Helper, UT Weather

Key Messages

- Widespread precipitation returns Wednesday morning across southern Utah, with coverage expanding northward through Friday. Many areas will see precipitation accumulations between 0.5-1.5" through this period, with local totals in excess of 3" possible.

- The heavy rain will bring a threat of flash flooding to southern and central Utah, and there is a Slight Risk of Excessive Rainfall across southern Utah Wednesday and Thursday.

- A few strong thunderstorms may be capable of producing gusty winds and hail across southern Utah on Wednesday and statewide on Thursday. A Marginal Risk for severe thunderstorms is in place on Wednesday across far southern Utah, and much of Utah on Thursday.

- The late week storm will also bring accumulating snowfall to the high terrain across northern and central Utah on Friday, with 3-6" possible mainly above 9000 feet. Locally higher amounts are possible in favored locations.

Discussion

Early afternoon satellite imagery shows an upper low spinning off the CA coast near 130W, while a fetch of low-mid level southerly flow is beginning to pull tropical moisture from the Baja region northward. As this upstream low begins to move inland, this moisture will quickly spread northward into southern Utah by Wednesday morning, and into central Utah by afternoon, bringing the potential for heavy rainfall and flash flooding. This moisture will remain in place through Thursday, resulting in a relatively long-duration window of potentially heavy rainfall across central and southern Utah, where storm totals may locally exceed 5" in upslope-favored areas such as the Pine Valleys and areas near Brian Head. As such have gone ahead with a Flood Watch for much of southern and eastern Utah for Wednesday through Thursday evening.

As the area comes under the influence of the upstream low Wednesday, enhanced low and deep layer shear combined with low LCLs will support supercells capable of all severe weather hazards assuming sufficient instability is able to develop. This appears most likely to occur across southwest Utah in closer proximity to the upper dynamics. This threat will persist into Thursday and expand northward into central and perhaps northern Utah assuming sufficient instability.

The upper low is forecast to lift through the forecast area Thursday night into Friday, focusing precipitation across northern Utah and southwest Wyoming. As colder air spreads into the area, snow levels will fall to around 8500 feet with accumulating snow likely above 9000 feet. Snow accumulations of 2-6 inches above 9000 feet look likely, with the potential for higher totals depending on how the upper low evolves as it lifts through the region. A secondary trough digging into the region may keep precipitation going into the weekend, although confidence is fairly low at this time with respect to how the overall pattern evolves.

Aviation

KSLC...VFR conditions will persist at the terminal through the TAF period. The diurnal shift to NW winds is expected to be delayed to 22-23z. Ceilings near 7000 feet will develop Tuesday afternoon as isolated showers develop in the mountains, with no other impact to the terminal expected. Winds will return to SE between 03-04z.

REST OF UTAH AND SOUTHWEST WYOMING...Winds will remain mainly light and diurnally driven through the TAF period. Isolated showers and thunderstorms will develop across much of the area this afternoon and evening, with minimal impact expected at most terminals.

Slc Watches

UT...Flood Watch from Wednesday morning through Thursday evening for UTZ117-123>131.

Flood Watch from Wednesday afternoon through Thursday evening for UTZ120-121.

WY...None.