Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 151031

Area Forecast Discussion
National Weather Service Salt Lake City UT
431 AM MDT Sun Oct 15 2017

.SYNOPSIS...High pressure will build into the region for the
first part of the week, bringing a warming trend. The high breaks
down for the latter part of the week with the next storm system
forecast to cross the area Friday into the weekend.


.SHORT TERM (Thru 00z Thursday)...An upper ridge is centered
over CA early this morning with a dry nwly flow over UT. Skies
across the CWA are clear and winds have dropped off allowing temps
to dip to chilly levels. The low so far this morning at SLC has
been 33F. The last time it was this cold was Apr 9. If we dip to
32, which appears likely, the last time we reached 32 or below was
Mar 7, 2017 when the low was 29.

The airmass aloft has warmed considerably in the last 24 hours
however going from -9C at 700 mb at 12z Sat to a forecast +3 or 4C
by 12z this morning. This warming aloft is creating stable
inversion conditions that will prevent the warmer air from mixing
fully to the surface today. The inversions are forecast to be
strongest over the northern valleys where temps will only warm
5-10F from yesterday, while the higher elevations and the south
warm 10-20 degrees.

The ridge stays centered to out west thru Mon keeping dry mild
conditions over the CWA with some additional warming Mon. The
ridge starts to shift east and break down Tue thru Wed bringing a
small increase in winds aloft and variable high clouds. It also
results in slightly better mixing allowing temps to warm a bit

.LONG TERM (After 00z Thursday)...After several days of quiet
weather, the zonal flow pattern shifts as a trough off shore of
the Western CONUS becomes amplified moving inland late in the
week. Models have been fairly consistent with this trough feature,
while differences among models continue, though model run to run
consistency has performed better. The ECMWF has leaned toward the
GFS with respect to keeping the trough an open wave as it moves
east through the weekend, while the GFS continues to split the
trough and stretch it farther south. Nonetheless, a cooling trend
and an areawide precip event will unfold late in the week.

By late Thursday, the trough deepens as it swings inland and taps
some subtropical moisture from the eastern Pacific. Per anomaly
tables, the integrated water vapor transport (IVT) has a pretty good
signature across south-central California through the Great Basin
into Utah for Friday`s precip event. Will continue to watch as this
unfolds, but made some tweaks to the PoPs in the far extended just
trying to better time the best window for precip across the area.
Temperature wise, this system does not look quite as cold as it did
24 hours ago. Extended models eject the trough eastward fairly
quickly, with a weak ridge and zonal flow settling back over the
area late in the upcoming weekend.


.AVIATION...Clear skies and light winds will prevail at the KSLC
terminal through the TAF period. Southeast winds expected to shift
to the northwest by 18z today.


.FIRE WEATHER...Dry high pressure will build into the district
starting today and remains in place Monday. Temperatures will warm
back up but the airmass aloft warms more bringing stable
conditions. This, combined with light transport winds, will result
in poor clearing indices today and Monday. The high begins to
weaken Tuesday and shifts east Wednesday, with an increasing
southwest flow for Thursday. Transport winds will increase and
clearing indices will improve through this time. A weather system
will bring increasing moisture and winds Friday into the weekend.





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