Floods in the Pacific Northwest

November 16th, 2021 |
MIMIC Total Precipitable Water fields, 0000 UTC 10 November 2021 – 2300 UTC 15 November 2021 (Click to enlarge)

MIMIC Total Precipitable Water, shown above, shows a narrow ribbon of rich moisture stretching from north of Hawaii northeastward to the Pacific Northwest. Rainfall associated with this Atmospheric Rivr resulted in widespread flooding over Washington State (USA) and British Columbia (Canada). The system also generated very strong winds.

CMORPH estimates of rain, below, from Real Earth, show substantial 24-h rain amounts on 14-15 November, with peak values on 15 November of 75 mm in southern British Columbia. (This automated gauge along the Nooksack River at North Cedarville WA showed >4″ of rain (graph)) The 7-day accumulation ending at 2359 UTC on 15 November shows a few values in excess of 200 mm. CMORPH estimates suggest that heaviest rains were just north of the US-Canada border.

CMORPH estimates of 24-h rainfall, 13-16 November 2021 (Click to enlarge)

The excess rain’s impact on Nooksack Falls, north of Washington’s Mt Baker are shown below.

Nooksack Falls, 14 November 2021 (video credit: Olivia Ray)

Satellite estimates of flooding are available at this website. For example, the image below (from this direct RealEarth link) shows flood extent over northwestern Washington (note the US-Canada border in the image) on 16 November 2021.

VIIRS/ABI Flood Extent, 0000 UTC on 16 November 2021 (Click to enlarge)

News videos of the impact of the flooding on the Sumas Prairie near Abbottsford are here, here, here and here. Click here for video footage from near Sumas, WA. Other Washington imagery is here. This storm was well-forecast, as noted here.

Measured streamflow on the Nooksack River reached historic or near-historic volumes, as shown in these streamflow plots at North Cedarville (graph), Everson (graph) and Ferndale (graph) (all from this site).

NOAA-20 true-color imagery, below, from 31 October and 16 November, taken from the VIIRS Today website, show silt from this flood event.

NOAA-20 true-color imagery, 31 October and 16 November 2021 (Click to enlarge)

The difference between the 16 November and 17 November Joint ABI/VIIRS Flood Extent product is shown below. The extensive flooding on the Sumas Prairie near Abbotsford in Canada is apparent.

Joint VIIRS/ABI Flood Product, 16 and 17 November 2021 (Click to enlarge)

Tropical Storm Wanda

November 2nd, 2021 |
GOES-16 Band 2 Visible (0.64 µm) Imagery, 1250 -1740 UTC on 2 November 2021

CSPP GeoSphere imagery, above, (click here for a direct link to the animation above in CSPP Geosphere; it will remain there for about 2 weeks before the data are overwritten) shows the evolution of Tropical Storm Wanda on 2 November 2021. (Wanda had transitioned to a Subtropical Storm on 31 October). Convection developed near the storm center and wrapped about halfway around the center. Dry air is also affecting this storm. A 24-hour animation of MIMIC Total Precipitable Water (from this site), below, shows an absence of deep moisture, with the driest air to the west and south.

MIMIC Total Precipitable Water, 18z 01 Nov – 17z 02 Nov 2021 (Click to enlarge)

GOES Imagery also shows dry air near Wanda. Both the low-level water vapor (Band 10, 7.34 µm) and the level 2 Total Precipitable Water product (a clear-sky only product) show dry air signatures: for the water vapor imagery, orange and yellow enhancements; for the total precipitable water, yellow and green enhancements signifying values around 1.3″. The airmass RGB shows Wanda far removes from the tropical airmass that is characterized by a deep green color.

GOES-16 Band 10 infrared (7.34 µm) imagery, GOES-16 Total Precipitable Water, and GOES-16 Airmass RGB, all at 1800 UTC on 2 Nov 2021 (Click to enlarge)

Moisture returns to the US West Coast

October 22nd, 2021 |
MIMIC Total Precipitable water, rocking animation from 0000 UTC on 11 October to 2300 UTC on 21 October (click to enlarge)

A sequence of two intense storms in the north Pacific Ocean, noted in the GOES-17 airmass RGB below, has drawn moisture into the northwestern United States. A MIMIC (Morphed Integrated Microwave Imagery at CIMSS) Total Precipitable Water rocking animation, above (rocking animation from this site), shows the development of a ribbon of moisture that moved into the northwestern United States.

GOES-17 Airmass RGB with/without 0900 UTC analysis of fronts/pressure (Click to enlarge)

Advected Layer Precipitable Water (ALPW, from this website), differentiates the moisture into layers. At 1200 UTC, one moisture axis was right across the Bay Area of California, with 20-24 mm of moisture in the sfc-850 mb layer, 10-12 mm of moisture in the 850-700 mb layer, and 5 or 6 mm in the 700-500 mb layer.

Microwave estimates of total precipitable water in layers: Surface-850 mb, 850-700 mb, 700-500 mb, 500-300 mb, ca. 1200 UTC on 22 October 2021 (Click to enlarge)

Accumulated 1-hour precipitation (estimated with CMORPH-2) for the hour ending at 1200 UTC on 22 October, below, shows a ribbon of rain from just north of the Bay Area to central Oregon; largest amounts over northern California are 6-8 mm for the one hour. CMORPH-2 estimates of precipitation are available at RealEarth.

CMORPH estimates of 1-hour rainfall ending at 1200 UTC on 22 October 2021 (Click to enlarge)

Kompasu skirts to the north of Luzon

October 11th, 2021 |
Himawari-8 clean window infrared (band 13, 10.4 µm) imagery, 0232 – 1502 UTC on 11 October 2021

Severe Tropical Storm Kompasu moved westward just north of the island of Luzon in the Philippines on 11 October. The Himawari-8 Target Sector clean window infrared (Band 13, 10.4 µm) imagery, above, from 0232 – 1502 UTC (Imagery courtesy JMA; imagery available here), shows deep convection becoming more organized as the storm center moved.

Moderate wind shear that had been affecting Kompasu slowly relaxed in the 24 hours before the storm moved north of Luzon, as shown in the wind shear tendency map shown below (imagery obtained from this link at the CIMSS Tropical Website). Shear over/around the storm has been relaxing.

Wind shear tendency, 1500 UTC 10 October 2021 – 1200 UTC 11 October 2021 (click to enlarge)
Wind shear over the western Pacific, 1200 UTC 10 October – 1200 UTC 11 October 2021 (Click to enlarge)

Computed shear (imagery also taken from the CIMSS Tropical Website) is shown in the animation above. Wind shear for both animations above is defined here. A relatively small area of favorable wind shear was near the storm center as Kompasu became better organized in the band 13 imagery above.

Scatterometry imagery, below, from various satellite platforms at this site, tracked the system’s motion from 0100 to 1130 UTC on 11 October, as it moved north of Luzon.

Scatterometer imagery from HY-2B and HY-2C, and from ASCAT A, B and C, between 0100 and 1130 UTC on 11 October (2021)

Kompasu is forecast to move due west across the South China Sea in the next days, affecting the island of Hainan on the 13th before 1200 UTC. (Forecast, from JTWC; Here is a similar plot from JMA). Wind shear is not forecast to relax further in the next days so significant stregthening is not forecast.