Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 251018

Area Forecast Discussion
National Weather Service Grand Junction CO
418 AM MDT Sat Mar 25 2017

.SHORT TERM...(Today through Sunday)
Issued at 418 AM MDT Sat Mar 25 2017

Skies will start off mostly sunny this morning with clouds
increasing from the west by late morning into the afternoon ahead
of the next disturbance, currently pushing onto the west coast
and moving into the Great Basin. Southwest flow will increase
ahead of this system with H7 winds of 20 kts, resulting in breezy
conditions by late morning into the afternoon. Showers will
develop over the higher terrain of eastern Utah late this morning
with scattered convection developing over the western Colorado
mountains by afternoon with isolated thunderstorms possible given
the low CAPE around 200 to 400 J/kg and steep lapse rates. Showers
are expected to spread into the valleys by late afternoon into
the evening as the trough axis passes over the region as an open
wave tonight. This system is not overly impressive with limited
upper level support and moves across the region fairly quickly,
with the best chance for precipitation this evening through Sunday
morning. A low tries to split off from this open trough and form
over southeast Colorado and northeast New Mexico by early Sunday
morning, which may result in better precipitation for the San
Juans and southern valleys as an area of low to mid level
convergence is seen over the San Juans tonight. Model QPF and snow
amounts indicate a very scattered convective nature to this
system, so some valleys may not see much precipitation or fairly
light amounts, while the location of the best snowfall seems to
change from run to run. Most areas will see rain throughout the
afternoon with a rain/snow mix in the mountains and snow at the
highest peaks, before snow levels lower with the passage of this
system down to 8000 feet this evening and 6500 to 7000 feet after
midnight into Sunday morning. Overall, it looks like roughly 2 to
4 inches of snow is possible for the mountains this evening
through Sunday morning, not enough to warrant an advisory. Some
orographic snow showers may linger over the western Colorado
mountains through Sunday morning before drier air and another
quick ridge of high pressure slides into the region by Sunday
afternoon, bringing dry air and clearing skies.

.LONG TERM...(Sunday night through Friday)
Issued at 418 AM MDT Sat Mar 25 2017

Weak ridging will move through the central Rockies on Monday
morning before our next (and more complicated) storm system moves
in for midweek. Several pieces of energy will come ashore along
the Pacific northwest early in the week, with the final and most
significant vorticity maximum diving into the desert southwest on
Tuesday. Guidance has varied significantly over the past several
days with regard to the strength and depth of this system. Today,
some clarity has been realized as all three major global models
now show a cutoff low at 500mb centered just south of the Four
Corners region by Tuesday afternoon. Precipitation onset time will
vary depending on elevation, with the higher terrain seeing a few
showers as early as Monday afternoon, and the valleys (including
Grand Junction, Montrose, and even Durango) by 6pm Monday. The
cutoff low pressure will deepen and slow significantly over
northern New Mexico through the day on Tuesday, bringing an
extended period of light to moderate precipitation to the central
Rockies, especially in southern Colorado. Ensemble guidance has
remained consistent in showing 500mb heights near 2 sigma below
mean seasonal values over the southwestern CONUS with this system.
The result will be cooler temperatures aloft and the opportunity
for another early spring snowfall event in the higher terrain.
Exact snowfall totals are still uncertain at this time, however a
mean of available guidance suggests around 0.5 to 1 inch of liquid
in the higher elevations above 9000 feet with this system.

By Wednesday afternoon, guidance indicates precipitation should
be winding down over the central and southern ranges in Colorado.
Unsettled northwesterly upper-level flow appears to remain in
place behind this system however, with yet another storm system
moving in on its heels by Thursday evening into next Friday.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 418 AM MDT Sat Mar 25 2017

VFR conditions will prevail this morning with mostly sunny skies
to start the day. Clouds will increase from west to east
throughout the morning into the afternoon becoming mostly cloudy
by late afternoon. Showers will also develop over eastern Utah
late this morning with scattered showers developing over the
higher terrain of western Colorado this afternoon. Showers will
increase in coverage and spread into some valleys late this
afternoon into the evening with the best chance this evening
through Sunday morning as a disturbance tracks across the region.
Lower valley TAF sites will be least impacted with ceilings
staying above ILS breakpoints but mountains will be obscured at
times from late afternoon onward in clouds and showers, impacting
higher TAF sites like KASE and KTEX with ceilings below ILS
breakpoints by late afternoon into the evening hours.




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