Spanish Fork, Utah 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

330
FXUS65 KSLC 240450
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
950 PM MST Sat Nov 23 2024

.UPDATE...As of 9 PM MST, surface cold front had progressed
southward to the Millard/Juab county line, and had moved across
the entirety of the Wastach Front, as the boundary was located
in the Payson area. An abrupt wind shift along with winds in the
30-40 mph range proceeding the front were in place for up to 2
hours. Low to mid-level frontogenesis is quite strong, and as a
result a band of radar echos was filling in quickly from near
Ibapah northeast to near Bear Lake. Given impressive well-mixed
boundary layer (see inverted V on 24.00Z SLC sounding), an hour or
two of virga has been observed before precipitation has fully
saturated the boundary layer sufficiently enough for precipitation
to reach the surface. Circling back to the strong low to mid-
level frontogenesis, 00Z model suite depicts the strongest SW-NE
oriented band located from the west desert to the Utah Valley to
the Uintas. Precipitation production is maximized just NW of this
line, and this is where 25.00Z HREF maximizes precipitation
rates, particularly in the 2AM-6AM window. Most likely location
for these higher rates stretches from Dugway northeastward across
the southern half of the Tooele Valley, south half of the Salt
Lake Valley, stretching farther northeastward across the Upper
Cottonwoods and finally across SW Wyoming. With this period of
enhanced rates, have issued a Winter Weather Advisory for Uinta
County, WY, with 2-5" of snow now in the forecast here.

Farther southwest under the axis of forecast heaviest rates,
latest HREF mean produces 1-2" of snow from Dugway northeastward
across the southern half of the Salt Lake and Toole Valleys, with
less than 1" in valleys north and south of here. With any
frontogenetically-forced band, there are typically sharp
gradients in precipitation over short distances, and a slight
shift in any direction would alter the location of potentially
heaviest snow. A peak at ensemble max (with an associated <10%
chance of occurrence) snowfall amounts shows 3-6" in the above-
mentioned areas. The evolution of this band will be monitored
closely through the night for any necessary adjustments to the
forecast and headlines as confidence in snowfall amounts for most
valley locations is low. Previous discussion follows below.



&&

.SYNOPSIS...A strong cold front will cross northern Utah tonight
into early Sunday before continuing into central and southern Utah
during the day Sunday. High pressure will bring a break in the
action for Monday before a moisture-rich system makes its way
across the area Tuesday into Wednesday.

&&

.SHORT TERM (Through 12Z Monday)...A broad Pacific Northwest storm
system is approaching Utah and southwest Wyoming this afternoon,
with the associated cold front nosing into far northwest Utah.
Ahead of this system, southwesterly flow has picked up, resulting
in breezy winds over much of the area and some strong winds,
primarily focused over southwest Utah where a Wind Advisory
remains in effect through the afternoon.

Precipitation is currently focused over the frontal boundary over
northwest Utah, with just a few showers out ahead of it. High res
guidance indicates there will be a period of frontogenesis this
evening as the boundary continues southeast, moving into the
Wasatch Front mid to late evening. This will result in a period of
intense snow for the mountains of northern Utah through the early
morning. Guidance is trending a bit later with the arrival of the
front but a bit faster with its speed afterward, which has brought
snow totals down slightly. Still, mountain accumulations will be
significant enough to warrant current headlines.

Valley snow accumulations remain a bit of a question mark. Given
the unseasonably warm airmass over the area, road temperatures
will still be high with the front. Additionally, snow levels
should not get low enough to warrant snow until a couple of hours
before sunrise. Higher rates with the frontal band could still
provide light accumulation, but it may not get cold enough until
after the most intense precipitation has ended.

As the front moves through central and southern Utah late morning
into the afternoon, it will lose its upper level support and
weaken, resulting a decrease in snowfall rates and thus amounts.
Meanwhile, over northern Utah and southwest Wyoming, precipitation
is expected to taper off a bit faster than usual, during the early
afternoon, with high pressure quickly moving into the area behind
the system.

.LONG TERM (After 12Z Monday)...A moisture-rich storm system
will bring several days of mountain snow and mainly valley rain
preceding Thanksgiving. Those with travel plans through mountain
passes this week should monitor the forecast, as mountain snowfall
could last as late as Thursday morning.

Shallow shortwave ridging will favor a relatively quiet Monday
morning ahead of the next storm system. Moisture from a weakening
atmospheric river will wrap around the southern end of the Sierra
Nevada, arriving in SW-UT mid-day Monday and quickly overspreading
Utah and southwest Wyoming Monday afternoon. Overall, expect a
period of southwesterly flow within deep column moisture between
Monday afternoon until the frontal passage sometime late Tuesday. As
is typical with atmospheric rivers, snow levels will remain fairly
high, resulting in valley rainfall and wet snow in the mountains.
Mountains favored in SW to WSW flow regimes will do quite well
during this period due to high moisture availability, despite
relatively unimpressive synoptic dynamics.

A trough will make its way southeastward, reaching our area roughly
late Tuesday into Wednesday. There is some uncertainty in its exact
track through our area, resulting in uncertainty in which areas will
receive the most rain/snow. However, favorable jet support and mid-
level dynamics will likely result in heavier precipitation across
the area as this trough and surface cold front move through. Behind
the frontal passage, lingering low-level moisture will favor
mountain showers in northwesterly-favored terrain, potentially
lingering as late as Thanksgiving morning. Temperatures at 700-mb
are likely to drop to around -8C to -11C, thus many valley locations
could see some light snow Wednesday night into Thursday morning,
with minimal accumulations.

As far as QPF goes, there is still a decent amount of spread due to
uncertainties in the location of the best dynamics. Broadly, NBM
50th percentile QPF favors around 0.5-1" in most valleys, with 1-
2.5" in the mountains over a 3-day period. It`s worth noting that
the EC Extreme Forecast Index (EFI) is currently highlighting the
central mountains, though again, this ultimately will depend on the
track of the low.

Finally, Thursday and beyond appears to favor a drier pattern as a
ridge builds over the west coast. This time of year, this means
there is a chance for valley inversions to develop given low sun
angle.


&&

.AVIATION...KSLC...A storm system will track in through the evening,
with rain and snow into Sunday. Gusty southeast winds will last
through around 01Z when winds transition to northwest. Northwest
winds will prevail after, with scattered light rain showers pushing
in around 04Z. Rain showers are likely through around 08Z. Showers
could bring enhanced outflow winds, especially as showers start.
Rain will transition to snow likely from 08-10Z. VFR conditions will
prevail until rain transitions to snow, with IFR conditions with
snow through around 15Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Gusty winds from the southeast
to southwest will continue into the evening for southwest Wyoming
and northern Utah and through the evening for southern Utah. A storm
system will bring valley rain that will transition to snow for most
northern valleys from roughly 05-10Z. VFR conditions will prevail
where there is rain, with a transition to IFR and LIFR conditions
with snow. Snow will taper off through the morning for southwest
Wyoming and northern Utah. VFR conditions will prevail for southern
Utah. Scattered snow showers after 12Z will be capable of MVFR or
IFR conditions at KCDC and KBCE.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until 5 PM MST Sunday for UTZ110>113-117.

WY...Winter Weather Advisory until 11 AM MST Sunday for WYZ021.

&&

$$

ADeSmet/Traphagan/Cunningham/Wilson

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