Atmospheric River brings precipitation to south-central Alaska

November 12th, 2018 |

Blended Total Precipitable Water product [click to play animation | MP4]

Blended Total Precipitable Water product, with Upper Air sites plotted in white [click to play animation | MP4]

The NESDIS Blended Total Precipitable Water (TPW) product (above) showed an atmospheric river that was transporting moisture northward from the tropics to south-central Alaska during 11 November – 12 November 2018. TPW values were in excess of 2.0 inches near the leading edge of the moisture plume early in the period.

The corresponding Percent of Normal Blended Total Precipitable Water product (below) indicated that these values of TPW were at or above 200 percent of normal (yellow).

Percent of Normal Blended Total Precipitable Water product, with Upper Air sites plotted in red [click to play animation | MP4]

Percent of Normal Blended Total Precipitable Water product, with Upper Air sites plotted in red [click to play animation | MP4]

Using the MIMIC Multi-layer TPW site, you can see how TPW is partitioned within various layers of the atmosphere (below). This TPW product uses microwave data from POES, Metop NOAA-20 and Suomi NPP satellites (description). It’s important to keep in mind that the location and continuity of a plume of TPW (such as an atmospheric river) might not always exactly agree what is seen on geostationary satellite Water Vapor imagery, since water vapor spectral bands usually sense radiation being emitted from levels above where the bulk of TPW is normally found (as discussed here).

MIMIC Multi-layer Total Precipitable Water product [click to play animation | MP4]

MIMIC Multi-layer Total Precipitable Water product on 12 November [click to play animation | MP4]

Anchorage, Alaska rawinsonde data (below) showed that TPW values reached a maximum of 0.73 inch at 00 UTC on 12 September.

Sequence of Anchorage, Alaska rawinsonde data from 00 UTC on 11 November to 00 UTC on 13 November [click to enlarge]

Anchorage, Alaska rawinsonde data from 00 UTC on 11 November to 00 UTC on 13 November [click to enlarge]

The arrival of this moisture produced heavy rainfall and mixed winter precipitation across the region — Portage Glacier (about 50 miles southeast of Anchorage) received 9.99 inches of rainfall in 48 hours, and Anchorage set a new daily precipitation record on 11 November with 0.89″ (which included 1.0 inch of new snow). A summary of temperature and precipitation reports can be seen here.

A comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November (below) revealed widespread layered clouds across most of south-central Alaska.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November [click to enlarge]