textproduct: Salt Lake City

KEY MESSAGES

- A marginal risk (level 1/5) is outlooked for strong to severe thunderstorms across portions of central and eastern Utah this afternoon and evening. There is a 5% chance of wind gusts in excess of 58 mph and hail larger than quarters in this area.

- A slight risk (level 2/4) remains in effect for excessive rainfall across much of Utah through tonight.

- A moderate risk (level 3/4) is now in effect for excessive rainfall 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

Another day of deep moisture across the region will bring an elevated threat of flash flooding. While most of the region is seeing conditions favorable for heavy rain associated with thunderstorms, the highest chance will continue across eastern and southern Utah. Some areas, including Castle Country, the Sevier and Sanpete Valleys, the San Rafael Swell and most of the Grand Staircase area have already had one day of heavy rain and flooding. With saturated soils, these areas will be even more prone to flooding this afternoon and evening.

As far as Monday, PW anomalies at or above 97-99 percentile will shift into southern and eastern Utah. This...combined with widespread large scale ascent, significant deep layer shear and sufficient instability will support widespread thunderstorms with very heavy rain. Average return intervals (ARI) for precipitation are exceeding 10-20 years across much of eastern and southern Utah, with localized areas seeing maximum ARIs in excess of 50 years. Rainfall rates in previous days have exceeded 0.30 inches in 10 minutes in stronger thunderstorms. Given this, coordinated with the Weather Prediction Center to introduce a moderate risk within the Excessive Rainfall Outlook (ERO) for Monday. This will be only the second time WFO SLC has been included in a day 2 moderate risk ERO.

Much drier conditions will work into the region in the wake of the shortwave trough that spurred Monday's convection as drier southwest flow filters into the area. That said...this break from flash flooding is short as a number of ensemble members are suggesting tropical moisture from an eastern Pacific tropical cyclone approaching the Baja California area may shift into Utah ahead of another trough by Friday into Saturday. Something to monitor.

AVIATION

KSLC...Primarily VFR conditions are expected to persist through the TAF period. Confidence regarding thunderstorms remaining away from the terminal this afternoon has increased, resulting in the removal of the PROB30. Otherwise, diurnal wind shifts are expected with the next wind shift expected to occur around 19z as northwest winds push into the area.

REST OF UTAH AND SOUTHWEST WYOMING...Showers and thunderstorms with gusty outflows are expected this afternoon at KPVU, KHCR, and KCDC from 20-24z, though some may linger a couple hours later. Otherwise, diurnal flows will prevail at all other sites with VFR conditions persisting.

FIRE WEATHER

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.