by 6pm, the
atmospheric column really dries out from top to bottom and snow
showers are expected to diminish through the evening.

The active weather pattern that has characterized this winter
season will continue through the end of the long term. Another
winter storm will move in from Wednesday night through Friday.
Some differences in forecast guidance remain with this event, with
the GFS favoring a more cut-off and farther south low pressure
system on Thursday and Friday. The ECMWF is farther north
initially, but eventually comes into line with the GFS by early
Friday morning. Temperatures look to remain quite cold with this
system, and another healthy dump of snow is becoming more likely
for the mountains. The San Juans appear favored once again with
this system, and current guidance averages would likely support
another foot of snow here.

By Friday evening, this system winds down and heads east. An early
look at the weekend reveals fairly dry weather and westerly flow.
However, by Sunday night faster westerly flow in the Pacific
Northwest will dip southward. Moisture associated with this
faster flow currently appears too far north to impact the Uinta
and Park ranges. We will see if this system trends southward with
time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 445 PM MST Sun Feb 17 2019

A disturbance in southwest snow was bringing scattered snow
showers to areas of southeast Utah with more scattered activity
over southwest and portions of central Colorado. This disturbance
brings a good chance for brief MVFR conditions at KCNY, KGJT and
KMTJ this evening. KTEX and KDRO have better chances for snow
showers with similar conditions. After a lull later tonight, snow
is expected to become widespread over southwest Colorado with MVFR
and periods of IFR conditions likely at KDRO and KTEX. Elsewhere,
KRIL, KEGE and KASE will experience prolonged periods with CIGS
below ILS breakpoints with low end chances for light snow.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Storm Warning until 6 PM MST Tuesday for COZ018-019.

     Winter Weather Advisory until 6 PM MST Tuesday for COZ017-020-
     021.

     Winter Storm Warning until 6 PM MST Tuesday for COZ022-023.

UT...Winter Storm Warning until 6 PM MST Tuesday for UTZ028.

&&

$$

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


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