Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
950 am MST sun Dec 8 2013
Synopsis...a second weak weather disturbance will enter the
region from the north this evening. High pressure aloft along the
West Coast will maintain a stable northwest flow across the Great
Basin through much of the upcoming week.
water vapor loop shows the storm system pulling east over
Colorado...while the next one drops south over the northern
rockies. Acars 400-250mb wind observations place a cyclonic
125-150kt jet from northern California into The Four Corners.
GOES/GPS/rap/12z radiosonde observation indicate the precipitable water value is
between 0.03" and 0.15".
Dropped all remaining winter storm warnings. The synoptic snow is
long gone...with only a few showers in the vicinity of the Great
Salt Lake (decaying lake band) and on northwest facing slopes. These
two mechinisms will remain in place today though low quantitative precipitation forecast is expected
with subsidence in place between the two systems. Sref indicates
little to no instability today for redeveloping showers over the
While significant snowfall has ended...please treat travel with
caution and expect areas of winter driving conditions due to the
very cold Road temperatures (all below 25f).
Added indications of ongoing light to moderate downslope flow across
western Uinta Basin and Castle country. Lowered temperatures based
on observations and newest guidance. Expect stratus to break today
with some middle and high clouds invading from the north later this
afternoon. Rest unchanged.
Previous discussion follows...
the axis of the cold upper trough currently across eastern Utah
will exit off to the east later this morning. Widespread...and
often heavy snow has ended across the forecast area as dynamic
subsidence begins to takes hold behind the trough. The airmass in
place still remains quite moist with modest...albeit fairly
shallow instability this morning. A few select areas that can
utilize favorable terrain will continue to produce accumulating
snows this morning. Have left winter weather highlights going
along portion of the I-15 corridor from the northern metropolitan areas
south to around Cedar City. Will also maintain the highlights for
the mountains adjacent to I-15 corridor. Suspect that all of the
remaining highlights will be dropped either late this morning or
early this afternoon.
A secondary trough trailing the exiting system over eastern Utah
will enter Utah from the north this evening. This feature will
encounter a still fairly moist but substantially more stable airmass
across the forecast area. Dynamic lift generated from the middle-level
trough along with modest thermal advection will still struggle to
generate much more than light snow across the far northern zones
High pressure aloft over the eastern Pacific will bring a bout a
stable and somewhat drier/warmer northwest flow aloft to the Great
Basin early in the week. Very cold temperatures Monday morning in the wake
of the weekend storm will likely continue with only minor
modification into Tuesday. Tightening inversions due to the rapidly
warming aloft will bring about increasing urban haze and introduce
fog back into the forecast by midweek. Temperatures will struggle to
get back to seasonal norms...especially with all of the new snow
cover and poor mixing early in the week.
A cold northwest flow will remain in place for Tuesday and
Wednesday...with only the mountains of far northern Utah retaining
enough low level moisture to possibly initiate showers on Tuesday.
Heights will begin to rise Wednesday night and Thursday as a ridge
migrates through the western Continental U.S.. this will lead to a substantial
warming trend in the mountains...but most valley locations will
likely remain cold...with inversion conditions becoming well
Beyond Thursday remains a lower confidence forecast...as global
models continue to differ on how to handle the next trough to move
through the west. The European model (ecmwf) has been fairly consistent in digging
this trough into a closed low over Southern California and Mexico on
Friday through Sunday...which would keep mostly stable and dry
conditions over the forecast area. Since this has been the more
consistent model...the forecast is mostly trended toward this ec
solution. However...have kept slight chance probability of precipitation in the forecast for
Friday to account for the GFS solution...which brings a low
amplitude trough directly through the County Warning Area...before moving it quickly
into New Mexico and Texas on Saturday. Because of this major
discrepancy...temperatures remain even more uncertain than
usual...and the current forecast mostly represents a slow warming
Aviation...IFR snow showers will continue at the slc terminal
through 17z...with a 40 percent chance of continuing through 18z.
Scattered light snow showers or flurries are expected through the
afternoon but should not amount to more than brief intermittent snow
with a 20 percent chance of lowering to MVFR. North winds will
prevail through the day and night...albeit light.
Light snow is likely to develop across the terminal after 03z.
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