Area Forecast Discussion
Issued by NWS Grand Junction, CO

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276
FXUS65 KGJT 170443
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1043 PM MDT Sat Sep 16 2017

.SHORT TERM...(Tonight through Sunday night)
Issued at 104 PM MDT Sat Sep 16 2017

Dry westerly flow has returned to the central Rockies this
afternoon in the wake of yesterday`s frontal passage. High
temperatures will run 5-10 degrees below average today with this
slightly cooler and dry airmass in place. Light flow aloft will
turn southwesterly this evening and a cool, tranquil evening is
forecast. No major changes in the near term today.

Overnight, light flow aloft will turn southwesterly as a very
subtle mid-level feature lifts northeast from Arizona toward
southern Colorado. This system is discernible on GOES16 Water
Vapor imagery this Saturday afternoon as a weak spiral moving over
far southern California. H5 vorticity prognosis also hints at this
feature and its general motion toward southern Colorado. As it
approaches on Sunday morning, isolated convection may fire fairly
early in the San Juans and southern Continental Divide regions,
especially given sufficient lingering moisture in the lower half
of forecast soundings. Have nudged PoPs upward from mid-morning
onward through Sunday afternoon given trends in CAM guidance
today.

Convection will come to an end after sunset on Sunday as a weak
500mb trough axis passes east of the Divide. Temperatures on
Sunday/Sunday night will run around 5 degrees below seasonal
averages.

.LONG TERM...(Monday through Saturday)
Issued at 104 PM MDT Sat Sep 16 2017

Dry zonal flow will move in on Monday morning, lasting through
Tuesday morning. An active pattern resumes on Tuesday afternoon as
a large scale trough works south out of the PACNW. Several
shortwaves will pivot around the broader flow through the middle
and end of next week. The first will arrive on Tuesday afternoon
in northeast Utah and northwest Colorado, resulting in a few
showers along and north of the US40 corridor. An uptick in winds
north of I-70 will accompany this system as the nose of a 120
knot jet at 300mb heads through southern Wyoming. Forecast
confidence is much higher today regarding the Tuesday-Wednesday
forecast, as both the ECMWF and GFS both indicate the weak
shortwave passing Tuesday night followed by a dry day on
Wednesday. Forecast confidence decreases by Thursday and Friday of
next week. The ECMWF drives a deep trough southward on Thurs-Fri
which eventually cuts off over Utah on Saturday. The GFS keeps the
late-week trough shallower and more progressive. Regardless, much
of western Colorado should remain dry on Thursday, with northeast
Utah and far NW Colorado seeing showers by the afternoon. The
Friday- Saturday timeframe looks to remain active in both model
solutions, with showers and thunderstorms common throughout the
Four Corners and another good opportunity for early- season
snowfall above treeline.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1030 PM MDT Sat Sep 16 2017

VFR conditions will prevail at all TAF sites the next 24 hours.
Isolated showers and thunderstorms are possible after 18z Sunday
near the Continental Divide and over the San Juan mountains. Local
mountain obscurations are expected but this activity should not
affect any TAF sites.

&&

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

$$

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



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