Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
355 PM MDT Sat Mar 28 2015
Synopsis...the cold front over northern Utah late this afternoon
will sweep south into extreme southern Utah tonight .A weak
weather disturbance off the California coast will move east into
southern Utah by Sunday night. High pressure aloft will return to
the area by late Monday.
Short term (through 00z wednesday)...the surface cold front
currently over the southern Wasatch front will continue south
through all but extreme southern Utah overnight. Low-level cold
advection supporting the front generating fairly strong Post-
frontal northwest winds at this time. Suspect that these winds
will become less strong as the cold advection becomes less strong
across central/southern Utah later tonight.
Convection springing up along and ahead of the front struggling to
generate even light precipitation. The supporting middle-level shortwave
will continue to shear to the east through the northern rockies...
leaving little in the way of dynamic support over cold air aloft
to support convection. Will keep a few evening showers mentioned
in the forecast...with this activity confined to the northeast and
For Sunday the various model guidance continue to develop
convective precipitation across the southern/central mountains during the
afternoon. What little moisture that does exist will pool over
southern Utah north of the surface boundary near the Arizona
border. Weak low-level convergence indicated in the guidance may
find some support for lift from the shortwave currently off the
central California coast. This shortwave is scheduled to drift
east along the boundary late Sunday afternoon through early
Monday. Suspect that the models are a bit too aggressive generate
precipitation...but will include the possibility of light precipitation for the
mountains in the current forecast package.
A low amplitude ridge axis will shift east across the Great Basin
late Monday through early Tuesday. An increasingly warm southwest
flow aloft trailing the ridge will bring breezy and warm
conditions to much of Utah Tuesday afternoon.
Long term (after 00z wednesday)...both the GFS and ec
have a cold front moving into northern portion of the County Warning Area Tuesday
night with decent baroclinicity but neither show much in the way of
quantitative precipitation forecast. Left the slight chance probability of precipitation in for now. However if the upstream
trough becomes stronger this will tend to weaken the first trough on
Wednesday and consequently reduce the shower threat.
Wednesday will be a cooler day but with temperatures still about 5
to 10 degrees above normal.
The next upstream trough looks stronger and will likely bring
temperatures down to near normal Thursday with the bulk of
precipitation over the northern half of the County Warning Area. Have increased probability of precipitation
over northern half of County Warning Area but because there is about 30-50 meter
variation in the 500 mb heights in the GFS model runs over Utah
Thursday night wanted to leave room for the possibility of a weaker
system moving through.
Snow levels could lower to near the valley floors of northern Utah
by Thursday night. Depending on cloud cover sub freezing
temperatures are possible late Thursday night over many valley
excluding Dixie. Cool temperatures will linger through Friday but
temperatures are expected to rebound nicely Saturday through Sunday.
Aviation...northwest winds are expected through the evening at the
slc terminal then north winds through the rest of the night before a
shift to southeast sometime after 11z. There is a 20 percent chance
of maintaining a north wind through the morning. No other
operational weather concerns through the taf period.
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