Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 111149

Area Forecast Discussion
National Weather Service Salt Lake City UT
449 AM MST Mon Dec 11 2017

.SYNOPSIS...Strong and persistent high pressure aloft will remain
the dominant weather feature across the western states through at
least the middle of this week.


.SHORT TERM (Through 00Z Friday)...A high amplitude mid level
ridge continues to encompass much of the western CONUS early this
morning, and will remain the dominant weather feature through the
short term period. This will maintain valley inversions across
northern and central Utah with strengthening inversions and a
continued decline in air quality, as well as areas of overnight
and morning fog/stratus.

In the near term, fog and low stratus has once again developed
across the Cache Valley and Bear Lake areas, as well as over the
Great Salt Lake and locations immediately south and southeast. If
a southerly drainage wind fails to establish itself over the next
hour or so, this fog may have an impact on the morning commute,
along I-80 as well as Legacy Parkway and portions of I-215. These
areas will likely continue to experience overnight/morning
fog and stratus, and have included a mention throughout the short
term, with the fog/stratus likely to expand across the Great Salt
Lake basin and possibly the Wasatch Front through the week.

Aside from fog/stratus, the primary challenge in the short term
period remained temperatures. With 700mb temps forecast to
continue warming today, reaching 4C this afternoon across northern
Utah, will see the inversion continue to strengthen and lower,
likely resulting in a continued decrease in air quality. Have kept
temperatures near or slightly cooler than Sunday`s max temps
across the lower elevations, while warming temperatures above the
inversion across the higher terrain as well as the south for
today. Little change in the overall pattern is expected Tuesday to
trended temps toward persistence.

By Wednesday the mid level ridge is forecast to retrograde a bit
westward, allowing a weak shortwave to dig through the central
Rockies. It`s unlikely this will have any impact at all on valley
inversions as 700mb temps cool to near 0C, however should realize
a cooling trend across the higher terrain Wednesday. Little
overall change is expected Wednesday into Thursday, and again have
maintained a persistence temperature forecast.

.LONG TERM (after 00Z Friday)...Friday looks to be the last day of
haze along the Wasatch Front and fog in the Cache Valley as both the
EC and GFS show a shortwave trough moving across northern one half
of Utah Friday night with roughly -7 to -10C 700mb temps. Although
QPF maybe rather light the airmass should be cold enough to turn
over the atmosphere and erase the inversion.

The latest 06Z GFS just got amped up with this Saturday shortwave.
Although have downplayed the QPF in the official forecast this
latest run is not totally out to lunch as there were 2 or 3 ensemble
members from the 00Z run that had a much stronger trough. Will not
adjust forecasts at this time, but something to be aware of for the
12Z package. Perhaps the SuperBlend was catching onto it and I
ignored it as the operational GFS was not too impressive as well as
the EC. Some forecast surgery may be needed in the extended if the
12Z GFS follows suit.

.AVIATION...At the SLC terminal...VLIFR conditions are expected
to prevail through at least 15Z with a 40% chance of lasting through
17Z or 18Z. Winds will remain nearly calm through 17Z then become
northwest at light speeds. MVFR conditions are expected through this
afternoon, although there is a 30 percent chance that IFR or LIFR
conditions will continue. There is a high probability that VLIFR
conditions will return after 02Z tonight.





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