textproduct: Salt Lake City

KEY MESSAGES

- Thunderstorms capable of periods of heavy rain and flash flooding will once again be possible Sunday and Monday, particularly east of the I-15 corridor and south of I-80. A Flood Watch is in effect.

- A few isolated thunderstorms may become strong to severe Sunday and Monday, capable of strong winds and hail. - Generally drier conditions return Tuesday on through the work week, though more isolated showers and thunderstorms will remain a possibility many of those days.

DISCUSSION

After an active day, weather remains active across portions of Utah this evening. This is to an extent the result of a deepening PacNW trough helping to strengthen a Pacific moisture tap within the associated enhanced southwesterly flow. To that end, mesoanalysis maintains widespread PWAT values in excess of 1" across the majority of Utah, or around 150-200% of climatological normal for late August. Further, the aforementioned deepening PacNW trough has allowed a frontal boundary to slowly advance into northern Utah, and the abnormally strong deep layer flow overhead has allowed for impressive effective shear on the order of 40-60 kts across the northern half of Utah, and around 20-40 kts across southern Utah. This anomalous combination of ingredients has yielded numerous strong to severe thunderstorms with strong winds and hail, and heavy rain resulting in multiple instances of flash flooding.

Looking ahead to the overnight hours, while overall instability will decrease with the lack of sun, enough will remain in combination with ample moisture to result in continued showers and thunderstorms. In general, anticipate these to tend to be weaker than those during the daytime Saturday. That said, wouldn't rule out one or two pulsing up at times, and with the moisture rich environment, any stronger Storm or training storm impacting a rain sensitive basin in particular could pose a flash flood threat. In terms of coverage, models largely support the bulk of the scattered activity across portions of central Utah, in the rough vicinity near and to the south of the frontal boundary.

Sunday appears to have potential to be another active day capable of strong storms and flash flooding. In terms of the broader synoptic environment, the ingredients don't appear to change significantly, with an embedded midlevel shortwave impulse also shifting through. Strong flow will remain overhead allowing moisture will continue to advect into the region. One difference is it appears some slightly drier air will start to shift into Utah from the west, with the best available moisture becoming positioned across eastern Utah to southwest Wyoming, generally along/east of the I-15 corridor and south of I-80. As such, this area is highlighted as Slight Risk (categorical 2/4) for excessive rainfall from WPC, and much of it is also included in a Flood Watch for potential flash flooding. Elsewhere across all but far west to northwest Utah, a Marginal Risk (categorical 1/4) of excessive rainfall is noted. These areas will need to remain weather aware for strong storms capable of periods of heavy rainfall once again, with flash flooding especially possible in those typically sensitive basins (recent burn scars, slot canyons, typically dry washes, and slickrock areas). One possible difference is that shear appears to be maybe around 20 kts or so weaker than Saturday, which may limit the coverage of strong to severe storms. Still, would anticipate a few organized storms will still be capable of strong gusty winds and hail.

Monday will yet again see the potential for flash flooding and strong storms. Overall, the synoptic elements once again do not shift significantly, and another shortwave impulse will lift through overhead during the day. Like Sunday, the expectation is that while strong to maybe a few severe storms will certainly be possible, the moisture rich environment will favor flash flooding as the primary risk. As far as the excessive rainfall outlook, the slight and marginal risk areas change very little from that of Sunday, and thus the same areas will remain more favored for the threat. With multiple days of repeat thunderstorms, saturated soils and any remaining high creeks/rivers/etc. may further exacerbate this potential.

The deep PacNW trough will more or less maintain its position Tuesday onward through the upcoming week, but the moisture tap will become less defined. As such, a general drying trend is expected across the forecast region, and the threat of widespread heavy rainfall generally appears lower. Still, the PacNW trough will offer potential for some grazing shortwaves, and there will still be enough moisture lingering to result in the development of some showers and thunderstorms day to day. Even if the threat of widespread heavy rain may be lower, any stronger or slower moving storm that gets over a rain sensitive basin will pose a risk, so cannot say the threat is zero. Overall though, there is some uncertainty noted in the day to day specifics.

Though on the tail end of the forecast range, next weekend bears at least some watching. Deterministic models show potential for the Pacific moisture tap to become reestablished, with ensembles showing a corresponding increase in mean PWAT values. It does appear there are some factors that'll influence how it trends though, particularly the exact position of the PacNW trough, a broad central Plains to Rockies ridge, and position/strength (if it exists) of an east Pacific tropical system. So, not much in the way of specifics, but as typically the case a week out, worth watching trends.

AVIATION, Issued 551 PM MDT Sat Aug 29 2026

KSLC...Southerly winds are expected to prevail through the evening and into the morning, with passing showers and thunderstorms causing periodic gusty and erratic winds. The strongest storms will be capable of producing heavy rainfall that may result in periods of MVFR to IFR conditions.

REST OF UTAH AND SOUTHWEST WYOMING...For northern terminals, widespread showers and thunderstorms are expected to persist through the evening and into early morning before dissipating. The strongest storms will be capable of producing gusty and erratic outflow winds and heavy rainfall that may result in periods of MVFR to IFR conditions. Southern terminals will remain gusty into early evening.

FIRE WEATHER, Issued 1226 PM MDT Sat Aug 29 2026

Active weather continues today with strong to severe thunderstorms developing this afternoon across northern and central Utah with a flash flooding threat also developing this afternoon across central and southern Utah. Regarding the severe threat further north, wind gusts in excess of 58-70mph and hail to around 1" are expected this afternoon with any of the stronger storms that form. Across southern Utah, monsoonal moisture continues to surge north bringing an attendant flash flooding threat to the area through at least Monday. While storm development across southern Utah may be somewhat muted Sunday afternoon, Monday appears somewhat concerning regarding rainfall high rainfall rates and amounts. Regardless, a wetting rain is expected across the entirety of Utah through early next week.

Following this active patter, a drying and cooling trend will take place as most showers and thunderstorms appear to remain confined to the higher terrain at this time. Temperatures will run roughly 5F below seasonal normals with RH approaching normals around mid- week.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Flood Watch through Monday evening for UTZ116>121-123>131.

WY...None.