textproduct: Salt Lake City

KEY MESSAGES, Issued 1046 PM MDT Sun Aug 30 2026

- A moderate risk (level 3/4) for excessive rainfall is in effect across portions of eastern and southern Utah Monday.

- A flood watch for flash flooding remains in effect across much of central and southern Utah through Monday 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. - 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 Friday into next weekend.

DISCUSSION, Issued 1046 PM MDT Sun Aug 30 2026

Convection has largely waned late this evening across the area, with most of Utah and southwest Wyoming seeing some relief from the rainfall during the overnight hours. Far southeastern Utah, largely near Lake Powell, may still see some shower and isolated thunderstorm development tonight and during the morning hours as a weak shortwave trough passes across the Four Corners. Uncertainty still remains with the timing of this wave, which will ultimately determine the coverage/intensity of afternoon convection across far southeastern Utah. Earlier model runs suggested showers moving into the area by 9AM which would likely result in more limited afternoon instability. However, recent model trends show this a bit later, coincident with daytime heating/instability.

Across the rest of the area, widespread thunderstorms will develop during the afternoon, owing to anomalous moisture in place coupled with broad-scale dynamics. The aforementioned shortwave trough moving through the Four Corners will move in sync with a separate shortwave trough crossing western Utah from southwest to northeast, providing plenty of lift and deep layer shear, especially when considering upper-level diffluence already in place. Thunderstorms will form as this shortwave lifts, first entering the St. George vicinity late morning and becoming widespread by mid-afternoon as instability peaks.

While outflow winds are also possible along the leading edge of these storms (especially over west-central and northwest Utah), the environment will be very favorable for flash flooding, notably across southern and eastern Utah and over sensitive areas such as slot canyons and near recent burn scars. This flash flood threat is especially high given recent rainfall across much of the state. High-res guidance suggests storms will be capable of producing rainfall rates potentially in excess of 1-2"/hr, with average return intervals (ARIs) exceeding 10-20 years across much of eastern and southern Utah...locally higher in places.

Conditions trend much drier after Monday, and even drier following the passage of another shortwave trough mid-week. However, this break may be short-lived. Model guidance suggest moisture of tropical origins returns by the weekend, coupled with another disturbance from the PacNW. Plenty of uncertainty still remains, but this could yet again increase the flash flood threat heading into next weekend.

AVIATION, Issued 1046 PM MDT Sun Aug 30 2026

KSLC...There is around a 40% chance of light north to variable winds for a period overnight. Southerly winds likely to increase by mid morning Monday. Monday afternoon will see convection chances increase through the afternoon, especially after around 21Z to 04Z Tuesday. Storms will be capable of brief periods of heavy rain, lightning, and gusty erratic outflow winds. Additionally, stronger storms will be capable of brief categorical VIS reductions to MVFR or so, as well as lowered CIGS.

REST OF UTAH AND SOUTHWEST WYOMING...Isolated showers and thunderstorms will be possible overnight, especially across central Utah. Winds will generally favor a diurnally normal direction. on Sunday, southerly flow will increase as will cloud cover. Afternoon showers and thunderstorms will once again become more widespread through the afternoon hours, especially along and east of Utah's high terrain. Like previous days, these storms will be capable of periods of heavy rain, lightning, gusty erratic outflow winds, and small hail. Additionally, the stronger storms will be capable of periods of decreased VIS to around MFVR or so, as well as some lowered CIGS. In general, coverage of showers and thunderstorms will begin to wane late evening into the overnight hours.

FIRE WEATHER

A significant push of moisture alongside a low pressure system will bring widespread showers and thunderstorms across a majority of Utah today, with high probability of wetting rains (50 to 85 percent) across the high terrain of central and southern Utah. In concert with the widespread rainfall and thunderstorm activity, high humidity is expected areawide, with very few locations falling below 30 percent, and many struggling to fall below 40 percent.

A drying airmass will begin to push into the region on Tuesday, initiating a drying trend through at least Thursday. While humidity will remain relatively high on Tuesday, a more substantial drying is expected into the middle of the week, with minimum afternoon humidity falling back into the teens across the western half of Utah. By Thursday, afternoon humidity in the teens is expected to spread into the lower elevations of eastern Utah. An active area of low pressure on the west coast will bring an increase in southwest winds alongside this drying trend, bringing elevated to near critical fire weather conditions across a portion of west- central and southwest Utah on Wednesday and Thursday afternoon. For the high terrain across the state, very little, if any, shower and thunderstorm activity is expected. Moisture looks to return by the end of the week and over the weekend, bringing increasing chances for showers and thunderstorms, as well as an increasing trend in humidity.

SLC WATCHES/WARNINGS/ADVISORIES

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

WY...None.