Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 181023

Area Forecast Discussion
National Weather Service Salt Lake City UT
423 AM MDT Mon Sep 18 2017

.SYNOPSIS...A cold front will cross northern Utah tonight through
Tuesday. A deep cold upper trough will move into Utah starting
late Wednesday night and will linger over the area through next


.SHORT TERM (Thru 00Z Thursday)...A short wave ridge is moving
east of UT early this morning as an upper trof moves into the
PacNW states. Skies have cleared across the CWA and the morning
will stay mostly sunny with some high clouds starting to move into
the nw.

The upper trof will cross the nrn Rockies later today thru Tue
with the nrn portion crossing nrn UT. Winds will pick up out of
the south today as the swly flow ahead of this trof surfaces this
aftn and the southerly surface gradient tightens.

The associated cold front reaches nwrn UT around 00z today and SLC
by 12z Tue. Models indicate some convection develops ahead of the
front starting late aftn and increases after 00z across the nrn
CWA north of about I-80. This convection moves away by midnight
but showers along the cold front will fill in overnight then end
fairly quickly by Tue aftn as the upper trof axis passes. The
southern extent of the precip looks to be about Utah County and
the best chances will be north of SLC. Snow levels will dip to
near 7000 ft across the far north but the showery nature of the
precip should preclude much accumulation.

Highs today will climb above normal then the airmass cools
considerably Tue behind the front across the north with highs
falling 15-20 deg from today. The front stalls before reaching
southern UT and the south will stay breezy, warm and dry on Tue.

The flow backs around to swly again on Wed as a deeper colder trof
digs into the PacNW states. Winds will increase by Wed aftn and
temps will warm back up to near normal. The cold front with this
trof is forecast to be still upstream of the CWA at 00z Thu. Not
expecting much convection ahead of this front and have trimmed
pops back on Wed from prev forecast.

.LONG TERM (After 00Z Thursday)...The EC remains the model of
choice through the extended as it was the first to latch onto the
slower and deeper solution with the GFS running 6-12 hrs behind
the curve on the EC solution. With the front being slower have
backed off on the PoPs across northeastern Utah and southwest
Wyoming until after 12Z Thursday. The EC shows good frontogenesis
from northwest central Utah to along the northern Wasatch Front
between 12 and 18Z Thursday and then pushes this convergent zone
farther east between 18Z Thursday and 00Z Friday. The GFS is
similar to the EC in regards to indicating a tightening baroclinic
zone between 18Z Thursday and 06Z Friday, but its slower in
weakening this baroclinic zone Friday evening. Used a blend of the
EC and GFS for this 12 hr period between 18Z Thursday and 06Z
Friday for the purpose of creating the QPF grids.

The 00Z run of the EC has backed off on the timing of closing off
the 500 mb low over south central Utah by late in the weekend with
the trough now remaining an open wave until Monday night over far
northeastern Utah. Therefore the cold core does not remain over
the heart of Utah so have backed on the PoPS over western and
southern valleys Saturday and all areas Sunday into Monday.
However, a rather cold northerly flow will remain in place.

Snow levels will lower down to about 6500-7000 ft between 21Z
Thursday and 21Z Friday across northern Utah mountains with
several inches possible above 8000 ft. Of course this will
depend on where exactly the baroclinic band sets up Thursday

Max temperatures will be 15-25 degrees below normal through this
period and some normally colder valleys could see their first
frost Friday night or Saturday night depending on cloud cover.


.AVIATION...South winds at the SLC terminal will ramp up this
morning between 15 and 16Z with gusts over 25kt and further
increase by midday with gusts greater 34 kt. There is a 20
percent chance of showers after 06Z tonight. Winds will remain
gusty through the overnight period.


.FIRE WEATHER...Warmer and windy conditions are expected across
the region today. A cold front will cross northern and central
Utah on Tuesday bringing cooler temperatures and some rain for the
north with a little snow at the higher elevations. The front will
stall before it reaches southern Utah and it will stay breezy,
warm and dry south of the front. Temperatures warm back up and
southwest winds will become strong on Wednesday lasting into
Wednesday night ahead of a stronger cold front. This system will
bring cooler temperatures along with fairly widespread mountain
snow and valley rain starting Thursday. The cool and unsettled
conditions are expected to continue into the upcoming weekend.





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