Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 211043
Area Forecast Discussion
National Weather Service Salt Lake City UT
343 AM MST Sat Jan 21 2017
.SYNOPSIS...The active weather pattern will continue across the
region, with a series of weather systems crossing the area through
the first half of next week.
.SHORT TERM (THROUGH 12Z TUESDAY)...
Water Vapor Satellite shows a closed low off the Pacific Northwest
coast, with another compact one to its west. Meanwhile a shortwave
is lifting into Southern Utah. 400-200mb MDCARS wind
observations place a 140-180kt northwesterly jet from the eastern
Pacific over southern California and into northern Mexico.
GOES/SLC 00Z RAOB/HRRR indicate that precipitable water values
vary from 0.10"-0.25" mountains to 0.25"-0.45" valleys.
Aforementioned shortwave will traverse from southwest Utah as of
this writing across the eastern valleys through the remainder of
the morning hours. Expecting to see a significant reduction in
PoPs/QPF with the passage of this wave, through continued cold
advection and northwesterly flow will provide orographically forced
snow in favored areas through the evening hours.
Flow will back and become warm advective as the night progresses
under a shortwave ridge. Most precipitation will be ending,
however a few pockets favored in west-southwest flow may linger
in the mountains.
Jet buckles to our west Sunday and Sunday night shifting the ridge
to our east. This next storm system has a nice atmospheric river,
thus expecting precipitation to continue to expand in the warm
advective flow. Southwest winds will be gusty as wind field
continues to accelerate with the buckling jet arriving. 700mb
winds in excess of 50 kts, building southeasterly pressure
gradient and pressure falls will support gusty winds.
Cold front quickly crosses Utah Monday according to the GFS, while
the European and Canadian are a bit slower with this progression.
Strong height falls followed by the arrival of the cold pool aloft
Monday night along with continued cold advection and northwesterly
upslope flow should bring another round of decent QPF to the
Anticipate the next shift raising advisories and warnings for
tomorrow and tomorrow night. Did not want to confuse the issue
with the ongoing event on this shift.
.LONG TERM (AFTER 12Z TUESDAY)...
The front end of the trough is progged to exit the area by
Tuesday morning, but cold pool instability will keep snow going,
primarily over the higher terrain of northern and central Utah,
Tuesday into Wednesday. Global models indicate this precip
tapering off behind the back side of the trough, but some
differences in timing remain. EC is a bit faster, ending most
precip by Wednesday evening but the system takes a bit longer to
move out in the latest GFS, with at least some precip persisting
Behind the system, EC/GFS now both showing a drier and more stable
northerly flow with rather unseasonably cool temperatures. Overall,
models are in better agreement with temperatures, with the GFS
indicating 700 mb temps in the -14C to -16C range by Wednesday
afternoon as opposed to -12C to -14C in the EC. Both models show a
weak wave moving across Utah on Friday, but the dry airmass is
expected to limit precip.
At the SLC terminal...prevailing VFR conditions are expected to
deteriorate to IFR between 13Z and 15Z as snow increases in
coverage with the arrival of a cold front. IFR conditions should
then prevail through the morning before VFR conditions return by
mid- afternoon as snow ends. Southerly winds are expected to shift
to the northwest with the arrival of the front.
UT...Winter Weather Advisory until noon MST today for UTZ005-011>016-
Winter Weather Advisory until 8 PM MST this evening for
Winter Weather Advisory until 5 PM MST this afternoon for
Winter Storm Warning until 8 PM MST this evening for UTZ518.
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