Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
340 PM MST Monday Dec 9 2013
Synopsis...high pressure aloft off the West Coast will maintain
a stable and increasingly dry northwest flow across the Great
Basin through midweek.
Short term (through 00z friday)...
water vapor loop shows the disturbance moving into the central
rockies while ridging occurs over the eastern Pacific. Acars
400-250mb wind observations place a cyclonic 100-155kt jet from
Alberta into The Four Corners and northeast into the Great Lakes.
GOES/GPS/rap/12z radiosonde observation indicate the precipitable water value is
between 0.03" and 0.12".
The main focus in the short term will be how the inversion will
affect tempeartures...visibility and stratus.
Highly confident inverted conditions last through Thursday due to
extensive snowpack and stable airmass moving into the region. Went
well below guidance for valley temperatuers but without a good
starting point hard to utilize the modified persistence approch so
more fine tuning will be needed.
Not confident in fog except near water bodies due to such a dry cold
airmass in place. As we put a lid on the airmass this will become a
more extensive possibility. Additionally...stratus will become more
of a concern in a few days...though did start advertising where most
confident in the Uinta Basin. Urban haze will thicken as well...and
carry a mention Wednesday and Thursday as high resolution BUFKIT
data indicates lack of drainage flow during this time.
Long term (after 00z friday)...
global models show a Pacific storm system moving across Arizona
Friday through early Saturday. 700 mb temperatures look to drop to the
-8c to -10c range with the system...and increasing flow aloft
might be enough to provide at least partial mixing of valley
inversions. Because of this...have indicated modest warming of
valley temperatures for the weekend. This system could bring some snow
showers over the higher terrain of northern and central Utah.
Northwest flow is expected to build back over the forecast area
behind the exiting trough. Models have backed off on the trough for
Sunday/Monday...with the European model (ecmwf) showing a grazing system that might
bring some clouds into northern Utah while the GFS indicates a
system even weaker than that. Both models deliver colder 700mb temperatures
with quick subsidence behind the system to squelch precipitation
Aviation...VFR conditions are expected through the taf period at
the slc terminal. Light and variable winds are expected become
decidedly southeast by 03z...remaining light through Tuesday
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