Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 231018
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
418 AM MDT Sat Mar 23 2024

.SYNOPSIS...A strong cold front will cross the area Saturday
afternoon into Saturday evening heralding the beginning of an
active storm cycle through the next week. Unsettled conditions
will continue in the wake of this weekend`s storm system with the
next significant system impacting the area Thursday into Friday.

&&

.SHORT TERM (Through 12Z Monday)...The beginning of a prolonged
active storm cycle will commence today, with a strong cold front
crossing northern Utah this afternoon into this evening. Early
morning upper air and satellite analysis indicates one of the more
meteorologically interesting pictures of the last few weeks. A
strong subtropical jet is streaming across the southern tier of
the United States. Meanwhile, an active northern jet associated
with an upper level low near coastal areas of the Pacific
Northwest continues to slowly shift eastward. Broad upper level
diffluence is noted across the Great Basin. Looking further west
into the Pacific, a notable Rossby wave train extends far into
the northern Pacific. An area of moderate to heavy precipitation
is noted in California associated with the 700mb baroclinc zone.

Prior to the cold front, expect gradual destabilization across
northern and central Utah. CAMS indicate SBCAPE around 500 J/kg or
so by early afternoon across the area. With deep, dry southwest
flow in place, model soundings confirm the anticipated inverted-v
type environment. Expect isolated to widely scattered relatively
high-based convection to develop ahead of the front, with the
potential for graupel and gusty winds.

Speaking of winds, 700mb winds approaching 50 kts will be present
across western Utah ahead of the front. This will bring
widespread gusts up to 50 mph (80%+ probability) to western
valleys from roughly Juab County to southern Iron County.
Alternatively, guidance suggests a less than 10 percent chance of
wind gusts in excess of 55 mph. Going wind advisories are on
track. Gusty winds up to 40 mph are also expected this afternoon
and evening across eastern and southern valleys, however the
probability of winds remaining below wind advisory criteria is
greater than 80%.

The strong cold front looks to reach the Wasatch Front after 5 PM,
bringing a period of moderate to heavy valley rain and mountain
snow. Snow levels are likely to dip as low as 5000 feet, with snow
mixing in potentially to valley floors in the heaviest
precipitation (current guidance suggests a 10-20% chance of snow
for valley floors with little to no accumulation).

Moderate to heavy precipitation is expected to last 2 to 5 hours
or so for most locations across northern Utah, closer to 2 for
valleys. The cold front looks to gradually weaken across central
Utah this evening. Meanwhile, strong jet support for precipitation
will develop across southern Utah this evening into tonight.
Expect another area of moderate to heavy precipitation to develop
south of I-70 and continue into the overnight hours.

Given widespread snow totals around 6 to 12 inches for the
mountains with locally higher amounts up to 15 inches in the upper
Cottonwoods and 18 inches for the Tushars and near Brianhead,
issued a winter weather advisory. Note that for the northern and
central mountains, the heaviest snow will be that 2 to 5 hour or
so period with the front. For the southern mountains, the heaviest
snow will be with the jet support this evening into tonight.

Expect widespread showers to develop associated in an environment
with steep lapse rates Sunday afternoon into Sunday evening.

.LONG TERM (After 12Z Monday)...Active weather resumes through a
majority of the upcoming week as the forecast area remains under a
colder, more unstable airmass alongside lingering lower level
moisture. Though models continue to indicate a brief period of
shortwave ridging mid-week, consensus points toward yet another
trough moving into the West through the second half of the week,
bringing potential for another widespread round of precipitation
across Utah and southwest Wyoming, and perhaps some wind across
the western valley areas.

