Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 220032
Area Forecast Discussion
National Weather Service Salt Lake City UT
632 PM MDT THU JUL 21 2016
.SYNOPSIS...Moisture over southern and eastern Utah will allow for
showers and thunderstorms to continue across southern and eastern
Utah into this evening, while a dry air mass will remain over the
rest of Utah. The dry air will spread south and east, limiting
any chance for showers and thunderstorms to the southeast third
of Utah on Friday. Generally dry conditions can be expected this
weekend, with just some isolated shower and thunderstorm activity
over the higher terrain of southern and eastern Utah.
Water vapor loop shows a closed low off the Pacific Northwest
coast,with a ridge over the central Plains. In between, there are
several weak waves over Nevada and Idaho. MDCARS observations show a
90-110kt southwesterly jet from the California/Oregon coast
across the far northern Rockies. GOES/HRRR/00Z KSLC RAOB indicate
the precipitable water value ranges from 0.30"-0.40" northern
mountains to 0.75"-1.15" most valleys.
Updating to add convection to the forecast for the entire forecast
area through the overnight hours. The most numerous of this activity
will continue to be across the central and eastern mountains, and
will fade diurnally gradually through the late evening, impacting
eastern valleys as well.
A second area of convection is firing on the eastern Nevada ridges
with aid of a disturbance. Due to this additional forcing, it is
expected that an increase in mid level clouds will take place across
the north with virga/a few areas of measurable rainfall. Timing
for the Wasatch front and Cache valley region is a couple hours on
either side of midnight, though locally a few showers will be
possible near the higher terrain.
Have indicated thunder possible for much of the area outside of the
Logan to SLC corridor this evening, then no mention of thunder after
midnight, per SPC SREF instability parameters.
Another mild night given the daytime temperatures and areas of cloud
cover overnight, with a forecast low near 80F for SLC.
Monsoon moisture remains entrenched across much of central and
eastern Utah today as the upper level ridge centered over the
southern plains allows flow of moisture to continue into Utah.
Moisture has stretched a bit further west today and isolated
showers and storms developed in axis of weak instability across
southwest Utah. Deeper moisture, with precipitable water values in
excess of 1 inch, remains in place across central and eastern
Utah. Instability remains a limiting factor with SBCAPE values
only around 500 J/kg this afternoon. Scattered convection over the
higher terrain and more isolated storms over the valleys of
central and eastern Utah will linger into the evening before
dissipating overnight. Another very warm night is in store across
much the state with lows well above normal along the Wasatch
As ridge retrogrades slowly to the west and an upper low off of the
Pacific Coast lifts into the northern intermountain region the mid-
level flow aloft veers to the southwest allowing drier air to begin
moving into the state tonight and Friday. Moisture will linger in
the east on Friday, but anticipate the coverage of convection will
decrease while the west dries substantially. High temperatures will
again be around five degrees above normal on Friday in many areas.
A weak dry cold front then moves through the northern half of Utah
Friday night before stalling out. This should lower high
temperatures about five degrees on Saturday and allow dry air
to overspread all of Utah and southwest Wyoming.
With an elongated ridge of high pressure from the southern plains
to the desert southwest, generally dry conditions should prevail
on Sunday, with nothing more than some isolated showers and
thunderstorms over the higher terrain of southern and eastern
ECMWF and GFS both suggest some backing of mid level flow on
Monday and Tuesday as a trough of low pressure progresses from the
West Coast to the western Great Basin. The somewhat more southerly
flow may lift moisture into the southeast third of forecast area,
with models indicating precipitable water values around .75" on
Tuesday. Coupled with potential for a weak disturbance to rotate
around upper ridge, will increase pops a bit across southern and
eastern Utah for Tuesday afternoon and evening. Ridge elongates
and lifts northward for Wednesday and Thursday. Thus, any moisture
will remain well to south of forecast area. Given extremely warm
temperatures aloft and very dry air mass, will see yet another round
of hot temperatures across entire forecast area.
.AVIATION...There is a 10 percent chance that the SLC terminal
could see erratic winds due to showers through this evening, but
most of the thunderstorm activity should remain well south of the
area. Otherwise, expect VFR conditions to prevail, with winds
switching back to the southeast around 02-04Z.
.FIRE WEATHER...Upper level ridge remains centered over the
southern plains allowing southwest flow to bring deep monsoon
moisture into central and eastern Utah. With more southerly flow
aloft moisture has been able to stretch a bit into western Utah
today. Scattered thunderstorms over the higher terrain of central
and eastern Utah will continue this evening. Isolated showers and
thunderstorms can be expected in valleys locations across roughly
the southeast half of the state this evening.
The western third of the state dries out on Friday ahead of an
approaching cold front while isolated storms continue in the
central and east. The front will move through the northern half of
Utah Friday night before stalling. This will usher in drier air
and again bring critically low relative humidity values to valleys
across much of the state. Dry weather can be expected statewide
this weekend into early next week.
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