Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 200115
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
615 PM MST Tue Feb 19 2019

.UPDATE...
Issued at 615 PM MST Tue Feb 19 2019

Received a late report from the Colorado Avalanche Center San
Juan District regarding heavy convective snow in the Uncomphgre
Gorge. Therefore, extended the Winter Storm Warning from just
north of Ouray to the Monument on Highway 550 north of Red
Mountain Pass through 9 PM MST. Drivers can expect a snowpacked
roadway and significantly reduced visibility at times due to the
convective nature of the snowfall. Winds shift to the west late
this evening while the atmosphere stabilizes, therefore this
hazard is not expected to persist. Elsewhere, the remaining
warnings and advisories were allowed to expire.

Winter Storm Warnings for the San Juan, La Sal and Abajo Mountains
are still slated to go into effect with the next storm to impact
the region late Wednesday afternoon, with Winter Storm Watches for
the lower elevations of southeast Utah and southwest Colorado.

&&

.SHORT TERM...(Tonight through Wednesday night)
Issued at 317 PM MST Tue Feb 19 2019

Latest water vapor imagery shows the midlevel trough progressing
eastward over the region this afternoon, which has focused the
large-scale lift east of the divide. Terrain-driven convection
will persist under the steep midlevel lapse rates through the
evening. Tonight the flow becomes more westerly and the sufficient
moisture stays confined to northern areas therefore snow showers
may linger long enough to produce minor accumulations especially
in the Elkhead and Park ranges. Some locations could clear out
tonight to support efficient radiational cooling and allow lows to
reach the 10 to 20 below zero in the favorable southern valleys.
Tomorrow the polar jet dives southward over the West Coast guiding
the next midlevel low pressure over CA/NV. Terrain-driven
convection will be possible again during the afternoon before the
large-scale lift increases.

.LONG TERM...(Thursday through Tuesday)
Issued at 317 PM MST Tue Feb 19 2019

The modest lift will move into southeast Utah and southwest
Colorado tomorrow evening with increasing southwest flow. As the
low drops over southern Nevada on Thursday the flow backs
slightly favoring the southern facing slopes more. The forcing
becomes maximized early Thursday morning into mid day Friday as
the systems digs over Arizona and New Mexico. Any perturbation
lifting out ahead of the main low could enhance the precipitation
rates during this period. The moisture quality is not that high
relative to the AR event we had last week with PWAT anomalies just
above normal. This system should make up for that with colder
temperatures and the duration of lift over the same areas. The
warmest 700 mb temperatures are Friday morning around -7C in the
San Juans, but most other places do not drop below -10C. Snow
ratios should range from 20:1 in the highest elevations to 12:1 in
the lowest elevations. Breaks in the precipitation and cloud
cover could lead to temperatures above or near freezing during the
day Thursday mainly below about 5 kft. If the precipitation and
cloud shield is more expansive then temperatures could stay
mainly near or below freezing. Otherwise we are expecting mostly
snow even in the lowest valleys.

The midlevel trough passes over the area on Friday afternoon,
which pushes the forcing east of the divide and leaves behind
terrain-driven convection that persists into the evening. The
highest snowfall totals will be across southeast Utah and
southwest Colorado with lesser amounts to the north. The Abajo, La
Sal, San Juan, Elk and West Elk mountains, as well as the Grand
Mesa and Uncompahgre Plateau could range from 12 to 36 inches.
Given the cold air in place the San Juan valley and lower
elevations of southeast Utah could receive amounts of 8 to 16
inches. The the potential for accumulating snow in the remaining
valleys will be Thursday night. The main concerns with this event
will be the snowfall rates over the roughly 36-48 hour period.
Also, how much snow the northern valleys can get after the limited
moisture gets rung out over the southern areas. Higher elevations
along and north of I-70 could be looking at 6-12 inches, and the
valleys around 1-4 inches.

The flow aloft becomes more zonal into next week so temperatures
are able to moderate. Multiple systems dropping out of the
Pacific Northwest look to clip portions of northern Utah and
Colorado. Each will bring rounds of light snow to the northern
and central mountains.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 444 PM MST Tue Feb 19 2019

Instability snow showers are holding in across some of the
mountains this afternoon including KASE and KTEX where IFR and
MVFR conditions are still in place. TAFs could be a bit too
optimistic in improving these conditions by sunset so will be
watching this if it lingers. Otherwise ILS conditions could
persist over many areas along with terrain obscuration. Otherwise
VFR conditions should dominate much of the next 24 hours before
the next storm begins to move in.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Storm Warning from 5 PM Wednesday to 5 PM MST Friday for
     COZ018-019.

  Winter Storm Warning extended until 9 PM MST this evening for
 the Uncompahgre Gorge from Ouray to the Monument in COZ018.

     Winter Storm Watch from Wednesday afternoon through Friday
     afternoon for COZ020>023.

UT...Winter Storm Warning from 5 PM Wednesday to 5 PM MST Friday for
     UTZ028.

     Winter Storm Watch from Wednesday afternoon through Friday
     afternoon for UTZ022-029.

&&

$$

UPDATE...NL
SHORT TERM...KJS
LONG TERM...KJS
AVIATION...TGJT


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