textproduct: Salt Lake City

KEY MESSAGES

- Mild temperatures to record warmth along with some high elevation showers return through early next week.

- Pattern will begin to shift by Tuesday, bringing cooler temperatures, valley rain, and snow above 7500 to 8500 feet or so.

- Gusty winds develop Wednesday and Thursday ahead of a deeper system. This colder system will maintain widespread valley rain chances, and result in further mountain snow accumulations.

DISCUSSION

A benign and arguably pleasant evening ongoing across much of the forecast region. Temperatures remain cooler than some of the record heat of the prior days, but still north of 10F above at most areas. Water vapor loop shows the expansive ridge responsible for the prolonged heatwave now more centered throughout the southern Plains, with some upper level moisture wrapping up along the western to northwestern periphery of it. As a result, seeing some high clouds filtering through overhead, especially across northern Utah and southwest Wyoming, but conditions remain dry.

As the ridge further shifts and flattens, subtle embedded impulses within the zonal flow aloft will push through. While not too substantial, PWAT anomalies of around 100-150% of normal should prove sufficient for at least some isolated daytime showers over the high terrain, and maybe a rumble of thunder or two. As the post-frontal airmass continues to moderate, H7 temperatures increase back into around the 6C to 10C range, and in turn widespread daytime highs 10F to 20F above normal return. As was the case this last week, anticipate we'll have good potential to see several more temperature records broken. On Monday an approaching system will result in falling mid level heights and a slight uptick in isolated to scattered terrain based showers, as well as a slight decrease to temperatures.

Monday night into Tuesday look to be the start of a pattern change as a somewhat grazing northern stream trough sends a cold front southward into the area, in turn interacting with energy/forcing from an enhanced southern jet stream shifting through overhead. In addition to temperatures falling back to near climatologically normal values for a change, precipitation will become more widespread across the region. The highest chances and water totals will remain in the terrain (and particularly the northern terrain) given the enhancement from orographic forcing. Another embedded impulse then passing through Wednesday further enhances precipitation chances areawide, along with precipitation rates at higher terrain. Even after the initial cooldown this will still be a "mild" system in terms of snow levels, with current forecast snow levels around 7500 to 8500 ft. Given that, what snow does fall at those higher elevations will tend to be more dense in nature with snow:liquid ratios around 7:1 or so. Still a good bit of water possible though with 25th to 75th percentile amounts for northern mountains around 0.40" to 1.00" SWE, and closer to 0.20" to 0.50" at terrain further south. Similarly water amounts around the Wasatch Front and Back are roughly in the 0.15" to 0.40" range, with more modest amounts of around 0.05" to 0.15" elsewhere. In any case, just seeing favorable odds of any measurable precipitation across the area is a welcome change.

While a good bit of uncertainty is noted thereafter, the pattern evolution Thursday onward continues to look intriguing. Models have continued to hint at a more marked trough in this time range for a bit now, and continue to do so. Additionally, as currently forecast this trough has more favorable odds to take on an orientation that would allow a better tap of cold air from the north, with median H7 temps falling to around -6C to -10C behind an associated frontal boundary Thursday night or so. There is some question to just how deep the trough is though, and in turn how far south the colder air can progress. There is also uncertainty on if and to what extent this northern trough can phase with the southern stream, which will likely influence which way QPF may trend in the coming days. As it currently stands, forecast carries post-frontal snow levels falling to around 4500 to 6000 ft, with enough water to bring a more healthy shot of snow to the northern mountains, and maybe even some flakes mixing in to lower elevations. Again, still plenty of uncertainty in the specifics being close to a week out, but a much more favorable setup for cooler/wetter weather than the prolonged ridging of recent.

Another facet of this complex pattern evolution to keep an eye on will be wind. Depending on the exact evolution and trough depth, anticipate to see increasingly southwesterly flow through Wednesday, bringing widespread afternoon gusts around 15-35 mph. So long as frontal timing does not speed up, these gusts then look to increase more into the 25-45 mph range Thursday ahead of the front.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will prevail through the TAF period. Winds will generally remain terrain driven through midday Saturday, with southwesterly winds mixing down during the afternoon at most terminals.

SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...Red Flag Warning from noon Saturday to 9 PM MDT Monday for WYZ277.