Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 240353

Area Forecast Discussion
National Weather Service Salt Lake City UT
853 PM MST Mon Jan 23 2017

.SYNOPSIS...The recent storm cycle impacting Utah will begin to
wind down over the next couple of days. Strong high pressure
aloft will lock in over the west coast states for late in the week
and on through the upcoming weekend.


.SHORT TERM (UNTIL 12Z THURSDAY)...Evening satellite imagery is
showing the trough that lifted northeast through Utah today is
becoming organized into a definable upper low over south-central
Wyoming this evening.

The widespread precip associated with this feature from earlier
today is now concentrated along the urban corridor and adjacent
Wasatch range this evening. Looking at the decreasing trend in
precip to continue until late tonight, then pick up late
tonight/early Tuesday as increasing low-level cold advection
works through northern Utah with a few degrees of additional mid-
level cooling to help support lift. Suspect that most of the
increase in precip will remain in the Salt Lake valley and points
north Tuesday morning. Giving serious consideration to extending
the winter weather advisory for the far norther zones passed 10
pm MST, with the possibility of adding blowing and drifting snow
to the extended advisory.

Over extreme southwest Utah convective precip remains focused
along the surface trough in the area of weak low-level confluence
underneath the mid-level cold pool. The individual cells will
continue to track east overnight, though the entire area will
shift south to the near the Arizona border by early Tuesday.

The end of the recent storm cycle looks to be approaching as
heights build over the eastern Pacific and a series of
disturbances drop south across the interior west. The long
overland route these disturbances will take will generate some
snow as they move through Utah, but will also begin to sweep
moisture out of the region, with the last of these features
reaching far northern Utah by early Thursday.

.PREVIOUS LONG TERM (AFTER 12Z THURSDAY)...An e-w extension of
the recently departed upper trof sits across the nrn Plains thru
the nrn Rockies then west off the OR coast at the start of the
long term period. A continued cold nwly flow to the south of this
feature will be over our CWA and a weak low that slid thru the
ridge in the ern Pac is forecast to phase with this trof and
slide sewd across the CWA as the main e-w trof shifts south. This
generates a period of weak warm advection lift over the nwrn CWA
starting early Thu and lasting into Thu eve. This could generate
areas of light snow across the nrn and central mtns and the wrn
valleys from ID south into w central UT. Do not expect much out of
this but with cold temps in place by this time, even a little
light snow could bring some accumulation on all surfaces. Have
kept a low pop in the forecast for Thu and Thu night to address

The e-w trof drops south across the CWA Thu night exiting srn UT
Fri morning. This will bring strong stabilization to the CWA on
Fri as the upstream ridge noses in and begins a period of dry
weather with strengthening valley inversions.

The EC maintains the ridge thru the weekend and into next week
gradually flattening it but keeping temps aloft mild after Sat.
The GFS shows a couple of weak grazing short waves Sun night and
Mon night that would bring some cloudiness to the north, a little
increase in winds and prevents temps aloft from warming as fast.
These grazing waves could weaken the inversions a little but do
not see any threat of precip from them.

Other than the threat of stronger inversions in the EC solution,
these differences are minor and have kept the forecast dry thru
the extended after Thu night. Also slowly warmed the higher
elevations and some of the southern valleys but kept the nrn
valleys cold.


.AVIATION...VFR conditions will generally prevail at SLC terminal
through tonight. However, there is a 30 percent chance of MVFR
conditions in light snow periodically through 06Z and then again
after 13Z Tuesday. Between 06Z and 13Z there is a 10 percent
chance of light snow and MVFR conditions. Winds are expected to
become southeast by 06Z, but could remain light and variable
throughout the night.


UT...Winter Storm Warning until 10 PM MST this evening for UTZ006-012-

     Winter Storm Warning until 4 AM MST Tuesday for UTZ007>010-517-

     Winter Weather Advisory until 10 PM MST this evening for

WY...Winter Weather Advisory until 10 PM MST this evening for WYZ021.



LONG TERM...Wilensky

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