Scientific Forecaster Discussion
fxus65 kslc 190334
Area forecast discussion
National Weather Service Salt Lake City Utah
934 PM MDT Fri Oct 18 2019
a colder and wetter storm system will move from the Pacific
northwest and into Utah late Saturday. This storm will bring
colder temperatures to the state, with widespread precipitation
affecting mainly northern and portions of central Utah along with
southwest Wyoming this weekend.
Short term (through 00z tuesday)...
the cold core upper trough currently over the eastern Gulf of
Alaska will move onshore through the Pacific northwest by early
Saturday. From there this trough will continue southeast into Utah
late Saturday afternoon.
Deep layer, but weak, warm advection out ahead of the main trough
will produce an expanding area of mostly light precip across far
northern Utah beginning early Saturday afternoon. The colder air
associated with the trough will arrive over the north late in the
afternoon. Frontogenic forcing will develop along the leading edge
of the low-level cold advection by early Saturday evening. This
low-level forcing along with increasing instability/dynamic
forcing with the arrival of the mid-level trough will create a
broad area of synoptic-scale lift across northern Utah/southwest
Wyoming into early Sunday. Favorable jet support late Saturday
night/Sunday morning will serve to maximize lift. Anticipating a
fairly rapid increase in intensity and areal coverage of precip
during this time, with heavy snow for the northern mountains,
rapidly lowering snow levels will also bring snow down to many
valley locations, with a few inches accumulation possible in the
higher valleys and bench areas.
The trailing cyclonic northwest flow behind the trough passage
Sunday combined with the mid-level cold pool overhead could
maintain orographically-enhanced snow across the northern and
central Wasatch Range Sunday. Lake enhanced snows not out of the
question as the gsl to 700mb Delta-T will run between 18-20
degrees during the day. Low-level moisture looks adequate for lake
enhanced showers, though fairly strong near 700 mb winds and the
absence of a surface convergence boundary over the Lake May
confined the heavier snows to the downstream higher terrain with
only minimal shower activity in the lower valleys.
One last organized precip event could develop across the far north
Sunday night/early Monday. Deep layer and still relatively moist
warm advection will develop once again ahead of the upper ridge
advancing toward the West Coast. Looking at the potential for a
short duration precip event across the far north driven by the
thermally generated lift. This precip will likely winds down
beginning late Monday morning as warming/drying aloft takes hold
during the afternoon hours.
Long term (after 00z tuesday)...
global models remain in good agreement regarding building
heights, increased stability and lighter winds going into the
midweek period. Afternoon high temperatures ramp up to seasonal
norms across the forecast area on Tuesday.
A system sliding through the northern rockies will reiterate a
chance of precipitation Wednesday and Thursday for higher elevations
of northern Utah and southwest Wyoming. Models in disagreement about
extent of cooling by the end of the work week, currently leaning
toward the colder GFS solution for this period.
southeast winds will increase at slc overnight before becoming
gusty after about 15z Saturday. A cold front will cross the
terminal between 21z Saturday and 00z Sunday producing a wind
shift to the northwest with a few hours of continued gusts behind
the front. Rain showers will fill in along and behind the front
with cigs lowering to the 3-5kft range and resulting in mountain
the upper trough advancing into the Pacific northwest early
Saturday will continue southeast into Utah by late Saturday. This
trough and associated surface cold front will generate
increasingly strong southerly winds Saturday afternoon, followed
by gusty northwest winds behind the front through Sunday. Looking
at what could be borderline hazardous fire weather conditions from
winds and relative humidity Saturday afternoon. For now will hold off on any
fire weather highlights as the current thinking is that the
duration of the hazardous weather conditions will be below
Widespread, and at times, heavy rain/snow will be confined to
northern Utah, with several inches of snow accumulation possible
over the northern mountains. Snow levels will lower Saturday
night, leading to rain changing to snow in many of the northern
valleys by Sunday morning.
Utah...Winter Weather Advisory from 4 PM Saturday to 6 PM MDT Sunday
Winter Weather Advisory from noon Saturday to 6 PM MDT Sunday
For more information from noaa's National Weather Service visit...