A large low pressure system, slammed into the western United States (US), bringing heavy rain and snow, high winds, along with producing blizzards (for the Sierra Nevadas) and localized flooding for low-lying areas.
The areal extent of the system is seen via ‘Preliminary, Non-Operational‘ GOES-17 Day Cloud Phase Distinction RGB (below) at 1925 UTC, 16 January 2019, as the storm approached the Western US. The RGB differentiates between liquid water clouds (blue), glaciated clouds (green) and mid-to-high level ice clouds (yellow-to-red clouds). Note the elongated rope cloud, associated with the cold front, in the southwest portion of the image, depicted in quasi-linear blue and green colors.
The winter storm can also be seen via Advected Layered Precipitable Water (ALPW) product, that is derived from polar-orbiting satellites and identifies areas of high moisture content and moisture transport that can lead to heavy precipitation and flooding. Animation below, shows the ALPW product from 06 UTC, 16 January 2019 –> 15 UTC 17 January 2019, highlighting Winter Storm Harper as it moves into California, Oregon and Washington. The colorbar is at the top of the animation depicting 0-32 mm (black to pink colors) precipitable water values. ALPW is different from Total Precipitable Water (TPW) products, in that ALPW identifies precipitable water from four atmospheric layers (surface-850mb, 850-700mb, 700-500mb, and 500-300mb), rather than specifying the total precipitable water values for the entire atmospheric column.
In this case, as Winter Storm Harper approaches land, notice high concentrations of precipitable water between the surface-to-500mb (blue/aqua colors), and significantly lower precipitable water concentrations in the upper atmosphere (i.e. 500-300mb, grey to black colors). Also note an elongated atmospheric river on the southeast side of the low pressure system. The atmospheric river moved into and impacted south-central and southern California, where the Sierra Nevadas experienced heavy snowfall rates (up to ~3 inches per hour) and high snow accumulations.
Speaking of the Sierras, earlier this morning there were reports of thundersnow in the Sierras. Reports were near Mammoth Mountain, CA, in which the ‘Preliminary, Non-Operational‘ GOES-17, Geostationary Lightning Mapper (GLM) detected lightning signatures near Mammoth Mountain. Animation below shows GOES-17 GeoColor imagery overlaid by GLM – Group Flash Count Density signatures. Time period observed is between 12-1445 UTC, 17 January 2019. Notice the lightning signatures observed in the Sierras that experienced thundersnow.
Winter Storm Harper plans to create more havoc throughout today and into the weekend, moving into and impacting the Rocky Mountains, Central Plains and Eastern United States.