Scientific Forecaster Discussion
fxus65 kslc 222209
Area forecast discussion
National Weather Service Salt Lake City Utah
409 PM MDT Sat Jul 22 2017
Synopsis...drier air will gradually spread back into the area
from the northwest through Sunday. Deeper moisture will return to
Utah early next week.
Short term (through 12z tuesday)...the mid level high circulation
continues to center over central portions of the area this
afternoon maintaining a drying west/northwest flow aloft over the
far north, while the south retains a northeast/east flow in
general. Modest low level moisture remains across all areas with
dewpoints in the mid/upper 40s north, while the deepest moisture
profiles exist across far southern Utah (namely the southwest)
where mid level moisture remains more plentiful and dewpoints
generally remain in the 50s. Convective initiation has been
focused within the deepest moisture across the southwest as
anticipated, but have noted isolated storm formation over the
terrain as far north as the northern Wasatch Plateau/Eureka area
during afternoon destabilization. Convective trends moving
forward through the evening point towards focused coverage
remaining across the southwest, while the remnant north-central
Utah cells look to dissipate fairly rapidly over the next few
hours as minimal additional support exists.
The mid level high circulation will begin to shift downstream over
the next 24 hours providing more favorable trajectories to allow
deeper moisture advection north along the Utah/Idaho border by late day.
The deepest moisture is expected to remain tied to the southwest
where another round of isolated/widely scattered storms are
expected, but isolated activity could push as far north along the
Utah/Idaho border as kenv by the evening. Northwesterly moisture
advection will continue through Monday allowing increased pwats
and convective potential for most all areas by late day.
Long term (after 12z tuesday)...the rather broad upper ridge
centered across the southern/Central Plains states with an upper
trough parked along the California coast will leave the Great Basin
in an ideal position to bring monsoonal moisture back into Utah for
Tuesday/Wednesday. Model guidance bring between 1.00" and 1.50" of
precipitable water across the area, which seems reasonable considering the
moisture currently positioned across southern Arizona/northwest
Mexico. Will keep pops fairly high as it's likely that weak dynamic
features embedded between the ridge and trough work slowly north
through the forecast area.
A change in the mean layer flow will develop late in the week as the
the upper ridge becomes more west-to-east oriented across the
southern half of the conus, with the remnant of the West Coast
trough ejecting east-northeast into the northern rockies.
Anticipating some drying to the air mass, though not so much as to
eliminate convection. Southern and eastern Utah should remain under
a substantial amount of moisture with fairly widespread convection
each day. Areal coverage across the west and north will likely be
isolated to scattered, with much of this activity tied to the higher
terrain or any weak dynamic features moving through the area.
Aviation...isolated convection tied to the higher terrain south and
east of the terminal is not expected to have a direct impact on the
terminal this evening. Light northerly winds will persist until
around 04z, then turn to a light southeast drainage for the balance
of the night through Sunday morning.
Fire weather...the deepest moisture remains pinned down south this
afternoon, with the greatest potential of wetting rains across
the southwestern portions of the district through this evening.
Enough low level moisture remains in place for isolated storms as
far north as the 478/492 border area, but these cells are expected
to largely remain over the highest terrain. Similar conditions
are expected on Sunday, but mid level moisture looks to begin
spreading north along the Utah/Idaho border again by late day. This
surge will continue in earnest early next week becoming deeper in
nature with a net uptick of showers/storms and wetting rain
potential each day through midweek. The leading edge of this
moisture could bring a threat of isolated mixed wet/dry storms
over extreme western 478 later Sunday/Monday, but that threat
remains quite small.
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