Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 241712 AAD
AFDGJT

Area Forecast Discussion...UPDATED
National Weather Service Grand Junction CO
1112 AM MDT SAT SEP 24 2016

.UPDATE...
Issued at 1112 AM MDT Sat Sep 24 2016

Let the remaining Winter Weather Advisories expire at 11 am.
Webcams and observations indicate just light snow occurring with
wet roadways as snow either was cleared or melted off. Radar and
IR satellite show decreasing trends in intensity of the snowbands
and precipitation. Snow continues for some of the higher peaks and
passes along the central and northern Colorado mountain corridor,
but roadways remain wet or dry with little if any accumulation on
roads. Impacts appear minimal. Did increase pops and clouds again,
extending the area further south as the low pressure system
expands a little and continues to shift eastward. Also, bumped up
pops along the central divide areas where radar and satellite
indicate the best precipitation to be occurring. Rest of forecast
remains on track.

UPDATE Issued at 903 AM MDT Sat Sep 24 2016

Updated to remove Winter Weather Advisory mention from UTZ023. Let
it expire at 9 am as webcams show wet roads with little snow
accumulation on the grassy areas. Snotels do not indicate much
aside from a couple inches at a few sites. IR Satellite is
showing some enhancement in Wyoming over Rock Springs with rain
occurring there. This enhancement looks to clip northeast Utah as
the low continues tracking eastward. Temperatures are right
around or a little above freezing, so roads are expected to
remain wet with little impact. The rest of the highlites for NW
Colorado mountains and the Grand Mesa remain on track through 11
am.

UPDATE Issued at 842 AM MDT Sat Sep 24 2016

Looking at webcams, Highway 65 over the Grand Mesa near Skyway
showing snow accumulating on the roads with snow continuing to
fall. Radar and IR Satellite indicate enhancement and snow bands
over this area moving southeastward. This looks to continue over
the next couple hours so decided to include COZ009 in the Winter
Weather Advisory until 11 am. Independence Pass and Vail Pass
currently look dry with rain and wet roads at Aspen and Vail. Will
continue to monitor this area for potential inclusion but
thinking that roads will remain wet with little impact by the time
these showers arrive to the central mountains along the divide.

UPDATE Issued at 741 AM MDT Sat Sep 24 2016

Lowered max temps for today as guidance has come in much cooler
than forecast. This seems reasonable given the precipitation and
clouds associated with the low pressure system spinning over
south-central Wyoming, bringing a colder air mass into the region.
Light snow was seen falling on webcams over the eastern Uintas in
northeast Utah as well as over Rabbit Ears Pass in northwest
Colorado. A couple inches look to have accumulated on the grass
near Rabbit Ears Pass with a dusting in northeast Utah. Not too
much impact on the roads as they remain fairly wet with maybe a
few slick spots over Rabbit Ears. Mountain snotel observation
sites are not indicating too much snow accumulation with maybe a
couple inches at a few of the sites in the northern mountains
where temps are below freezing. Otherwise temps seem to be
hovering right around or slightly above freezing at most snotel
sites. Will let current advisories continue this morning as the
low continues to make its push eastward. Radar and IR satellite
this morning is showing enhancement over northeast Utah and
northwest Colorado, extending into west central Colorado along the
I-70 corridor. Rain is occurring underneath this area of
enhancement with snow limited to the mountain passes and higher
peaks. Increased and expanded area of cloud cover and pops this
morning through early afternoon as a result.

&&

.SHORT TERM...(Tonight through Sunday night)
Issued at 314 AM MDT Sat Sep 24 2016

The current satellite water vapor image continues to show a strong
storm system centered over Southwestern Wyoming this morning. This
storm system is still supporting showers over portions of Eastern
Utah and Western Colorado. The current IR satellite image is
showing enhanced cloud activity entering Eastern Utah and
Northwestern Colorado as a portion of the jet stream begins to
pass over the area.

The 0000Z runs of the NAM12, GFS20 and ECMWF have initialized well
with this storm system and slowly slide it to the east northeast
today with the center reaching Southwestern North Dakota by this
evening. High pressure will then begin to build in over the Great
Basin and Rocky Mountain states on Sunday.

In the meantime the lingering storm system will provide showers
across the area this morning with potential thunderstorms this
afternoon as the low ejects to the northeast. Cold air filling
into the area has also lowered snow levels down to between 8000
and 9000 feet which will support high elevation snow. An early
season Winter Weather Advisory is in place for portions of
Northeastern Utah and Northwestern Colorado through this morning.
Additionally, today will be chilly with afternoon high
temperatures only reaching into the mid 60s to lower 70s in the
valleys and low to mid 40s in the mountains.

.LONG TERM...(Sunday through Friday)
Issued at 324 PM MDT Fri Sep 23 2016

Dry weather is expected to return to the forecast area Sunday and
Monday. The storm which brought wind, heavy rain, and mountain
snow splits Saturday night with the bulk of the energy moving to
the northeast. However, a portion of the jet digs southward
carving out a closed low over central New Mexico. The moisture
wrapped system to the south will retrograde west-southwestward
across northern Mexico to the Gulf of California by Monday
evening. During this period, a dry northeast flow Sunday will
give way to dry easterlies on Monday. Forecast highs Sunday will
remain below average, though temperate in the valleys with cool,
crisp fall conditions in the mountains. Continued sunshine on
Monday will bring afternoon temperatures back to near normal
levels.

From Monday night into Tuesday the closed low will move from the
northern Baja region to southwest Arizona. Models indicated a
weak lobe of vorticity moving northward along the eastern edge of
the low could bring some light showers to the San Juan Mountains
during the afternoon/early evening. Chances improve Tuesday and
Tuesday night as the low lifts across Arizona and becomes
entrained in the prevailing continental flow. Confidence is very
good up to this point as both the ECMWF and GFS were in solid
agreement. However, Thursday`s weather is less clear as the GFS
becomes more progressive and dryer, in stark contrast to the ECMWF
which indicated showery and cool conditions will persist. Given
model differences am forced to accept the blended solution which
features a little of both. By Friday however, both models were
back in agreement over eastern Utah and western Colorado with
moisture in southwest flow feeding localized moist convection
during the afternoon. Except for some cooling Wednesday resulting
from cloudy/showery conditions in response to the passage of the
low, temperatures are expected to hover right around normal for
the last days of September.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1112 AM MDT Sat Sep 24 2016

Showers will continue through early afternoon across northwest
Colorado and west-central Colorado as the low pressure storm
system over eastern Wyoming continues to track further eastward.
Reduced cigs/vsby is expected among heavier showers with frequent
mountain obscurations through about 21z in snow. TAF sites are
expected to remain light rain with low ceilings until late
afternoon when clearing skies are seen behind the exiting storm.
VFR conditions will prevail this evening through Sunday morning
as a drier airmass takes hold.

&&

.GJT Watches/Warnings/Advisories...
CO...None.
UT...None.
&&

$$

UPDATE...MDA
SHORT TERM...Larry
LONG TERM...NL
AVIATION...MDA


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