Previous studies have indicated a widespread decline in snowpack over Utah accompanied by a decline in the snow-precipitation ratio while anecdotal evidence claims have been put forward that measured changes in Utah's snowpack are spurious and do not reflect actual change. Using two distinct lines of investigation, this paper further analyzes the winter precipitation regime in the state of Utah. First, by means of observationbased, gridded daily temperature, precipitation, and remotely sensed data, as well as utilizing a climatological rain-snow threshold (RST) temperature method, the precipitation regime of Utah was scrutinized. Second, a comprehensive synoptic analysis was conducted as an alternate means that is independent from surface observations. It was found that the proportion of winter (January-March) precipitation falling as snow has decreased by 9% during the last half century, a combined result from a significant increase in rainfall and a minor decrease in snowfall. Meanwhile, observed snow depth across Utah has decreased and is accompanied by consistent decreases in snow cover and surface albedo. Weather systems with the potential to produce precipitation in Utah have decreased in number with those producing snowfall decreasing at a considerably greater rate. Further circulation analysis showed that an anomalous anticyclone has developed over western North America, which acts to reduce the frequency of cyclone waves impacting Utah. Combined with the increased precipitation, this feature suggests that the average precipitation per event has intensified with more of it falling as rain than as snow. Trends in the hydroclimate such as these have implications for present and future regional water policy in the state of Utah.

Persistent winter inversions result in poor air quality in the Intermountain West of the United States. Although the onset of an inversion is relatively easy to predict, the duration and the subsequent breakup of a persistent inversion event remains a forecasting challenge. For this reason and for this region, historic soundings were analyzed for Salt Lake City, Utah, with reanalysis and station data to investigate how persistent inversion events are modulated by synoptic and intraseasonal variabilities. The results point to a close linkage between persistent inversions and the dominant intraseasonal (30 day) mode that characterizes the winter circulation regime over the Pacific Northwest. Meteorological variables and pollution (e.g., particulate matter of #2.5-mm diameter, PM2.5) revealed coherent variations with this intraseasonal mode. The intraseasonal mode also modulates the characteristics of the synoptic (6 day) variability and further influences the duration of persistent inversions in the Intermountain West. The interaction between modes suggests that a complete forecast of persistent inversions is more involved and technically beyond numerical weather prediction models intended for the medium range (;10 day). Therefore, to predict persistent inversions, the results point to the adoption of standard medium-range forecasts with a longerterm climate diagnostic approach.

A 10-yr record of PM 2.5 (particulate matter of aerodynamic diameter # 2.5 mm), collected in Cache Valley near downtown Logan, Utah, reveals a strong peak in the PM 2.5 concentration climatology that is tightly localized in mid-January. The cause of this subseasonal variation in the PM 2.5 climatology is investigated through dynamical downscaling and large-scale diagnostics. Climatological analysis of the U.S. winter mean ridge reveals a mid-January subseasonal shift in the zonal direction, likely in response to variations in the Rossby wave source over the central North Pacific Ocean. This displacement of the winter mean ridge, in turn, has an impact on regional-scale atmospheric conditions-specifically, subsidence with local leeside enhancements and midlevel warming over Cache Valley. The analyses of this study indicate that the subseasonal peak of long-term mean PM 2.5 concentrations in Cache Valley is linked to the large-scale circulations' subseasonal evolution, which involves remote forcing in the circumpolar circulations as well as possible tropicalmidlatitude interactions. This subseasonal evolution of the winter mean circulation also affects precipitation along the West Coast.

Regressions on 30 years' precipitation datg from five stations for the calculation of the monthly amount of precipitation falling on the land portion of the Lake Ontario basin are presented. Verification on three years' test datg shows a maximum cumulative annual error of 4%, with individual monthly errors as high as 17%. Provision for missing data. is made.