textproduct: Salt Lake City

KEY MESSAGES

- Modestly breezy conditions with gusts around 25-40 mph persist through Sunday afternoon, primarily west of the I-15 corridor.

- Flash flooding risk increases Sunday, especially from southwest to central Utah as tropical moisture increases. A Flood Watch is in effect accordingly.

- Isolated severe storms capable of strong to severe wind gusts and small hail will be possible across portions of northwest Utah Sunday afternoon.

- Drier conditions return for early next week, with uncertainty noted on potential for more unsettled conditions from midweek onward.

DISCUSSION

Evening water vapor analysis shows a broad trough extending southward through the PacNW with deep southerly flow noted locally overhead. While a plume of tropical moisture is evident lifting northward through the Desert Southwest, most locations across Utah and southwest Wyoming have remained largely clear, if not sunny. The southwesterly flow has resulted in some modestly breezy conditions around the area, but temperatures have remained seasonably mild for early September.

The moisture plume will continue to advance northward overnight, beginning to encroach into southern Utah with associated shower activity closer to sunrise. This moisture will then continue to overspread the majority of the forecast region as the day progresses, with PWAT anomalies rising to around 150-200% of climatological normal. Concurrently, will see flow overhead increase with an embedded shortwave shifting through, providing increased synoptic forcing for ascent. While mean instability is only progged to increase to around 150-300 J/kg in the afternoon, and will to a degree be predicated on cloud cover and degree of stratiform rain, anticipate the enhanced synoptic forcing will allow pockets of embedded thunderstorms to develop. Models suggest any such activity will have potential for rain rates in the 0.5" to 1.0" per hour range, and with the deep moisture, would expect even showers will be capable of fairly efficient rainfall production. Additionally, continued moisture advection in the southwesterly flow may help bring redeveloping and/or training storm activity.

Given the setup, Sunday will see potential for excessive rainfall and instances of flash flooding. The WPC Excessive Rainfall Outlook includes southwestern to central Utah within a "Slight Risk" (level 2 of 4) of excessive rainfall, and the majority of the remainder of the forecast region in a "Marginal Risk" (level 1 of 4). General model consensus supports the highest focus of activity from southwest Utah through central Utah, especially along the high terrain and nearby areas. For now, have maintained the ongoing Flood Watch for this general area, though a shift in the plume by even 20 miles or so may necessitate expansion of the watch area. Will have to monitor trends accordingly. Per usual, the highest threat will be for typically rain sensitive locations such as recent burn scars, slot canyons, typically dry washes, and slickrock areas. Those with recreation plans in such areas should stay weather aware and consider alternatives.

Aside from the flood threat, models also support potential for more isolated convection forming on the periphery of this plume, particularly in portions of northwest Utah. While also dependent to an extent on the degree of destabilization, the enhanced flow aloft will result strong deep layer shear in excess of 40 kts or so. This area will also be nearer a slowly approaching front from the larger PacNW trough. While conditional, any storms that can become better organized will have at least some threat of strong to severe wind gusts and small hail.

Precipitation will gradually diminish overnight moving into Monday morning as the moisture plume exits and the deep PacNW trough's evolution will allow a drier and more zonal flow to develop. The associated cold front will also progress as far south as central Utah in vicinity of the I-70 corridor or so, bringing cooler temperatures behind it. Afternoon highs behind the front Monday will tend to run around 5-10 degrees below normal, with temperatures ahead of it near to slightly below normal. The front will begin to wash out quickly, with temperatures for Tuesday moderating back upwards nearer to typical levels.

Uncertainty increases from Wednesday onward with models diverging on the exact pattern evolution. There is support that mid to upper level ridging will be centered somewhere in the southwest CONUS, but with varying placements. If centered more atop the Four Corners region the local area will see better potential for moisture returning, with decreasing favorability the further to the west it ends up. Around 30% of ensembles support a more marked moisture surge and higher precipitation potential, around 30% have a more muted moisture return and likely more isolated precipitation potential, and the remaining 40% remain on the drier side of the envelope.

AVIATION, Issued 701 PM MDT Sat Sep 5 2026

KSLC...Southerly winds remain generally light overnight into Sunday morning, gradually increasing after 14z. Winds further increase around 20z, with gusts exceeding 25 kts developing through the evening. An influx of tropical moisture into northern Utah will result in gradually increasing cloud cover and lowering CIGS Sunday morning. Steady rainfall is expected to move into the vicinity of the terminal after 20z, with potential to produce brief MVFR CIGS through the evening.

REST OF UTAH AND SOUTHWEST WYOMING...Gusty southerly winds across the airspace taper overnight before increasing gradually after roughly 13-16z. Wind gusts in excess of 25 kts are expected to develop through the afternoon for most regional terminals. An influx of tropical moisture into the region will result in gradually increasing cloud cover overnight into Sunday morning, with lowering CIGS as widespread rain moves in from the south through the day. Showers and thunderstorms taper off by early Monday morning.

FIRE WEATHER, Issued 208 PM MDT Sat Sep 5 2026

Moisture will continue to gradually increase into sunday as southwesterly flow pushes moisture further north. This afternoon, expect locally critical fire weather conditions primarily across the West Desert and Great Salt Lake Desert where humidities have been observed dropping below 15%. Additionally, strong wind gusts across areas primarily west of I-15 will range from 30-45mph each afternoon into Sunday.

On Sunday, a stronger push of moisture arrives to Utah with widespread showers and thunderstorms across the state, though primarily across central and southern Utah. The highest rainfall totals are expected across higher terrain of central and southern Utah, though lower elevation areas further east may see higher isolated totals from stronger storms. For lower lying areas west of I-15, generally a trace or less of precipitation is expected on Sunday. A drying trend is expected to develop Monday and Tuesday with more precipitation expected after midweek next week across at least southern and central Utah.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Flood Watch from 9 AM MDT Sunday through Sunday evening for UTZ113-114-116>120-122-124>128.

WY...None.