Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 171042
Area Forecast Discussion
National Weather Service Salt Lake City UT
342 AM MST Tue Jan 17 2017
.SYNOPSIS...High pressure aloft will settle over the Great Basin
for the first half of the week. A return to an active weather
pattern will occur late in the week.
.SHORT TERM (THROUGH 12Z FRIDAY)...
Water Vapor satellite shows a ridge building in from the
northwest. Our next storm system is approaching from near 40N over
the Pacific. 400-200mb MDCARS wind observations place a 75-120kt
anticyclonic jet from British Columbia, over the Northern Rockies,
Eastern Great Basin and southern California. GOES/SLC 00Z
RAOB/HRRR indicate that precipitable water values vary from
0.03"-0.10" mountains and west central/southwest Utah to
0.20"-0.30" most valleys. Blended precipitable water product shows
an atmospheric river associated with the approaching storm system
with origins from west of Hawaii.
00Z KSLC RAOB placed the base of the 4.9C inversion near 789mb.
This inversion is the focus of the forecast through tomorrow
evening. Will continue to advertise urban haze, especially now
that the work week will get going. Patchy radiational fog is
expected in valleys adjacent to the Idaho border. Stratus
continues to affect portions of the West Desert, valleys from
Bryce Canyon to Lehi, and the Western Uinta Basin. Show
improvement from cloudy to mostly cloudy during the next 36 hours
as southerly winds increasing with the next storm approaching.
Thick fog still possible where the cloud layer intersects the
terrain in the aforementioned areas.
Strong Pacific jet will continue to encourage forward progression
of the aforementioned wave, even forcing it to split as it runs
into the ridge overhead Thursday and Thursday night. Upper level
diffluence increases ahead of the approaching trough Thursday
morning. A cold front crosses the state through the day from the
west-southwest and continue cooling through Thursday night. Later
Thursday night shortwave ridging begins to build in, decreasing
coverage of rain/snow.
Despite the splitting nature of this system, the atmospheric river
tap along with decent cold advection should provide rather
widespread precipitation to the region. Mountains should average
4-8" with light accumulations for most valleys as well.
.LONG TERM (AFTER 12Z FRIDAY)...
Global models continue to indicate a very active period is on tap
for the entirety of the long term forecast, with multiple storms
forecast through the period.
The shortwave associated with the Thursday system will be pulling
away from the area Friday morning. Sufficient moisture will remain
behind this system for showers to continue in the mountains into
The next trough is expected to cross central/southern California
into Arizona Friday evening into Saturday. Lift from this wave
combined with favorable jet dynamics should provide a fairly
widespread precipitation event across the state. 700mb temperatures
between -8 and -10C across the state should keep snow levels at
valley floors except the St. George area. By midday Saturday, the
associated cold front will cross the state, bringing a moist, deep
northwesterly flow. This should allow for substantial accumulation
of snow in the Wasatch, central and southern Utah mountains.
A brief period of shortwave ridging Sunday will be followed by yet
another trough approaching the Pacific Coast. With a 150kt jet max
directly overhead, more than sufficient lift will exist for another
round of widespread precipitation. Global models vary on the timing
of this system with about 12-18 hour difference between the various
solutions. Leaned toward the more progressive solutions for now and
kept well above climo pops through day 7.
Main takeaway continues to be...Utah is expected to continue to see
a very active weather pattern through the long term forecast period.
Through 240 hours, the EC stays largely active, where the GFS tries
to build in a large western ridge toward the 26th.
Stratus appears to be having a difficult time developing near the
SLC terminal early this morning. Expect occasional dips to MVFR
visbys at the terminal today as inversion conditions develop.
Otherwise, northerly winds will redevelop between 17-19Z.
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