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More Precipitation for the West Coast, 3 February 2017

Posted On: February 3, 2017 - By: Barbra Lashbrook


Who would have thought that the West Coast would get more precipitation? In a series of atmospheric river events that pummeled the West Coast a few weeks ago, another synoptic-scale precipitation event approaches….yet again. As of this morning, parts of Washington, Oregon and California are expected to have 3-5 inches of rain and from 1-3 feet of snow in the Sierra Nevada and Cascade Mountains.

Figure 1 below, shows the latest Near-Constant Contrast (NCC) satellite imagery of the storm, as of this morning at 1057Z, 3 February 2017. If not familiar with the NCC, it is a derived product of the Day/Night Band (DNB) which utilizes a sun/moon reflectance model that illuminates atmospheric features, senses emitted lights and assists with cloud monitoring during the night-time. The DNB is a sensor and is apart of the 22 spectral channels on the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on-board the Suomi-National Polar-orbiting Partnership (Suomi-NPP) satellite.

NCC_modifiedFigure 1: NCC imagery taken at 1057Z, 3 February 2017 of the synoptic-scale system moving towards the West Coast of the United States. Although with no moon present, the NCC is able to detect the storm, the clouds and the emitted city lights along the coast. 

What’s unique about this precipitation event is that the moon is still below the horizon (i.e. no moon present to assist in sensing atmospheric features), but the clouds are still recognized. This unique situation is due to an atmospheric phenomenon called ‘atmospheric nightglow’. Nightglow is caused by photochemical reactions that occur during the day-time and illuminate a faint glow during the night-time. The DNB sensor recognizes the nightglow and senses the ambient atmospheric features.

In complement to NCC in analyzing the storm, the NOAA Unique Combined Processing System (NUCAPS), is an operational Cross-track Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS) physical retrieval algorithm that display vertical temperature and moisture soundings, spaced apart at ~50 km (30 miles). NUCAPS also contains data quality flags (Figure 2) that are assigned to each colored sounding: good soundings are in green, use caution with yellow soundings, and bad soundings are in red.

NUCAPS_modifiedFigure 2: NUCAPS soundings overlayed onto NCC imagery of the storm moving towards the West Coast. The data quality flags are partitioned into 3 colors: green, yellow and red.

The NUCAPS soundings can be investigated more in depth via the animation link shown here. In the animation (embedded with Skew-T plots), one can see the instability, and the moist and dry layers of the atmosphere within the storm.

Furthermore, the last bit of eye candy highlighting the storm is the ATMS Total Precipitable Water (TPW) Product (Figure 3), which shows the total amount of water vapor (expressed in inches) within a vertical column of the atmosphere. The color scale range goes from 0-2.5 inches, where the storm is apparent and has TPW values of ~0.7 inches.

ATMS_TPW_020317Figure 3: The ATMS Total Precipitable Water product at 1033Z, 3 February 2017, which shows the amount of water vapor within a vertical column of the atmosphere.


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