Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 252353
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
453 PM 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 (THROUGH 00Z THURSDAY)...
Antecedent Conditions:
Severe drought ongoing Salt Lake City southward and eastward.
Moderate drought most other locations, although areas near the
Idaho and Wyoming border are fairing better, just Abnormally Dry.

Big Picture:
The Pacific ridge has retrograded westward into the Central
Pacific, allowing the storm track to affect the Western CONUS
during the past 10 days. This would allow the next storm to track
well to our west. Water Vapor loop indicates the next system is
diving southeast from off the British Columbia coast.

400-200mb MDCARS wind observations place a 100-145kt northwesterly
jet from western Alaska to off the British Columbia coast. Meanwhile
a 140-165kt jet was entering the western Pacific.

GOES/SLC 12Z RAOB/HRRR indicate that precipitable water values
vary from 0.05"-0.10" mountains to 0.10"-0.20" most valleys.
Blended Precipitable Water product shows the next atmospheric
river nosing into the Pacific Northwest.

Local Trends and Observations:
1032mb High pressure over west central Utah this morning has moved
into central Utah while weakening to 1027mb. Gusty south winds
over the Pacific Northwest and northern Rockies are occurring
with coastal rainfall and interior snowfall spreading into
southern Idaho and eastern Nevada.

24hr temperature trend is warmer by 5-15F. Dewpoints are little
changed, except 5-15F lower across far northwest Utah.

Valley road temperatures have warmed into the 40s, except upper
30s near the Idaho border. Meanwhile mountain routes remain at or
below freezing this afternoon.

Forecast:
Warm advection already setting up with the warm front crossing
southwest Utah during the afternoon, lifting into northern Utah by
early tomorrow morning. This along with increasing south winds
will bring much warmer temperatures to the area. The exception is
closer to the Idaho border where warm advection precipitation will
spread in from Idaho late tonight through tomorrow. While valley
accumulations will generally be light, roads will be quite cold
across far northern Utah allowing snowfall to rapidly accumulate
on roads for the morning commute. The northern Wasatch look to do
quite well in this pattern, generally 6-12" with accumulations
nearing 18" near the Idaho border by late Tuesday.

Confidence on the southern progression of this area of
precipitation is low at this time. While Winter Weather
Advisories were posted generally Odgen northward, that does not
mean the southern Wasatch or western Uinta mountains will miss
out. Snow will reach these areas slower, mainly Monday afternoon
and night. However travel issues including I-80 cannot be ruled
out for the Monday morning commute. This area will have to be
closely monitored by later shifts, advisories further south are
possible in later forecasts.

Height falls reach northwest Utah late tonight, with the decaying
cold front weakening over northern Utah Monday night into Tuesday.
Light accumulating snowfall may impact the Wasatch Front during
this period.

The storm track will be much further west than previous storm
systems during this storm cycle. This is due to the retrograding
central Pacific ridge, and northerly jet from Alaska. Height falls
track down the west coast Monday and Monday night. Significant
snow accumulations are possible along the Nevada border late
Monday into Tuesday with the deformation zone setting up over the
area.

The storm tracks east across Arizona Tuesday into Tuesday night,
bringing the chance of accumulating snowfall to many parts of
southern Utah. Instability increases during this period so bands
of showers are expected rather than a widespread area of
precipitation.

Strong height rises expected Wednesday with a shortwave ridge
building into Nevada, bringing benign weather during the mid week.

.LONG TERM (AFTER 00Z THURSDAY)...
Changes with the latest 12z model guidance observed this
afternoon has the EC slowing the Pacific Northwest trough down as
it moves into the West coast and into the Great Basin Friday, and
the GFS is trending a bit toward the latest EC. So, minor changes,
but it appears they continue to merge toward one another, so
confidence is building with timing and details for the trough
moving through late week into next weekend.

Tried not to alter the previous forecast much, as it was in good
shape portraying the trough progression Thursday through Saturday.
Exactly placement of the trough and best dynamics will depend on
whether or not the southwest flow rounding the bottom of the trough
persist longer or not and southwest favored slopes accumulate more
ging the chance of accumulating snowfall to many parts of
southern Utah. Instability increases during this period so bands
of showers are expected rather than a widespread area of
precipitation. snow or not. One aspect that continues to come in
good agreement is increasing southwest winds ahead of the front
late Thursday through early Saturday mainly across west and
southwest Utah. Made some minor PoP changes with areal coverage
but trended the values near the same.

Timing of the 700mb front differ among models and where it stalls
but the big picture remains the same. Temperatures aloft don`t
appear to remain very cold for very long with the weak northwest
flow behind the front and warm advection quickly trying to push in,
so daytime temperatures should reach near or just above seasonal
normal going into the weekend. Precipitation behind the front on
Saturday remains spotty so kept mention to chance for the mountains
and slight chance for valleys. And looking farther out to day 7 and
beyond, high pressure ridging builds in over the West Coast with
another trough feature trying to develop out over the central
Pacific.

&&

.AVIATION...
Winds at the SLC terminal should remain south through the
evening, with a 30 percent chance of gusts exceeding 30 mph before
06Z. Ceilings will likely lower through the evening, but should
remain well above 7000 feet through at least 06Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory from midnight tonight to 11 AM MST
     Tuesday for UTZ007.

     Winter Weather Advisory from 3 AM Monday to 11 AM MST Tuesday
     for UTZ001-002-005-006.

WY...None.
&&

$$

SHORT TERM...10
LONG TERM...Dewey
AVIATION...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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