Avalanche in Utah, January 18, 2019

Area Forecast Discussion
National Weather Service Salt Lake City UT
326 PM MST Fri Jan 18 2019

.SYNOPSIS...High pressure aloft will settle over the area this
weekend. A new storm system will enter the Great Basin for Sunday
night through Monday. This storm will bring widespread precipitation
to the area to begin the week.

&&

.SHORT TERM (THROUGH 12Z TUESDAY)...
Headlines...
* None in effect

Potential Impacts...
* Snow showers quickly diminishing for the mountains through
  sunset
* Small chance of light freezing rain West Desert late tonight
  into tomorrow morning
* Light snow and riming expected in the northern mountains
  tomorrow
* Next windy and cold state-wide storm on track for Sunday Night
  through Monday Night. Expect widespread winter driving
  conditions.

Antecedent Conditions...
Exceptional Drought is occurring near the Four Corners. The
remainder of the state is under Severe Drought, with exception of
southwest Utah and near the Wyoming border which is under Moderate
Drought.

Big Picture...
During the past 5 days, the pattern across the Pacific shifted
from strongly zonal to amplified. The pattern is beginning to
become blocked.

Water Vapor loop shows the storm system moving into the Central
Rockies as a ridge amplifies along the West Coast.

Local Observations...
12Z KSLC RAOB shows saturation in a deep unstable layer to about
500mb. Flow aloft was moderately strong from the Northwest.

Precipitable Water values range from 0.05"-0.15" mountains to
0.25"-0.35" most valleys.

A 999mb surface cyclone is located across the Texas Panhandle,
with a 1030mb surface anticyclone building across Utah. The
pressure gradient is beginning to relax across the state.

24 hour trends:
* Precipitable Water 0.15"-0.40" lower
* Temperatures are 5-15F cooler, except 5F warmer southern and
  eastern valleys
* RH values are generally 20%-50% lower

Forecast...
With strongly rising heights and warming aloft, the last of the
snow showers will continue to dissipate in the mountains through
sunset.

Warm advection ensues tomorrow, with the passage of a warm front.
This will bring thickening cloud cover and the chance for precipitation
near the Idaho border. Cannot rule out light freezing rain around
daybreak for the West Desert, but the chance is quite low at this
time. Riming is a concern for the northern mountains tomorrow.

Valleys will begin to invert tomorrow, lasting into Sunday for
some areas. Went on the low side for daytime temperatures,
especially areas with a snowpack. The good news is this will be a
brief period for the inversion as increasing southerly winds begin
to erode it Sunday.

A significant winter storm remains on track for Sunday Night into
Monday Night. Expect widespread winter driving conditions during
this period. This storm has been well advertised by computer
models, a product of amplifying flow across the Pacific. Its
associated Atmospheric River moistens the column Sunday night,
with the cold front barreling through the state Monday. The
boundary looks Frontogenetic, which would support heavier banded
precipitation. Its a colder storm which will support far more
impacts across the valleys, with a foot or two of new snow for the
mountains. One negative is a quick transition to northerly flow
Monday evening, which will limit the duration of heavy orographic
accumulations for areas traditionally favored in northwest flow.

The combination of the proximity to a strong jet, strong high
pressure building in, along with significant cold advection will
favor high winds for the mountains and adjacent downslope areas
Monday Night into Tuesday.

Went on the cold side of guidance for temperatures Monday and
Monday Night, after a warm night Sunday Night ahead of the storm.

.LONG TERM (AFTER 12Z TUESDAY)...
Typical North American pattern of a long wave trough over the
central and east and a sharp ridge near the west coast puts Utah
in between...in northerly upper flow. With the ridge now more
longitudinal, weak disturbances that clip the state will be colder
and not be able to tap as much Pacific moisture.

Though the details differ, operational model solutions and ensembles
generally agree on a disturbance clipping the state in the
Wednesday/Wednesday night timeframe. Beyond that there's little
agreement on when or if another disturbance slides by Thursday or
Friday.

Snow levels will remain low enough with any of these features to be
all-snow events in the valleys. Best chances will be in the northern
mountains. At least for now the Wednesday system looks to be quick
hitter with advisory level or less snow amounts. Given the northerly
flow and the passage of a disturbance or two, valley inversions
should not be too persistent.

&&

.AVIATION...
The SLC terminal will see VFR conditions through the night with
cigs expected to rise above 6000 feet AGL by early evening. Light
northwest winds are expected to shift to the southeast between 03Z
and 05z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

SHORT TERM...10
LONG TERM...Billingsley
AVIATION...Traphagan

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

Hazardous Weather Outlook
National Weather Service Salt Lake City UT
242 PM MST Fri Jan 18 2019

UTZ001>016-019>021-517-518-WYZ021-191400-
Cache Valley/Utah Portion-Northern Wasatch Front-
Salt Lake and Tooele Valleys-Southern Wasatch Front-
Great Salt Lake Desert and Mountains-Wasatch Mountain Valleys-
Wasatch Mountains I-80 North-Wasatch Mountains South of I-80-
Western Uinta Mountains-Wasatch Plateau/Book Cliffs-
Western Uinta Basin-Castle Country-San Rafael Swell-
Sanpete/Sevier Valleys-West Central Utah-Southwest Utah-
Utahs Dixie and Zion National Park-South Central Utah-
Glen Canyon Recreation Area/Lake Powell-Central Mountains-
Southern Mountains-Southwest Wyoming-
242 PM MST Fri Jan 18 2019

This Hazardous Weather Outlook is for the western two thirds of
Utah and southwest Wyoming.

.DAY ONE...Tonight

There is an outside chance of light freezing rain across the West
Desert late tonight into Saturday morning.

.DAYS TWO THROUGH SEVEN...Saturday through Friday

The next winter storm will affect the region Sunday Night into
Monday Night, bringing significant snowfall and winds, along with
much colder temperatures. Winter Driving conditions are expected
Monday.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to standard operating procedures.

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

For information on potential road travel impacts visit...
http://www.udottraffic.utah.gov/roadweatherforecast.aspx