Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Junction Colorado
951 PM MST Friday Nov 27 2015

issued at 912 PM MST Friday Nov 27 2015

Area of cooler cloud tops in advance of vorticity lobe rotating
around cut-off low to our west has now moved over NE Utah and northwest Colorado.
Streaks of lower clouds continue to develop in the vicinity of the
abajos and San Juans and move north. Under these bands...snow has
been falling...moderate to heavy at times. The vorticity lobe will
pass north of Colorado/NE Utah by 1 or 2 the organized snowfall
we have seen this evening should be waning by then. Rifle area
already reporting 2 inches with more on the way. Roads beginning
to accumulate snow in the Grand Valley. So issued Winter Weather
Advisory for Grand Valley and I-70 corridor to New Castle. Should
have 2 to 4 inches of snow in the Parachute to New Castle
areas...with lesser amounts in the Grand Valley. However...with
temperatures quickly falling into the middle 20s...expect roads in the Grand
Valley to become treacherously icy overnight and early Saturday as
snow that melted earlier freezes or has a thin coating of snow on
them. Also boosted probability of precipitation and snow amounts over NE Utah overnight as
that area will be favored for some additional snowfall.
Elsewhere...forecast on track. Will continue to have periods of light
snow over the rest of the mountains.

Update issued at 525 PM MST Friday Nov 27 2015

Current coverage of precipitation over western Colorado and eastern Utah associated with
vorticity maxima rotating around the Great Basin cut-off low has
increased and models keep this area under precipitation in large
part for the next 6 hours. Have updated forecast to boost
probability of precipitation...lower snow level for the valleys where predominate p-type
should now be snow...and adjusted snow amounts accordingly. Have
issued a Winter Weather Advisory for the Uncompahgre Plateau and
Grand Mesa as they should get a quick bust of accumulating snow
tonight with additional snow showers and accumulations Saturday
for a total of 5 to 9 of fresh snow. Lower Valley locations in the
I-70 corridor and Highway 50 to Montrose will likely see snow this
evening...but any accumulations be light. A few lightning strikes
have been observed over SW Colorado north of Cortez...and this
area appears to remain unstable through 9 PM or so. Added mention
of thunder to that region.


Short term...(this evening through Saturday night)
issued at 240 PM MST Friday Nov 27 2015

The closed low in its retrograde west today is pulling energy a
little further west than it has been the last couple of days. That
being said...showers today have not been accumulating much if any
due to significant dewpoint depressions. The shortwave energy
passing through tonight is aided by a 100 knots jet aloft...which
will help the continuation of shower development and activity
tonight. Qg vertical velocity indicates good upward motion across
northwest Colorado and NE Utah through tonight. The focus tonight looks
to be across northwest Colorado and NE Utah...with a few inches of snow
possible across Moffat and Rio Blanco counties.

Current satellite indicates drier air across NE Arizona and northwest New
Mexico...however afternoon instability has caused convective
shower activity along the edge of the cloud shield in southwest
Colorado. Letting the Winter Weather Advisory continue for the
southern San Juans...though short term models indicate a break
later tonight for SW Colorado.

Saturday and Saturday night...the shortwave trough that moved
south to north across the area last night is projected to remain
an open wave in the GFS and European model (ecmwf)...but the nam12 actually closed
it off at 500 mb over SW Wyoming this morning and is projecting
this trough to become the stronger component of the system
tonight. The other models catch up with this and by late Sat night
the SW component of this multi-centered trough that extends over
Utah will be weaken and be drawn east beginning late Sat night.

Long term...(sunday through friday)
issued at 240 PM MST Friday Nov 27 2015

Sunday through Monday night...the southern component of the
dumbelling broad upper trough will move over the forecast area
Sunday and should produce a bit of an increase in clouds and
precipitation that is reflected in the grids. The troughline should cross
the Colorado/Utah border Sunday evening with northwest flow...cold
advection and diminishing moisture late Sun night through Monday

A Sharp Ridge will build over the western U.S. With another deep
trough developing off the West Coast Tuesday and Wednesday. Conditions
should be dry through Thursday then Ridgeline will move east of
the area Thursday evening. The Pacific coast trough will move
inland and reach the Great Basin Friday. It shows signs of
splitting as it approaches the eastern Great Basin Friday
afternoon...with the European model (ecmwf) giving the southern part of the more
energy over Southern California and western Arizona.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 941 PM MST Friday Nov 27 2015

Showers will continue rotating to the north and west tonight
through Saturday morning bringing periods of snow and Lower
Valley rain to the northern half of the area and the San Juan
Mountains through Saturday. The best chances of precipitation
will be north of a line from kpuc to kpso. Through 18z Saturday
mountains north of this line will be obscured and most airports
will have ceilings below ils breakpoints and frequent MVFR ceilings and
visibilities in show showers. Southeast Utah and lower elevations of
SW Colorado will see mostly clear skies with these improving conditions
gradually spreading north. Conditions across the area will
gradually improve after 18z.


Gjt watches/warnings/advisories...
Colorado...Winter Weather Advisory until 5 PM MST Saturday for coz009-017-

Winter Weather Advisory until 9 am MST Saturday for coz006-007.



short term...cirrocumulus
long term...cirrocumulus

National Weather Service Glossary of Abbreviations