748
FXUS65 KSLC 021015
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
415 AM MDT Mon Jun 2 2025

.SYNOPSIS...An active pattern will continue through the week.
There is a heightened threat of flash flooding across portions of
southern Utah Monday through Wednesday. Consensus favors a drying
and warming pattern by next weekend.

&&

Key Points:

-An area of low pressure containing remnant tropical moisture will
 move across southern Utah today, increasing the risk for flash
 flooding across southern Utah, especially this afternoon and
 evening. There is uncertainty surrounding the amount of cloud
 cover, and flash flood risk will ultimately be tied to the extent
 of afternoon cloud cover. Less cloud cover than currently
 forecast will increase convective strength and coverage, and
 therefore attendant flash flood potential.

-Risk for isolated flash flooding continues across southern Utah
 Tuesday afternoon/early evening.

-Another system will bring a renewed risk of showers and
 thunderstorms with associated flash flood potential Wednesday
 afternoon through at least Wednesday night across southern Utah.
 There are some indications within the model guidance that a flash
 flood threat expanding into central and portions of northern Utah
 Thursday (specifically for burn scars across central Utah).

- High temperatures warm day after day from Wednesday through at least
  Monday.


.SHORT TERM (Through 12Z/6AM Wednesday)...Early morning satellite
imagery indicated the presence of a closed low over Arizona, with
a well-defined deformation axis located to its north and east
across Arizona, southern Nevada and southern Utah. Latest PW
analysis showed PWATs approaching 1" across extreme SW Utah. A
shield of light to locally moderate rain was observed across
northern Arizona and southern Nevada associated with the strongest
forcing within the deformation axis. As we head through the
morning, models are well-clustered around the idea of the
northern extent of this rain pivoting across southern Utah,
before gradually diminishing by late morning and early afternoon.
Farther north, a cold front was moving across northern Utah, and
this front is forecast to settle across central Utah by this
afternoon. Isolated showers and thunderstorms will accompany this
front, with seasonable temperatures forecast to build in behind
it through the remainder of the short term.

The most uncertain aspect of the forecast is centered around the
Monday afternoon and evening timeframe. At present, a thick and
extensive cloud deck is in place across northern Arizona, southern
Nevada and southern Utah, with this cloud cover only thickening
trough the morning across southern Utah. Most guidance suggests
this thick canopy of overcast will remain in place for much of the
day, with only a few breaks in the cloudiness developing. There
is a subset of guidance that is more aggressive with the
clearing, however. Should cloud cover remain extensive, convective
development and associated flash flood risk will be limited. The
opposite is true in a scenario where cloud cover thins more
aggressively. Thus, the convective and flash flood threat is
rather conditional, and because of this uncertainty, we held off
on a Flood Watch. The most likely scenario thorough this afternoon
resembles one that lies between the two forecast extreme
outcomes, where isolated to scattered showers and thunderstorms
develop initially across favored high terrain areas of southern
Utah, with the greatest coverage from the Iron/Juab county line
eastward through Goblin Valley, with more isolated coverage north
of there. CAMs then allow convection to drift southward off of the
terrain across the Grand Staircase/Escalante and the Paria basin,
as well as across Zion. Ensemble mean SBCAPE is progged to be
modest, or in the 250J/Kg-750J/Kg range. Deep-layer shear is
forecast to be in the 15-25kt range through most of the day,
increasing to 25-35kt after 00Z this evening, just enough to
sustain updrafts and enable maintenance of cold pools. PWATs are
forecast to increase to 1" in Zion and Lower Washington County
today, or reaching the low-end threshold of the concern zone.

Heading into this evening, bulk of CAMs merge southern Nevada
convection with a lingering cold pool over Iron County, wherein a
cluster of organized showers and thunderstorms blossom. CAMs take
this activity from Cedar City and Enterprise southward through
the St. George metro and Zion through the first half of the
evening. This cluster is expected to develop/congeal across Iron
County beginning around 5PM, before spreading across Zion and St.
George metro between 6PM-9PM. This cluster appears to have the
best potential to bring locally heavy rain and isolated flooding
to these areas, along with gusty winds in the 35-45 mph range,
with a 10% chance for gusts around 50 mph. Heading through the
remainder of Monday evening, expectation is for shower and
thunderstorm activity to gradually wane. Main theme of the Monday
afternoon/evening forecast period is a conditional threat for
convection strong enough to tap into its full potential. The flash
flood threat hinges on this potential, and a scenario with less
cloud cover than currently forecast is a more hazardous one in
terms of flash flooding, especially for slickrock, normally dry
washes and slot canyons. WPC ERO marginal risk covers the area of
concern well for today.

