220 
FXUS65 KSLC 060418
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
1018 PM MDT Sat Nov 5 2022

.UPDATE...Updated aviation section below. The remainder of the
forecast remains in good shape and thus the previous discussion
follows below (with the exception of the updated aviation
section).

&&

.SYNOPSIS...A series of winter storms will impact the region, with
the first ending tonight into early Sunday. The next winter storm
will begin with strong winds Monday and then widespread
precipitation later Monday through late Wednesday.

&&

.SHORT TERM (Through 12Z Thursday)...An eventful November
continues to unfold with two separate, significant winter storms
in the short term forecast period. Afternoon upper air and
satellite analysis indicates a broad ridge remains in place across
the eastern Pacific while an aggressive and active northern stream
continues to impact the PacNW and the Interior West.

Afternoon mesoanalysis indicates a cold front is approaching the
Utah/Idaho border at this time. RADAR imagery depicts a broad band
of moderate to at times heavy precipitation associated with this
front. Blowing dust and strong winds associated with this front 
closed I-15 near Idaho Falls earlier this afternoon.

Reviewing the latest CAMS runs, much of the CAM guidance suggests
this band of moderate to at times heavy precipitation will
maintain coherence into northern Utah, reaching the Cache Valley
near 4 PM and gradually shifting south along the Wasatch Front,
reaching northern Utah County by 8 PM or so. This may bring a
period of moderate to heavy rain/snow mix or even snow to the
valleys during some of the higher travel times as large events 
are ongoing or let out.

As far as heavy, dense mountain snow, this will continue into the
evening and overnight period. Winter Storm Warnings remain in
effect for the Wasatch Mountains, with winter weather advisories
for the western Uintas (with the heaviest accumulations restricted
to western portions of the chain). Winter weather advisories also
remain in effect for the Bear River Valley, Bear Lake area and the
Uinta County, WY area. Winds have gusted as high as 55 mph in
light snow at the Evanston airport. 

Attention then turns to what is looking like the most significant
winter storm of the fall season. A deepening upper level trough
will gradually shift south along the Canadian Pacific Coast
through early Monday. As this trough deepens, multiple jet maxes
will be rotating around the base of the trough. This will help to
set up the first part of the storm...strong winds across western
Utah Monday afternoon and evening. 

With 700mb winds in excess of 50kts to some guidance indicating 
as high 70kts across western Utah, the bulk of guidance supports 
widespread gusts in excess of 60 mph across the western valleys of
Utah. These values are near to outside the CFSR climatology, or 
to put it another way, anomalous even for November, in a normally
windy location. Given all of this, issue a high wind watch for 
the western valleys including the Tooele Valley Monday afternoon 
and evening. Additional locations will need wind advisories, but 
for now wanted to highlight where the threat is the highest to 
exceed 58 mph.

As this strong, deep trough with a landfalling atmospheric river
around the southern Sierras begins to shift eastward toward the 
California Coast, a band of moderate to heavy precipitation will 
cross into western Utah. Expect precipitation to begin as early as
Monday afternoon across far northwestern Utah, gradually shifting
south and east through Monday night. By Tuesday afternoon, a well
forced band of moderate to heavy precipitation is expected to be 
located from roughly Logan to west of Cedar City. This band is
going to be slow to move through much of the Tuesday/Wednesday
period. 

While the coldest temperatures at 700mb lag behind the main band,
expect through a combination of dynamic cooling and heavy 
precipitation, that rain may mix with or change to snow in valley 
locations under the band as early as 18Z Tuesday. This is an area 
of lower confidence as some of the guidance suggests even with 
these processes, snow levels will remain above valleys until 
Wednesday morning. The current forecast represents a blend toward 
this colder range of guidance given the well forced, moderate to 
heavy banding represented in the bulk of the model guidance. 

This band of moderate to heavy precipitation only intensifies in
the guidance Tuesday night into Wednesday as a 160kt+ jet max with
attendant diffluence aloft sets up right over Utah. If this heavy
band is snow at this point, valleys under the band could see heavy
snow accumulations. As the 500mb low ejects crosses northern Utah
Wednesday afternoon, moderate to heavy precipitation will likely
continue across much of Utah. Flow is expected to turn west to
northwest in the wake of this feature and much colder 700mb
temperatures will build into the state. This will usher in the
last round of orographically enhanced precipitation from 
Wednesday evening into Thursday morning. 

Either way, the potential for 1-2 inches of
snow water equivalent/rain/snow looks likely for the western
valleys from St. George to the Wasatch Front to the Cache Valley.
East of the mountain spine will see significant less. The northern
mountains are currently expected to see on the order of 1.5-3.0
inches of snow water equivalent with this storm. Similarly the
western portion of the southern mountains looks to see somewhere
between 1.5-2.5".  

We don't want to get our snow lovers too excited, but confidence
is growing quickly that 1 to 2 feet to perhaps some locations
seeing 30 inches + is looking more and more likely for the
northern mountains. Confidence is quite high this will be a
significant mountain storm...however whether some areas will see
30 inches + is something that is too early to tell.  

.LONG TERM (After 12Z Thursday)...The extended forecast period 
looks to turn quiet behind the extensive trough pattern effecting 
the CWA during the short term. By Thursday morning the trough axis
will be through the region but could leave some lingering 
mountain precipitation for the northern mountains of Utah and into
SW Wyoming. Any lingering showers will likely shut off by the 
afternoon hours as the backside of the trough will promote 
northwesterly flow and subsidence over the region. This will drive
back in very cold and dry air back into the region which will 
bring clearing skies and dry conditions through the end of the 
extended. The deep cold pool behind the trough is expected to 
bring some of the coldest temperatures of the season so far as 
most valley highs are in the 30s and 40s while overnight 
temperatures fall into the teens and even single digits for a 
majority of the CWA. Deterministic models show potential for a 
shortwave to move through towards the very end of the extended 
that could bring back some precipitation for northern Utah and SW 
Wyoming but there is much uncertainty at this time with the timing
among both models and ensemble guidance.


&&

.AVIATION...KSLC...Surface cold front has moved through the area.
Band of precipitation associated with this boundary expected to
persist through 06Z per his-res models, however radar trends 
suggest precipitation will linger beyond 06Z. Rain is expected 
through around 06Z, with a 40 percent chance snow will mix in. No 
snow accumulation is expected. CIGs expected to largely remain VFR
with a 30 percent chance for MVFR CIGs. Low confidence in wind 
speed and direction forecast through 06Z. Thereafter, models are 
in good agreement that winds will ultimately shift to the SSE. 
Gusty S winds of 15-25kts expected to develop after 21Z as the 
frontal boundary moves back north as a warm front. 

.REST OF UTAH AND SOUTHWEST WYOMING...Snow with IFR or LIFR 
visibility and ceilings will last through around 05Z in southwest 
Wyoming. Much of northern Utah will have rain that tapers off from
north to south during the evening and overnight. Rain may mix with 
snow at valley locations in northern Utah, but no snow 
accumulation is expected. Elsewhere, conditions will stay dry.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...High Wind Watch from Monday morning through Monday evening for 
     UTZ101-102-115-122.

     Winter Weather Advisory until 2 AM MST Sunday for UTZ109.

     Winter Storm Warning until 4 AM MST Sunday for UTZ110.

     Winter Storm Warning until 9 AM MST Sunday for UTZ111.

     Winter Weather Advisory until 9 AM MST Sunday for UTZ112.

WY...Winter Weather Advisory until 5 AM MST Sunday for WYZ021.

&&

$$

ADeSmet/Kruse/Selbig/Wilson

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