NWS Salt Lake City, UT wrote its last area forecast discussion before the first event at Jan 28, 5:00 AM MST, 9 hours earlier.
Area forecast discussion, Jan 28, 5:00 AM MST, 9 hours before
Area Forecast Discussion
National Weather Service Salt Lake City UT
500 AM MST Sat Jan 28 2023
.SYNOPSIS...An upper level weather system will impact northern
Utah and southwest Wyoming through Saturday morning. A cold front
will drop south through the area Sunday through Sunday night,
followed by much colder air for early next week.
&&
.SHORT TERM (Through 12Z Tuesday)...Another busy short term
discussion with widespread impacts to work through.
Morning upper air and satellite analysis indicates an amplified
ridge offshore the Pacific Coast. A north-south oriented jet with
a series of shortwave troughs is noted near the Pacific Coast.
Another shortwave trough noted near the Utah/Nevada/Arizona
triple point, shifting east with time.
As is the case with a north-south highway from the arctic, the
Great Basin will experience a very cold, quasi continental storm
early Sunday into Monday. Light snow from the first system across
northern Utah will gradually come to an end this morning, with a
few snow showers remaining into the evening.
An upper level low is expected to develop in a southward shifting
trough near the northern California area by Sunday morning. The
bulk of model guidance suggests an associated band of snow, ahead
of the coldest 700mb temperatures, will shift into northern Utah
early Sunday morning, reach the northern Wasatch Front around 3
AM, Salt Lake around 6 AM and Provo around 9 AM. 700mb
temperatures will be near -10 to -12C with this band of snow and
surfaces will trend quite cold. Expect a general 1 to 4 inches of
snow for the Wasatch Front, a bit higher from Brigham City
northward and into Cache Valley where the snow will start earlier
and have a longer residence time. Northern mountains will see
closer to 6 to 12 inches of low density snow.
The band of snow will continue to shift south, reaching the Cedar
City area by around 5 PM Sunday. CAMS nearly universally suggest
there will be a period of convective, heavier snow from roughly
Delta to Cedar City 5 PM Sunday through 3 AM Monday. If this does
occur, expect locally heavy snow totals in areas impacted by
heavier snow.
As the upper level low shifts further south into southern
California Monday morning, light snow will continue across
portions of central and southern Utah. By later Monday morning,
the upper level low will continue to cut off and shift
southwestward, largely ending snow across southern Utah Monday
night.
There is a window for rain/snow mix or even light snow across the
St. George area Monday morning. Current expectation is generally a
few tenths of an inch of snow will be possible in the city itself
at best. If one were to look at EPS/GEFS plots for the St. George
area, typically tuned to 10:1 ratios, some of these are showing
higher amounts of snow. A reminder though, that these plots
generally smooth out the terrain in the area and do not depict the
actual elevation of St. George properly.
Snow accumulations across central and southern Utah look to be a
general 1 to 4 inches across most valley locations above 4000
feet, up to 2 inches between 3000-4000 feet and up to an inch St.
George.
Given snow accumulations look to be in the solid advisory range
for most locations, did not issue any winter weather advisories on
this shift...and will allow day shift to coordinate with
transportation partners.
Behind the band of snow, aggressively cold temperatures will build
into the area. Current guidance suggests wind gusts to 60 mph
will be possible across the Great Salt Lake Desert Sunday
afternoon into early Monday. Will be interesting as more of the
high resolution guidance becomes available how strong winds will
be forecast by this guidance. With such a strong gradient, decided
to issue a high wind watch for the area.
A portion of the guidance also suggests gusty easterly winds will
develop across canyons of the northern Wasatch Front Sunday
evening into Monday morning. While the temperature gradient and
advection component will be there for gusty easterly winds, 700mb
flow is largely northerly and will not be very conducive to any
type of downslope wind. Expect gusts to 40 mph at best near canyon
mouths BUT if there is a change in the expected 700mb flow, this
would transition to a more supportive environment for stronger
winds.
