Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 181749

Area Forecast Discussion
National Weather Service Grand Junction CO
1049 AM MST Mon Nov 18 2019

.SHORT TERM...(Today through Tuesday)
Issued at 330 AM MST Mon Nov 18 2019

Latest satellite imagery showed a broad altostratus deck over the
upper Yampa and Colorado River basins and the adjacent northern
and central mountains early this morning. Models indicated the mid-
level moisture entrained in northwest flow will diminish during
the morning as a transient ridge of high pressure moves over the
region. Expect cirrus to continue streaming through the ridge, but
plenty of sun should get through which will help raise
temperatures by a few degrees.

Flow aloft shifts to the west tonight as a trough deepens over
the West Coast causing the ridge axis to shift east of the
Continental Divide by sunrise Tuesday. As the western trough
continues to dig southward on Tuesday it begins to lift a closed
low off the Baja Peninsula northeastward. As this occurs, a surge
of subtropical mid-level moisture is driven northward, reaching
the Four Corners region during the afternoon. Weak isentropic
upglide combined with jet-level divergence will bring scattered
light showers to much of southeast Utah and portions of southwest
Colorado. Despite increased clouds ahead of the approaching
system, warm air advection is expected to bring afternoon highs of
10 to 15 degrees above normal.

.LONG TERM...(Tuesday night through Sunday)
Issued at 330 AM MST Mon Nov 18 2019

Tuesday night will see the Baja system, now a shortwave
disturbance, lift onshore across southwest Arizona with
subtropical moisture advecting out ahead into the Desert
Southwest. Showers will continue over southeast Utah and southwest
Colorado overnight with activity spreading northeast across the
majority of the forecast area by daybreak Wednesday. The shortwave
and associated vorticity maximum look to trek overhead mid to
late Wednesday morning, enhancing precipitation rates over the
southern mountains. 700mb temperatures Tuesday night will range
from 1 to 3 degrees C, only dropping to -0.5 to 2.5 degrees C by
midday Wednesday. As a result, precipitation will fall in the form
of rain below 9000 feet. Regardless, much needed precipitation is
expected as the aforementioned surge of subtropical moisture will
allow precipitable water values to climb to well over 200% of the
climatological around 0.65 inches Wednesday morning.
Scattered to numerous showers will persist throughout the day on
Wednesday with the shortwave progressing east into the Plains by
early evening. During this time the closed low over Southern
California will slowly drift into the Great Basin, allowing the
moist, unsettled southwesterly flow to persist across eastern Utah
and western Colorado Wednesday night. Forecast confidence begins
to dwindle Thursday onwards as timing inconsistencies continue to
plague the extended models. The GFS continues to remain the more
progressive solution as it transitions the closed low into an open
wave by midday Thursday across western Colorado before quickly
ushering it east onto the Front Range by Thursday night. The Euro
on the other hand keeps this system closed off, not lifting across
the Western Slope until early Friday. The Canadian solution
remains a balance between the two. Even with said model
differences the cool, showery weather is expected to persist
throughout the day on Thursday, though coverage is likely to
diminish gradually across the north by Thursday night. As far as
snow levels go with Thursday`s storm, 700mb temperatures will drop
to -3 to -6 degrees C across the majority of the region.
Therefore, snow levels will remain high, though they should drop
to around 8000 feet or so. Thursday night will see 700mb
temperatures drop even further to between -6 and -9 degrees C
across the area. This will allow the lower valleys to possibly see
a wintry mix or even a brief period of all snow through early
Friday morning but confidence is low on potential accumulations at
this time. This will also highly depend on how quickly the storm
exits the region, so stay tuned.

The anomalously high moisture content and favorable southwesterly
flow will allow the San Juan Mountains to do particularly well,
both with the initial shortwave Wednesday and the subsequent
midlevel trough set to move through the region on Thursday.
Preliminary snowfall totals of 5 to 10 inches look to be possible
above 9000 feet for the San Juans on Wednesday with an additional
5 to 12 inches projected for Thursday`s storm. Again, these
amounts are subject to change so please continue to monitor the
latest forecast.

Showers will taper off on Friday as the disturbance weakens or
exits the area depending on which model you favor. Regardless,
residual moisture should allow for at least isolated orographic
showers to persist through Friday evening. The overall ensemble
synoptic forecast looks to favor northwesterly flow in the wake of
this storm through Saturday. This will allow temperatures to
remain below seasonal normals through the weekend. Guidance once
again diverges for Sunday but conditions should remain dry over
eastern Utah and western Colorado.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1040 AM MST Mon Nov 18 2019

VFR conditions with light winds and CIGS above ILS breakpoints
will prevail for the next 24 hours. Mid and high level clouds
will continue to stream overhead. In the vicinity of KSBS expect
some low stratus to produce CIGS about 5000 ft AGL through about




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