While the cold front associated with the anticipated storm
(today...March 23) will be well downstream of the forecast area
on Monday, a mean longwave trough will be settled over much of the
West to start the week. Under this trough we`ll find colder
temperatures and general instability within the lower to mid-
levels of the atmosphere. This instability, paired with lower
level moisture, will help to bring diurnally driven snow showers
across the high terrain and higher elevation valley areas, with
mixed precipitation in the lower elevation valleys (outside of
lower Washington County). Given relatively weak synoptic forcing,
thinking that impacts will be isolated and limited to the
mountainous terrain where locations seeing several series of snow
showers could see upwards of 3 to 5 inches of accumulation,
especially in areas with favored orographics in W to NW flow (i.e.
northern Wasatch, Bear River Range, Western Uintas). Valley areas
on the Wasatch Back may be able to squeeze out up to 2 inches in
the higher elevation areas, however, surfaces will be competing
with late March solar insolation. For the Western valleys, snow
levels are likely to rise to 4500-5200ft MSL, limiting the
potential for snow to the benches. Heavier showers may allow a
quickly cooling environment under the shower itself which could
help lower snow levels to valley floors, however, given strong
solar and instability, we`ll probably end up seeing more graupel
like showers quickly melting once done. So again, impacts limited
to the high terrain.

Overnight Monday into Tuesday, models indicate a weak shortwave
translating over the region which will help boost potential for
overnight precipitation... but again, expecting very limited, if
any, impacts from showers induced by this weak wave. Overall,
Tuesday should look pretty similar to Monday, though coverage of
showers and potential for higher precipitation intensity within
showers will likely be higher given the increase in synoptic
support. For both days, temperatures across the forecast area will
generally run 5-10 degrees below average for this time of year.

A brief lull in activity is anticipated on Wednesday, mainly from
the morning hours through the evening hours as a shortwave ridge
builds over the area. Even then, will maintain a slight chance for
showers across the area as lower level moisture lingers and
afternoon cloud buildups continue. Ensemble mean 500mb heights
place this ridge axis downstream of the forecast area during the
overnight hours into Thursday, opening the door to another colder
Pacific trough. Ahead of this trough, expecting an overall
increase in lower level flow and atmospheric stability, both of
which will help to increase the overall chances for afternoon
showers and stronger winds across the western Utah valleys.
Current NBM guidance showing the lower end of wind gust potential
across southwestern Utah to be in the 35-40 mph range with the
upper end in the 50-60 mph range (mean values 40-45 mph). There
are a handful of guidance (about 25%) showing peak gusts above the
60 mph for southwestern Utah, so will have to monitor this threat
over the coming days.

Thereafter, there is some uncertainty with how quickly this
Pacific trough moves inland and what kinds of impacts will be seen
across the forecast area. As of right now, thinking that this
will be a similar event to what we`re about to see... with impacts
from snow being limited to the higher terrain. However, there is
greater potential for the southern half of the area to become the
target for higher precipitation totals, particularly heading
through the weekend.

&&

.AVIATION...KSLC...VFR conditions will remain in place over the
KSLC terminal through the late afternoon, with gusty south winds
prevailing through around 01Z. Shower activity will increase in
the vicinity around 18-19Z, causing obscuration of local
topography. A focused band of precipitation is expected along a
frontal boundary around 01Z, bringing a NW wind shift, a round of
precipitation, and lowering CIGs to the airfield. Precipitation
type is expected to stay rain, though there is a 15% chance that
snow becomes the dominant precipitation type after 02-03Z.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions are expected
across the area through about 18Z. Thereafter, shower activity
will increase across much of the western half of the forecast
area, lowering CIGs into the MVFR to IFR category. Early in the
afternoon, showers will be largely confined to the high terrain
and downwind valleys, however, a band of heavier precipitation
will be focused along a frontal boundary during the afternoon and
evening hours. This band will become pronounced across the
northwestern portion of Utah around 21-22Z, shifting into the
Wasatch Front by 01-03Z, and dissipating after 06Z. Otherwise,
gusty southerly winds are expected across much of the area through
the timing of the cold frontal passage.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory from 3 PM this afternoon to midnight MDT
     Sunday night for UTZ110>113.

     Wind Advisory from 9 AM this morning to 9 PM MDT this evening
     for UTZ115-116-122.

     Winter Weather Advisory from 6 PM this evening to midnight MDT
     Sunday night for UTZ117-125.

WY...None.

&&

$$

Kruse/Webber

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


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