Dense Fog in Utah, February 15, 2025

Area Forecast Discussion
National Weather Service Grand Junction CO
957 PM MST Fri Feb 14 2025

.KEY MESSAGES...

- Moderate to heavy snow is ongoing for most mountain ranges.
  Travel may be significantly impacted this evening especially
  over mountain passes.

- Mountain snow and scattered valley showers will continue
  tonight and Saturday before coming to an end Saturday
  evening.

- Total snowfall amounts are likely to range from 1 to 3 feet in
  the mountains and upwards of 6 to 12 inches in the high valleys.
  Elevations below 7000 feet will receive less than 6 inches in
  general.

- Another system arrives late Sunday bringing more snowfall to
  the area through Tuesday. The northern and central mountains
  will be favored. The potential for significant snowfall has
  increased.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 331 PM MST Fri Feb 14 2025

Latest RAP13 500 mb analysis confirmed model predictions of a
shallow short wave trough moving across western Colorado this
afternoon. This combined with divergence beneath the left exit
region of the 115+ knot jet flowing eastward just south of the
Utah and Colorado borders continued to bring widespread showers
to the region. In the lower valleys and far north, showers have
transitioned to rain while snow continued over the high country.
As predicted, a number of mountain areas received well over one
foot of new snow with some observations close to two feet in the
southwest San Juan Mountains and the Elk and West Elk Mountains.
Areas above 6500 feet in southwest Colorado indeed saw the 6 to
12 inches earlier predicted. Though snow continued, little
additional accumulation has occurred during the afternoon.

The axis of the main trough was pushing toward the eastern
periphery of the Great Basin this afternoon and will continue
eastward, passing over the forecast area tonight. In response,
flow aloft shifts to the northwest and a broad area of mid-level
subsidence fills in over the region later tonight. However, 700
mb winds of 15 to 20 knots combined with steep lapse rates
beneath the -25 C cold pool aloft will continue to generate
orographic snow over the mountains with more scattered coverage
at lower elevations, especially across eastern Utah extreme
northwest Colorado. Ample moisture remains for an additional 3
to 6 inches of new snow with northwest facing slopes favored.

A secondary short wave trough in strengthening northwest flow
aloft will enhance snowfall across the Colorado mountains on
Saturday bringing an additional 4 to 8 inches to the northern
and central Colorado mountains along the Continental Divide.
Given lack of upward dynamic forcing, showers over the valleys
will be more scattered in coverage bringing only light
accumulations. Subsidence and drying finally begins to have an
impact Saturday night with showers for all but the northern
Divide where some scattered showers are expected to linger,
though additional accumulations will be light.

Given the previous discussion, will continue the current slate
of Winter Storm Warnings and Winter Weather Advisories through
Saturday afternoon. That said, later shifts may want to consider
ending the highlights for eastern Utah early based on latest
model trends.

Temperatures will continue to hover near seasonal norms with
this mild system. However, suspect the blended solution may
again be a bit too warm for highs on Saturday. Therefore,
blended in a heavy dose of 25th percentile temperatures which
appeared to do well today.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 331 PM MST Fri Feb 14 2025

Another wave of active weather, albeit less intense and
widespread, is poised to impact the region beginning mid-day
Sunday. This weather pattern stems from a weak to moderate
atmospheric river pushing over a ridge setting up over the Great
Basin. Available moisture will be more limited with this system
compared to what we are presently seeing, but PWAT's are still
150-175% of normal across the northern CWA. Couple this with
favorable upper-level flow for orographic support, and we have
ourselves another bout of snow across the northern Colorado
mountain ranges and Flat Tops. As the AR dips southwards along
the Pacific coast, the Sierra Nevada quickly blocks strong
moisture advection from reaching the Intermountain West late on
Sunday, and near mid-day to sunset on Monday we will have mostly
dried out back to near-normal values. Where we lose out on
favorable moisture though, good upper-level support takes its
place during the later period Monday and into Tuesday as a
shortwave trough dips southwards through Utah and into the
Desert Southwest. This should be enough to prolong the wintery
weather for us through Thursday, although in lighter amounts.
Confidence in the details with this system isn't as high as we'd
hope yet as cluster analysis isn't so convinced in the moisture
content of this storm, with GFS-favored outcomes running
notably drier in terms of QPF. The NBM is in a similar boat,
with 48-hour snow accumulations across high elevations in the
northern CWA ranging by up to nearly a foot. Regardless, current
indications are for accumulations to reach 1 to 2 feet with
localized higher amounts over the Park Range, 8-12 inches over
the Flat Tops and Gore Range, and up to a half a foot over most
other high terrain.

Orographically-driven snow showers may persist into Wednesday
morning, but transient ridging should soon after give us a brief
break from the snow. Ensembles are beginning to get a little
shaky around this forecast period though, and the behavior of
upper-level features is rather uncertain. Of the ECMWF and the
GEFS, the latter depicts a broader, lower-amplitude ridge. While
the passage of this ridge seems likely to begin near mid-day on
Wednesday, the anticipated shortwave behind it could bring an
uptick in precipitation to the region anytime between late night
on Wednesday to late Thursday morning. The nature of this
trough is too variable between models for the time being, so we
will keep an eye on it for now and save elaborating on details
until better agreement in guidance presents itself.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 935 PM MST Fri Feb 14 2025

This Winter storm will continue through the next 24 hrs with
conditions improving slowly west to east after 18Z. LIFR
ceilings, fog and snow showers have developed or are forecast
to develop overnight at most TAF sites with the northwest facing
slopes favoring low stratus and fog. Winds aloft increase after
20Z with gusty west to northwest winds at most TAF sites lasting
well after 00Z. Low-Level Wind Sheer (LLWS) may become a factor
through the afternoon abd evening with mountain wave action. KHDN,
KRIL, KEGE, KASE and KGUC will remain below ILS breakpoints
through about 00Z.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory until 6 PM MST Saturday for COZ003.
     Winter Storm Warning until 6 PM MST Saturday for COZ004-005-
     009-010-012-013-017>019.
UT...Winter Weather Advisory until 6 PM MST Saturday for UTZ023.
     Winter Storm Warning until 6 PM MST Saturday for UTZ028.

&&

SHORT TERM...NL
LONG TERM...BW
AVIATION...DB

Preliminary Local Storm Report
National Weather Service Grand Junction CO
1042 PM MST Fri Feb 14 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1042 PM     Snow             7 NE Sawpit             38.06N 107.91W
02/14/2025  M12.3 Inch       San Miguel         CO   Trained Spotter

            24 hour snowfall.

&&

gjt