Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 151529

Area Forecast Discussion
National Weather Service Salt Lake City UT
929 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.


Water Vapor Satellite shows a ridge building in from the southwest.
400-200mb MDCARS wind observations place a 75-115kt anticyclonic
jet from British Columbia into the Northern Rockies. GOES/SLC 12Z
RAOB/HRRR indicate that precipitable water values vary from
0.05"-0.10" southern Utah and mountains to 0.15"-0.25" northern

Temperatures tanked early this morning owing to good radiational
cooling conditions with winds slackening and a very dry airmass in
place. For this afternoon, lowered high temperatures across the
northern valleys due to developing inverted conditions. Warming
will continue to occur aloft as the ridge gradually builds in.
Late day cirrus may begin to waft into western Utah.


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

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.


Little operational concerns at KSLC with VFR conditions and
clear skies prevailing through the TAF period. Southeast winds
should shift to the northwest between 17 and 18Z.





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