NWS Salt Lake City, UT wrote its last area forecast discussion before the first event at Apr 17, 3:34 AM MST, 1 hour 56 minutes earlier.
Area forecast discussion, Apr 17, 3:34 AM MST, 1 hour 56 minutes before
Area Forecast Discussion
National Weather Service Salt Lake City UT
434 AM MDT Thu Apr 17 2025
.SYNOPSIS...A strong cold front will work through the area Thursday,
generally bringing widespread valley rain and mountain snow.
Unsettled conditions and much cooler conditions then hold into
Saturday. Thereafter, seasonable temperatures with weaker grazing
systems expected through the upcoming week.
&&
.SHORT TERM (Through 12Z/6AM Saturday)...Morning GOES-W mid level
water vapor loop currently showing a robust shortwave dropping
towards the region through the PacNW while a more broad cutoff low
continues to lift in through CA/AZ/NV. The combination of
increasing moisture and synoptic forcing is yielding scattered
showers across central and northern UT as well as SW WY
accordingly.
As the two aforementioned synoptic systems continue to
interact/phase, the more robust amplifying northern system will
help push a strong cold front into and through the forecast region
from north to south Thursday. Already, there is evidence of this
front starting to encroach through the UT/ID/NV border region.
Timing of the front hasn't shifted significantly overall, with
passage along the Wasatch Front generally expected in the 6-11 AM
range or so, location dependent (e.g. from north to south). The
highest precipitation intensity is expected to be along and
immediately following the front. Mild antecedent conditions will
help precipitation begin as valley rain and mountain snow, but
strong cold air advection in the wake of the front will rapidly
lower snow levels. Given potential for continued moderate
precipitation rates, rate driven cooling may further help push
snow levels down a bit to get some snow mixing in at lower
elevations. That said, not anticipating appreciable valley snow,
but even then the rain will likely result in a less than ideal
commute with road spray and potential for some ponding water in
spots.
The cold front will continue its southward advance as Thursday
progresses. Ahead of the front, a corridor of H7 winds in the
30-45 kt range will help mix down correspondingly moderate gusts
across southern Utah. The highest gust potential is noted across
portions of the Grand Staircase Escalante area into the southern
portions of the San Rafael Swell, but current suite of guidance
suggests conditions generally remain below advisory criteria.
Additionally, will see some modest destabilization occur ahead of
the front given the increasing daytime heating. High resolution
NAM is most aggressive with this (MUCAPE ~500-750 J/kg), while
other CAM guidance is more meager (MUCAPE ~100-300 J/kg). In any
case, this may help add some convective elements to the frontal
precipitation, adding to intensity as well as increasing the
chance for a few thunderstorms. Given the strong prefrontal flow,
wouldn't be shocked to see any more organized segments along the
front carry potential for a few strong wind gusts as well.
Conditions broadly speaking become more showery and remain
unsettled following the frontal passage later Thursday on into
Thursday night as the cold base of the northern trough continues
to sink into the region. One interesting feature to watch is the
evolution of precipitation as the troughs base and surface
reflection begin to sink through Utah. Some of the high resolution
models show something of a deformation axis trying to form and
sit/pivot through the Wasatch Front (seemingly Salt Lake
Valley/Tooele Valley/Utah Valley favored) into Friday morning.
Given the snow levels, this could yield a more snow dominant mix
to all snow, and given sufficient residence time (as can happen
under a deformation band), localized accumulations cant be
entirely ruled out. Aside from that, GFS derived lake effect probs
increase into the 40-60% range, and some CAM guidance also
supports this, though forecast flow seems more likely to support
some shower enhancement rather than a focused band. All that said,
mild surface temps would likely preclude much stacking up outside
of grassy and elevated surfaces if either of these scenarios does
manifest. Still, given timing once again around commute time,
will be something to watch.
Precipitation wise, this storm system overall remains favored to
bring more impactful conditions, at least in a winter weather
sense, to the mountains. Snow is expected to come in something of
two waves of higher intensity, first with the primary frontal
passage, and then second later on as the trough/low sink through.
Storm total snow amounts have increased slightly in the northern
mountains with this morning's guidance, with amounts more into the
5-10 inch range with locally up to 12 inches or so possible in
favored locations such as the Upper Cottonwoods. For the central
and southern mountains, a general 5-10 inches remains, with
locally 12-15 inches in places such as the Tushar Range, Boulder
Mountain, and the Henry Range. Opted to maintain Winter Weather
Advisories for the central and southern mountain zones
accordingly.
Finally, Friday mid afternoon into early Saturday morning, the
progression of the trough/low will help to impart an easterly
gradient across portions of northern Utah. Overall setup continues
to look unfavorable for a stronger downslope wind type of event,
but as is often the case when this gradient sets up, anticipate
some enhanced canyon wind gusts in typically prone spots along the
northern Wasatch Front.
.LONG TERM (After 12Z/6AM Saturday)...An upper level low will be
positioned across the four corners to start the period with most of
the precipitation having exited our CWA to the south and east.
Clearing skies and light winds will make for a cold morning Saturday
morning with most locations outside of lower Washington county and
the Lake Powell area getting near or below freezing. Highs on
Saturday will likely be the coldest of the long term period as
temperatures run 5-10 degrees below normal.
The rest of the period will be under the influence of westerly zonal
flow that will help to keep temperatures near normal to slightly
above normal further south. Northern Utah and SW Wyoming will be
susceptible to some shortwaves grazing by to the north. The
proximity to these will be just enough to keep PoPs, particularly
in the mountains, slightly elevated through much of next week.
Southern Utah will be further removed from these shortwaves and will
likely remain mostly dry. Ensembles are in agreement that there
shouldn't be any highly amplified trough or ridge through next week.
&&
.AVIATION...KSLC...A cold front will move through the terminal ~15Z
with rain showers increasing ahead of and along the front. Ahead of
the front, winds will be mostly southerly with some variability
owing to passing showers. Winds will become stronger and out of the
north behind the front with more stratiform rain through ~18Z before
a switch to more isolated convective showers developing in the late
afternoon and evening. All in all, conditions should remain mostly
VFR with brief MVFR periods along with mountain obscuration.
.REST OF UTAH AND SOUTHWEST WYOMING...A cold front will be moving
from northwest to southeast across the airspace throughout the day
with valley rain and mountain snow along the front creating brief
periods MVFR along with mountain obscuration. Gusty northerly winds
will follow the front as it moves through the north in the morning
and arrives in the south by the evening. Isolated convective showers
will develop late in the afternoon across the north that could
create brief MVFR/IFR conditions.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory from noon today to 9 PM MDT Friday for
UTZ117.
Winter Weather Advisory from 2 PM this afternoon to midnight MDT
Friday night for UTZ125.
WY...None.
&&
Warthen/Mahan
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