344
FXUS65 KSLC 181842
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
1226 PM MDT Fri Sep 18 2026

.KEY MESSAGES, Issued 1110 AM MDT Fri Sep 18 2026...


- Periods of showers and thunderstorms will continue tonight into
  Friday, with the best coverage over northern Utah and southwest
  Wyoming. Hail, heavy rain, and lightning will be the primarily
  threats. Flash flooding remains a threat as well.

- A weak cold front will bring drier conditions with more
  seasonable temperatures Saturday through the remainder of the
  weekend.

- Moisture is expected to increase again Tuesday, with another
  period of shower/thunderstorm chances Tuesday onward,
  especially for areas east of I-15.

&&

.DISCUSSION, Issued 1110 AM MDT Fri Sep 18 2026...
A busy morning for northern Utah and southwest Wyoming with
multiple rounds of convection moving through. Water vapor
satellite imagery shows a circulation center upstream along the
NV/OR border, with broad southwesterly flow into the eastern Great
Basin and implied synoptic lift over our area. SPC mesoanalysis
shows a favorable shear environment as would expected upstream of
a closed low, with 30-50kts of effective bulk shear. It also
shows plenty of instability to realize with around 1000 J/Kg of
MUCAPE, less than the KSLC morning sounding which has an
impressive (for our area) 1700 J/Kg of surface-based CAPE. Also
worth noting, the morning sounding shows a freezing level of
9,700` MSL, which places the majority of that instability in the
hail growth zone.

Convection this morning has been linear and quick moving, as would
be expected from the strong southwesterly steering flow aloft.
Have already had reports of nickle-sized hail and minor urban
flooding, particularly in Utah and Wasatch counties which
received the brunt of the convective activity from about 7a to
10am. For the rest of today, convection-allowing models have been
showing a general theme of a late-morning / early afternoon lull
(if you could call the current activity north of I-80 a lull),
followed by another round this afternoon. Current visible
satellite imagery suggests the next round is soon to materialize,
given the streets of agitated CU showing up in the area of
general clearing from around I-80 south and US-89 west. Machine
learning guidance has been suggested a hail threat in particular
over northern Utah, matching up with the thermodynamic indicators
mentioned above, especially in vicinity of the Great Salt Lake and
into western Box Elder County. SPC has this area generally
highlighted with a 5-14% chance of severe hail in vicinity. Based
on 12Z CAMs, the main threat period extends through about 7pm, and
potentially a little later.

In addition to the severe hail and general thunderstorm risk,
given the PWATs of around an inch (about 150% of average) and the
instability yet to be realized, there is a flash flood risk if
training lines of storms park over the same sensitive area. We`ll
be watching the usual burn scars, slot canyons, and urban areas
for that threat. Castle County and the San Rafael Swell are at
particular risk because of recent heavy rains that have left soils
near saturation.


The closed low to our west that is responsible for the increased
moisture and convective activity is forecast to lift northeastward
and brush by our area to the north Saturday, pushing a weak cold
front through northern and central Utah this evening and
overnight. The passage have a noticeable effect on temperatures
for all but southern Utah, with highs into the weekend running
5-10F below seasonal normals for northern Utah and southwest
Wyoming, and near seasonal normals for southern Utah. As the
trough exits, the flow aloft will move to a more west to
northwesterly direction, allowing some drier air to move in. With
the trough not entirely out of the picture on Saturday, still
anticipating some scattered convection focused over northeastern
portions of the forecast area, with Sunday expected to be dry with
weak ridging moving in.

Guidance indicates the break in the action will be short lived,
however, with yet another low approaching the Pacific coast Sunday
afternoon. Most guidance shows this system tracking eastward into
the Desert Southwest to start the work week, but the ensembles
diverge noticeably with the regard to the potential track of the
system and how much it will weaken once onshore. Still, confidence
is increasing with regard to a relatively quick return to
unsettled weather, at least for southern Utah.




&&

.AVIATION, Issued 12:15 PM MDT Fri Sep 18 2026...

KSLC...The SLC terminal will see VFR conditions through the TAF
period, with a 10% chance of brief high MVFR conditions in any
passing thunderstorms this afternoon into early evening. The primary
impact from any potential storms will be gusty and erratic winds up
to 30kts. Southerly winds may transition to northerlies around 21z,
for now carrying VRB with prob30 storms for that window. Storms are
expected to diminish by 04z with the diurnal wind switch to
southeasterlies or potentially light and variable delayed until 05-
07z.


REST OF UTAH AND SOUTHWEST WYOMING...Showers and thunderstorms are
expected to persist across the northern terminals through early
evening, with periodic IFR windows possible in the heaviest storms.
Winds will be primarily driven by these storms, with gusty and
erratic periods when storms impact terminals, with diurnal patterns
expected to resume after sunset.


&&

.FIRE WEATHER, Issued 1140 AM MDT Fri Sep 18 2026...
Scattered thunderstorm development is forecast to
continue through the morning, peaking just after 1200 across
northern and central UT, with southern UT following shortly after.
Thunderstorm coverage is expected to be higher across northern and
central UT today, with large hail potential in addition to the
lightning. Across southern and eastern UT, thunderstorms will
remain isolated to widely scattered. Any storms will have a high
chance of wetting rains.

On Saturday, a cold front will continue to sag as far south as
about I-70, ushering in a drier and cooler airmass which will
remain in place through Monday. This is expected to be short
lived, however, as moisture looks to return by late Monday into
Tuesday as southerly flow redevelops, pulling moisture back into
the region. That said, at present it appears showers/thunderstorms
will be less numerous with this next period of active weather in
comparison to recent days. Far northern and northwest Utah look to
be on the periphery of this moisture return, and are currently
expected to remain drier through the week.


.FIRE WEATHER...

&&

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

$$

PUBLIC...Van Cleave
AVIATION...VERZELLA
FIRE WEATHER...Van Cleave

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity