Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service Grand Junction Colorado
834 PM MST Sat Nov 28 2015

issued at 833 PM MST Sat Nov 28 2015

Another interesting overnight period as upper level low and
vorticity center over southern Utah moves northeast across eastern Utah
and northwest Colorado overnight. Upper level qg forcing and weak middle level
frontogenetical forcing lines up from Moab through the Grand
Valley and over the northwest Colorado plateau region between 9 PM and 6 am.
Various weather models carry the same general solution. So have
updated forecast to boost probability of precipitation in this corridor overnight. Radar
returns are getting brighter over the Uncompahgre and Grand Valley
in the last hour...but have yet to see or hear of snow reaching
the ground. With clouds enhancing to the southwest...expect light
snow to start fairly soon and continue for much of the night.
Expecting accumulations to range from 1 to 3 inches...with
heaviest amounts located under stronger bands...the locations of
which are too hard to know right now. Have decided not to issue
an advisory for the valleys at this time...but will later if the
snow really gets going and it looks like travel will be impacted
early Sunday morning.


Short term...(tonight through Sunday night)
issued at 238 PM MST Sat Nov 28 2015

A bit of a lull in activity today as one piece of upper level energy
shifts to the north while the large area of low pressure just to
our west reloads thanks to another piece of energy approaching
from the southwest. As far as sensible weather is concerned...a few
showers possible this afternoon and evening over higher terrain
with more widespread precipitation expected from about midnight onwards. response to a jet streak that will move overhead causing
lift while moisture increases and what was essentially two areas
of low pressure consolidate and become one. Would not be surprised
to see similar snowfall to that seen last evening with some
banding possible over generally the same areas. That is..Moab to
Vernal shifting eastward overnight. Snowfall amts look to be in
the 1 to 2 inch range at this time. SW flow also favors some snowfall
over the San Juans but the 1 to 2 inch range.

Precipitation will clear Sunday late morning as the closed low
elongates across Wyoming. A disturbance will swing around from
the southwest on Sunday evening...bringing additional snow to
western Colorado...especially the San Juans. Qg vertical velocity
indicates the timing of best instability will be between about 3pm
and 8pm Sunday. Initial amounts in the San Juans...on the Grand
Mesa...and in the west elks look to be about 2 to 5 inches during
this time.

Long term...(monday through saturday)
issued at 238 PM MST Sat Nov 28 2015

Some lingering showers will persist in westerly flow on Monday
morning and taper off from south to north throughout the day
Monday as the closed low quickly exits The Rockies. The
NAM/ec/sref/CMC all indicate showers ending across the Elk/Gore
ranges by Tuesday morning...but the GFS is an outlier in keeping
showers going in westerly/northwesterly flow early Tuesday
morning. By Tuesday afternoon...conditions will be mostly clear
across all of eastern Utah and western Colorado as high pressure
builds back into the region. Temperatures will bounce back to near
normal midweek in most areas. With added snow cover in many
locations...low temperatures will likely remain below normal since
we are entering December. Patchy dense fog in low valleys could be
an issue as well as the high pressure builds in.

The next weather system makes its way inland across the West Coast
on Thursday and progresses eastward. Thursday afternoon looks like
the warmest day of the week with stronger southwest flow
developing aloft. Amplitudinal differences between the GFS and ec
exist for the incoming well as the timing of a cut
off low indicated by both solutions. Both solutions show an "el
nino low" across The Four Corners on this looks to
be the next day for any potential precipitation.


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 446 PM MST Sat Nov 28 2015

Skies cleared nicely this afternoon with mostly sunny skies being
reported across much of the forecast area. The next disturbance is
entering southeast Utah with clouds on the increase. This trend will
continue through the evening hours with generally scattered skies
becoming broken to overcast. Snow is possible as the clouds thicken and
lower but did not mention in many tafs as confidence not high
enough that they will affect aerodromes. Other concern will be
fog especially for gjt...vel...and mtj. Any fog that does form
should burn off by 17z or so tomorrow.


Gjt watches/warnings/advisories...


short term...tgr/jam
long term...jam

National Weather Service Glossary of Abbreviations