Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 150005 AAA

Area Forecast Discussion...UPDATED
National Weather Service Salt Lake City UT
505 PM MST Sat Jan 14 2017

.UPDATE...Updated Aviation section.


.SYNOPSIS...An upper level low pressure system crossing northern
Mexico this weekend will continue to spread moisture northward
into southern Utah. High pressure aloft will settle over the Great
Basin for the first half of the week, followed by a return to an
active weather pattern late in the week.


.SHORT TERM (Through 00z Wednesday)...An upper low spinning
across the Baja region will slowly meander east across northern
Mexico over the next 24 hours. Moisture associated with this low
has spread across the Desert Southwest and into southern Utah,
and will remain in place overnight into the day Sunday before
the airmass begins to dry as the upper low pulls further east.
Given the weak isentropic upglide have maintained likely POPs
across much of southern Utah east of I-15 through Sunday morning.
Snow levels should remain in the 5500-6000 foot range with little
if any accumulation.

Further north, an extensive stratus deck remains in place across
most valleys of northern and central Utah, and anticipate this
stratus deck to expand further north overnight. As such have
raised min temps along most of the Wasatch Front as well as the
central valleys. Could see patchy fog develop north of this
stratus plume across the Cache Valley and Bear Lake areas. This
cloud cover will likely remain in place through at least Sunday
morning, before the flow becomes northerly and drier air aloft
spreads into the area. Have gone with a decreasing trend in cloud
cover Sunday afternoon through Sunday night, however its possible
the stratus deck could remain intact and simply lower. Should
skies clear out Sunday night, fog would become a concern given the
ample boundary layer moisture.

Mid level ridging is forecast to build across the forecast area
Monday into Tuesday bringing a warming trend to the higher
elevations as well as the southern valleys, while strengthening
valley inversions across northern and central Utah. As such have
maintained a steady or slightly downward trend in valley temps
where inversions are expected to remain in place and/or

.LONG TERM (After 00Z Wednesday)...Sharp ridge axis overhead at 00Z
Wednesday will be suppressed southward overnight as the westerlies
break into the western CONUS. Some moisture spills in over northern
Utah Wednesday afternoon with just a minor threat of precip from
about I-80 northward by late in the day. The models show a weak
surface ridge remaining in place across northern Utah so have
undercut the MOS guidance by several degrees. Therefore, despite the
warm 700mb temps of near 0 degrees C, have gone with snow in the
valleys. May even see pockets of freezing rain.

The GFS is faster than the EC by 6-9 hrs on bringing a strengthening
trough into the Great Basin Thursday. The GFS operational run
appears to be the outlier compared to the GFS ensemble which is
closer to the EC (operational and ensemble). However, even with
timing differences it looks like Thursday will be a wet day across
the CWA. While the mountains will see snow as the snow level lowers
from near 7000-8000 ft in the morning to the valley floors of
central and northern Utah by evening the precip type and change over
to snow timing is difficult. Have leaned toward the slower EC
solution which gives the primary precip type as rain for most
western valleys Thursday. The cold air moves in Thursday night for a
transition to snow for most valleys.

After this point, the fast active westerlies makes it nearly
impossible to determine the strength and timing of the troughs
progged to come into the CWA Friday into the weekend. Have gone with
above normal PoPs and leaned towards slightly cooler temps, but
confidence is low on the details.


.AVIATION...MVFR CIGS are expected to prevail at the SLC terminal
through the night and into the midday hours Sunday. VSBYs will
occasionally dip into the MVFR range after about 02z and there is
a 20 percent chance of periodic IFR VSBYS between 06 and 18Z.
Winds will be light northerly through the period.





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