Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 262150

Area Forecast Discussion
National Weather Service Salt Lake City UT
350 PM MDT Wed Apr 26 2017

.SYNOPSIS...A series of progressively colder systems will cross
the region through Saturday, with high pressure returning late in
the weekend.


Water vapor loop shows a strong zonal flow across the Pacific with
atop a ridge. AMDAR 400mb-200mb wind observations reveal a
130kt-145kt anticyclonic jet from Oregon into Utah. GOES/HRRR/12Z
KSLC RAOB indicate precipitable water values range from
0.10"-0.20" mountains to 0.35"-0.50" most valleys. Blended
Precipitable Water Product shows an atmospheric river with origins
northwest of Hawaii penetrating the western Great Basin.

A strong northwesterly jet will continue to send disturbances into
the region through the short term period. Each one will be a bit
colder than the last.

The first disturbance affects the region tonight into tomorrow,
shown by height falls. Warm advection is underway with
precipitation expected to fill in north of Salt Lake by sunset.
Cold front makes it through the remainder of Utah this evening.
Snow levels are expected to fall from 8000 feet to 6000 feet by
morning. Snow may mix in on some bench locations late tonight.
Spotty impacts possible on mountain routes heading into rush hour
tomorrow morning. 8mb westerly pressure gradient and 40kts of
700mb flow with 3-5mb/3hr pressure rises should support stronger
gusty winds across portions of the west desert, western Uinta
Basin, and Castle Country beginning overnight and continuing

There is also a good chance for contribution from the Great Salt
Lake in the morning. Current lake temperature is about 55F while
700mb temperatures fall to between -9C and -11C. Adjusted BUFKIT
forecast profiles suggest the lake may contribute 500-1000J/KG of
CAPE with an equilibrium level of 15-20kft. If winds remain too
strong expected scattered showers off the lake as opposed to a
band. These could add to travel impacts and will need to be
monitored closely.

Cold unstable northwest flow should keep orographic precipitation
going later tomorrow into tomorrow evening, but little is expected
for the adjacent valleys.

Cold core aloft will arrive Thursday night and Friday bringing
another round of precipitation with 700mb cold advection
increasing as lapse rates steepen. Light valley accumulations are
expected with this system, providing some impacts to travel.
Another bout of wind is expected Friday and Friday night as the
closed low takes form over the four corners.

As the deep upper level low digs farther south and east, the jet
on the back side rushes down into Arizona as ridging builds in
across the West. The cold air aloft slowly begins to diminish as
the trough exits, but remains overhead long enough to keep another
chilly morning across the area for Sunday morning.

The long fetch of moisture stretching eastward across the Pacific
Ocean gradually breaks down with a sharp trough digging south out of
Alaska by early next week. How this translates to the pattern
overhead will be both a cool airmass and a relatively drier airmass.
The position of the ridge centered in the east Pacific is holding
strong in both the GFS and the ECMWF and is also reflected well in
the ensemble output.

Going forward into Monday, a weak brush-by front dips southeast
through Montana and Idaho into Wyoming. Global forecast models in
the extended don`t have much in the way of precip reflected across
Utah, and 700mb temperatures dip to -3C to -4C. Beyond Tuesday,
differences are present as expected in the extended. A hint at
possible afternoon thunderstorms with some instability present in a
shortwave feature may be possible. Decent moisture advection and
diffluence aloft, though details and timing is not in sync at this


VFR conditions are expected to prevail at the SLC terminal into
the evening hours. Cigs are expected to drop to or below 6000 feet
AGL by 00Z as coverage of showers increases in the vicinity of
the terminal. Rain should become more widespread beginning between
01Z and 03Z, with periods of MVFR conditions expected in heavier
showers, primarily before 06Z. Light but prevailing southeasterly
winds are expected to shift to the northwest between 04Z and 06Z
with the passage of a cold front. There is a 30 percent chance
this shift occurs later than expected.




SHORT TERM...Rogowski

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