textproduct: Salt Lake City

KEY MESSAGES

- 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

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

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, Issued 208 PM MDT Sun Aug 30 2026

An ongoing monsoon surge will continue to bring the threat of thunderstorms with strong winds, hail and very heavy rain today. A further increase in moisture will bring an even higher threat of heavy rain Monday, especially across southern and eastern Utah.

A drying trend will begin Tuesday, with humidities falling to near critical levels across western Utah by Wednesday. Friday into the weekend, moisture will again shift into the region with increasing humidities and the threat of heavy rainfall once again.

SLC WATCHES/WARNINGS/ADVISORIES

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

WY...None.