textproduct: Salt Lake City

KEY MESSAGES

- Widespread heavy rainfall is expected to occur across the entirety of the forecast area starting Saturday afternoon/evening as Tropical Storm Rachel transitions to an extratropical system to our southwest and interacts with a strong midlevel trough. Widespread rainfall amounts from 1-3" are expected across much of the forecast area, with localized amounts potentially reaching 4+" across locations such as higher terrain locations across southwest Utah, the Book Cliffs, and locations within and adjacent to the Bear River Range.

- A wind threat is expected to accompany this system as it begins to take on extratropical characteristics. Advisory level winds will begin to develop across most Utah valley locations starting just after midnight tonight, becoming more widespread Saturday afternoon. Advisory level winds are forecast to remain in place through at least Monday afternoon.

- The potential for severe weather exists across southern and eastern Utah Sunday into Monday morning. The primary threat will be severe thunderstorm gusts and possibly isolated tornadoes.

- Significant mountain snowfall is possible as a closed low moves through Monday through Wednesday with areas that do well in northerly/northwest flow receiving the highest amounts.

DISCUSSION

Current radar analysis shows light showers with embedded thunder across central and northern Utah with more robust convection across southern Utah that has been producing 0.25-0.5"/hour. Additionally, southerly winds are picking up ahead of an approaching trough. Gusts in the 40s and a few isolated 50s are noted across most of western Utah. These winds will continue through the evening and into tomorrow as remnants of tropical storm Rachel move into the area.

Rachel is currently moving northwest toward the northern Baja California with an anticipated landfall overnight tonight. NHC has noted that Rachel has been tracking to the right of the forecast track which has shift the forecast track slightly more towards the east compared to yesterday when the center of circulation was expected to move through southern Nevada. Now that track is more likely moving through southwestern Utah. However, guidance still continues to struggle with the exact track, but regardless the impacts will primarily remain the same: widespread rain, heavy at times, strong southerly winds, and the potential for strong to severe thunderstorms.

The most widespread activity today will be across eastern Utah with moderate to heavy rainfall rates possible along with frequent lightning. The more widespread precipitation move in tonight through tomorrow with a moderate risk of flash flooding across southwestern Utah where upslope flow along southerly facing terrain will enhance precipitation totals. Areas along northerly facing aspects that tend to do poorly in southerly flow could be shadowed a bit, such as the northern half of the Salt Lake Valley and Cedar City. This has been evident in the CAMs, but the globals struggle depicting these smaller scale features. Additionally, a favorable shear signature and strong synoptic flow will help fuel some strong to severe thunderstorms, primarily across the southern half and eastern half of Utah. These will be capable of strong gusty winds, an increased risk of flash flooding due to higher rainfall rates, and a tornado or two.

Overall precipitation will be between 1-3 inches with locally higher amounts of 4"+ across the favored upslope regions. This amount is just through early Monday morning. Areas of central and northern Utah may actually see more precipitation with the closed low that slowly moves through Monday-Wednesday. This will bring colder air aloft with snow levels falling to ~7500 feet by Wednesday along with 6-12 inches of snow above 9000 feet with some locations that are favored in northwest flow receiving over 15". Some ensemble members are showing upwards of 30" of snow at the top of the Cottonwoods which might be a bit aggressive, but a stout northwest flow wrapping around this closed low and a warm lake that could lead to some lake effect could make for an overperforming event.

AVIATION

KSLC... VFR conditions will prevail over the KSLC terminal through the remainder of the afternoon hours and the first half of the overnight period. Gusty south winds will remain in place through the TAF period, with gusts around 25-30 kts expected before nightfall, then increasing to 30-35kts. There is around a 30% chance of isolated showers and/ or thunderstorms over the terminal through around 22Z. Thereafter, dry conditions will prevail through around 06-07Z with persistent rainfall and lowering CIGs into Sunday morning.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail across a majority of the region today, with areas of showers and thunderstorms mainly east of the I-15 corridor. Gusty south to southwest winds can be expected across a majority of Utah (outside of Box Elder County) and southwest Wyoming, with peak wind gusts expected around 25-30kts. A significant amount of moisture will spread into the region this evening, bringing persistent rainfall (spreading from south to north) as well as lowering CIGs across the area.

FIRE WEATHER

A storm system is approaching the area with plenty of tropical moisture to work with. Southerly winds will be strong across the area today, with widespread gusts 30-50 mph. Scattered showers and thunderstorms will also develop across the area today, primarily across the eastern half, with increasing chances for wetting rain. The storm will pull in tropical storm remnants late tonight through Sunday, with widespread moderate to heavy rainfall expected. Winds will also likely remain strong and out of the south in association with the remnants. The storm system will then slowly cross the area Monday through early Wednesday, although the heavier rainfall rates will decrease. We will maintain an active and cooler pattern with widespread wetting rains and high elevation snow through this timeframe. A drying and warming trend is likely for the latter part of the week.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Wind Advisory until 6 AM MDT Sunday for UTZ101>109-115-116-118- 119-122-126-127.

Flood Watch from midnight MDT tonight through Monday afternoon for UTZ101>112-114-115.

Flood Watch through Monday afternoon for UTZ113-116>131.

High Wind Watch from Sunday morning through late Sunday night for UTZ115>117-119-122-125>127.

WY...None.