A strengthening high-pressure ridge is expected to bring extremely hot temperatures to Utah through the weekend, increasing the risk of heat-related illnesses, according to the National Weather Service. While daytime temperatures are expected to peak Saturday, meteorologists note that rising overnight minimum temperatures have become a significant long-term trend in the region.
Weekend Heat Forecast
The National Weather Service Salt Lake City announced Wednesday that a broad ridge is expected to re-orient itself over the West, with its center moving directly over Utah for the weekend. This shift will draw a drier airmass into the area, decreasing the threat of convection but causing temperatures to become increasingly hot.
Temperatures are expected to peak on Saturday, with 700mb temperatures forecasted to be in the lower 20s Celsius across the entire area. While there is high confidence in the potential for very hot maximum temperatures for Saturday and Sunday, officials noted uncertainty regarding how much overnight relief the area, particularly northern Utah, will receive. Due to this uncertainty regarding the length of the event, the National Weather Service has not issued an Extreme Heat Watch at this time.
Moisture and Fire Risk
The upcoming heat wave follows a period of increased moisture. The National Weather Service reported that monsoon moisture has been increasing and spreading northward, bringing a heightened threat of flash flooding through Wednesday.
By Thursday, high pressure is expected to strengthen across the western United States, flushing monsoonal moisture out of the state and introducing a much drier airmass. This pattern is expected to result in temperatures trending 5 to 10 degrees warmer this weekend. The combination of unseasonable heat and critical relative humidity values will lead to heightened fire weather concerns through the weekend, especially across the western half of the state.
Long-Term Temperature Trends
The focus on rising temperatures highlights a long-term trend in Utah's climate. According to a 2017 report from Wasatch Weather Weenies, both mean maximum and mean minimum temperatures in Salt Lake City have exhibited a long-term warming trend since at least 1874.
Notably, the report observed that minimum temperatures have seen a rapid increase at a rate faster than the increase in maximum temperatures since the 1970s. This phenomenon results in a reduction of the diurnal temperature range, which is the difference between the daily maximum and minimum temperatures.
Drivers of Rising Minimums
Several factors may contribute to the reduction in the diurnal temperature range and the rise in overnight lows. One primary driver is the urban heat island effect, caused by the dramatic growth of the population in Salt Lake City, Salt Lake County, and the Wasatch Front. For example, the population of Salt Lake County grew from under 200,000 in 1928 to over 1,000,000 in recent decades.
Typically, urban heat islands have a stronger influence on minimum temperatures than maximum temperatures, contributing to the reduction in the diurnal temperature range. Other potential contributors include changes in site characteristics at the Salt Lake City International Airport and changes in instrumentation used by the National Weather Service over the years.
Global and Regional Factors
Beyond local urban development, broader climatic shifts play a role in these changing patterns. The 2017 report noted that a decrease in the diurnal temperature range and a more rapid increase in minimum temperatures are consistent with an enhanced greenhouse effect and expectations of global warming.
Regional climate change and variability, such as variations in large-scale circulations like the North American Monsoon, may also influence these trends. While the relative importance of these factors remains unquantified, they collectively contribute to the shifting thermal landscape of the Wasatch Front.
Health and Safety Outlook
As the heat intensifies, the National Weather Service warned that the potential for heat-related illness will increase, particularly for valley locations. While the current forecast for Wednesday includes showers and thunderstorms that may keep high temperatures near seasonal normals, the transition to a dry, high-pressure regime will significantly alter the local weather pattern by the weekend.
