Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 200515

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1115 PM MDT Tue Sep 19 2017

Updated aviation discussion

Issued at 707 PM MDT Tue Sep 19 2017

Allowed wind advisories to expire as winds have decreased to below
advisory criteria. Breezy conditions and a few showers across NW
UT and NE CO will continue through the evening before winds
decouple in all valleys and precipitation ends before midnight.


.SHORT TERM...(Tonight through Wednesday night)
Issued at 318 PM MDT Tue Sep 19 2017

The main weather story this Tuesday afternoon continues to be the
strong winds affecting much of eastern Utah and western Colorado.
Gusts in the 30 to 50 mph range have been recorded at several
observing sites and this will be common through the remainder of
the afternoon and early evening hours. The Wind Advisory for
several northern Colorado zones continues until 7pm and no changes
have been made in this forecast package. Radar has been picking up
on a few showers along the US-40 corridor, however no observing
sites have reported any rainfall thus far today. A few showers
may make it to the ground early this evening, especially in the
Flat Tops and Park range before this weak impulse heads east of
the Continental Divide.

The strong jet maximum responsible for the windy weather today
will slowly shift north overnight and into Wednesday. Winds are
expected to die down overnight as valley regions decouple, however
the higher terrain especially in the north will hold on to a stiff
westerly breeze. Wednesday`s wind forecast is less than today,
however areas along and north of I-70 will remain on the fringes
of the jet max and another breezy day is expected. Temperatures
will run near average area-wide.

.LONG TERM...(Thursday through Tuesday)
Issued at 318 PM MDT Tue Sep 19 2017

Deterministic forecast guidance is in good agreement this
afternoon showing a large trough diving southward into the Great
Basin by Thursday afternoon. Winds will turn southwesterly across
eastern Utah and western Colorado through the day, and will
increase in speed as the jet stream moves south over the region by
Thursday night. Will have to monitor the forecast overnight
Thursday through the day on Friday for possible wind headlines
once again as the center of a 120 knot jet streak passes over the
region. Precipitation will also return to the region by Friday
afternoon as PWAT values nudge upward ahead of the trough.
Guidance does indicate a bit of instability west of the divide on
Friday afternoon, and with plenty of speed shear in place,
some sustained thunderstorm activity is possible.

Forecast confidence decreases substantially for the weekend and
into early next week. All major global models indicate that the
large western trough will cut off and stall over the Rocky
mountains, however exactly where this will occur is still quite
uncertain. 700mb temperatures underneath this cutoff upper level
low will drop, with the GFS indicating temps from 0 to -2 or so
at that level in northern Utah and Colorado by late Sunday into
Monday. It appears as though the general pattern will remain
unsettled with the low centered somewhere over northeast Utah or
southern Wyoming, and afternoon showers and thunderstorms common
throughout much of the higher terrain of Colorado and northeast
Utah. Ensemble guidance favors below normal temperatures through
the weekend and into early next week.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1115 PM MDT Tue Sep 19 2017

A final push of showers north of I-70 will end shortly after 06z
as strong upper level jet support pushes northward over the next
24 hours. Winds aloft will still be quite breezy Wednesday with
wind gusts to 30 mph possible at many of the TAF sites. No
precipitation is anticipated Wednesday after 09z. ILS breakpoints
could linger through 12z near KSBS before skies clear across the
north. Elsewhere, VFR conditions will prevail with cigs
significantly above ILS breakpoints.




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