Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 151155

Area Forecast Discussion
National Weather Service Salt Lake City UT
455 AM MST Wed Nov 15 2017

.SYNOPSIS...A weak ridge will build briefly over the area tonight
into early Wednesday. A stronger and colder storm system will
cross the region Thursday into Friday.


.SHORT TERM (Through 00z Sunday)...Mid level ridging remains in
place across the forecast area this morning, though pattern
evolution will phase the ridge axis east during the day allowing
a strengthening southwesterly flow aloft to develop overhead. Not
much to note over the next 24 hours as temps will rebound to
unseasonably warm levels (per norm as of late), and a net influx
of mid/high clouds should yield another notable sunset this eve.

Focus lies on the upstream trough currently off the PacNW coast,
and the confluent moisture stream in advance of its progression.
All guidance continues to point towards a positively tilted
trough progression into the Great Basin Thu, rapidly sharpening
overhead Thu night through Friday. Elevated deep layer moisture
remains a player on the warm side of the trough, and with ample
forcing within diffluent flow and WAA aloft do anticipate precip
to develop over the north Thu focused across the southwesterly
flow favored areas (Tony Grove/Ben Lomond the likely standouts
with snow levels near 8kft). Areal coverage of precip will
increase overnight Thu into Friday morning as low/mid
destabilization ensues with passage of a modest mid level front.
Expecting coverage of precip to encompass much of the north
through that time, though breadth of CAA should limit accumulating
snow to elevations largely over 7kft across the north through at
least Friday morning.

With the deeper moisture tap remaining on the warm side of the
trough, and its increasingly progressive nature whilst sharpening,
do not anticipate much more than snow showers in the air for the
valleys Fri as the trough and associated cold pool transition
overhead. Current thoughts point towards the likelihood of
Advisory snow amounts for the northern/central mtns, but that`s
about it, with only light accums for the mountain valleys Friday.

Aforementioned progressive nature of the trough will allow for a
rapid building of heights beginning Friday night, with the lingering
post frontal orographically induced precip gradually waning along
the I-15 corridor and surrounding mtns overnight. Much colder
temps are expected overnight into Saturday.

Outside of the precip and snow potential, southwesterly winds in
the prefrontal environment Thu afternoon will likely become
strong across the southwestern valleys per norm. Looks like a
solid Advisory attm as well.

.LONG TERM (After 00Z Sunday)...An upper level ridge will be in
place for the start of the long term portion of the forecast. This
ridge will begin to flatten by later Sunday, with zonal flow
developing. An upper level trough will approach the Pacific
Northwest later Sunday.

Model to model consistency on the evolution of this system across
the West Monday into Tuesday has been poor to very poor over the
last few model runs. Global models have ranged from a closed low
digging south across Nevada and then east across Arizona to a large
winter storm across Utah. The GFS has been the most favorable over
the last several runs with a consolidated trough crossing the state
early Monday into Monday night, bringing a period of precipitation
with snow levels possibly to valley floors.  The EC on the other
hand indicates a weakening system with limited precipitation across
the state.  Continued to trend toward the GFS though with lower pops
than would be indicated as a nudge toward the EC solution.


.AVIATION...Light and variable winds at the SLC terminal will
become predominately southerly after 12Z. There is a 30 percent
chance winds will shift to the northwest between 20-22Z this





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