Evanston, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

237
FXUS65 KSLC 221041
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
341 AM MST Mon Dec 22 2025

.KEY MESSAGES...

- Temperatures will remain well above normal, with additional
  record temperatures likely through midweek.

- A landfalling atmospheric river will bring valley rain and
  mountain snow above 8000 feet to much of the region Wednesday
  into Thursday.

- The heaviest rain, below 8000 feet or so, will occur across
  southern Utah Wednesday into Thursday. Enhanced runoff is likely
  across this area, with all streams, slot canyons, and other
  waterways running high.

- The heaviest snow will occur above 8000 feet through Thursday
  across the southern mountains, with accumulations in excess of a
  foot likely across the Brian Head area, the Tushars, and near
  Boulder Mountain.

- The unsettled pattern will continue with gradually falling snow
  levels, reaching as low as 6000 feet by Friday evening and
  continuing to fall toward valley floors by Saturday morning.
  There is a 25% chance of measurable snow for the valley floors
  of northern Utah Friday night into Saturday morning.

&&

.DISCUSSION...It is going to be a very warm, very active week
across the region as Utah remains locked in a warm, moist,
southwesterly flow pattern. It is currently 60F at the KSLC
terminal (as of 245 AM or so), which is the 27th warmest day on
record already. Given it is mid-December, still expect the
northern Utah valleys to decouple to an extent between now and 9
AM...but if that doesn`t occur, temperatures will start the day
exceedingly warm...and even more records will likely be broken.

Early morning upper air and satellite analysis indicates an active
jet remains in place from the eastern Pacific into the Interior
West. A deep, relatively cold trough and associated upper level
low is located in the Gulf of Alaska. The eastern Pacific ridge
has retreated well off the coast. Additionally, deep moisture
advection from the ITCZ is shifting north and entraining into the
previously mentioned jet circulation.

With the somewhat tropical origin of this landfalling atmospheric
river, PW and IVT anomalies will reach the maximum in the
climatology for the NAEFS by Wednesday afternoon into Wednesday
evening. EFI (EC based Extreme Forecast Index) also highlights
this area for both high values of the extreme forecast index and
areas in the Pine Valleys show a shift of tails, indicating
members of the EPS show even more extreme values.

By early Wednesday afternoon, the trough and associated jet max
will shift eastward, into California. This will bring strong
southwesterly flow and deep moisture advection to southwestern
Utah as early as late Wednesday morning. By Thursday morning, the
25th to 75th percentile range for rain (and snow water equivalent
above about 8000 feet) will range from 0.50-1.50" for the St.
George area and Zion National Park, 1.00-2.00" for the Pine
Valleys and other areas in which southwesterly flow presents a
preferential upslope regime. The Boulder Mountain area will trend
about 6 to 12 hours later, but with a 25th to 75th percentile
range around 0.65-1.25" by Thursday evening. This will translate
to 6 to 12 inches of snow, locally up to 15 inches above 8000 feet
for the southern slopes of the southern mountains. Will let the
next shift coordinate with transportation partners, but at least
some headline seems appropriate for winter conditions.

With moderate to heavy rain across southern Utah Wednesday into
Thursday, the Weather Prediction Center has outlooked the area in
a marginal risk for at least a 5% chance of rainfall exceeding
flash flood guidance with 25 miles of a point across southwestern
Utah. While any flash flooding threat is remote given the rates
will be more synoptic than convective, all area streams, river,
slot canyons, etc will be running Wednesday through at least
Friday and any recreational activities should avoid these areas.
As an example, the current forecast from the Colorado Basin River
Forecast Center indicates the North Fork of the Virgin River will
rise from 45 cfs of flow today to over 500 cfs by Thursday
morning.

Precipitation will reach northern and central Utah by Wednesday
evening. The heaviest precipitation will impact areas that see
preferential upslope in moist, southwesterly flow. 25th to 75th
percentile ranges by Thursday afternoon for northern and central
Utah average around 0.25-0.75" for most valleys and 0.60-1.50" for
most mountains. Snow levels will be higher across northern Utah,
around 8500-9000 feet during this period.

BUT...

As the previously mentioned cold upper level low shifts south and
east with the longwave trough, colder air will shift into the
region by later Friday. Showers will continue across much of the
region through the day Thursday and into Friday...but snow levels
will likely fall through the evening Friday. By 11 PM Friday, the
25th to 75th percentile range for snow levels for the central
Wasatch Front (as an example) will be about 6500 feet to 4200
feet. By Saturday morning this range is 6000 feet to below valley
floors. The big question for those waiting for measurable snow to
valley floors across the Wasatch Front, will precipitation be
ongoing with the arrival of this cold air? The NBM suggests around
a 25% chance of measurable snow for the valley floors by 5 AM
Saturday, increasing with elevation from 30 to 60% between 4400
feet and 5500 feet. So there is some hope that the valley floor
will see the first measurable snow of the season by Saturday
morning (Dec 27th). This would be the second latest first
measurable snow for the KSLC and third longest period of no
measurable snow at KSLC (284 days). That aside, storm totals
between Thursday night and Saturday evening look to approach 6 to
12 inches for most mountain locations (25th/75th percentile), with
up to 0.5 inches for northern valley floors, up to 2 inches
benches.

Precipitation will slowly come to an end by later Saturday as a
much colder airmass builds into Utah. Temperatures will be around
15 to 25 degrees colder Saturday into Sunday than much of the
week.

&&

.AVIATION...KSLC...Strong southerly winds with gusts to 25-30kts
are likely to continue through the morning, though there is chance
that winds temporarily decrease to around 10kts between ~12-15z.
The lake breeze will try to overcome these southerlies during the
afternoon, but there is some uncertainty with if/when flow
transitions to northwesterly; current timing is around 22-00z. VFR
conditions will prevail with BKN mid- to high-level clouds.

.REST OF UTAH AND SOUTHWEST WYOMING...Higher elevation sites and
some valleys downwind of higher terrain (Tooele, Salt Lake, Cache
Valleys) will see gusty southerly winds through the morning, with
gusts becoming more widespread after 18z. Showers will develop
along the UT-ID border this afternoon, with the highest chances
for precipitation reaching KLGU expected before 22z. VFR
conditions will prevail with SCT-BKN mid- to high-level clouds.

&&

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

$$

Kruse/Cunningham

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