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 increases statewide today and tomorrow, with both days featuring much of UT outlined within a slight risk (2/4) of exceeding flash flood guidance.

- The potential for severe weather across UT this afternoon appears to be increasing. Severe wind gusts (>58mph) appears to be the main threat, particularly across southeast UT later this evening.

DISCUSSION

A stronger monsoonal push is forecast to occur across much of UT today as robust mid-level moisture returns to the region. Currently, subsidence has built in across much of southern and central UT following this mornings thunderstorms. This will serve to offset convective initiation until around 1400-1500, enabling the environment to destabilize further with CAPE general ranging from 1000-1500J/kg statewide, though CAPE ~2000J/kg appears possible closer to southwest UT. With PWATs generally 1.2" or greater in place across much of UT (0.8-1.0" PWAT anomalies for this time of year), thunderstorms today are forecast to be efficient and heavy rainmakers.

Of note, mid-level southwesterly flow will see an increase to around 20-30kts with multiple embedded shortwave perturbations providing enough forcing for ascent. This will support multiple rounds of storms this afternoon and through the evening hours as well as storms propagating off terrain, which will be the opposite of what we have been seeing through much of this recent monsoonal pattern with storms remaining anchored to terrain. Typically, enhanced flow would limit the flash flooding threat areawide as storms would not remain over problematic basins and burn scars long enough to produce flooding. However, given the efficient rainmaking status of these storms with multiple rounds expected, the flash flooding threat continues to exist, particularly if redevelopment occurs across a single area in a short period of time. Additionally, the presence of bulk shear to around 35kts supports organized storms sustaining themselves for longer. Additionally, shear on this magnitude is supportive of a supercell or two, particularly across southeast UT where shear is greatest, which would increase the threat of flash flooding further.

Regarding severe weather this afternoon and evening, the Storm Prediction Center has placed much of UT within a Marginal Risk (1/5) for severe weather with an emphasis on severe wind gusts in excess of 58mph. Across most of UT, primarily western and northern, DCAPE potentially in excess of 1500J/kg will exist this afternoon as storms begin to develop ahead of the initial shortwave. This will yield a scattered threat for strong to severe gusts through much of the afternoon today as the enhanced flow aloft finds a better medium amidst the higher DCAPE to mix down to the surface with.

Later this evening across southeast UT where forecast confidence in wind shear to around 35kts is greatest, a westward propagating MCS is forecast to move into the area from southwestern CO. Some mid- level flow enhancement is possible around the time of initiation (to around 30-40kts) with 1600-1800J/kg of DCAPE in place. This supports an organized severe wind threat with a few severe gusts potentially reaching as high as 70mph this evening across areas such as Glen Canyon/Lake Powell and adjacent areas within eastern Wayne, Garfield, and Kane counties.

A similar setup for flash flooding exists on Wednesday, though storm motions are forecast to be somewhat slower as mid-level flow sees a slight decrease. Fortunately, this will reduce wind shear somewhat as well potentially reducing the longevity of storms. However, with deep moisture remaining in place and weaker flow aloft, efficient rainmaking thunderstorms remain expected with a slightly higher chance of storms remaining anchored to terrain tomorrow.

From Thursday on, mid-level moisture will see a slight decrease areawide. However, with ridging remaining overhead, daily chances for thunderstorms will continue across much of the state and favor terrain as steering flow aloft gradually weakens. The forecast becomes somewhat muddied as we enter the weekend with global suites continuing to disagree on moisture scouring, though the broader pattern in place continues to support at least some continuation of the monsoonal pattern into at least Saturday.

AVIATION

KSLC...Mostly VFR conditions will persist for the KSLC terminal through the period. Winds this morning will be light southerly transitioning to light northerly this afternoon. Convection develops this afternoon across northern Utah with ~30% chance of convection moving over the terminal. Convection could switch us to predominate southerly quite a bit earlier than usual. Lightning, gusty and erratic winds, and brief heavy rain will be the primary concern with this convection. This convection will remain on and off through the evening and potentially overnight, albeit weaker overnight.

REST OF UTAH AND SOUTHWEST WYOMING...Mostly VFR conditions will persist through the period for the area. Monsoon moisture remains in place with a lull in activity through ~2pm before convection begins to develop areawide. Storms will primarily produce lightning, gusty and erratic winds, and brief heavy rain. This activity will continue through the evening with storms weakening, but persisting to some capacity, through the overnight.

FIRE WEATHER

Monsoonal moisture remains in place throughout UT increasing humidities and chances for showers / thunderstorms across the state, helping moderating fire weather conditions statewide. Chances for showers and thunderstorms see a notable uptick across the entirety of the state today as a stronger monsoonal push arrives this afternoon. 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. Some storms this afternoon, particularly across northwest UT and southeast UT may feature severe wind gusts in excess of 58mph. Winds will generally remain light terrain driven / diurnal over the next several days other than thunderstorm influenced winds and gusts.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Flood Watch through late tonight for UTZ113-115>131.

WY...None.