Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 232117

Area Forecast Discussion
National Weather Service Salt Lake City UT
317 PM MDT Fri Mar 23 2018

.SYNOPSIS...Southwesterly flow aloft will prevail across the
region into the day Saturday. A cold upper level trough along the
Pacific Northwest coast will move east and impact mainly northern
and western Utah along with southwest Wyoming during the latter
portion of the weekend into early next week.


.SHORT TERM (Through 00Z Tuesday)...Southwesterly flow aloft
continues to prevail across the Intermountain region this
afternoon, downstream from an upper low spinning off the Pacific
Northwest coast. An embedded shortwave which brought widespread
valley rain and mountain snow has lifted northeast of the area,
with subsidence in its wake allowing skies to generally clear out.
Daytime heating has allowed isolated showers to develop across the
north, however these should quickly die off by early evening.

The upstream upper low is forecast to slowly move inland through
the upcoming weekend. An initial shortwave which is forecast to
eject through the northern Rockies Saturday will push a trailing
cold front into northern Utah. The entrance region to an upper jet
associated with the ejecting wave coupled with the surface
boundary should allow for showers to develop during the day across
areas generally north of I-80.

A stronger shortwave is forecast to translate inland and into the
Great Basin Sunday, pushing a stronger front through the area
Sunday through Sunday evening. This will likely bring a period of
snow to much of northern and central Utah, with snow levels
expected to fall to the valley floors as 700mb temps fall to -12C
in the wake of the front. Have increased PoPs across these areas
associated with the frontal passage.

This shortwave trough is forecast to slowly evolve into a closed
low as it sags southward through the area Monday. Temperatures
will remain below climo as 700mb temps remain near -12C, and with
the cold pool aloft overhead will likely see showers develop
during the afternoon hours.

.LONG TERM (After 00Z Tuesday)...The upper level low will
continue its slow trek southeastward during the day Tuesday. Given
the cold/moist airmass in its wake some lingering orographic
showers are possible Monday night into Tuesday morning but
precipitation should be on a downward trend overall. One concern
as this feature moves into Arizona Monday night into Tuesday
morning will be the potential for enhanced canyon winds in SW
Utah. Although the MSLP gradient and cold advection are marginal
700 flow approaches 30 knots which according to local study data
may support advisory criteria for prone areas in Washington
county. However, this can be nailed down in future packages as the
relevant parameters come into focus.

Longwave ridging begins to build eastward just off the Pacific coast
towards the middle of next week. Guidance has come into agreement
that a northern branch shortwave will dive southeastward over the
top of the ridge and clip the northeastern part of the CWA Wednesday
into Thursday. Although this system is not particularly impressive
dynamically and only clips the area it does contain sufficient
moisture (especially considering its continental trajectory) to
generate some (primarily orographic) precipitation over northern and
eastern Utah. After this feature slides by Thursday, anticyclonic
northwesterly flow will prevail with a warming and drying trend in
store for the end of next week as the west coast ridge begins to


.AVIATION...Ceilings at the SLC terminal are expected to lift to
7000 feet by 22Z and then diminish completely after 01Z. Light
easterly to northerly winds are expected to continue before
shifting to the south between 01-03Z.





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