textproduct: Salt Lake City

KEY MESSAGES

- Scattered showers and thunderstorms are expected to develop across portions of central, southern, northeast UT, and southwest WY each afternoon within this forecast as monsoonal moisture continues making its way north.

- The risk for flash flooding continues across the majority of the forecast area, highlighted by WPC with a Marginal Risk (1/4) of exceeding flash flood guidance each day encompassing nearly all of UT through at least Friday. A Slight Risk (2/4) of exceeding flash flood guidance exists across the majority of UT Tuesday and Wednesday afternoon, expanding into southwest WY Wednesday afternoon.

- Hazardous temperatures look to develop across northern UT this afternoon, particularly along the I-15 corridor and Great Salt Lake Desert. As such, a heat advisory remains in effect.

DISCUSSION

Monsoonal moisture remains in place across the southwest as high pressure meanders over the four corners. Beneath this ridge, PWATs in excess of 1" continue to push north across most valley locations this afternoon. Daily chances for showers, thunderstorms, and potentially flash flooding continue through at least Friday across much of UT with this pattern in place, expanding into southwest WY Tuesday and Wednesday. Deeper moisture looks to advect further north starting Tuesday as some stronger synoptic forcing moves in from the west, increasing PoPs Tuesday afternoon bringing heavy rainfall and potentially flash flooding to all of UT and southwest WY.

Thunderstorm development across central and southern UT will occur around 1200-1400 this afternoon. PWAT anomalies across southern and central UT once again range from 0.5-1" of water supporting a heavy rain threat. However, compared to other days, mid-level moisture has decreased slightly as dry air has moved into the mid-levels. This will serve to impact vertical development and overall intensity of storms this afternoon. Regardless, instability in excess of 1000J/kg with deep warm cloud layers up to 3km continue to support the development of efficient rainmakers, though more isolated this afternoon, with heavy rain expected from well established storms. One failure mode that may occur today would be the increase in 500mb flow, assisting storms off the terrain which have otherwise remained anchored over the past few days. With faster moving storms, heavier rain rates may be needed in order to produce flash flooding, yielding some uncertainty with todays forecast given moisture quality is not as good as previous days keeping the flash flooding threat more isolated.

As the ridge builds overhead, temperatures this afternoon are forecast to reach into the upper 90s to low 100s across most valley locations across northwest UT. This has resulted in widespread "major" HeatRisk values, primarily within valley locations along the I-15 corridor and Great Salt Lake Desert, with a few areas reaching "major". As such, a heat advisory has been issued for the aforementioned locations.

On Tuesday and Wednesday, moisture return increases with the mid- levels moistening once again ahead of stronger synoptics further west. Additionally, moisture is forecast to advect further north during this time expanding the flash flooding threat to northern UT on Tuesday, then to southwest WY on Wednesday. Enhanced flow aloft may hinder the overall flooding threat, though anomalously deep moisture (PWAT anomalies on the order of 0.5-1") remain in place, supporting potentially heavy rainmakers. Additionally, some shear will be in place (0-6km shear on the order of 20-30kts) which will help storms sustain themselves rather than pulsing and gusting out, potentially enhancing the flash flood threat. Currently, the WPC has outlined much of UT on Tuesday and Wednesday in a Slight Risk (2/4) for exceeding flash flood guidance, with southwest WY outlined in a Slight Risk on Wednesday.

Some severe potential exists on both Tuesday Wednesday across northern UT and southwest WY as a few shortwaves traverse the Great Basin in the afternoon hours. With ample shear (0-6km 20-30kts) with CAPE from 500-800J/kg, a few longer-lived storms, perhaps a couple transient supercells, may develop in the afternoon hours each day. Confidence regarding timing and location of these shortwaves remain highly uncertain at this time, though the broad synoptic pattern associated with this would support a potential damaging wind threat and potentially some small hail if it were to materialize.

AVIATION

KSLC...Northerly winds are expected to become dominant by 20z, with a 20 percent chance of delaying until around 2030z. Isolated thunderstorms will begin to develop over the Wasatch after 20z, with the highest chance of a couple of rogue storms coming into the vicinity of the terminal between 22-00z and 04-06z (15-20% chance).The primary impact of any nearby storms will be gusty and erratic outflow winds, potentially including an earlier switch to southerly, or a prolonged northerly. VFR conditions are expected throughout the TAF period.

REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and thunderstorms will develop across much of the area after 19z, first developing across higher terrain. These storms may be capable of producing heavy rain, gusty outflow winds, and brief VIS reductions. While the strongest storms will likely diminish by 02z, showers may continue into the overnight hours, particularly across southern Utah.

FIRE WEATHER

Monsoonal moisture remains across UT increasing humidities while raising chances for showers and thunderstorms across the state moderating fire weather conditions overall. Chances for showers and thunderstorms continue to be elevated across central and southern UT this afternoon, and the Uintas ranging from 50-80%. A wetting rain remains favored this afternoon across each mentioned location. Expect showers and thunderstorms to develop along higher terrain parallel to I-15 each afternoon over the next several days around 1200-1400 with gusty outflow winds, heavy rainfall, and lightning. Winds will generally remain light terrain driven / diurnal over the next several days. Chances for showers and thunderstorms increase across northern UT starting Tuesday with notably higher chances across the entirety of UT Tuesday and Wednesday afternoons.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Heat Advisory until midnight MDT tonight for UTZ101>105.

Flood Watch from Tuesday afternoon through late Tuesday night for UTZ113-115>131.

WY...None.