Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 251025

Area Forecast Discussion
National Weather Service Salt Lake City UT
425 AM MDT Sat Jun 25 2022

.SYNOPSIS...Weak high pressure will steadily build into the region
through early in the week, with isolated shower and thunderstorm
activity expected to continue across southern Utah. Moisture
increases going into Sunday, setting the stage for another day
with higher potential for heavy rainfall and localized flash
flooding in central and southern Utah. Warm conditions with
isolated shower and thunderstorm activity continue into early next


.SHORT TERM (Through 12Z/6AM Monday)...High pressure ridging will
slowly build across the region through the short term period as
500mb height rises of ~6dm are progged through Sunday night, per
deterministic and ensemble guidance. Moisture quality and depth
will slowly increase through Sunday, particularly across south
central and southeast Utah. Per TPW products, axis of deepest
moisture currently resides across Arizona, New Mexico northeast
into Colorado. Across our area, PWAT values range from near to
just below normal across northern Utah and SW Wyoming to 125-150%
of normal across SE Utah, with the bulk of this moisture residing
in the 750-500mb layer. This moisture will be sufficient to
support the development of shower and thunderstorm activity today,
developing during the late morning and early afternoon hours
across high terrain areas of central and south-central Utah. Weak
steering flow suggests storm motion will be slow and meandering.
Given slow storm motions, heavier cores will have the potential to
put down locally heavy rainfall. Relatively dry sub-cloud layers
will support microbursts/gusty outflow winds with additional
shower/thunderstorm development and propagation where cold pools
merge. Given the lack of synoptic support, shower and thunderstorm
organization will gradually wane with the loss of daytime
heating after sunset this evening.

Moist advection will be underway overnight tonight as low to mid
level southeasterly flow develops across southeastern and south-
central Utah. This flow regime will tap into the deeper moist
reservoir residing across Arizona and New Mexico. This theta-e
advection will support a few nocturnal showers across southeast
Utah Saturday night. With sustained theta-e advection, PWAT
values are forecast to increase to around 175% of normal across
south-central and SE Utah by Sunday afternoon. Deeper moisture
and associated instability/buoyancy will support greater
shower/thunderstorm coverage on Sunday, as convective initiation
once again gets underway across higher terrain areas. Weak
steering flow once again suggests slow and meandering storm
motions. Increased moisture (when compared to today) along with
continued weak flow will lead to a localized flash-flooding threat
across normally dry washes, slot canyons and slickrock across
southern and SE Utah Sunday afternoon and evening. HREF ensemble
PPM QPF Sunday afternoon advertises a few blobs of 1-2" of QPF
with a 50% probability contour of 3-hr QPF of >1" across the
Boulder Mountain and Capitol Reef area. Areas generally east of
I-15 and south of I-70 are contained within the 30% probability of
>1" QPF contour, thus those with outdoor plans should be mindful
of the possibility of flash-flooding.

Temperatures will warm a couple of degrees each day through the
weekend across northern Utah, with more limited day-to-day
variations across southern Utah as the warming effects of the
building ridging will be damped by the presence of deeper

.LONG TERM (After 12Z/6AM Monday)...Monsoonal activity will be on a
downward trend as the forecast period progresses. By the end of the
period expect only isolated high elevation storms to form in
southern and eastern Utah. Otherwise, ridging will keep temperatures
5-10 degrees above climo across the northern CWA and near
climo for the southern CWA throughout the period.

Ensemble members are in good agreement with the upcoming pattern
shift to a high pressure regime and limitation of storm development
to the highest terrain of southern/eastern Utah. With a lack of any
apparent and substantial synoptic level support expect storms to
remain mostly terrain and thermally driven throughout southern and
eastern Utah. Temperatures still appear to peak near the triple
digits across the Wasatch front on Tuesday as the ridge axis centers
over the CWA. Low pressure moving ashore in the Pacific NW will
flatten the ridge and bring temperatures aloft and at the surface
down several degrees. With a mostly zonal westerly flow aloft for
the remainder of the period there won`t be much day-to-day
variability in the sensible weather besides a slow degradation of
PoP chances.


.AVIATION...KSLC...VFR conditions will persist throughout the period
for the KSLC terminal. Weak high pressure is building into the
region which will keep skies mostly clear and winds light. Winds are
likely to remain light and northerly due to a north to south
pressure gradient. By tomorrow evening expect typical southerly
drainage winds to return.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail
throughout most of Utah/SW Wyoming throughout the period. Weak high
pressure is building over Utah which will keep northern Utah/SW
Wyoming mostly clear. Across southern/eastern Utah afternoon
thunderstorm development will occur mostly in the higher elevations
which would create brief MVFR/IFR conditions. Otherwise, winds will
be light and diurnal throughout the area.


.FIRE WEATHER...A ridge of high pressure is expected to gradually build
across the Great Basin and Desert Southwest through Tuesday. This
will force a gradual warming trend through Tuesday across the
region, especially across northern Utah where moisture will be
more limited. Across central, southern and eastern Utah, a gradual
increase in moisture is expected through the weekend, as a
moisture reservoir to our south is tapped into. This increase in
moisture will help promote shower and thunderstorm development
over high terrain areas of central and southern Utah this
afternoon, with some of this activity spilling off into adjacent
valleys. As moisture quality further improves on Sunday, more
numerous showers and thunderstorms are expected, again across
primarily southern, central and eastern Utah. Shower and
thunderstorm activity is expected to develop on terrain once
again, with showers and storms gradually moving off the terrain
into adjacent valleys. Cores will become increasingly wet through
the weekend, with an isolated dry storm possible. Isolated dry
storms will primarily be confined to the western and northern
periphery of the best moisture. Showers and storms will be capable
of producing frequent lightning, gusty/erratic outflow winds and
locally heavy rainfall and wetting rains, especially on Sunday.

Moisture quality will diminish slightly on Monday and Tuesday,
but enough moisture will linger to promote additional isolated
showers and storms over the same southern, central and eastern
portions of the state, with storms once again firing off of the
terrain, while some will migrate into adjacent valleys. As alluded
to earlier, northern Utah and the western valleys will be drier,
and shower/thunderstorm chances will be less here through Tuesday.
Given the drier conditions, these areas will warm to above normal
by Tuesday while warming is more muted down south owing to higher
moisture. This pattern will limit any widespread combination of
critically dry humidities and winds.

By midweek, a trough is expected to graze northern Utah as it
passes eastward across the Northern Rockies. While exact details
regarding the strength and timing of this trough remain uncertain,
it does appear increasingly likely that this system will graze
northern Utah and shunt the ridge southward, rather than a
complete ridge breakdown. This system has the potential to
increase winds across the area by midweek as well as increase
shower and thunderstorm chances area-wide. There does appear to
be an increasing likelihood of the development of a trough across
portions of the west just beyond the forecast period, and we`ll
continue to monitor this trend as the time period approaches.





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