Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 161720

Area Forecast Discussion
National Weather Service Grand Junction CO
1120 AM MDT Tue Oct 16 2018

.SHORT TERM...(Today through Wednesday)
Issued at 423 AM MDT Tue Oct 16 2018

As mentioned in previous discussions, the forecast challenge in
the near term focuses on the closed low circulation over Arizona
early this morning. Models all seemed reasonably well initiated
with regard to this feature. Latest runs indicated that the low
will remain quasi-stationary during the day, though a vort lobe
rotating through its base will shunt moisture northward to the
UT/CO border by 00Z/Wed. It should be noted that this solution is
about 6 hours slower than those presented 24 hours ago.
Consequently, cut back precipitation chances across southeast Utah
and southwest Colorado during the afternoon. There is no chance of
precipitation elsewhere. In fact, expect plenty of sunshine across
areas north of a line extending through the Abajo Mountains and
Red Mountain Pass in the San Juan Mountains. Solar insolation
should help temperatures rise by 5 to 10 degrees compared to highs
on Monday.

The closed low drifts northward tonight according to models with
the NAM the most progressive of the lot. Cold air ( 0 to -2C) in
the core of the low will cause snow levels to lower to near 7000
feet during the latter part of the night when snow becomes likely
over the southwest San Juans and the Abajo and La Sals of
southeast Utah. Models diverge a bit with the track of the low on
Wednesday with EC and Canadian farther west than either the NAM or
GFS. As a result, the EC solution is drier over the San Juans
compared to the other models.

Per previous discussion, seems reasonable to expect accumulating
snowfall to have some impacts over the southern mountains from
late tonight through Wednesday and a period beyond, though mainly
above 9000 feet. However, models routinely struggle with timing
and movement of vertically stacked systems over the southwest and
my suspicion is that this solution is too fast. There does appear
to be a strong possibility of advisory level snow over the San
Juan, La Sal and Abajo mountains at midweek, however given
questionable track and timing of the storm will hold off issuing
with this package. Instead, will issue an SPS to raise awareness
of the impending weather change in concert with messaging via
social media.

As for temperatures in periods 2 and 3, look for milder overnight
lows tonight, followed by cooling across the southern and central
zones due to increased clouds and precipitation.

.LONG TERM...(Wednesday night through Monday)
Issued at 423 AM MDT Tue Oct 16 2018

The upper level low bringing light precipitation to the area on
Wednesday will be filling and lifting northward Wednesday night
and Thursday. This will send a little better moisture northward
across our northern zones and kick off a few light showers as the
low phases with a system kicking out of Canada and across the
Northern Plains. As mentioned in earlier discussion, the flow will
become a bit more favorable for the San Juans late Wednesday night
and early Thursday as it swings to the southwest before the newly
opening trough axis slides through Thursday evening. So expect
showers to continue off an on through Thursday afternoon before
shutting down Thursday evening. Focus will generally be across the
San Juans, but some activity will occur to the north as well,
although more scattered in coverage. H7 temps through Thursday
night are expected to hold in the 0 to -2C range, which keeps snow
levels up above the valleys with best accumulating snowfall
confined to elevations above 9k.

Strong ridging is then expected to move in over the weekend
promising a rebound in temperatures with readings reaching above
normal by a few degrees. The ridge is not expected to park over
the west as we have become accustomed to this year. Instead, it
gets kicked eastward by another round of storms that will be
driving into the Pacific Northwest with unsettled conditions
returning by early next week.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1117 AM MDT Tue Oct 16 2018

A system working north of the 4 Corners region will continue to
push mid and low level cloudiness north as well. VFR conditions
with no restrictions are very probable at all the TAF sites over
the nett 6 to 12 hours. Beyond this...the probability of ILS and
terrain obscuration will increase across SW Colorado and SE Utah
as precipitation breaks out.




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