textproduct: Salt Lake City

KEY MESSAGES

- There is a Marginal Risk (level 1/4) for excessive rainfall across most of the region through the weekend.

- There is a Marginal Risk (level 1/5) for severe thunderstorms across portions of northwestern Utah today. There is a 5-10% chance of wind gusts in excess of 58 mph in this area through the evening.

- A Slight Risk (level 2/5) for severe thunderstorms is outlooked for Sunday afternoon and evening across much of northern Utah. There is a 10% chance of wind gusts in excess of 70 mph with these thunderstorms Sunday afternoon and evening.

DISCUSSION

Increased moisture across the region will support thunderstorms capable of heavy rainfall rates. With relatively slow storm motions today, already seeing convection anchored on terrain training in locations and producing localized flooding of small streams and dry washes. Will need to continue to monitor central and southern Utah through the evening as rainfall rates in excess of 0.50-0.75 inches per hour have been observed. The most prone locations will be slot canyons, normally dry washes, slick rock areas, areas with poor drainage and of course the numerous recent burn scars across the region.

Across northwestern Utah, CAMS suggest the threat of strong to severe microburst winds. One inhibiting factor will be the mid- morning to early afternoon convection that moved across northwestern Utah. This likely stabilized the atmosphere a bit...and additional convective potential may be suppressed for several hours. While earlier runs of the HRRR showed significant wind gusts impacting northwestern Utah and perhaps the Wasatch Front in the 21Z-02Z timeframe, later runs have largely shifted away from this solution. Mesoanalysis correlates a fair amount of inhibition...and guidance suggests this CIN may not be overcome by the end of peak heating.

Sunday looks to be a potentially interesting day convection-wise. A weak area of convergence associated with a Pacific trough will shift into northwestern Utah. Mean HREF SBCAPE values will near 1000 J/kg across much of northern Utah by noon to 1 PM. This combined with deep layer shear around 25-30 kts and general synoptic scale lift will support convective development across much of Utah after noon. The most intense convection will likely be across northern Utah. HREF suggests a neighborhood probability of wind gusts in excess of 55 mph around 15-25%, especially near and west of the Great Salt Lake, and 10% or so in excess of 60 mph. The Storm Prediction Center has outlooked this area with a slight risk (level 2/5) for Sunday afternoon and evening including the Wasatch Front.

Across central and southern Utah, another day of thunderstorms with the threat of heavy rainfall is expected. Peak rainfall rates in guidance are notably lower than Saturday, correlating well with a net drying trend. That said, the threat of at least isolated flash flooding in the most prone locations will continue Sunday afternoon and evening, especially across central and southern Utah.

The Pacific trough will finally shift into the northern High Plains, shifting any large scale forcing for convection to the east. Given there wasn't a front to sweep out the low-level moisture in the low desert areas, expect the threat of isolated flash flooding to persist in any areas that develop convection through at least Monday...if not longer.

AVIATION

KSLC...There is low confidence in wind direction this afternoon and evening, particularly near any storms. High-based showers and thunderstorms will begin to develop over the Oquirrh Mountains after 20z, with storms potentially moving over the terminal after 21z or so, resulting in gusty and erratic outflow winds reaching 40kts for a brief period (10% chance). BLDU may result in brief VIS reductions. The threat of showers will linger well into the evening/overnight hours (until 09-10z), with a continued threat of outflow winds.

REST OF UTAH AND SOUTHWEST WYOMING...High-based showers and thunderstorms will continue to develop across much of the area (all but KCDC-KSGU) this afternoon, first over higher terrain. These storms will be capable of producing gusty and erratic outflow winds up to 40kts (up to 50kts across NW-UT). Storms will likely subside across southern UT between 02-04z, though showers are likely to linger through the overnight hours across the rest of the area...gradually weakening through the night. Outflow winds will result in low confidence in wind direction through much of the valid TAF period.

FIRE WEATHER

Afternoon and evening showers and thunderstorms will become more isolated through early Monday, and largely tied to terrain. Any showers and thunderstorms this weekend will have the threat of strong, gusty microburst winds.

Over the work-week, valley humidities will fall slowly each day, reaching near critical to critical levels as early as Monday. There is little sign of an additional monsoon surge after this weekend until after the next weekend.

SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...None.