NWS Salt Lake City, UT wrote its last area forecast discussion before the first event at Mar 27, 2:34 AM MST, 11 hours 26 minutes earlier.
Area forecast discussion, Mar 27, 2:34 AM MST, 11 hours 26 minutes before
Area Forecast Discussion
National Weather Service Salt Lake City UT
334 AM MDT Wed Mar 27 2024
.SYNOPSIS...High pressure will briefly build over Utah and
southwest Wyoming through early Thursday. A potent cold front
will cross northern Utah and southwest Wyoming Thursday afternoon
before stalling over central Utah Thursday night into early
Friday. A stormy pattern will continue for the weekend and into
early next week.
&&
.SHORT TERM (Through 12Z/6AM Saturday)...Utah and southwest
Wyoming are sandwiched in between a ridge centered over Nevada and
the exiting trough, with its back edge currently entering
Colorado. In west to northwest flow, seeing enough lingering
moisture and instability for some persistent showers over the
Great Salt Lake. As the ridge continues east, bringing a drier and
more stable airmass, anticipate these showers to taper off over
the next couple of hours. This will usher in a dry day over the
forecast area, something that has been rare lately, and a modest
warming trend. Maxes are expected to approach seasonal normals
over southern Utah while staying around 5F below climo over
northern Utah.
Our break in the action will be short lived as the ridge is
expected to quickly make its way into Colorado by Thursday
morning. As this happens, a large Pacific Northwest trough will
make its way onshore, with an associated cold front on its front
edge on track to move into far northwest Utah by midday Thursday.
Guidance is coming into better agreement with the timing and
evolution of this cold front, indicating it will cross northern
Utah and southwest Wyoming during the afternoon, undergoing
frontogenesis as it does so. Thus, there is a high chance this
will bring a potent band of valley rain (with a medium chance of
snow or graupel in the heaviest precipitation) and mountain snow
as it moves by. Ahead of the front, southerly winds will become
quite gusty, particularly over west central and southwest Utah.
Peak flow aloft in the guidance at 700mb looks to be in the 40-45
kt range, so it seems likely to see isolated gusts in excess of 40
mph in these wind prone areas, but confidence is lower as to how
long the highest gusts will persist, so have held off on headlines
at this time.
By Thursday evening, the vast majority of the guidance indicates
the front will stall roughly along a line stretching from
southwest Utah to the Uintas, weakening as it does so. Areas under
the band when it stalls will obviously see greater precipitation
accumulations than those areas away from the band so this
introduces a bit more uncertainty than usual in the forecast of
accumulations. However, given the increased model agreement, seems
prudent to raise totals in the Uintas a bit. Will also see
southerly winds stay elevated ahead of the front overnight and
into Friday morning, though these winds will most likely stay
below advisory criteria.
As the front edge of the trough and the associated front impact
the area, the main trough is expected to hang back over the
Pacific Northwest, but by Friday afternoon it is expected to merge
with another Pacific trough and slide south along the California
coast. As it does so, it is expected to link back up with the
stalled front over Utah, allowing it to slide back north as a warm
front Friday afternoon into early Saturday. At this point the
front will be significantly weaker, but there seems to be a high
chance of some additional accumulations for northern Utah at this
time, particularly over the higher terrain.
.LONG TERM (After 12Z/6AM Saturday)...Model guidance shows decent
agreement that on Saturday morning a deep Pacific trough will be
near the central California coast. Less certainty is noted on an
associated baroclinic zone, but general consensus is a stalled
boundary somewhere from western to northern Utah. Given strong
southwesterly jet support with embedded PVA and moisture advection,
would expect fairly widespread scattered precipitation, with a bit
more of a focus nearer to where any surface boundary may remain.
Uncertainty begins to increase later Saturday onward due to how the
trough begins to move inland, and if/to what degree the trough can
cut off. Currently, guidance seems to favor more of a broad and
elongated positively tilted trough progression (some minimal cutoff
lobe therein), with the associated baroclinic zone being gradually
nudged through the forecast region from west to east overnight into
the day Sunday. With this boundary progression, would anticipate a
period of more widespread/focused precipitation once again.
Following the frontal passage, colder H7 temperatures would promote
steepened lapse rates, and as a result would expect some general
instability driven shower activity to persist as the trough axis
remains overhead. This would likely once again remain the case
Monday, though again, uncertainty (especially in exact timing) is a
bit high given a more complex pattern evolution with the trough than
usual.
Total rain/snow amounts generally did not show much in the way of
trends with this forecast cycle. Southwesterly flow with the leading
edge of the trough and ahead of the baroclinic zone will promote
good orographic enhancement in those favored mountains, with that
initial time period especially favoring the southern Utah mountains.
Central and northern Utah mountains then become more favored as the
baroclinic zone pushes in, and likely thereafter until the trough
finally exits. By events end, almost all mountains look favorable to
see widespread SWE in excess of 0.75", with up to 2" possible in
some of the highest locations and locally favored areas (noting
these totals don't include precipitation prior to Saturday morning
as well). With the storm generally on the milder side, largely
expect lower valley locations to see rain, though some of the higher
elevation mountain valleys (such as the Wasatch Back) will see more
favorable chances of light accumulations following the frontal
passage. That said, wouldn't be too surprised to see some brief
periods of rate driven snow (or graupel) at lower elevations in some
of the post-frontal showers, especially nearer diurnal minimum
temps/snow level.
Tuesday into midweek, guidance leans in favor of increased ridging
building in from the west, though some ensemble members do keep a
bit more of a trailing section of the departing trough hanging on
into portions of the Desert Southwest. With ridging becoming the
favored influence, forecast carries minimal precipitation chances,
with warming temperatures back nearer to climatological normal.
&&
.AVIATION...KSLC...A low chance (~10%) of lake effect showers
remains possible through Wednesday morning. Any shower moving over
the terminal could bring about brief MVFR conditions and more
variable winds. Otherwise, VFR conditions expected to prevail with a
gradual increase in mid/upper cloud cover from late afternoon
Wednesday on into the overnight hours. Southerly winds favored to
hold, with increasing magnitudes Wednesday night into Thursday.
.REST OF UTAH AND SOUTHWEST WYOMING...A brief period of ridging will
result in more benign conditions across area terminals Wednesday,
though will see increasing mid/upper cloud cover Wednesday afternoon
on into the overnight hours as the ridge quickly begins to shift
east. Otherwise, anticipate winds to follow something of a typical
diurnal pattern with magnitudes largely expected below 15 kts.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
SHORT TERM...Traphagan
LONG TERM/AVIATION...Warthen
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