textproduct: Salt Lake City

KEY MESSAGES

- Deep moisture will continue to bring an elevated threat of flooding to portions of southern and eastern Utah through at least Friday.

- A Flood Watch for flash flooding has been issued from late tonight through Thursday morning for portions of southern and eastern Utah including Zion National Park, Capitol Reef National Park, Glen Canyon Recreation Area, the greater Grand Staircase- Escalante National Monument area, and the lower Paria including Buckskin Gulch and Paria Canyon north of the Arizona border.

- A marginal risk for severe thunderstorms (level 1/5) continues for Wednesday morning into Wednesday afternoon across portions of northern Utah.

- A marginal risk for excessive rainfall (level 1/4) continues for Thursday and Friday across southern and eastern Utah.

DISCUSSION

An upper level low will continue to shift down the Pacific Coast through later Thursday into Friday and then gradually eject across the Great Basin through Saturday. Diffluent southwest flow will remain in place, with modest moisture transport through at least later Thursday. Embedded in this southwest flow will be a multitude of weak shortwave troughs or remnant MCVs. This, combined with PWATs in the 96-99th percentile, and broad ascent will support periods of convection with very heavy rainfall, especially through Friday morning.

Earlier thunderstorms, with occasional embedded supercells produced rainfall rates as high as 0.50 inches in 20 minutes, causing multiple flash floods in the Wahweap, lower Paria drainages as well as various slot canyons in the San Rafael Swell including Little Wildhorse north of Goblin Valley State Park.

Current model trends indicate another subtle shortwave ejecting across northern Arizona/southern Nevada and southwest Utah will aid in the development of convection overnight through about 6 AM this morning across lower Washington County, Iron County and western Kane and Garfield Counties. Rainfall rates in excess of 0.25 inches an hour will be possible with this convection, with around a 10% chance of rainfall rates in excess of 0.50 inches per hour. A Flood Watch for flash flooding begins at midnight tonight and continues through Thursday morning for Zion National Park and points east. No changes have been made to the going Watch.

The Storm Prediction Center has outlooked portions of northern Utah for a marginal risk for severe thunderstorms, particularly for Wednesday morning into early Wednesday afternoon. A few strong thunderstorms will be possible along the periphery of the deeper moisture in this area.

Afternoon convection will kick off across the region, with a multitude of CAMS showing very widespread heavy rain across most of southern Utah after about 00Z. This may require the expansion of the Flood Watch into lower Washington, Iron and Beaver Counties for late Wednesday night into Thursday afternoon. Something to monitor for future adjustments if CAMS remain consistent.

It is not recommended to have plans into slot canyons, normally dry washes, and other areas prone to flash flooding over the next several days. Nearly all National Park and Rec areas are currently at Probable for the next several days in the flash flood potential product.

AVIATION

KSLC...There is a 30% chance for showers and thunderstorms at the terminal accompanied by gusty winds in excess of 30 kts and occasional lightning during the 08-12Z timeframe. Otherwise winds will remain predominantly southerly through the TAF period, with gusts in excess of 20 kts developing by 12z and persisting through the day. Additional showers and thunderstorms are possible Wednesday afternoon and evening, however the chance of a shower or thunderstorm impacting the terminal is less than 30%.

REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and thunderstorms will develop overnight and impact terminals south of I-80 during the 08-14Z timeframe. After 14Z, the chance for showers and thunderstorms impacting northern terminals will fall below 30% through the remainder of the period as VFR conditions and south winds prevail. Across southern terminals, the chance for showers and thunderstorms will increase to 30% again this afternoon, with widespread showers and thunderstorms beginning 02Z Thursday.

FIRE WEATHER

An ongoing moisture surge will bring an increased threat of showers and thunderstorms across eastern and southern Utah through at least Friday. For locations west of I-15, humidities will increase above critical levels by Wednesday, however gusts to 30 mph will continue through Thursday.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Flood Watch from Wednesday afternoon through late Wednesday night for UTZ121-129.

Flood Watch through late Wednesday night for UTZ124-128-130-131.

WY...None.