With 700mb temperatures near -14C or so across northern Utah by
Monday morning, expect dangerously cold wind chills from roughly
Utah County northward. Current forecast suggests wind chill watch
criteria will be met from roughly Ogden to the Idaho border as
well as the Cache Valley and the Great Salt Lake Desert. While the
criteria for the Bear River Valley and Uinta County WY is a bit
colder (ie -30F), wind chills will approach these levels for these
locations too Sunday night into Monday.
For now, have issued a wind child watch for the northern Wasatch
Front, eastern Box Elder County, the Cache Valley and the Great
Salt Lake Desert (particularly near the Idaho border). Salt Lake
and Utah County will see wind chills between 10 to 0F, though
there is a chance they will fall below 0 as well. Regardless of
specific numbers, dangerously cold wind chills are expected across
much of northern Utah Sunday night into Monday morning, with
somewhat of a moderation Monday night into Tuesday with less wind
(but still near to below 0 across the Wasatch Front and Cache
Valley, even colder in normally cold locations such as the Cache
Valley, Bear River Valley and Uinta County WY). Wind chill
products may need to be extended into this time period.
Unsheltered populations and those who are unprepared for
conditions will be at high risk for frostbite and hypothermia.
.LONG TERM (After 12Z Tuesday)...The active weather pattern
experienced over the past week will gradually taper off as our
upcoming storm system departs the region and is replaced by mean
ridging Wednesday forward. That said, there is indication that a
weak trough could translate through the mean ridge, bringing
chance for light snowfall across the higher terrain and
potentially some valley areas of northern and central Utah late in
the week.
The storm impacting the region Sunday through early Tuesday will
remain well south and west of the forecast area to start the day
on Tuesday, however, continued weak lift is anticipated over the
area before the axis of the parent trough slides eastward. With
lingering moisture in the lower levels, thinking that this weak
lift could be enough to allow for continued snow showers over
portions of southern Utah, but very minimal impact will come of
this. The biggest thing to note for Tuesday will be the
continuation of cold temperatures across the region and the
maintenance of a low level inversion as a ridge begins building
into the West.
The lower level inversion should be maintained through much of
next week as ensemble guidance remains in good agreement of a
ridge building over the West, which may limit the amount of
warming that we see across the western valleys of Utah. In general
though, temperatures should remain ~5-10F below normal. Another
thing to keep an eye on as this inversion establishes is the
accumulation of valley haze through the week. As mentioned above,
there is a hint of a weak trough translating through the mean
ridge which may provide enough cooling in the low levels to weaken
the inversion and potentially mix out valley areas. Current
guidance is supportive of moving this weak wave trough the ridge
Friday through early Saturday. Will need to track the strength of
the associated cold pool over the coming days to determine how
much relief from inversion conditions we will see.
In addition to potential relief from inversion conditions, this
wave will carry with it at least some Pacific moisture. As such,
the combination of weak synoptic lift and moisture could be
supportive for some light mountain snowfall and valley rain/snow.
Just how much we will see out of this, and where, are still very
uncertain, but not anticipating any significant impacts at the
moment.
&&
.AVIATION...KSLC...VFR conditions will be maintained under an
area of low stratus with mountain snow showers through ~18-19Z.
CIGs will be low enough to create obscuration of the local
topography through much, if not all, of the day. Otherwise, light
and variable winds will persist through the early morning, taking
on a weak northwesterly component after ~15Z.
Rest of Utah and Southwest Wyoming...For areas north of about
KDTA, expect low hanging clouds with bases around 4-5kft AGL
through much of the day. Local mountain obscuration will be the
greatest impact here, but VFR conditions should be maintained
across much of the area (with the exception of higher elevation
airfields). Mountain focused snow showers will continue through
the day for areas north of KPVU, where intermittent MVFR to IFR
conditions are expected. For eastern and southern Utah, expect VFR
conditions under gradually clearing skies through the day.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...High Wind Watch from Sunday afternoon through late Sunday night
for UTZ101.
Wind Chill Watch from Sunday evening through Monday morning for
UTZ101-103-104-107.
Winter Weather Advisory until noon MST today for UTZ108-110-111.
WY...None.
&&
Kruse/Webber
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