Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 212135

Area Forecast Discussion
National Weather Service Salt Lake City UT
335 PM MDT Sat Oct 21 2017

.SYNOPSIS...High pressure will result in dry conditions with
temperatures warming through tomorrow. Seasonable conditions will
continue through midweek before a storm system impacts the area
Wednesday night into Thursday.


.SHORT TERM (Through 00z Wednesday)...The nose of an anticyclonic
northwesterly oriented jet will continue to shift across the area
this afternoon, prior to lifting north tonight. WAA associated with
this evolution is expected to increase mid level clouds across the
north tonight, but stable conditions aloft coupled with the mean jet
position should limit any tangible precip, even along the UT/ID
border region where some guidance points to isolated shower
development over the highest terrain.

WAA aloft will continue Sunday under building heights allowing a net
warming trend, with temps expected to climb some 10 degrees above
today`s highs during the peak heating hours. Decent mixing should be
present aiding this warm up.

A progressive short wave remains on track to cross the northern
Rockies region Sunday night into Monday, allowing a shallow (dry)
boundary to shift south across the area. Outside of the potential of
a few degrees of cooling across the north, this boundary should
largely slip through the area unnoticed.

High pressure will build across the area thereafter through midweek
allowing a more notable warming trend to take form. Temps across the
area are expected to once again rebound to above seasonal norms
under largely clear skies.


.LONG TERM (After 00Z Wednesday)...The ridge over the forecast
area is expected to break down during the day Wednesday ahead of
an approaching Pacific Northwest trough that is expected to impact
the area Wednesday night into Thursday. Noticeable differences
continue to exist among the global models with regard to the
strength of this system and the expected amount of associated
precipitation and colder air.

EC continues to indicate a stronger and colder system, dropping
700 mb temps to as low as -8C over southwest Wyoming and more like
-3C to -5C over northern Utah with the passage of the front. The
12Z run does keep some of the coldest air (700 mb temps in excess
of -10C) east of the area over Wyoming and Colorado, which was not
the case in some previous runs. Moisture does not look super
impressive in the EC, but would certainly produce some valley
rain/mountain snow for northern and central Utah.

The GFS has been consistent in showing a weaker system, with 700mb
temps only dropping to as low as 0C or -1C over northern Utah with
even less moisture than indicated in the EC. Have leaned a bit
toward the GFS in this forecast package as it has been more
consistent overall, but have kept in isolated to scattered POPs
and cooled temperatures a bit more than the GFS would indicate to
account for the EC solution.

Behind the exiting system, a drier northerly flow is expected to
develop on the front end of a ridge centered near the Pacific
coast. This would bring a drying trend with only slow warming
through day seven.


.AVIATION...Winds at the SLC terminal are expected to switch back
to the southeast between 01-02z. There is a chance winds shift
as early as 23-00z. Ceilings will form near 7000 feet after about
00-01z. There is also a chance of cigs near or below 6000 ft at
times overnight.




SHORT TERM...Merrill
LONG TERM...Traphagan

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