Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 152055

Area Forecast Discussion
National Weather Service Salt Lake City UT
255 PM MDT Sun Oct 15 2017

.SYNOPSIS...High pressure will build into the region for the
first part of the week, bringing a warming trend. The high breaks
down for the latter part of the week with the next storm system
forecast to cross the area Friday into the weekend.


Water Vapor Satellite shows a ridge building in from the
southwest. 400-200mb MDCARS wind observations place a 75-115kt
anticyclonic jet from British Columbia into the Northern Rockies.
GOES/SLC 12Z RAOB/HRRR indicate that precipitable water values
vary from 0.05"-0.10" southern Utah and mountains to 0.15"-0.25"
northern valleys.

With a dry airmass and inverted conditions, took a few degrees off
of temperatures across the valleys, especially tonight and tomorrow
before clouds start to increase.

Cirrus expected to increase Tuesday on approach of a shearing and
weakening wave currently over the southern Pacific. Weak height
falls are expected Tuesday and Tuesday night. Very little thermal
gradient and moisture with this system so not anticipating
anything more than an increase in cirrus. Tuesday and Tuesday
night the subtropical jet noses into the Southwest CONUS which
should favor high clouds. Sky should clear most areas Wednesday as
the subtropical jet becomes anticyclonic as upper level ridging
amplifies to our west.

Clouds should weaken inversions allowing for a warming trend into
mid week.

A shortwave trough will move through the southern part of the
fcst area early Thursday ahead of a larger trough centered over
the Pacific Ocean. The passage of the shortwave will have little
impact on sensible weather, but it will a cause the flow to back
to a southwesterly direction. With improved mixing due to the
increasing southwesterly flow and fairly warm temperatures aloft,
Thurs will likely be the warmest day in the extended for most of
the fcst area as maxes run 5-10 degrees above climo.

The large trough over the Pacific will move inland and amplify
during the day on Friday. With the approach of the trough gusty
southwest winds will overspread much of the area particularly in the
west desert. The trough will tap into some subtropical moisture and
this additional moisture combined with modest low lvl isentropic
upglide will result in elevated precip chances Friday afternoon over
the western 2/3rds of the forecast area. This initial precip will
likely fall primarily as rain as snow levels look to be in the 9-10k
foot range. The trough will push a cold front through the area late
Friday into early Saturday. This front looks to be quite active from
a precipitation standpoint, but not particularly cold as snow levels
will only drop to around 6500-7000 feet after the passage of the

The trough moves east of the area Saturday and building heights will
put an end to any lingering orographic showers. Although guidance is
in general agreement that ridging will build over the Western US
early next week there are some discrepancies over how quickly this
occurs. The GFS operational closes off a piece of the passing trough
southeast of the fcst area on Sunday which puts the area under a
cooler northerly flow before the ridge axis starts to push overhead
on Monday. Meanwhile the EC, Canadian, and the GFS ensemble mean
quickly build the Pacific ridge eastward putting the area under a
warmer westerly flow. Leaned towards the latter scenario this
forecast package and raised Sunday maxes a few degrees. Regardless
the building ridge should kick off a general warming trend and the
beginning of next week looks dry with temps running a few degrees
over climo for most of the area.


Little operational concerns at KSLC with VFR conditions and clear
skies prevailing through the TAF period. Mainly northerly winds
will shift to the southeast between 02 and 04Z.




SHORT TERM...Rogowski

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