Spanish Fork, Utah 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

311
FXUS65 KSLC 172257
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
357 PM MST Fri Jan 17 2025

.SYNOPSIS...A cold front will sweep through the region overnight,
bringing primarily light snow through Saturday morning. Heavier snow
will be possible in potential lake effect snow Saturday morning.
Behind the front, a very cold airmass will settle into the region
and linger into next week.

&&

.SHORT TERM (Through 12Z/5AM Sunday)...Forecast progressing largely
as expected with increasing mid level moisture ahead of an
approaching shortwave yielding increasing cloud cover through the
afternoon across the north. Ground observations suggest the
surface reflection of the cold front associated with the system is
currently sinking into northern Utah, with satellite data showing
the mid level vort max likely pivoting down through southern
Idaho.

The cold frontal boundary and parent shortwave will continue to
push south over the coming hours. While upslope flow ahead of the
front is already resulting in some high elevation orographic snow
showers, lower elevation snow potential will increase as the front
pushes through. Observational data suggests there is still a bit
of dry air to contend with in the lower levels, but should see
this moisten up and allow increasing low elevation snow chances as
the front passes. Snow chances are reinforced overnight into
early Saturday then as the vort max swings through. Moisture then
gradually scours out through the day Saturday, with remaining snow
showers becoming more confined orographically to the terrain.

One forecast element that continues to be a source of uncertainty
is the potential for lake effect snow overnight into Saturday
morning. Despite the current cold temperatures of the Great Salt
Lake, the very cold nature of the airmass will allow a sufficient
temperature difference to result in lake induced instability.
Model soundings continue to suggest fairly uniform north to
northwesterly winds in the vertical column, which would further
support lake effect potential. At a minimum, this setup should
yield some lake enhanced snow showers. The more impactful (but
still uncertain) scenario would be a more focused lake band rather
than looser showers, and several high resolution models depict
this. If this occurs, more locally higher snow totals downstream
of the lake would be realized. The general time frame where
elements align most favorably for lake effect snow appear between
roughly midnight and 10 am. Initially flow looks to favor more
east Salt Lake Valley towards the Cottonwoods, gradually shifting
south and west eventually favoring somewhere between west Salt
Lake valley to east Tooele valley.

Given that the nature of the system results in already limited
moisture, and the uncertainty of the aforementioned lake effect
potential, there is still a good bit of uncertainty in forecast
accumulations. Given the cold airmass though, precipitation type
is more or less guaranteed to remain snow, and with good (15:1 to
20:1) snow to liquid water ratios. For most of the northern
Wasatch Front, the 25th to 75th percentile range is about
0.5-3.0". For areas that manage to sit under the potential lake
band, amounts near or above that 75th percentile would certainly
be a reasonable amount (with of course higher amounts on benches).
Most of the central to northern mountains sit in the general
1.0-5.0" range, with locally higher amounts at typically favored
spots like the bear River Range and Upper Cottonwoods. The Upper
Cottonwoods specifically could overachieve closer to 10"+ if a
lake band can manage to get focused up the canyon. For much of the
Wasatch back, forecast range is similar to the lower elevation
valleys, generally in the 1.0-3.0" range. With the moisture
limited nature of the system, snow will become increasingly
limited the further south in Utah go, with little to no precip
expected for terrain much further south than the Manti Skyline.

The final piece of this system will be post frontal winds. For
most non-sheltered locations, just a period of somewhat gustier
northwest winds are expected. However, will likely see some amount
downslope acceleration into terrain adjacent locations downwind
into Castle Country and The Swell through the day. While there
remains some potential for some slightly enhanced gap/canyon winds
into lower Washington County, guidance continues to favor a less
favorable alignment of the pressure gradient. Overall in both
scenarios, current forecast carries values that remain below Wind
Advisory criteria, but it`ll be something to keep an eye on as the
day goes on.

.LONG TERM (After 12Z/5AM Sunday)...Cold temperatures will be the
main theme for at least the first portion of the long-term period,
with a trailing wave producing light mountain showers late Sunday
into Monday. Temperatures are likely to be coldest on Tuesday
morning before rebounding heading into mid-week.

Looking at the longwave pattern, cool, northwesterly flow will be in
place on Sunday morning, with the aforementioned trailing wave
beginning to strengthen and drop southward from the Interior
Northwest. There is some uncertainty with the strength of this wave,
though ultimately will just act to reinforce cold air and produce
some orographic showers across northern Utah. Lack and moisture and
synoptic support will result in little to no snow accumulations.
Lake-effect snow chances are low (10-20% chance), but could result
in some light flurries, mainly in the Salt Lake Valley.

With this wave producing a decrease in 700-mb temperatures down to
-16C to -20C, expect additional cooling by a few more degrees
between Sunday and Tuesday, with the coldest temperatures likely on
Tuesday morning. Current forecast minimum temperatures are in the
low teens/single digits along the Wasatch Front, below zero across
the Wasatch Back and the Cache Valley, and the upper teens in St.
George, resulting in hazardous conditions for vulnerable populations
across the forecast area. Apparent temperatures will be even lower,
up to 10 degrees below the air temperature. With strong warm-air
advection at 700-mb expected to take over sometime between Monday
morning and Monday evening, it is possible that higher elevation
mountains may be on the higher end of forecasts by Tuesday morning.
However, in general, surface temperatures will lag behind this
warming aloft, thus the coldest temperatures are still expected on
Tuesday morning.

Temperatures will rebound closer to normal for the rest of the long-
term period, though a potential shortwave trough on Wednesday or
Thursday could act to slightly lower temperatures again. Moisture
will once again be lacking with this system, with little to no
impacts. Overall, large-scale northwest flow will continue through
the week as a strong ridge builds over the west coast. Looking to
the weekend, roughly 50% of ensemble members favor the
aforementioned ridge breaking down by late Friday as a trough enters
the PacNW, with this value increasing to 80% of members by Saturday.
So, despite uncertainty in the details, it appears the pattern will
remain fairly active moving forward.

&&

.AVIATION...KSLC...Increasing northerly flow this evening behind a
cold front will bring gusts to around 20 knots. Snow showers will
develop in the vicinity of the airfield this evening with about a
30% chance of brief IFR visibility in any snow showers that impact
the terminal. Snow showers may become more widespread after 6-9Z
through about 15Z in lake effect / lake enhance snow showers with
periods of IFR possible (30%) as any lake bands oscillate across the
airfield. Expect improving conditions after 15-18Z as drier air
brings and end to snow showers. High confidence in northerly winds
prevailing through the forecast period.

.REST OF UTAH AND SOUTHWEST WYOMING...Cold front continues to
advance southward through far northern Utah late this afternoon,
with the front in the Wasatch Front between 21Z-00Z, central Utah
between 00Z-03Z and to the Arizona border between 12Z-15Z Saturday
morning. Cold front will mix out any remaining northern Utah valley
haze. Period of mountain obscuration for the northern and central
mountains is likely along/behind the front and through the end of
the forecast period due to mountain snow showers. 15-30% chance for
snow showers in terminals, with VFR-MVFR CIGs. Exception is across
SW Wyoming, where occasionally heavier snow showers have the a
medium potential to create IFR/LIFR CIGs at times between roughly
00Z Sat through 12Z Sat.

&&

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

$$

SHORT TERM...Warthen
LONG TERM...Cunningham
AVIATION...Church

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