Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 092215
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
315 PM MST Sat Dec 9 2017

.SHORT TERM...(Tonight through Sunday night)
Issued at 240 PM MST Sat Dec 9 2017

As of 21z, a 584 dm h5 ridge was centered over the western Great
Basin this Saturday afternoon. This ridge is providing the western
CONUS with dry and generally cloud-free weather which will remain
the case over the next several days. As mentioned in previous
discussions, the only notable challenge in the forecast is
overnight temperatures. Higher-altitude valley low temperatures are
notoriously difficult to forecast this time of year, and guidance
has been all over the place in terms of verification. In general,
drying near the surface will allow for overnight lows to run at
least as cold as last night and in some cases, colder. Despite the
general lack of snow cover, have dropped low temperatures from
lower guidance consensus in the valleys each of the next three
nights. Strong inversions underneath warming temperatures aloft
will result in poor conditions for anyone wishing to engage in
prescribed burning over the western slope over the next few days.


.LONG TERM...(Monday through Saturday)
Issued at 240 PM MST Sat Dec 9 2017

The long term forecast will be dominated by the western ridge of
high pressure. Dry weather and light northwest flow is expected
each day through Friday afternoon over eastern Utah and western
Colorado with temperatures generally running 5 to 10 degrees
above average through the period. Of note for stargazers this week
is the Geminid meteor shower, one of the most prolific meteor
showers of the year, which peaks on the 13th and 14th. Popular
dark sky locations in southeast Utah and southwest Colorado should
see near-perfect conditions for the event. A few high clouds may
drop into northern Utah and northern Colorado by midnight on
Friday.

By the very end of the forecast period on Saturday, GEFS and EPS
ensemble guidance finally begin to hint at a breakdown in the
sprawling west-coast ridge. An analysis of ensemble h5 height
anamolous reveals a gradual trend to near-normal or even slightly
below normal heights by the middle of next weekend. Various
iterations of a storm system bringing some moisture to the central
and northern mountains have occasionally appeared on the past few
deterministic runs, but any skill or confidence in forecasting
accumulating snow remains very low at this time. "Patience" will
remain the suggested advice for powder-hungry recreationalists at
this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1028 AM MST Sat Dec 9 2017

Northerly flow under building high pressure will result in mostly
clear skies for the next 24 hour period with VFR conditions
prevailing and light terrain-driven winds. Some patchy, localized
fog may develop near KEGE after 14Z through late Sunday morning as
seen the previous two days as valley inversions strengthen
overnight.


&&

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

$$

SHORT TERM...MAC
LONG TERM...MAC
AVIATION...MDA



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