Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 072202

Area Forecast Discussion
National Weather Service Grand Junction CO
302 PM MST Wed Dec 7 2016

.SHORT TERM...(Tonight through Thursday night)
Issued at 302 PM MST Wed Dec 7 2016

Radar and satellite imagery is showing convective nature to the
precipitation this afternoon with cold air shifting overhead. Do
expect much of this to dissipate over the next few hours though
some orographic showers are likely to hang on near the divide
through mid evening. A cold night on tap with very dry air in
place and we will start the evening under mainly clear skies as
the convection wanes. However we will be seeing some higher
clouds begin to invade from the southwest by late evening and it
could be a race between how far the temperatures drops before this
blanket arrives. Did lower the Yampa River Valley and Gunnison
Valley where this thicker cloud cover will arrive later to these
cold sinks. Most of the warm avective cloud cover will not produce
much snow through tomorrow afternoon but definitely could be some
isolated showers along the higher mountain tops. Warm air aloft
and cloud cover is leading to shaky confidence for temperatures
and warming today has been better than expected. Guidance is
warming things up a few degrees and did lean that way...probably a
regretful decision. Moisture...fed by a robust subtropical
tap...will be increasing by Thursday evening as PWAT begins to
push back above normal. The first of many passing waves in this
moist persistent flow is coming across late Thursday into Friday
with support aloft from a passing jet. The northern and part of
the central mountains...Park and Flat Tops look favored for the
heaviest snow and there could be some 4 to 8 inches near near Vail
to Rabbit Ears passes by the end of this wave. The precipitation
and cloud cover will limit radiational cooling and warmer
temperatures expected.

.LONG TERM...(Friday through Wednesday)
Issued at 302 PM MST Wed Dec 7 2016

Snow. Probably lots of snow. The moist westerly flow does not
abate through much of the upcoming week which means there will a
prolonged period of at least light snow falling somewhere across
the mountains and even some valleys at times. The tap of moisture
from the Pacific weakens a bit but still keep our PWAT near to
above normal through the middle of next week. Basically there will
be a large gyre of low pressure circling the northern latitudes of
central and eastern NOAM which will help supply cold air and
transitory upper jet to bring periods of heavier snow to
intermountain west including our mountains. There will be peaks
and lulls during this time as the upper and lower atmosphere gel
with favorable orographic flow. Timing of these waves are
difficult at best with confidence at this time pointing to early
to mid Saturday for the next passing disturbance. This flow will
help mixing and many of the valley inversions should be washed out
meaning rain could fall at lower elevations at times. By this
time next week the big winners should be the northern and central
mountains where totals will be measured in feet. The southern
mountains will not be left out totally but this pattern is not
overall as favorable. However expect the northern San Juans should
see some decent snowfall at times if the jet is able to dip far
enough southward. Stay tuned. Otherwise temperatures stay near to
below normal as cold air is ushered in behind waves and lifts out
ahead of the next.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 950 AM MST Wed Dec 7 2016

Isolated to scattered snow showers will continue across northwest
Colorado through early afternoon before gradually diminishing this
afternoon. Mountain obscurations will still continue through the
afternoon with clearing skies elsewhere. Some fog may linger along
rivers through early afternoon before lifting out behind the
departing system but will not impact TAF sites.  Expect VFR
conditions and CIGS above ILS breakpoints after 21z and through
Thursday afternoon.




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