Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
351 PM MDT Sat Aug 27 2022

.SYNOPSIS...Moisture will remain in place across mainly central and
southern Utah today, with a drying trend taking shape by Sunday.
Drier and warm conditions will continue to spread into the area for
next week.

&&

.SHORT TERM (Through 12Z/6AM Monday)...Early afternoon analysis
places a mid-level trough axis from western Montana stretching
southwestward into northern California. This is providing for
modest mid-level ascent across mainly northern Utah. Meanwhile, a
pocket of mid-level moisture is rotating northeastward, entering
western Utah at the moment. The leading edge of this moisture is
providing some additional forcing to aid in the development of
showers and thunderstorms, especially over Dugway and the West
Deserts. This pocket of moisture is centered mainly in the mid-
levels per blended TPW values as PWATs continue to drop, with the
1" contour now well south across central Arizona. Much of the
drying has been at the surface and in the upper levels.
Nonetheless, enough moisture, instability (500-1000J/kg of CAPE)
and lift is in place to support isolated showers and
thunderstorms this afternoon. While an isolated heavy rainfall
threat still exists, it is much lower than the past several days
and will be relegated to a heavier, slow-moving cell over a
vulnerable area or training cells over a vulnerable area, such as
slickrock, slot canyons, burn scars, normally dry washes and
areas of steep terrain. In addition, thanks to the relatively
drier column today, the risk for gusty outflow winds/microbursts
exists, with early afternoon DCAPE values already around 1800J/Kg
across Dugway. Shower and thunderstorm activity will continue to
gradually drift eastward through the rest of the afternoon and
evening while winding down as we approach sunset. However, due to
the presence of the mid-level trough and its associated lift, a
few showers may linger through the night across central Utah.

Given the presence of the trough, some breezy afternoons are in
store, especially near the Idaho and Wyoming borders, where
west/southwest wind gusts in the 25-35 mph range are expected,
with a few higher wind gusts possible across more exposed, wind-
prone areas in this westerly flow regime.

Drier air will filter into the region on Sunday thanks to broad
mid-level west/northwest flow in the wake of the above-mentioned
trough. In fact, PWATs are expected to fall to near to slightly
below normal for late-August. As a result, shower/thunderstorm
activity on Sunday should remain isolated and confined to higher
terrain areas of central and southern Utah before diminishing
during the early evening hours.

.LONG TERM (After 12Z/6AM Monday)...Westerly flow in the wake of
the weekend system passing by to the north will evolve to a
southerly flow regime on Monday. Meanwhile, a trough will move
northerly through California and Nevada Monday into Tuesday while
high pressure ridging begins to build across the Great Basin.
Uncertainty remains regarding the strength and track of the
California/Nevada trough. While the current official forecast
maintains dry conditions Monday and Tuesday, there remains a low
(generally less than 15% probability) that isolated showers and
thunderstorms could skirt the Utah and Nevada border region during
this time, especially during the afternoon/early evening hours.
Otherwise, deterministic and ensembles are in good agreement
depicting a building ridge across the Great Basin, with just some
minor strength and positioning differences. By Wednesday, 100% of
the solution space indicates a strong ridge either over or just
south of the Great Basin. As a result of this building ridge
across the region, temperatures will gradually warm through
midweek. High temperatures in the northern valleys will reach the
upper 90s to near 100 by Wednesday, while highs in St. George rise
into the 105-107 degree range. High temperature records for
Wednesday are 98F in Salt Lake and 108F in St. George. NBM
probability of exceedance for 98F in Salt Lake Wednesday is 15%;
and this is likely conservative. Probability of exceedance of 108F
in St. George is 11% on Wednesday.

Any shower or thunderstorm activity through midweek should remain
weak and confined to high-terrain areas due to the subsidence in
associated with the ridge and presence of dry air.

By late-week, clusters depict a ridge through Thursday before
ensembles shift the ridge axis just to our east by Friday and
Saturday, suggesting the development of enhanced southwesterly
flow across the region. Most ensembles indicate the presence of a
trough approaching the PacNW as well during this time. While
ensemble QPF is essentially zero during this time, a few members
begin to reintroduce some light QPF, possibly reflective of the
potential for weak disturbances embedded in the SW flow regime. As
the ridge slides off to the east, temperatures will cool only
slightly by late-week; remaining 5-15F above seasonal normals for
early September.

&&

.AVIATION...KSLC...Winds are likely to remain out of the WNW
through roughly 03z, with gusts to 20kts. Outflow from thunderstorms
over the West Desert may cause periods of higher gusts out of the
west prior to 03z. There is a 15% chance that an isolated shower
impacts the terminal this afternoon/evening, though most showers
will remain to the south. After 03z, light southeasterly flow will
prevail.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and
thunderstorms will continue to develop through roughly 02-03z across
locations south of KPVU. The biggest impact with these storms are
gusty and erratic outflow. Additionally, strong westerly flow is
expected across northern UT through 03z, with highest wind speeds
expected across southwest WY.

&&

.FIRE WEATHER...A trough moving by to the north will bring increased
winds to the area today ahead of a cold front, with the strongest
winds expected near the Idaho and Wyoming borders. These winds
will combine with low humidities to result in marginal/isolated
critical fire weather conditions across northwest Utah today and
across northeast Utah on Sunday. A weak cold front associated with
the trough will sag into northern Utah this evening, bringing a
modest and brief cooldown for Sunday. Despite an overall drying
trend, enough lingering moisture this afternoon will maintain
isolated to scattered showers and thunderstorms, mainly across
central and southern Utah. While the storms will be trending
drier, some of them will still be capable of producing wetting
rain. Showers and thunderstorms will be much more isolated Sunday
with little chance of wetting rain. Strong high pressure looks to
build across the area for much of next week, which would result in
warm and drier conditions with record or near record high
temperatures possible.

&&

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

ADeSmet/Cunningham

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