textproduct: Salt Lake City

KEY MESSAGES

- Temperatures will continue to average 10 to 15 degrees above normal through Sunday.

- A more active pattern will increase precipitation potential state-wide next week.

- With the exception of eastern Utah, there is a greater than 50% chance much of Utah will see at least 0.25 inches of precipitation between Monday evening and Wednesday night.

- Across the northern mountains, there is a 60% chance snow accumulations will exceed 6 inches between Tuesday morning and Wednesday night. For the remainder of the central and southern mountains, there is less than a 20% chance of snow accumulations exceeding 6 inches.

DISCUSSION

A welcome change in the pattern across the western United States will bring an increased threat of precipitation to much of the Beehive State most of the next week. Early morning upper air and satellite analysis indicates broad ridging remains across the southern Plains and northern Mexico. An upper level low is currently near San Diego/Baja California, with deep moisture advection noted across the Desert Southwest associated with this upper level low. A very active and very chaotic northern stream continues across the Gulf of Alaska and into the Pacific Northwest. It is not often that a forecast has the potential to have both atmospheric river paths that influence Utah the most significantly within a few days of each other (paths that go around both the northern side and southern side of the Sierras).

For the next 48 hours or so, the influence of broad ridging will continue to bring well above normal temperatures to the region. Expect temperatures around 10 to 15 degrees above normal in most locations. Utah DEQ continues to forecast yellow/moderate conditions for most northern monitored basins, with some improving to green/good conditions by Sunday.

As a stout 140kt+ jet max shifts into the Oregon/Idaho area Monday morning, the associated shortwave trough will push a cold front into northern Utah Monday morning into early Monday afternoon. While the cold air advection with this front will be significant...700mb temperatures will fall from around 0 to 1 C to -6 to -8C across northern Utah...the best forcing for any precipitation will quickly shift east of the region. Much of the ensemble members suggest this front will be transitioning to a frontolytic mode near the Utah/Idaho border. This will limit the precipitation potential with this initial shortwave trough, with valleys seeing less than 25% chance of 0.10 inches of precipitation or more. The northern mountains will see a little better chance for more than 0.10", around 35% south of I-84, 55-65% north of I-84, highest near the Idaho/Utah border. This distribution is quite typical for a frontolytic boundary. If this boundary is able to maintain coherency further into northern Utah, amounts will trend higher given this is a decaying northern Sierras atmospheric river (with IVT anomalies on the order of 90-95th percentile).

Most ensemble members indicate this cold front will lift north as a warm front ahead of the next shortwave trough Tuesday...and then shift south as a stronger cold front later Tuesday into Wednesday. This system has a much higher potential for more widespread precipitation, with a portion of the ensemble members indicating another decaying atmospheric river, this time around the southern Sierras, enhancing available moisture. The initial shortwave trough will cross into the western Great Basin Tuesday afternoon into Tuesday evening. Broad synoptic lift combined with a strengthening cold front will provide sufficient support for precipitation across northern Utah Tuesday evening, shifting south and east with time Tuesday night into Wednesday.

Yet another shortwave trough will shifting into southern California Thursday morning, likely enhancing precipitation along the front across central and southern Utah Thursday afternoon into Thursday evening before finally shifting away from the region.

As one would expect with decaying atmospheric river events...the threat for valley snow across northern Utah is limited. The best chance is behind the cold front late Wednesday morning into Thursday morning. Current ensemble members suggest around a 25% chance of at least 0.1" of snow in this period for valley floors, closer to 60% for the benches.

For the northern mountains, there is a 60% chance mountain snow accumulations will exceed 6 inches between Tuesday morning and Wednesday night. For the remainder of the central and southern mountains, there is less than a 20% chance of snow accumulations exceeding 6 inches. It is far too early to consider issuing winter weather advisories, but will be something to monitor moving forward.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions prevail for all regional terminals today. A weak upper-level disturbance brings a transient mid-to-high level cloud deck to northern Utah and southwest Wyoming through this afternoon. Generally light, terrain-driven winds are expected throughout today, except KEVW where increased westerly winds with gusts to 20kts are expected this afternoon.

SLC WATCHES/WARNINGS/ADVISORIES

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