Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 271557
Area Forecast Discussion
National Weather Service Salt Lake City UT
957 AM MDT Thu Oct 27 2016
.SYNOPSIS...A dry and unseasonably warm southwest flow will
will remain over the eastern Great Basin through Friday ahead of
a Pacific storm system approaching from the southwest. This
system will cross the area late Friday into Friday night. A second
and colder system is forecast for Sunday night into Monday.
.DISCUSSION...Morning water vapor and H5 analysis indicate an
downstream shift of the mean ridge ridge axis over the last 12
hours, this allowing a strengthening southwesterly flow aloft to
shift into the area from the west. Convergent mid/upper level flow
off the coast of Baja (due to return flow over the desert
southwest and advancement of a closed upper low off the SoCal
coast) is allowing for fairly expansive mid and upper level cloud
cover to stream NE over the western Great Basin, with the forecast
area remaining on the eastern fringe of this at this time. Further
encroachment of the aforementioned Low as it continues to track NE
will aid to shift this deck overhead over the next 12-18 hours,
though mild southwesterly flow in place will continue to drive
temps to unseasonably warm levels through tomorrow. Highs on the
order of 10-15 degrees above climo remain on tap today, with only
a slight downward tick tomorrow (due to a net increase of this
aforementioned cloud cover primarily, and increased shower threats
across the north/west).
Flow off of baja will continue to converge allowing increased
potential of tapping deeper subtrop moisture (largely from a
rapidly weakening hurricane Seymour) coincident and ahead of the
low as it comes on shore tonight, prior to rapidly lifting
northeast tomorrow into the overnight hours. Though significant
moisture advection will be occurring with passage of this, the low
will be filling and minoring out very rapidly over Nevada prior
tracking across largely western/northern Utah late day.
Essentially tracking through the ridge, vertical profiles will
remain quite stable, the mean jet will remain primarily west of
the border, and bulk of PWAT will remain at the mid/upper levels
(per BUFRS). Though scattered showers remain likely (primarily
north/west), QPF looks limited as does potential for any
significant impact. Will be taking a hard look at PoPs this shift
as may need to trend back a bit.
Details remain subject regarding the next trough Sunday
Night/Monday as well, primarily regarding amplitude and
significance of the trough as it tracks in from the west. Will be
taking a hard look at this as well for the afternoon package after
the full suite of 12z guidance becomes available.
Near term forecast remains on track however, and no updates were made
or are planned this morning.
.AVIATION...Increasingly gusty southerly winds will be maintained
at the kslc terminal through this evening, before backing off for
the overnight hours. A 70 percent chance exists that gusts over 30
mph will occur this afternoon, with start time as early as 16/17z.
Increasing mid/high level clouds are expected through the valid
TAF period, but VFR conditions will be maintained.
.FIRE WEATHER...Gusty afternoon winds especially across the far
southwest portion of the state are expected today and will become
stronger Friday. The ridge of high pressure in place today will
transition as an approaching low pressure system moves onshore
into California tonight and through the intermountain west on
Friday...bringing increased rain chances and cooler weather.
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