Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 251143
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
443 AM MST Sun Feb 25 2018

.SYNOPSIS...The upper level trough over eastern Utah will exit
the state early this morning, The next upper trough will settle
into California early in the week, then turn east and impact
mainly southern Utah midweek. A significant storm system could
impact much of the Great Basin late in the week.

&&

.SHORT TERM (Until 00Z Thursday)...The mid-level trough axis
moving into eastern Utah early this morning underperformed in
terms of snow overnight. Subsidence trailing the upper trough has
brought most accumulating snows to an end in the northern valleys,
with a another hour or two of accumulating snows possible along
the I-15 corridor in central/southern Utah. Have dropped all
winter weather highlights for the lower northern valleys, with the
central and southwest valleys to follow early this morning.

Orographic enhancement will be in play through at least mid-
morning across the southern Wasatch range south into central
Utah. Dynamic subsidence will take over by late this morning,
ending any lingering accumulating snows by afternoon. Will let
the current suite of mountain/mountain valley winter weather
advisories continue this morning, with the exception of the
southern mountains where minimal additional accumulations are
expected.

The progressive shortwave ridge moving across the Great Basin
later today will be followed by backing flow ahead of the next
upper trough advancing into the Pacific Northwest by this evening.
A return to moist warm advection tonight will bring clouds and
light precip back into the far north overnight and into Monday.
Not anticipating any significant precip as the best forcing will
remain north and west of the state.

The aforementioned upper trough will shear apart as it moves
inland with the northern portion racing east through the northern
Rockies and the southern piece developing into a closed low over
California Monday evening. In between these two features a weak
deformation axis could develop across the far north Monday
night/Tuesday. If the deformation does form, then precip will
form along and south of this boundary across west-central through
northwest Utah late Monday night/Tuesday. Confidence where and
even if precip forms is somewhat low at this point as the GFS has
this feature and the ECMWF does not. Have backed off a bit on the
high Pops in this forecast package due to the uncertainty that
exists.

The latest GFS and ECMWF both take the California upper low into
southern California Tuesday, then turn it east and gradually
weaken it as it moves into Arizona late Tuesday night/Wednesday.
Precip will concentrate across northern Arizona/extreme southern
Utah Tuesday night in response to vorticity lobes rotating north
ahead of the low into an area of good upper divergence and
terrain upglide. The current path of the upper low suggests that
the heaviest precip will stay south of the state, though any
northward deviation would greatly increase precip across southern
Utah midweek.

.LONG TERM (After 00Z Thursday)...A broad trough is expected to drop
south to the Pacific Northwest coast on Thursday. Ahead of this
system, the forecast area should see warm advection develop in
southwest flow Wednesday night through early Friday. This would
bring maxes near or slightly above seasonal normals during the day
Thursday. As the flow aloft increases with the approach of the
system, southwesterly winds are expected to increase, becoming quite
gusty for some locations Thursday into Friday.

Models remain in fairly good agreement with regard to the arrival of
the trough, bringing the associated cold front into northern Utah
during the day Friday before stalling it over central Utah on
Saturday. EC/GFS both show a good area of precip developing over
northern and central Utah during the day with this boundary and have
raised POPs with increasing confidence.

Precip along the boundary is progged to become more spotty along the
stalled front on Saturday, but the latest EC gets it going again
Saturday night/Sunday morning as the back side of the trough pushes
across the area. The GFS overall has the system weakening and taking
a somewhat more northerly track as it moves through and is therefore
not as bullish with the precip refiring along the front. Have kept
primarily in the isolated to scattered range for Saturday and Sunday
given that there is more uncertainty during this period. High
pressure is expected to return behind the system. High pressure is
expected to return behind the exiting trough after day seven.

&&

.AVIATION...VFR conditions are expected at the SLC terminal through
the morning. Cigs below 6000 feet AGL are expected to rise above
that value between 11Z and 13Z. There is a 30 percent chance lower
cigs will stick around longer than anticipated. Northwest winds are
expected to return to the south by 14Z, becoming gusty at times
during the afternoon.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until 11 AM MST this morning for
     UTZ006>010-517.

     Winter Weather Advisory until 6 AM MST early this morning for
     UTZ014>016.

WY...None.
&&

$$

SHORT TERM...CONGER
LONG TERM/AVIATION...TRAPHAGAN

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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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