textproduct: Salt Lake City

KEY MESSAGES

- Temperatures will remain well above normal through midweek, with additional record temperatures likely.

- A landfalling atmospheric river will bring valley rain and mountain snow above 8000 feet to much of the region Wednesday into Thursday, with the greatest accumulations across the Brain Head area, the Tushars, and near Boulder Mountain. Strong winds will develop, particularly over the western valleys, beginning Wednesday afternoon.

- The heaviest rain, below 8000 feet or so, will occur across southern Utah Wednesday into Thursday. Enhanced runoff is likely across this area, with all streams, slot canyons, and other waterways running high.

- The unsettled pattern will continue with gradually falling snow levels, reaching as low as 6000 feet by Friday evening and continuing to fall toward valley floors by Saturday morning. There is a 25% chance of measurable snow for the valley floors of northern Utah Friday night into Saturday morning.

DISCUSSION

Strong high pressure remains entrenched over the south central United States this afternoon, keeping a breezy and rather unseasonably warm southwest flow over Utah and southwest Wyoming this afternoon. Yesterday's moisture has lifted northward with the ridge building, with high clouds across the area and mid level clouds over northern Utah. High temperatures today are again averaging 20F above seasonal normals, with Salt Lake City exceeding today's daily record high by 10F.

Winds are expected to decrease slightly for Tuesday with dry and very mild temperatures continuing. By Wednesday morning, another storm system will approach the Pacific coast, with our southwest flow tapping into deep atmospheric river moisture, drawing it northward during the day. Associated valley rain and high elevation (8000-9000 feet+) snow will begin over southwest Utah, spreading across the remainder of the forecast area by Wednesday night. Some disagreement remains in the guidance with regard to the onset of precipitation, but southwest Utah should get going by Wednesday afternoon. Precipitation, widespread and persistent in this warm airmass, will continue through Christmas Day with snow levels above 8,000 feet.

Snow accumulations have the potential to be significant for the highest elevations of the southwest Utah mountains, including the Brian Head area and the Tushar mountains, but have held off on headlines at this time given the small area of potential impacts and remaining uncertainty about accumulations. Winds will also pick up Wednesday into Christmas Day, particularly over the western valleys where guidance continues to show an approximately 50 percent chance of wind gusts exceeding 40 mph. Given the lingering uncertainty, have also held off on any potential wind headlines at this time.

As the trough continues east, Utah and southwest Wyoming will finally move into a cold advection regime later on Christmas Day, bringing gradually falling snow levels. Most guidance indicates a drop into the 5,500-6,500 foot range for the northwestern half of the area by Friday afternoon and as low as northern Utah valley floors by Saturday morning. The question mark is how long precipitation will continue Friday into Saturday and how widespread it will be as the trough looks to be splitting and weakening on Friday. The majority of the guidance indicates precipitation will still be widespread for northern Utah on Friday, with the majority of the guidance showing most precipitation ending by Friday night. Thus, the chance of valley accumulations Saturday morning remains low, around 20 percent.

Overall, there is good agreement with regard to drier conditions for the upcoming weekend with temperatures finally returning to near normal for this time of year. By early next week, there are indications that another Pacific low will approach the California coast, potentially bringing more atmospheric river moisture into the forecast area, at least for southern Utah.

REST OF UTAH AND SOUTHWEST WYOMING

Strong westerly Pacific jet will largely maintain the ongoing pattern at area terminals, with abundant mid/upper level moisture resulting in a corresponding amount of cloud cover. At many terminals, especially more northern and exposed locations, this jet will also yield gusty southerly winds.

SLC WATCHES/WARNINGS/ADVISORIES

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