Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
412 PM MST sun Nov 29 2015
Synopsis...a cold upper low will move out of the area tonight.
High pressure will gradually build over the region through middle
Short term (thru 00z thursday)...the primary center of the cold
upper low sits over central Wyoming this afternoon with the deep trough
extending SW to a weaker center in central Utah. The Utah center will
continue moving east and will weaken through this evening moving out of
the County Warning Area by 06z. Snow has become somewhat convective this afternoon and
these showers will tend to taper off after sunset. However the low
level northwesterly flow will deepen through this evening and will get orographics
into play with snow either persisting or developing in northwest flow
upslope areas as we go into tonight. The favored areas shift northward
after midnight as the upper trough axis exits the region and the
best instability shifts closer to the Wyoming center.
There is a potential for a brief period of lake effect snow off
the Great Salt Lake this evening but the depth of the instability
lowers after midnight and winds in this layer start to back around
to westerly or even southwesterly breaking up any organized band that does form.
There is a small chance we will need winter weather highlights
for areas downwind of the lake and along the Wasatch front north of
slc into early Monday but confidence is too low to warrant issuinga
highlight at this time.
The whole system shifts east tomorrow with any lingering light
snow over the northern County Warning Area ending by midday as upstream ridging
advances into Utah. The airmass aloft warms through Wednesday with
inversions likely becoming established by Wednesday.
Long term (after 00z thursday)...shortwave high pressure ridging
in place will remain in place through early Friday. Warm air
advection aloft will help with inversion setup in valley locations
/700mb temperatures 0c to 2c through Thursday/.
The approaching trough feature is well depicted by global
operational models with differences in location and timing
beginning middle-late Friday. The overall pattern is essentially
the same...outside of the splitting nature of the system...with a
deep trough passing along the Utah/Arizona border. Model run to
run consistency has also not been in alignment with the European model (ecmwf)
dragging the trough farther south and deepening it...while the GFS
has trended a bit northward.
Ahead of the trough passage winds aloft will strengthen as the
gradient tightens /700mb winds 25 to 35kts across southwest and
south central Utah valley locations/. Have kept slight chance
mention of probability of precipitation for Friday into Saturday mainly confined to the
higher terrain areas of central and northern Utah for the best
opportunities and available moisture content.
Aviation...the primary time to focus on operational weather
concerns at the kslc terminal focuses on this evening through the
early morning hours of the night as the best chance for periodic IFR
snow showers rolling across the terminal. During that time a light
dusting to a half inch of snow remains possible with accumulation
potential increasing after dark on any untreated surfaces. This
said...a 20 percent chance exists for additional light accumulations
through 14z tomorrow morning.
For more information from National oceanic and atmospheric administration/S National Weather Service visit...
http://weather.Gov/saltlakecity (all lower case)
For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)