textproduct: Salt Lake City

KEY MESSAGES

- Dry conditions with valley inversions persist through the end of the week before valley rain and mountain snow arrive this weekend that will help to mix out the inversions.

- Guidance continues to show two more storms next week, but details remain uncertain.

DISCUSSION

A high-amplitude ridge sits directly overhead this evening, maintaining dry and stable conditions with light winds. The ridge axis will slowly shift east on Thursday, bringing southerly flow aloft over Utah which will increase through Friday ahead of the next approaching storm system. Surface winds are not expected to realize the increased southerly flow on Thursday, but by Friday, as the surface pressure gradient increases over western Utah, there will be a greater chance of enhanced winds which, could help to improve mixing mainly west of I-15.

Said storm system, an open-wave trough with a bit of a negative tilt, is expected to move through Utah relatively quickly on Saturday, bringing widespread valley rain and mountain snow to the area. While some models show a few showers developing as early as Friday afternoon, ensemble means are focusing on the Friday night through Saturday evening timeframe as the most likely for precipitation. Latest NBM shows 25th percentile QPF values generally between 0.35 to 0.7 inches over the mountains and I-15 corridor (less elsewhere), with 75th percentile values of between 0.75 to over 1.25 inches over the same areas (0.25-0.7 inches elsewhere). Behind the cold front, with H7 temperatures falling to between -4 to -6C by the tail end of precipitation, snow levels down to between 6-7kft can be expected. Latest NBM 25th-75th percentile snow amounts range from generally 4-8 inches with locally higher amounts in the upper Cottonwoods.

As the storm system exits the area Saturday night, high pressure will make a brief return, allowing for a quick break in the weather. However, the pattern is progged to remain progressive, with another storm system impacting the area around the Tuesday/Wednesday timeframe. Some model spread regarding the timing and evolution of this system exists, with global deterministics mainly tying this to the extent of splittiness exhibited by the storm as it approaches Utah. Some models suggest that this storm will be associated with colder temperatures that could bring snow levels down to at least the higher valleys (5-6kt) and potentially lower, though the probability of measurable snow along the Wasatch Front valleys remains generally under 10%.

AVIATION

KSLC...VFR conditions will prevail with light, terrain-driven winds. Southeasterly winds will likely persist overnight, but may become light and variable at times. Northwesterly winds are expected to return around 18-19z.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail with light, terrain-driven winds. Fog is unlikely in most locations except at KLGU, where there is a 60% chance of LIFR conditions developing between 11-16z.

SLC WATCHES/WARNINGS/ADVISORIES

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