textproduct: Salt Lake City

KEY MESSAGES, Issued 1117 AM MDT Mon Aug 31 2026

- Numerous showers and thunderstorms capable of producing heavy rain this afternoon and evening will result in a heightened risk of flash flooding for the southern two-thirds of Utah, where a Flood Watch for flash flooding is in effect through this evening.

- The threat of flooding is highest across slot canyons, normally dry washes, slick rock areas, recent burn scars as well as areas that have already received very heavy rainfall this weekend including the Sanpete and Sevier Valleys, Castle Country, and the San Rafael Swell. - After some modest drying for the middle of the week, there is an increasing probability that deep moisture associated with a tropical cyclone in the Eastern Pacific will spread northward into Utah ahead of a Pacific disturbance for Labor Day weekend.

DISCUSSION, Issued 1117 AM MDT Mon Aug 31 2026

High pressure remains in place over the central United States this morning, with a trough moving onshore over California and a stronger trough moving into the Dakotas. In between these features, Utah and southwest Wyoming are under a southerly flow that is drawing deep monsoonal moisture northward. Satellite derived PW values remain around 1.0 inch over southern Utah, with values predominately in the 0.7 to 0.9 range elsewhere, with the exception of far northern Utah.

Showers and thunderstorms have been bringing heavy rainfall across portions of southern Utah through the morning, with many of these cells producing flash flooding. The threat of flooding will only increase and expand this afternoon as the California trough moves across Utah, providing additional moisture and instability. Increased coverage of convection will only increase a risk of flash flooding that has been elevated all weekend, as indicated by the rare moderate (level 3 of 4) risk of excessive rainfall indicated bu the Weather Prediction Center. Additionally, many areas, especially eastern Utah, have already seen heavy rain, leading to saturated soils, further increasing the risk. With this in mind, have expanded the going Flood Watch for flash flooding to include the Book Cliffs, Uinta Basin, and west central and southwest Utah.

The California trough is expected to exit the area by tomorrow morning, with another low approaching the northern California coast. Guidance indicates this will allow the southerly flow to advect drier air into the area, at least over western Utah beginning tomorrow afternoon, with the drier air becoming more widespread Wednesday into Thursday as the second trough moves across the Pacific Northwest into the Dakotas. For Tuesday, guidance overall looks to be unusually quick with diminishing the potential of thunderstorms and thus flash flooding, so have increased POPs given recent trends.

The drying trend looks to be short lived, unfortunately, with a lot of the longer range guidance indicating the southerly flow increasing Friday into the Labor Day weekend with the approach of another Pacific Northwest trough. This would allow a tap into an even more deeply moist airmass from a tropical system, a rather substantial influx of moisture and something we are keeping a very close eye on.

AVIATION, Issued 1212 PM MDT Mon Aug 31 2026

KSLC...Showers/thunderstorms will develop mid afternoon over the Oquirrhs and begin to impact the terminal vicinity with a 30% chance of gusty winds and towering cumulus. Southerly winds will become established by mid-afternoon, gusty at times. There is then a 70% chance that a more organized and widespread area of showers with embedded thunderstorms will move through the Wasatch Front including KSLC between 23Z and 02Z, bringing a greater threat of gusty and erratic winds as well as heavy rain bringing a low chance of MVFR visibilities and lower cigs. There is a threat of wind gusts as high as 45 kts with this late afternoon/evening round of thunderstorms. Quieter conditions are expected overnight with lighter southeasterly winds.

REST OF UTAH AND SOUTHWEST WYOMING...Afternoon showers and thunderstorms will develop across the majority of the region today, initially over southern Utah (including KSGU and KCDC) through the early afternoon, higher terrain through the mid afternoon, and finally the majority of the Wasatch Front by late afternoon and early evening. There is a 70% chance that the late-afternoon and early evening thunderstorms over the Wasatch Front from Nephi northward becomes a large area of rain with embedded strong thunderstorms. Any storms will be capable of gusty and erratic winds in addition to very heavy rainfall reducing visibility to at least MVFR in addition to lowered ceilings. This activity should push northward out of the area and come to an end by 03-06Z, with light southerly winds persisting overnight into tomorrow. Shower/thunderstorm coverage tomorrow looks to be more limited as drier air moves into the region.

FIRE WEATHER

Showers and thunderstorms are continuing to develop and will only increase in coverage across the entire state into the evening as a low pressure system crosses the area in an already moist airmass. This will bring a high chance (50 to 85 percent) of wetting rain, particularly for the higher terrain of central and southern Utah. Relative humidities will also remain on the high side, with very few locations falling below 30 percent. Drier air will start to move in from the west on Tuesday, but this should not be noticeable for much of the area until Wednesday into Thursday. This is likely to push minimum relative humidity values into the teens across western Utah Wednesday into Thursday. In combination with breezy southerly winds due to a low along the Pacific coast, this could bring area of critical fire weather conditions. The period of dry weather should be short lived, however, with guidance increasingly indicating a substantial surge of tropical moisture into Utah over the weekend.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Flood Watch until 9 PM MDT this evening for UTZ113>131.

WY...None.