textproduct: Salt Lake City

KEY MESSAGES

- Generally dry and seasonable conditions will persist through Thursday, with a weak grazing system tonight bringing light precipitation to northern Utah and southwest Wyoming.

- Moisture will increase over the area beginning Friday, bringing an increasing threat of flash flooding. The area will see a more substantial increase in moisture and instability and thus the potential for flooding Sunday into Monday as a strong Pacific storm crosses the area.

- Much cooler temperatures will accompany the system for early next week, allowing snow levels to potentially drop as low as 7500 feet by Monday morning.

DISCUSSION

A weakening shortwave trough is currently swinging across northern Nevada and will cross far northern Utah tonight. Much like last night, this fast-moving wave will push a reinforcing cold front into northern Utah, bringing valley rain showers and light mountain snow once again. Precipitation is already ongoing near remnants of the existing boundary and will continue through late tonight. The boundary and associated precipitation is expected to remain north of around Utah County. Expect precipitation to wind down well before sunrise.

Fairly benign weather is expected on Wednesday and Thursday under a southwesterly flow aloft. Temperatures should cool slightly from today across northern Utah owing the the cold front, then rebound for Thursday. Models do depict yet another weakening trailing shortwave disturbance crossing Utah late Wednesday afternoon into Wednesday evening. The dynamics associated with that looks to be very insignificant, so very little if any precipitation is expected.

Main focus continues to be the storm system for the end of the week through the weekend. A low pressure system will slowly make its way to the PacNW coast on Thursday. On Friday, a subtle disturbance rounding the base of this low and lifting across Utah will start to spread some moisture into the area. However, with weak dynamics, expect mainly isolated to scattered showers and a few thunderstorms to develop. Main focus for heavier precipitation will be southwest Utah, otherwise amounts are expected to remain relatively light elsewhere. The 25th percentile of the NBM has no measurable precipitation for the vast majority of the forecast area and only a few hundredths of an inch in portions of southwest Utah. However, the 75th percentile has between 0.5-1 inch over portions of southwest Utah, so cannot rule out some heavier showers and isolated potential for flash flooding. On Saturday, the storm system will begin to move inland. This will maintain unsettled weather over the area, but with the better large-scale dynamics still upstream, expect generally isolated to scattered showers and isolated thunderstorms once again.

The storm system is expected to cross Utah on Sunday, although there is still some uncertainty regarding how deep it will carve into the area. This storm will also phase with a southern stream system that will be associated with an atmospheric river. The moisture plume will punch inland across far southern California and northern Baja. Some of this moisture will make it into Utah, with IVT anomalies in the 97th-99th percentile of climatology. However, there is still enough model spread regarding how much precipitation will develop over Utah. While the spread has decreased from what models were showing 24 hours ago, we are still looking at NBM 25th-75th percentile differences of 1-2 inches in areas favored in southwest flow and 0.5-1 inch elsewhere. Regardless, Sunday is expected to see the heaviest precipitation of this storm cycle, with the potential for widespread and moderate to heavy precipitation with an increased flash flood threat.

A cold front will also push into Utah on Sunday, bringing lowering snow levels. Snow amounts will be dependent on the strength of the trough and precipitation amounts, of which, as mentioned, there is still significant uncertainty. However, a general 3-6 inches with locally 10 inches or more in higher elevation sites such as near Brian Head, in the Tushars, the upper Cottonwoods, and high Uintas seem reasonable at this time.

Precipitation looks to mostly wind down Monday morning, leaving a cool northerly flow in place over the area. Models then start to diverge on the large-scale pattern, with how quickly the storm continues to progress east out of the area and whether a strong ridge builds into the area behind it or whether another storm system manages to move into the area midweek.

AVIATION

KSLC...VFR conditions will persist for the KSLC terminal through the period. Another weak cold front crosses the terminal tonight with only ~15% chance of showers impacting the terminal between 05-08Z while most of the precip stays to the north. Winds will remain mostly northerly, with some light and variable winds ahead of the front, and some mid level clouds. The frontal passage arrives ~0530Z in which winds will turn fully northerly. A brief southerly is expected tomorrow morning before a transition back to light northerlies during the day.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist for the entire airspace through the period. Another weak cold front will move through the northern airspace tonight bringing a brief window of showery activity to the northernmost terminals between 04-10Z. Otherwise, conditions will be dry with some mid level clouds and light and variable winds.

SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...None.