Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 222301

Area Forecast Discussion
National Weather Service Salt Lake City UT
401 PM MST Mon Jan 22 2018

.SYNOPSIS...A grazing storm system will exit northern Utah tonight.
High pressure aloft will return midweek before a fast moving storm
system impacts the area Thursday into Friday morning. High
pressure is expected to return for the upcoming weekend.


.SHORT TERM (Through 00Z Friday)...A weak storm system currently
grazing northern portions of the forecast area is bringing a
noticeable increase in cloud cover along with a few light showers
primarily focused near the Utah/Idaho border. With this cloud
cover, the relatively cool airmass in place, and snow cover
temperatures are struggling to warm in many locations, with maxes
staying at least a few degrees below seasonal normals.

As the system moves out tonight into tomorrow morning, high
pressure will build back over the forecast area through Wednesday.
This ridge will bring dry conditions and rapid warming aloft, with
700 mb temps rising from the -10C to -8C range today to the -2C to
0C range by Wednesday afternoon. However, given developing
inversions and the previously mentioned snow cover, temperatures
will likely be slow to warm in many valley locations and have
adjusted temperatures to reflect this thinking.

The next storm system is progged to impact the area Thursday into
Friday morning. 12Z guidance has trended weaker and less moist
with the system. GFS remains faster with the front compared to the
EC, bringing it through northern Utah Thursday afternoon while the
EC delays it until after 00Z Friday. Overall, have trimmed POPs
for the Thursday morning period given model trends and made little
in the way of changes Thursday afternoon.

.LONG TERM (After 00z Friday)...The latest guidance has trended
towards a lower amplitude wave moving thru the eastern Great Basin
at the start of the long term period and diverges on frontal timing
and srn extent of the precip. As a result, confidence in this
portion of the forecast is lower now.

Models have been indicating this system would have two separate
short waves but they are now interacting with one another a little
more, and GFS and EC now differ on which wave will be stronger,
but both are showing less amplitude with the initial wave.

Have kept pops fairly high along the I-15 corridor Thu eve in
deference to the slower EC but if the faster GFS is correct,
precip will be ending during this time.

A cold airmass still follows the front into the CWA and precip
will be all snow, still likely impacting travel late Thu aftn/Thu
eve thru the northwest and west central UT valleys and in the nrn
and central mtns.

The chance of snow for Fri with the second wave is also less
certain but the airmass is still forecast to get a little colder
across the nrn CWA.

Model solutions remain divergent going into the weekend and next
week with the EC indicating a much higher amplitude and drier
pattern while the flatter GFS keeps a threat of warm advection
precip going thru much of the weekend over the north. Both do
agree on drier ridge conditions over the CWA Sun night thru Mon


.AVIATION...Southerly winds at the SLC terminal are expected to
persist through the evening hours. Only a 10 percent chance that a
northerly switch takes place before 03z. Cigs around 5000ft AGL are
expected to remain through the evening hours, possibly obscuring
mountain terrain to the east and north.




SHORT TERM...Traphagan
LONG TERM...Wilensky

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