Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 231826
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1226 PM MDT Sat Sep 23 2017

.UPDATE...
Issued at 1219 PM MDT Sat Sep 23 2017

Reports from elevations above 10,000 feet on the Grand Mesa
indicate at least 3 inches of snow has already fallen as of noon
today. Given radar trends and additional precipitation forecasted
by short-term guidance, have issued the first Winter Weather
Advisories for this season in the Flat Tops, Grand Mesa, and West
Elk ranges. All advisories are for areas above 10,000 feet and
are in effect until midnight tonight.

&&

.SHORT TERM...(Today through Sunday)
Issued at 351 AM MDT Sat Sep 23 2017

A cold front beneath a strong jet stream will pass through the
area today and tonight. Behind the front much cooler air will move
in Sunday. A closed 500 mb low will travel from eastern NV to to
NE Utah, pushing the a surface front east of the area and drawing
a dry slot over in from the southwest. It still looks like snow
levels will lower to between 11k and 12k feet, with a few inches
of snow accumulation above treeline.

.LONG TERM...(Sunday through Friday)
Issued at 222 PM MDT Fri Sep 22 2017

Afternoon guidance is in good agreement showing the upper-level
low shifting northeastward through the Uintas and into southern
Wyoming on Sunday afternoon. Dry air will filter in south of
Interstate 70, however one more day of unsettled weather is
expected to the north before the low exits the Rockies. Sunday
will feature the coolest weather during the forecast period as the
upper low and trough axis pass over. Temperatures will run around
15 degrees below average. A consensus between MET and MAV MOS
guidance was used for Sunday highs, and was adjusted downward
based on 12z ECMWF ensemble guidance. If the ECMWF were to pan
out, the Grand Valley may struggle to reach the 60 degree mark!
Have not gone that low in this forecast package, however these
notably low forecasts are worth noting for now.

Lingering moisture along the Continental Divide and low heights
will remain on Monday, enough that showers and an isolated rumble
of thunder can not be completely ruled out of the forecast in the
higher terrain. Elsewhere, a drying trend will set in. By Tuesday,
our next weather disturbance will dive southward through the Great
Basin. Forecast confidence decreases from Tuesday through the
remainder of the week as major global models indicate another
cut off upper-level low developing in the southwest. This low will
keep things unsettled in the San Juans and Four Corner region.
Overall, the trend of below average temperatures will continue
into next week, although the airmass will not be quite as chilly
as the fall preview in store for this weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 351 AM MDT Sat Sep 23 2017

As scattered showers and thunderstorms pass through the region with
a good chance for impacts at TAF sites including rain and strong
outflow winds. VFR conditions are still most likely to continue
throughout the forecast period, however some CIGS are likely to
fall below ILS break points. Some riming or icing is possible as
well with freezing temperatures lowering toward mountain top level
early this morning.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until midnight MDT tonight for COZ009-
     012-013.

UT...None.
&&

$$

UPDATE...MAC
SHORT TERM...CC
LONG TERM...MAC
AVIATION...CC



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