Mountain Ice Fog and Visibility during CFACT

The objective of this study is to characterize visibility and microphysics of cold-fog conditions during The Cold Fog Amongst Complex Terrain (CFACT) project, which was designed to investigate the life cycle of cold fog in the Heber Valley, Utah. The field campaign was conducted from 7 January to 23 February 2022 and was supported with observations and resources from the NSF Lower Atmospheric Observing Facilities (LAOF), managed by NCAR’s Earth Observing Laboratory (EOL), as well as the University of Utah and Ontario Technical University. Heber Valley is surrounded by canyons, mountains and irregular topography where the Provo River streams along the valley floor from Jordanelle Reservoir at the north to Deer Creek (DC) Reservoir at the southeastern end at 1652 m above sea level (ASL). The highest peaks surrounding the valley are at about 3500 m (ASL) to the west and southwest of the project area.

The DC supersite had extensive ice and droplet microphysical as well as precipitation measurements obtained using a ground-based Gondola (composed of a Droplet Measurement Technologies (DMT) Cloud Droplet Probe - CDP and Back-scatter Cloud Probe - BCP), a DMT Fog Monitor (FM120), a Mesaphotonics Cloud Droplet Measurement System (CDMS), a DMT Ground-based Cloud Imaging Probe (GCIP), a Vaisala Present Weather Detector (PWD52), and an OTT Parsivel. During the project, aerosol measurements were performed using a GRIMM Aerosol Spectrometer, a T.S.I. Scanning Mobility Particle Sizer (SMPS), and a DMT Cloud Condensation Nuclei (CCN) counter, as well as filter samplers. These instruments covered a size range from 8 nm up to cm size range representing aerosols, fog particles, and precipitation. Measurements from a Halo Photonics doppler wind lidar, a Vaisala CL61 ceilometer, a tethered balloon system (TBS), and a 32-m turbulence tower were used to characterize vertical profiles of fog microphysics and aerosols, as well as the dynamic and thermodynamic structure. Eleven significant weather events occurred during the 47 days of the CFACT campaign that included snowfall, freezing fog, ice fog (IF), and light ice crystal precipitation when Vis<5 km. In the presentation, IF events will be discussed with respect to ice crystal particle size spectra and habit, visibility, physical parameterizations, as well as measurement and prediction challenges faced.