textproduct: Salt Lake City

KEY MESSAGES

- A couple of weak systems brushing northern Utah through mid-week will keep temperatures seasonably cool, with mostly dry conditions prevailing.

- Two storm systems bring wetter weather back to the region Friday into the weekend, with widespread precipitation through this period resulting in an increased risk for flash flooding.

- Colder air moving in Saturday into early Monday will result in lowering snow levels, allowing for accumulating snowfall generally above 8500 feet.

DISCUSSION

Generally benign conditions are expected for the first half of this week. While a couple weak systems are expected to brush northern Utah through mid-week -- the first moving through overnight tonight, and the second late Tuesday into Wednesday -- little impact is expected outside of a slight cooldown and some isolated showers near the Idaho border.

A more active pattern is expected late this week into the weekend as a couple stronger weather systems with more efficient moisture taps impact the region. The first system arrives Friday as a shortwave ejects around the eastern periphery of a deepening trough along the west coast. Increasing southerly flow aloft will bring an influx of tropical moisture to the region, with PWAT anomalies increasing to around 200-250% of normal across much of southern and central Utah on Friday into early Saturday. There is still quite a bit of spread on how much precipitation this system brings to the region, with the 25th percentile showing next to northing across much of Utah and southwest Wyoming, while the 75th percentile brings 0.3-0.5 inches to much of southern Utah except upwards of an inch across the southern mountains. Given recent rainfall across central and southern Utah, the flash flood risk is elevated Friday into Saturday despite this uncertainty. WPC currently highlights much of southern Utah under a Marginal Risk (Level 1 of 4) of excessive rainfall through this period.

Ensembles show good agreement on a brief lull on Saturday afternoon ahead of the second, more potent system. A strong atmospheric river is expected to make landfall along the southern California coast late Saturday, bringing a stream of very deep tropical moisture that will overspread much of Utah and southwest Wyoming on Sunday. Concurrently, an upper-level trough begins to dig southward into the Great Basin, resulting in substantial instability developing across the region. As such, ensembles are in good agreement on this portion of the storm bringing widespread moderate to heavy rainfall to the region. While heavy rain is likely across southern Utah, with a 75% chance to exceed 1" of rain across much of the area through Monday morning, models show quite a bit of spread in rainfall accumulations across central and northern Utah given some models indicate potential for a more southerly track of deepest moisture. Across these areas, the 25th percentile brings a widespread 0.2-0.5", while the 75th percentile indicates widespread accumulations of 1.0-1.5".

Cooler air moving in with the aforementioned trough on Sunday will result in snow levels dipping around 8000-8500 feet. As such, accumulating snowfall is expected for all Utah mountains into Monday morning. Current forecast indicates 3-6" of snow accumulations between Sunday and Monday morning for elevations above 8500 feet, with locally higher totals of 6-10" across the central and southern Utah mountains and the Uintas.

AVIATION

KSLC...The SLC terminal will see VFR conditions throughout the day with increasing high clouds. Occasionally gusty southerly winds are expected to shift to the northwest between 03Z and 05Z with the passage of a mostly dry cold front before returning to southerly during the early morning.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions are expected across the airspace through the evening with increasing clouds over northern portions of the airspace. A grazing storm system will bring a mostly dry cold front between 03Z and 08Z, bringing wind shifts to the northwest from about Provo northward. There is also a low chance of showers with the frontal passage for locations near the Utah/Idaho border as the system passing, bringing a low potential for gusty winds and brief mountain obscurations.