NWS Salt Lake City, UT wrote its last area forecast discussion before the first event at Apr 25, 3:28 AM MST, 6 hours 39 minutes earlier.
Area forecast discussion, Apr 25, 3:28 AM MST, 6 hours 39 minutes before
Area Forecast Discussion
National Weather Service Salt Lake City UT
428 AM MDT Thu Apr 25 2024
.SYNOPSIS...An active pattern beginning today will continue
into the weekend, resulting in valley rain and mountain snow along
with a cooling trend.
&&
.SHORT TERM (THROUGH 00Z SUNDAY)...The large-scale pattern this
morning consists of a storm system that is transitioning from an
upper low to an open wave trough as it continues to make its way
across the desert Southwest. A mean southwesterly flow aloft remains
in place across Utah, with an area of showers across northwest Utah
and along the Idaho border associated with a diffluent region ahead
of the approaching storm. As the trough axis crosses Utah this
afternoon, the flow will gradually turn northwesterly behind it with
precipitation spreading in from the northwest. Meanwhile, increasing
instability will aid additional showers and thunderstorms across the
area this afternoon, most notably near the mountains and northern
Utah. The HREF mean SBCAPE values top out at over 500J/kg along an
area extending from the Dugway Proving Grounds through northeast
Utah. Gusty microburst winds will be the main concern, although
surface dewpoints should be trending gradually higher.
Temperatures will trend a bit cooler today, but H7 cold advection
after the flow turns northwesterly will lead to more substantial
cooling tonight into tomorrow. Afternoon max temperatures today will
run closer to climatological normals. In addition, snow levels will
remain on the higher side today, above 8500-9000ft. Snow levels will
fall closer to 7500-8000ft tomorrow, while afternoon max
temperatures fall below normal, to the 50s across the northern and
western valleys and 60s across the far south and southeast.
Meanwhile, shower and thunderstorm activity will continue tonight,
tomorrow, and into Saturday as the next storm system carves into the
area, developing into a closed low over Utah by tomorrow night.
PWATs remain somewhat anomalous compared to climatology both
Friday and Saturday. The ECMWF-based Extreme Forecast Index
continues to indicate a signal for high QPF for Friday, and has
trended a bit in favor of high QPF for Saturday as well. Bottom
line, significant precipitation amounts will be possible, but may
not be that evenly distributed due to the somewhat showery nature of
precipitation. With the lower snow levels for Friday and Saturday,
the greatest snow accumulations are expected during this timeframe.
However, impacts could remain somewhat limited as significant
accumulation will likely remain confined to areas above 8000ft.
.LONG TERM (After 00Z Sunday/6PM Saturday)...By Saturday evening the
center of the storm system that is anticipated to bring widespread
precipitation will be downstream of the area, allowing wet
conditions to wane through the remainder of the day. With the
dynamical forcing east of the area, we'll see more of a transition
to orographically driven precipitation (as we typically do with
winter systems). Northern Utah and southwest Wyoming will be the
primary areas that will see additional precipitation as the storm
moves out of the region, with precipitation favoring the high
terrain and adjacent valley areas to the east of terrain features.
Models indicate a high amount of lower level moisture remaining in
place through the overnight hours, so anticipating precipitation to
last through the overnight.
Sunday will feature another round of showers as lower level moisture
lingers behind the departing trough, however, additional
accumulations of high elevation snow/ valley rain will be quite
light. With the coldest air departing the region, should begin to
see the start of a warming trend as we head into early next week as
high pressure attempts to build in from the south. With an active
storm track remaining in place across the PacNW region, the thinking
is that a full blown clear sky high pressure system will not take
control of the forecast area until the active storm track lets up.
Instead, we'll likely continue to see daily buildups of clouds
across the northern half of Utah where instability and moisture
combine while the southern half of Utah remains mostly cloud free.
At least for Monday, models show enough moisture in place to support
isolated to scattered light showers over the mountainous terrain of
northern Utah. Tuesday forward will likely just be cumulus buildups
during the afternoon, however, cannot rule out an isolated light
shower in the terrain.
Temperature-wise, models appear to be in solid agreement of a
rebound from below normal temperatures back to above normal by
Tuesday across Utah and southwest Wyoming. For the Wasatch Front,
could see temperatures push the 80 degree mark, or beyond. In lower
Washington County, daytime highs could be pushing 90 degrees, though
current NBM probabilities don't appear to be supportive of this
happening. Bottom line, temperatures will return to about 10-15
degrees above normal by Wednesday and Thursday. Southwesterly flow
increases ahead of another potential trough late next week, creating
dry and windy conditions across much of the area. Though fuels are
not of concern at this point, late week may serve as a reminder that
fire season is right around the corner.
&&
.AVIATION...KSLC...VFR conditions will prevail through the TAF
period, with increasing shower activity expected during the
afternoon hours and onward. As showers develop this afternoon, CIGs
are likely to lower to around 6-7kft AGL, beginning to obscure
portions of the local topography during the late afternoon/ early
evening. Periods of variable flow are expected through the morning
hours but will transition to a north wind around 18Z.
Rest of Utah and Southwest Wyoming...VFR conditions are expected to
prevail through a vast majority of the area through the valid TAF
period, however, increasing shower activity this afternoon may lead
to isolated MVFR conditions for the higher elevation terminals and/
or areas experiencing heavier showers. CIGs will lower through the
day, starting around 8kft AGL, dropping to around 5kft AGL by the
early evening hours. Local obscuration of local topography will be
the main concern. West to northwest winds are expected during the
afternoon hours across the western half of the area, with southwest
winds across the eastern half. Not expecting any significant gusts,
however, isolated strong gusts in excess of 35kts may be possible
around showers during the afternoon.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
Cheng/Webber
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