963
FXUS65 KSLC 171019
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
419 AM MDT Thu Jul 17 2025

.SYNOPSIS...Monsoonal moisture will spread northward into the area
through Friday. This will bring an increasing threat of heavy
rainfall across the area, particularly for southern Utah. A drying
trend will develop by early next week.

&&

.SHORT TERM (Through 12Z/6AM Saturday)...High pressure is starting
to re-amplify over the Great Basin this morning as a closed low
moves northward along the Baja California coast. The building
ridge is shifting the flow aloft over Utah and southwest Wyoming
to a southerly direction, allowing monsoonal moisture to be drawn
northward. This increase in moisture is already evident, with
satellite derived PW values in the 0.9 to 1.1 inch range over
southern Utah, highest near the Utah/Arizona border, with values
in the 0.6 to 0.8 inch range elsewhere. In this rather moist
airmass, will see a rather noticeable increase in coverage of
showers and thunderstorms, primarily for southern Utah, with some
more favorable dynamics expected to be provided this afternoon by
a couple of weak shortwaves rippling through. Thus, seeing a
heightened threat of storms with heavy rain capable of flash
flooding, and have increased the flash flood potential to probably
for a good portion of southern Utah.

The moisture will continue to spread northward through Friday.
However, the northward spread of the moisture will act to bring
PWs down a bit across southern Utah. Guidance is indicating PWs
primarily in the 0.8 to 1.0 inch range across all of Utah and
southwest Wyoming by Friday afternoon. By this point, the Baja low
is expected to be around southern California as another system
moves onshore along the Pacific Northwest coast. A boundary is
expected to develop between these two features over northern Utah
that could act as the focus for convection Friday afternoon,
though coverage of convection should be high over southern Utah as
well.

.LONG TERM (After 12Z/6AM Saturday)...By Saturday, a longwave trough
will dig into western Canada, while an expansive ridge of high
pressure from the southern plains into the southeast U.S. amplifies.
Flow for the region will become more southwest, which will advect
drier air into southwest Wyoming and Utah. Expect slightly less
coverage of showers and thunderstorms than prior in the week, but
enough moisture and forcing will be in place for gusty, erratic
outflow winds and localized flash flooding if a thunderstorm
producing heavy rain tracks into a vulnerable location.

The longwave trough will dig into the PacNW Sunday, while ridging to
the southeast amplifies. This set up will bring a downtrend in
precipitation, with most showers and thunderstorms isolated and
around mountainous terrain. The approaching longwave trough will
enhance southwest flow. Southwest winds will likely be below Red
Flag Warning criteria, but gusts will likely top out around 25 mph
for southwest Utah. Relative humidity will range from around 10-20%.

Critical fire weather conditions become more likely Monday as the
longwave trough will dig slightly further south and the ridge to the
southeast will be largely unchanged. Flow will be west to southwest,
gusting in excess of 25 mph throughout southwest Wyoming and most of
western Utah. Relative humidity values will likely range from the
single digits to teens.

Ensembles vary on the track of the longwave trough into the week,
with some members breaking off a closed low that would track
southwest to off the west coast. Other members slide the trough
eastward, with it remaining north of Utah. The ridge to the
southeast will likely retrograde into the week, which will allow for
lighter winds. It would also bring better moisture advection, with
more of a southerly flow. Models and ensembles are in good agreement
on that, with a general uptrend in precipitable water values Tuesday
through much of the week.

Valley high temperatures from the weekend through much of the week
will be near normal in the low or mid 90s.

&&

.AVIATION...KSLC...Mostly clear conditions will last into the
afternoon. Light southeast winds will increase around 15Z, with
gusts around 20 knots through 19Z. Winds will transition to
northwest around 19Z. Clouds will increase after 21Z, with isolated
showers or thunderstorms capable of gusty, erratic outflow winds.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered afternoon showers
and thunderstorms, primarily in southern Utah, will be capable of
gusty, erratic outflow winds and locally heavy rain from 18-00Z. VFR
conditions will prevail for southern Utah, but expect broken or
overcast clouds. Clouds will increase into northern Utah after 21Z,
with isolated showers or thunderstorms capable of gusty, erratic
outflow winds through 00Z.

&&

.FIRE WEATHER...With southerly flow across the area, monsoonal
moisture will be drawn upward into the area from south to north
through Friday. The presence of this moisture will bring
increasing coverage of afternoon and evening showers and
thunderstorms with a higher potential for wetting rains,
particularly on Friday. Moisture could begin to decrease as early
as Saturday, with a more pronounced drying trend expected to
commence on Sunday.

&&

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

$$

SHORT TERM/FIRE WEATHER...Traphagan
LONG TERM/AVIATION...Wilson

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