On Tuesday, skies will become mostly clear during the morning
hours. Lingering low-level moisture and associated buoyancy will
have a better potential to be fully realized, and as such ensemble
mean SBCAPE climbs to a healthy ~1000J/kg early Tuesday afternoon.
Expect isolated to scattered showers and storms to develop over
higher terrain areas, then drift ESE. The window for organized
activity appears to be smaller than Monday, with instability
quickly getting used up by late afternoon/early evening. However,
given a greater potential to tap into low-level moisture, we
can`t sleep on Tuesday`s flash flood potential. Another system and
attendant risk for showers and thunderstorms capable of heavy
rain and flash flooding then moves into southern Utah once again
Wednesday. More on that below:

.LONG TERM...(After 12Z/6AM Wednesday)...By Wednesday, deep layer
moisture shunted farther south will begin to make a resurgence
into central and northern Utah Wednesday and Thursday. Another
offshore low (currently located offshore of the San Francisco Bay)
will phase with the northern stream trough in a very similar
fashion to the current low over the southwestern U.S. The big
picture for weather hazards will remain largely the same to those
today (Monday)... IF we are able to see a break in a dense cloud
shield, the environment will become much more unstable and capable
of producing heavy rainfall. On the contrary, if we end up with
too much large scale forcing for ascent, the cloud cover will
significantly inhibit heavy rainfall potential. A scenario with
less cloud cover through the morning hours will be more supportive
of increased risk of flash flooding across southern Utah on
Wednesday while the opposite will be true with a scenario favoring
greater cloud cover.

Moisture spreads farther into the forecast area overnight Wednesday
and into Thursday, bringing increased chances for showers and
thunderstorms over the high terrain and adjacent valley areas. With
layer precipitable water still between 150-200% of normal, would
anticipate a risk of heavy rainfall capable of producing flash
flooding. This time, the threat looks to expand into central Utah`s
slot canyons, normally dry washes, and recent burn scars.

Friday forward, ensemble guidance shows moisture availability slowly
waning back to near normal (but still about 100-130% of normal) by
Monday which will coincide with a decreasing risk of flash flooding.
That said, we`ll still see potential for at least isolated to widely
scattered storm development over the high terrain through at least
Saturday. The influence of an upstream ridge will become more
prevalent by the end of the weekend as broad subsidence begins
working into the region.

&&

.AVIATION...KSLC...Northerly winds prevail through the day today
with periods of variable flow expected through the morning hours.
VFR conditions prevail with middle and high level cloud cover
gradually decreasing late in the morning and through the afternoon.

.Rest of Utah and Southwest Wyoming...Widespread light to moderate
rain with isolated heavy rain is expected across the southern half
of Utah today. While VFR conditions will prevail, temporary
reduction to MVFR to IFR conditions will be possible due to VIS
restrictions in heavier rainfall. Outside of any gusty and erratic
outflow wind gusts, winds will be out of the west to northwest
across the northern area, and southwest shifting to northwest across
the southern area.

&&

.FIRE WEATHER...As an upper level low shifts across the
Desert Southwest through Monday, deep moisture will build into
southern Utah. Depending on the degree of cloud cover, there is a
conditional threat of thunderstorms with very heavy rain,
particularly south of a line from Iron County to Goblin Valley.
Extensive cloud cover this afternoon will limit the extent and
intensity of showers and thunderstorms, while less cloud cover
than currently forecast will allow for greater coverage and
intensity of showers and thunderstorms. Meanwhile, across northern
Utah, cooler and drier conditions will build in Monday behind a
cold front.

On Tuesday, isolated afternoon and evening showers and
thunderstorms will develop across southern Utah, with mainly dry
conditions elsewhere with seasonable temperatures. The next upper
level low will cross the Desert Southwest Wednesday into Thursday,
bringing another round of thunderstorms to southern Utah with the
threat of heavy rain and isolated flooding once again. The active
pattern will continue through the remainder of the week, with
isolated showers and thunderstorms building northward into central
Utah, as well as high terrain areas of northern Utah, by
Thursday. Expect a similar pattern for Friday before drier air
gradually builds into the area by next weekend. From the middle of
this week into next weekend, temperatures will gradually warm,
reaching 5F to 15F above normal by next weekend.

Mixing heights are expected to fall into the typical range, or
the 50th percentile for Monday. Mixing will largely remain in the
50-70th percentile until Saturday, when deeper mixing is once
again forecast.

&&

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

$$

ADeSmet/Webber

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