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Area forecast discussion 
National Weather Service Grand Junction Colorado
1039 am MST Sat Dec 27 2014

Short term...(today through sunday)
issued at 447 am MST Sat Dec 27 2014

Satellite water vapor images showed an upper trough from Arizona across
Colorado to the northern plains early this morning. Backside jet energy
dropping into the trough base was hindering the eastward movement of
the trough. Low clouds and areas of light snow persisted before
sunrise with some valley fog also around. Expect these to diminish
by middle-morning as the jet energy reaches the trough base and the
entire system finally slips to our east by midday. Drier northwest flow
will bring mostly sunny skies to the area this afternoon. Stable
conditions this afternoon will inhibit mixing though...so cold air
will stay in the valleys.

The next storm system to affect our area was currently moving down
the Alaska Panhandle. Models show it crossing Washington/or early Sunday on
its way toward the eastern Great Basin while some energy peels off
across Wyoming per 1.5 potential vorticity. The associated upper jet
reaches NE Utah/northwest Colorado by 12z Sunday then settles southward to southeast Utah/SW
Colorado by evening. A combination of jet support and moistening westerly
orographic flow should result in light snow developing across the
northern mountains Sunday morning. One negative is that models are quite short
on moisture with precipitable water values 0.15 to 0.20 inch and
700 mb specific humidity 1.5 to 2.0 g/kg despite a current
moisture tap to a larger upper low north of Hawaii on the 11z
satellite water vapor image. The orographic flow is persistent
however...and temperatures aloft look favorable for good dendritic snow
growth. Thinking 1-3 inches of accumulations across the
Elkhead/park ranges and Flattops on Sunday. Snow expands into the
central mountains by late Sunday as the jet sags southward. The eastern
Uinta Mountains will tend to be shadowed in the westerly flow by the
higher mountains to their west.

Long term...(sunday night through friday)
issued at 447 am MST Sat Dec 27 2014

Sunday night through Monday...the Winter Storm Watch will continue
through Monday afternoon for much of the northern and central
mountains of Colorado and the eastern Uinta Mountains in NE Utah.

The midrange models are in good agreement through most of next
week. The system dropping in from the north should produce good
westerly orographic flow Sunday night as the jet passes over the
area. 700 mb temperatures from Sun night through Monday will span the
dendritic growth range...going from about minus 10 over the south
to minus 16 over the north. The front appears to come to rest over
SW Colorado near the southern Colorado border Monday afternoon. Specific humidity
remains relatively low in this cold air...and but there is an
unstable layer between 700 and 500 mb and good cold advection
Sunday night and Monday. These features provide the potential
periods of heavy snow especially on west-facing slopes through
Monday.

Looks like Colorado and Utah will contend with some part of this storm
through Friday. A second shortwave along the polar front in projected
to dig SW to western Nevada and California Monday night and Tuesday...forming
a tight circulation over Southern California Tuesday night. This initially
causing the cold front and main moisture band to wave north early
Tuesday then drop back to the south Tuesday afternoon and evening...
keeping a deformation zone over the area. The GFS moves the
Southern California low east into northwest Arizona Wednesday. This brings an area of
divergence aloft and enhanced upward motion over The Four Corners
region...along with strong southwesterly orographic flow. As the
low moves south of the area through Friday...SW Colorado and southeast Utah remain
beneath the active northeast and northwest quadrants of the
storm.

&&

Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1033 am MST Sat Dec 27 2014

Quiet day today inbetween weather systems. Expecting VFR at all
sites except for kvel for part of today due to hazy conditions.
Expecting kvel to reach VFR during the day today but revert back
to MVFR this evening. High clouds will increase later today and
overnight across the forecast area as the next weather system
approaches from the northwest. A few showers will be around the
north Central Mountain taf sites by 18z Sunday...but no
precipitation is expected at taf sites until after 18z Sunday.

&&

Gjt watches/warnings/advisories...
Colorado...Winter Storm Watch from Sunday evening through Monday afternoon
for coz009-010-012.

Winter Storm Watch from Sunday morning through Monday afternoon
for coz004-013.

Utah...Winter Storm Watch from Sunday evening through Monday afternoon
for utz023.

&&

$$

Short term...jad
long term...cirrocumulus
aviation...jam

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