Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 152226 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Salt Lake City UT
426 PM MDT Fri Sep 15 2017

Corrected Synopsis.

.SYNOPSIS...A cool upper trough will linger over the area tonight
then shift east on Saturday. A milder southwesterly flow will
return for Sunday and Monday. Another unseasonably cold storm
system will impact the region beginning Tuesday of next week.


.SHORT TERM (Through 12z Monday)...The first real taste of fall-
like weather was observed across northern Utah today, with daytime
temperatures this afternoon still only reading in the low to mid
60s and some places still in the 40s and 50s in the mountain
valleys. The cold front that moved through this morning brought a
decent amount of precipitation to the Wasatch Front, many areas
measuring close to or just more than 1 inch and even some snow to
places in the high Wasatch between 9,500 and 10,000 feet or so.

Visible and water vapor satellite showing a distinct clearing and
drying behind the cold front this afternoon. 700 mb temperatures
this morning were around +3C and forecast to continue to cool
overnight to near -3C across northern Utah, however the threat
for additional precipitation should subside by 03z or so. A
secondary shortwave moves through northern Utah overnight tonight
into early Saturday which should largely remain dry, however some
of the high resolution convective models have an enhancement
across northern Utah, so have kept mention of showers across the
north through the night period.

More milder temperatures are expected into the weekend with a
drying trend taking place under a shortwave ridge pattern.
Westerly flow aloft will bring in gradually warming temperatures
aloft and a drier airmass across the Great Basin through the

.LONG TERM (After 12z Monday)...A fall-like pattern will continue
through the extended portion of the forecast with multiple cold
fronts expected to impact the state. A large, cold Pacific system
will be nearing the British Columbia Coast Monday afternoon. This
system is associated with a strong jet streak with peak winds near
165kts. As this trough digs southeastward into the Pacific
Northwest, a strong cold front will develop and move into northern
Utah Tuesday.

The main shortwave associated with the leading edge of the trough
will shift to the north and east of Utah by Tuesday evening. This
will keep most of the precipitation with this system across mainly
northern Utah Tuesday into early Wednesday. Global models have
largely come into agreement with the strength and timing of this
front, with 700mb temperatures falling to near -3 to -5C across
northern Utah by Tuesday afternoon. Light snow accumulations will be
possible, mainly above 9000 feet by late Tuesday evening.

500mb temperatures remain cold behind this initial system...near -
20C...which should drive at least some mountain convection Tuesday
evening into Tuesday night.

Details become murky between the various global model solutions by
Thursday, with significant differences in the evolution of a cold
Pacific trough and attendant cold front expected to impact at least
northern Utah Thursday into Friday.  The GFS solution features a
much more dynamic and significant cold front Thursday. The EC
solution still brings a cold front into northern Utah but it is much
less organized and much drier. For now, left pops above climo in the
forecast with falling temperatures.


.AVIATION...VFR conditions will continue at the KSLC terminal
through the TAF period. Northwest winds will continue through the
evening and are expected to switch to the southeast between 0900-
1100 UTC. However, there is a 30 percent chance that the shift to
southeast winds will not occur at all overnight and winds will stay
out of the northwest.


.FIRE WEATHER...Behind the cold front today mixing heights and
clearing indicies will begin to lower to fair to poor levels by
Saturday as subsidence spreads into the district from the
northwest. A gradual drying trend will take place through Monday
as the convective activity comes to an end across the area this

Temperatures will remain on the cool side through Saturday before
a gradual warming trend takes place through Tuesday across the
area. Transport winds aloft will be elevated through Monday,
keeping the clearing indicies in the good to excellent category
through Monday as well.





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