Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 110545
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1045 PM MST Sat Feb 10 2018

.UPDATE...
Issued at 1045 PM MST Sat Feb 10 2018

Significant clearing has resulted across the forecast area this
evening behind the cold front as a weak transitory ridge of high
pressure builds overhead. High clouds will continue to stream
overhead for much of the region but most precipitation will end by
midnight. However, isolated snow showers will linger across the
higher peaks of the San Juan Mountains through around 3 or 4 AM
Sunday but additional accumulations will be light. Therefore, the
remaining Winter Weather Advisories for COZ018 and COZ019 will be
allowed to expire at 11 PM.

UPDATE Issued at 809 PM MST Sat Feb 10 2018

The upper level trough driving snow across the region continued to
drift southeastward over southeast Utah and southwest Colorado
this evening. Snow had largely diminished in the area of negative
vorticity advection over the northern half of the forecast area
or, more specifically, northeast Utah and northwest Colorado.
Therefore, allowed the Winter Weather Advisories expire over the
central Colorado mountains while allowing them to continue over
the San Juan Mountains through 11 PM.

&&

.SHORT TERM...(Tonight through Sunday night)
Issued at 355 PM MST Sat Feb 10 2018

Another open wave dropping in from the North with upper jet
support...moderate moisture and instability has produced another
decent precipitation event for portions of the northern and
central CWA. Much of dynamics are slipping to the southern CWA
along with the cold front which should keep some accumulating snow
going over the southern mountains through late evening before
this wave gets accelerated out by the next upstream system. There
will be a brief period for the southern valleys to pick up some
snow before it ends...generally and inch or less on grass as it
has warmed nicely down there in the pre-front environment.
Clearing should be full scale by the early morning hours and
continue into much of Sunday before high cloudiness begins to
increase with the next system settling into the Great Basin.
This next system looks to be a Pacific storm merging with an Polar
trough tomorrow night...with an upper closed low forming over
Northern Nevada by sunrise on Monday. This sets the stage for a
good return of moisture on the W to SW flow around the periphery
of the upper system. Some light precipitation may form over the
southern hills early Monday expect mainly virga most areas.
Temperatures will make a small rebound tomorrow with transitory
ridge and mainly sunny skies in place.

.LONG TERM...(Monday through Saturday)
Issued at 355 PM MST Sat Feb 10 2018

So the GFS was mocked by myself for being the outlier but here it
is leading the pack going into the early week period. The upper
low will be forced to retrograde back to the Left Coastline of
central California while a the arctic stream drops south of the
Canadian border by the mid-week time period. As mentioned earlier
this puts in a warm advective pattern with southwesterly flow
dominating the pattern over eastern Great Basin and Central
Rockies. Moisture and instability aloft combined with large scale
forcing form the jet energy aloft will lead to a more convective
or showery regime and models are picking up on this by producing
excessive pockets of QPF. This leaves little confidence in actual
numbers but fertile crescent of the San Juans and high terrain of
the Mesa to the West Elks should be favored in this flow Monday
into Tuesday. Snow levels with added moisture and warmer
southerly flow should creep back up to around 8000 feet but the
better accumulations may be much higher than than...it really will
depend on how forcing and instability alters the thermodynamic
profile. Late Tuesday into Wednesday the Upper low gets to far
Westward and forcing for precipitation will be lacking but warm
conditions continue. Beyond this the low stalls off then will try
and eject eastward through the end of next week. Agreement end
with models here...should we follow the GFS again is the 100k
dollar question. Warmer than normal conditions should stay in
place until this low moves in or the northern stream takes
control.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1045 PM MST Sat Feb 10 2018

Isolated snow showers continue over the San Juan Mountains as of
06Z this evening, impacting KTEX. Showers will quickly taper off
over the next couple of hours as dry air works into the region
from the northwest, though low CIGS will persist through
approximately 08Z. Fog is a possibility later tonight, however
model guidance suggests enough wind will persist to make it
unlikely for our TAF sites. Widespread VFR conditions will return
for Sunday under a weak ridge of high pressure.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.

&&

$$

UPDATE...MMS
SHORT TERM...15
LONG TERM...15
AVIATION...TGJT



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