Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 151444

Area Forecast Discussion
National Weather Service Salt Lake City UT
844 AM MDT Thu Mar 15 2018

.SYNOPSIS...A broad Pacific storm system will move across the
western United States in pieces through the upcoming weekend,
resulting in cool and continued unsettled conditions.


.DISCUSSION...Morning water vapor and H5 analysis continues to
depict a mean long wave trough encompassing much of the western
CONUS, this anchored around a closed low just off the PacNW
coast. Two short waves to note ejecting from the mean trough
position attm, with the first lifting NE across northern UT, and
the next punching through SoCal and poised to track into northern
AZ this afternoon. A slow moving inverted trough axis exists
across central Utah, and will continue to slowly pivot slightly
north today.

Have noted a rapid decrease of snow levels along the Wasatch
Front over the last few hours as PI rates increased coincident
with the northern Utah short wave passage. Elevations above 4500ft
did accumulate, with a few inches noted along the benches of the
SLC valley where slick road conditions impacted the commute. Do
expect wet snowfall to begin to taper through mid morning with
further progression of the short wave, but likely only relatively
as mid level cold advection will continue to destabilize the
low/mid levels steepening lapse rates for the afternoon hours.
Will likely transition more showery and cellular, with isolated
thunder possible as the northern region will continue to be
influenced by the inverted trough axis across the area (slowly

Precipitation will increase across southern Utah around midday as
the SoCal short wave progresses into the southern Great Basin
area. Noting a rapid cooling of cloud tops over far southern
Nevada within an increasing diffluent environment aloft with this.
Maintaining likely to categorical PoPs across the south this
afternoon as a trailing mid level vorticity maxima/deformation
axis lifts into southwestern portions of the state.

Previous forecast handled this set up well and have made no
updates to the going forecast this morning. Previous discussion

.PREVIOUS DISCUSSION...Mid level heights are expected to rise
later tonight into Friday, in response to the upstream upper low
digging south along the Pacific Coast, before eventually turning
inland later Friday. As such should see a period of dry weather
with a temporary warming trend.

This upper low is forecast to rotate across the Great Basin later
Friday through Friday night, before ejecting northeastward on
Saturday. The associated upper jet is forecast to nose into
northern Utah beginning Friday night, bringing an increase in
showers across the west. As the trough lifts northeast, anticipate
the greatest coverage in precipitation to come during the day
Saturday, with 700mb temps falling to -10C during the day
supporting snow levels to the valley floors.

As the trough impacting the area over the weekend pulls away from
the area, a few showers may continue across the higher terrain of
northern utah into late Sunday/early Monday. After this point,
shortwave ridging will build into the area bringing gradual
warming to the state.

As the ridge shifts eastward later Tuesday into Wednesday, the
next trough will approach the West Coast. Model discrepancies
increase at this point, but several global model runs/ensembles
attempt to tap into Pacific moisture with this system Thursday
into Friday. Definitely something to watch over the next several


.AVIATION...Periodic MVFR or IFR conditions are expected at the SLC
terminal through the day, due to rain/snow mix showers. Winds will
be light and variable at times through 18Z, after which northerly
winds should generally prevail. That said, erratic winds are
possible at times near shower activity.





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