Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 180547

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1047 PM MST Sat Feb 17 2018

.SHORT TERM...(Tonight through Sunday night)
Issued at 330 PM MST Sat Feb 17 2018

Afternoon GOES satellite imagery reveals clear skies across all of
eastern Utah and western Colorado. Some high clouds will drift
southward over northern Utah and northern Colorado this evening
and overnight. As our next storm system approaches from the
Pacific Northwest, a 120 knot jet will dive southward on Sunday.
As temperatures warm and we mix higher during the day on Sunday,
stronger winds are expected across the entire forecast area. Areas
along and to the north of the Tavaputs in northwest Colorado have
been placed under a Wind Advisory given the likelihood for some
gusts in excess of 45 mph during the afternoon hours. Elsewhere
across the western slope, the major weather story on Sunday will
be the mild temperatures. Have nudged highs upward across the
board, with several locations likely approaching or exceeding the
60 degree mark including Canyonlands, Delta, and Cortez.
Increasing cloud cover will likely determine where everyone ends
up on Sunday, but high temperatures should range from 10 to 15
degrees above average. As we saturate the atmosphere from top down
on Sunday evening, light snow will break out in the higher
elevations in the early evening. All current Watch, Warning and
Advisory products begin at 5pm on Sunday evening. Given the mild
temperatures, snow should be limited to the higher terrain to
start this event on Sunday evening with a few isolated showers in
the valleys. Models have backed off somewhat on start times...and
many locations may remain dry until after midnight.

.LONG TERM...(Monday through Saturday)
Issued at 330 PM MST Sat Feb 17 2018

Precipitation coverage will steadily increase through the early
morning hours on Monday. Attention will focus on a frontal
boundary which will track from northwest to southeast through the
day. The best lift and saturation (and thus, chances for heavy
snowfall) will be associated with this frontal passage, which is
easily tracked in 700mb temperature fields. The front will pass
through the eastern Uintas shortly after sunrise, and will stretch
across northwest Colorado, the Tavaputs, and down through Green
River Utah by noon. The progression of the front slows notably
through the day, finally reaching the San Juan mountains by
sunset. From there, this boundary diffuses and stalls over the
Continental Divide. This will lead to an extended period of
moderate snowfall across all mountain ranges on Monday afternoon
and evening. The larger-scale trough is also a bit more sluggish
in this run, keeping a good amount of moisture and lift present in
the mountains through Tuesday morning. As a result, storm total
QPF forecasts have increased slightly in this forecast package.
Confidence has increased enough to support upgrades to Winter
Storm Warnings for the San Juan mountains, as well as the West
Elks and the Grand Mesa. Advisories have been issued for much of
northern Colorado, including the lower elevation regions along the
US 40 corridor which will remain colder and should see a decent
shot of snowfall during the early morning period on Monday. For
specific snowfall totals and timing, see the latest WSWGJT

This storm will wind down gradually through the day on Tuesday as
the slow-moving trough lifts north and eastward. That being said,
all forecast guidance shows lingering moist upslope flow through
much of the day, including several hints at some low-topped
convective banded snowfall. Locations that do see these bands
could pick up several additional inches through the day on Tuesday
even after the bulk of the storm passes, especially given
cold temperatures in the -15 C range at 700mb on Tuesday.

By Wednesday morning, things should finally clear out across the
board with dry westerly flow taking over for the day. Forecast
guidance diverges significantly after Wednesday. The GFS implies
the chance for a moist, southwesterly flow snow event from
Thursday night through Friday. The ECMWF keeps the trough
responsible for that southwesterly flow much farther west, and
suggests a mostly dry forecast from Wednesday until Saturday.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1046 PM MST Sat Feb 17 2018

A few high clouds will move across the area but won`t pose any
threats to aircraft operations. Some breezy winds are expected
tomorrow afternoon with gusts of 20 to 30 mph being common.
Mountain TAF sites may see a few gusts higher than that.


CO...Winter Weather Advisory from 5 PM Sunday to 8 AM MST Tuesday for

     Winter Storm Warning from 5 PM Sunday to 8 AM MST Tuesday for

     Winter Storm Watch from Sunday afternoon through Tuesday morning
     for COZ004-010-013.

     Wind Advisory from 11 AM to 5 PM MST Sunday for COZ001>003.

UT...Winter Weather Advisory from 5 PM Sunday to 8 AM MST Tuesday for



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