Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 292224
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
424 PM MDT Wed Mar 29 2017

.SYNOPSIS...High pressure will build into the region today. The
next Pacific storm system will cross the area Thursday through
Friday. High pressure returns for the weekend.

&&

.SHORT TERM (Through 12Z Saturday)...A significant winter storm is
on tap for the CWA over the next several days. Upper level ridging
remains in place this afternoon with near normal temperatures and
sunny skies. This tease of spring weather will only make the
winter storm to impact the area more obvious.

An upper level trough and attendant jet maxima will approach the
PACNW Coast this evening and then strengthen and dig across
northern California Thursday morning. This system will gradually
close off through the day Thursday. The exact track of this low is
extremely important to the forecast details and several global
models offer slightly different scenarios. The associated cold
front is expected to cross northern/western Utah Thursday
afternoon. Several models stall the front along the Wasatch Crest
and develop mid-level easterly flow in response to the location of
the upper level low across northern Utah. This would keep
temperatures sufficiently warm to keep mainly rain or a rain/snow
mix for the Wasatch Front. The GFS on the other hand is more
ambitious with the front and by result would indicate more snow
for the Wasatch Front. Current forecast is a blend of the
solutions, with lower snow levels than the EC/Canadian would
suggest.

Outside the urban corridor, a long duration period of moist,
northerly flow and more than sufficient synoptic lift will bring a
period of snow to the I-15 corridor across west central and
southwestern Utah. The cold front surges further east across
central and southern Utah and the resulting lowering of snow
levels is further east in this area.

Expect significant snow accumulation for the central and southern
mountains closer to the upper level low Thursday evening into
Saturday morning. Further north, the northern mountains will see
lower amounts as these areas will have warmer temperatures and
less forcing. The exception will be the western Uinta Mountains in
areas that favor northeast to easterly flow.

Issued winter storm warnings for the central, southern Utah
mountains as well as mainly the I-15 corridor in west central and
southwest Utah. Also issued a winter storm warning for the
western Uinta Mountains. Advisories were issued for extreme
southwest Wyoming, the Wasatch Mountains and the Sanpete and
Sevier Valleys.

The other main issue is high winds post frontal Thursday afternoon
into early Friday. Issued a high wind watch for this period due to
differing model solutions regarding how tight the gradient is over
this area.

As the upper level low pulls away from the area, precipitation
will gradually diminish Friday night into Saturday morning from
northwest to southeast.

.LONG TERM (After 12Z Saturday)...By Saturday morning the mid-
level closed low will be centered near the four corners and most
precip will have ended across the forecast area with the exception
of some mountain areas in Central/Eastern Utah favored in the
northeasterly wrap- around flow west of the low. Heights rise,
temps slowly warm, and skies clear during the day on Saturday as
anticyclonic northerly flow translates overhead in response to a
NE- SW oriented ridge building over the west.

The ridge is pushed east of the area during the day on Sunday as a
Pacific shortwave begins to amplify and dig south over the Pacific
coast. Although the GFS/EC are in pretty good agreement on the
existence and general track of this feature there are some
timing/amplitude differences. Specifically the EC is slower than the
GFS and pushes the attendant cold front across the state Mon
afternoon/evening, while the GFS pushes the front through Monday
morning. The EC also amplifies the system a bit more, tracking the
low center directly over N.Utah late Mon/early Tues resulting in a
longer period of cold-moist NW flow over the area and thus
generating more precip over Northern Utah. Both models depict the
baroclinic zone being fairly active and significant postfrontal cold
advection occurring statewide... and postfrontal thermal profiles
would support snow down to valley floors. It should be noted, the
Canadian shows the system becoming much more amplified, and
consequently it digs much further south and is slower... resulting
in a similar track as tomorrow`s system. Did not put much weight in
that solution at this point as it is a clear outlier, but given that
models have not handled this progressive wave train particularly
well in the medium range it is a scenario that can not be completely
ignored.

Precip will likely taper off outside of some Northern/Central Utah
orographics during the day on Tuesday as ridging begins to build
just upstream of the area. Although Wednesday and potentially
Thursday look fairly tranquil with ridging overhead, the progressive
pattern of the last 10 days looks to continue as another trough
begins to deepen off the Pacific coast late next week.

&&

.AVIATION...Winds at the SLC terminal are expected to switch back to
the southeast around 03-04Z. Clouds will continue to increase
overnight, with a 20 percent chance that ceilings drop below 7000
feet between 08Z and 14Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Storm Warning from 6 PM Thursday to 6 AM MDT Saturday for
     UTZ009-015-016-517-518.

     Winter Weather Advisory from 6 PM Thursday to 6 AM MDT Saturday
     for UTZ007-008-010-014.

     High Wind Watch from Thursday afternoon through late Thursday
     night for UTZ005.

WY...Winter Weather Advisory from 6 PM Thursday to 6 AM MDT Saturday
     for WYZ021.

&&

$$

Kruse/Carr/Schoening

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php


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