Area forecast discussion
National Weather Service Salt Lake City Utah
514 am MDT Sat may 18 2013
Synopsis...a cool moist upper trough centered over Utah this
morning will move east of the area this afternoon. A colder system
will cross the region tonight through Monday morning. High pressure
will briefly return on Tuesday then shift east Wednesday.
&&
Discussion...the axis of the upper trough crossing the Great Basin is
over western Utah early this morning. An apparent circulation center has
formed in this trough over northern Utah evidenced by the comma head feature
on satellite and rotation in the precipitation echoes. This feature will
keep precipitation widespread across the northern County Warning Area as it tracks east this
morning with the upper trough. The steadier rain tapers off to showers
fairly sharply to the south of this center and expect this southern
edge to remain roughly over Utah County this morning with isolated
to scattered showers to the south of this.
Precipitation will taper to showers over the north by midday as the trough
shifts east but expect scattered coverage across much of the County Warning Area
this afternoon from low topped convection in the moist and
moderately unstable airmass. This wanes a bit this evening with the loss
of daytime heating but should increase again later tonight as a
colder trailing short wave drops into the northern Great Basin. This wave
looks like it will bring the best precipitation threat to the northern and
central County Warning Area Sun morning although instability showers will develop
across much of the area Sun afternoon. Snow levels will be a little lower
with this next round of precipitation but still dont expect any impacts
over any of the major passes.
Models indicate this next wave will also form a closed center over
northern Utah by 00z Monday and keep a threat of precipitation going over the
northern County Warning Area into Monday in the moisture wrapping around this small
low.
Ridging finally shifts into the Great Basin Monday night and over Utah on
Tuesday bringing a warmer and drier airmass. This ridge shifts fairly
quickly east Tuesday night as a deep cold closed low forms over the
pacnw states. Models continue to struggle with the details on how
this low evolves but the overall idea of keeping a warm dry
southwest flow over the County Warning Area with the cold air staying mostly to
our west seems sound and forecasts trend that way.
&&
Aviation...VFR conditions are expected to prevail at the slc
terminal through the day...though ceilings will remain at or below 6000
feet above ground level through the morning. Heavier showers will cause some brief
periods of MVFR ceilings/visibilities before about 16z. Light southerly winds
are expected to shift to the northwest between 15z and 17z...but
showers will cause periods of erratic wind directions this
morning.
&&
Fire weather...the first of two storm systems is making its way
across the district today resulting in showers...primarily over
northern Utah. There will be a lull in precipitation tonight...but
the second storm system will bring additional showers to primarily
northern Utah as well as a reinforcing shot of cold air on Sunday.
Northwest winds will become breezy at times due to these storm
systems this afternoon and tomorrow afternoon. The second system
will linger over the area Monday before high pressure returns for
Tuesday...bringing a warming and drying trend. Another storm
system may impact the area late in the week.
&&
Slc watches/warnings/advisories...
Utah...none.
Wyoming...none.
&&
$$
Wilensky/traphagan
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