Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Junction Colorado
450 PM MDT Sat Oct 25 2014

Short term...(tonight through Sunday night)
issued at 249 PM MDT Sat Oct 25 2014

Warm southwest flow with plenty of sunshine has allowed for
possible record high temperatures this afternoon. But the clear
skies will not last as middle level energy from Arizona streams
toward the north northeast into the western slope later tonight.
Latest visual satellite images show shallow convection over parts
of central Arizona. As this moisture gets lifted over the high
country...a few showers will develop over the mountain tops. Not
sure how much areal coverage of showers will actually occur...but
the higher resolution models give decent mountain coverage with
amounts around a tenth of an inch /0.10/. Would like to see some
dbz returns on the Arizona radars...but as of 2030z there have
been no echoes. In the grids will show at least isolated shower
coverage with the snow levels fairly high. Cloud cover will keep
temperatures relatively mild overnight.

The breakdown of the strong ridge will be well underway by sunrise
on Sunday as the polar jet reforms over the northern rockies and
pulls the western trough inland. The subtrop moisture source seen in
satellite imagery as cloudiness over western Arizona will be moving
through our County Warning Area during the early morning hours. The bubbly nature of
the cloud cover to the southwest suggests the presence of at least
weak instability. Large scale forcing will be absent Sunday morning
but cross sections show the moisture saturating mountain top level.
Orographics and instability appear to be sufficient enough to
produce showers at the high elevations over the Colorado mountains
and have higher probability of precipitation mainly above 10000 feet. Some of the models
guidance suggests mountain valleys getting some light precipitation.
Can not rule this out but confidence very low...so probability of precipitation are trended
this way in the lower elevations. Quantitative precipitation forecast amounts should be light with
this leading push of moisture. The push of stronger dynamics in the
form of qg forcing from the western trough and polar jet comes
Sunday evening into early Monday morning. The focus for this large
scale lift will be over northern Colorado where precipitation
remains favored over the northern Colorado mountains. A middle to low
level boost to the lift and orographics will come from a passing
front. The Flat Tops...park...northern Gore and high elks appear to
be the focus Point of the above ingredients. The missing piece will
be favorable dendritics for good snow production so sub advisory
amounts in the 1 to 3 inch range still look on track to affect the
higher peaks...and possibly Rabbit Ears and Vail Pass. The quick
movement of the system also should limit higher amounts.

Long term...(monday through saturday)
issued at 249 PM MDT Sat Oct 25 2014

By Monday the trough axis will have moved to the plains with
subsidence and drier northwest flow setting up across eastern Utah
and western Colorado. Cooler air aloft and residual moisture may
keep some showers over the eastern high mountains but isolated at
best. The bigger story will be the cooler air filtering in behind
the cold front. There is some fairly chilly air back in the
northern/Canadian rockies that will pulled down and highs will be
some 20 or more degrees colder than the record highs seen today
under the ridge. Clear skies in the airmass Monday night into
Tuesday looks more likely to bring a season ending freeze to all but
far southeast Utah by sunrise. The northwest flow will keep highs
more near normal through middle week as a passing system to the north
re-enforces the cool airmass. A ridge rebounds going in the late
week period and this should again push temperatures up above normal
going into next weekend...with dry conditions persisting.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 444 PM MDT Sat Oct 25 2014

Bands of high thin clouds will begin spreading across the area
from west to east this evening and the next Pacific system begins
affecting the area. By 06z scattered to broken clouds above the
mountain tops will spread across the region. A broken layer of
middle level cloud is expected after about 09z Sunday with isolated
light snow over the mountain peaks and ridges above 10k feet. VFR
conditions are expected to prevail for the mountain airports
through 18z Sunday afternoon.

&&

Gjt watches/warnings/advisories...
Colorado...none.
Utah...none.
&&

$$

Short term...pf/pf/15
long term...15
aviation...cirrocumulus

National Weather Service Glossary of Abbreviations