Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 061043

Area Forecast Discussion
National Weather Service Salt Lake City UT
343 AM MST Fri Dec 6 2019

.SYNOPSIS...High pressure aloft will shift overhead today. The
next storm system will impact the region during the upcoming


.SHORT TERM (Through 00Z Tuesday)...Early morning satellite
imagery and objective analysis show a shortwave ridge centered
across the eastern Great Basin, downstream from an upper low
spinning off the California coast. Regional satellite data coupled
with surface obs show an expansive area of stratus encompassing
much of northern Utah and southwest Wyoming which has helped kept
overnight temperatures fairly steady. Patchy fog is likely where
this cloud deck intersects the terrain and have maintained this
wording in the forecast.

As the ridge axis shifts east anticipate the inversion to
strengthen/lower through the day. This should allow higher
elevations to scatter out while the stratus deck will likely lower
later today into tonight. As such have maintained overcast skies
across the northern/western valleys as well maintained haze and
overnight/morning fog into the day Saturday.

The upstream upper low will fill as it approaches the coast,
before eventually crossing the forecast area as a positively
tilted weakening upper trough late Saturday night through Sunday.
The best chance for organized precipitation looks to come with the
weakening low level baroclinic zone early Sunday morning in the
north, then Sunday afternoon in the southwest. There is some
chance for patchy freezing rain/drizzle Saturday night across
northern valleys where shallow cold air keeps temperatures below
freezing, and this seems most likely near the Idaho border as well
as across the West Desert. Otherwise orographic precipitation
likely lingering through the day Sunday and into Sunday night in
areas favored by northwest flow. Snow levels will likely remain
above the valley floors through much of the event, with a
changeover to snow possible late. Increased PoPs a bit during the
late Saturday night/Sunday timeframe but little overall change to
the going forecast.

.LONG TERM (AFTER 00Z Tuesday)...The departing trough slides to
the southeast late Monday with rather large amplification of high
pressure from the west. Of notable mention is the differences in
timing of the ejecting trough between models and ensembles and
also the strength of the building ridge behind it. While not
focusing on specific model choices, the continuation of mountain
snow showers into Tuesday looks favorable under persistent cold
advection from northwest flow aloft. Temperatures at 700mb drop to
near -9C to -10C which should continue to be sufficient for
scooping out any leftover valley inversion through Tuesday.

Under high pressure, Wednesday could pose a chance for rebuilding
the inversion conditions with low clouds and poor visibilities
around northern Utah valleys. The far extended forecast begins to
differ on exact weather patterns or features, however, something
in the realm of a shortwave, quick moving latitudinal trough could
swing through late in the week. This should help keep the pattern
active and mixed around enough to limit the intensity of valley
inversion conditions. Confidence is low with this late week
feature, but it is something to watch.


.AVIATION...Conditions at the KSLC terminal will remain MVFR/IFR
through the day, with IFR possible intermittently through the
morning until 18z. Low stratus will keep Cigs IFR through the
period. Light southeast winds, and variable at times, will develop
by 14z and continue through the day.





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