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)

Historic rainfall and floods in middle Tennessee

August 21st, 2021 |
MIMIC Total Precipitable Water, 1000 UTC 20 August – 1200 UTC 21 August 2021 (Click to enlarge)

Training thunderstorms early Saturday caused historic rains and devastating (and deadly) flash floods early on Saturday morning 21 August 2021. (Click here for a listing of hourly precipitation totals at McEwen, TN; this excellent tweet from Tomer Burg shows the radar in the region). Were there satellite products that described the environment, rich in moisture, that allowed the flooding rains to occur? The animation above shows MIMIC Total Precipitable water at hourly timesteps from 1000 UTC on 20 August 2021 to 1200 UTC on 21 August 2021. There is a pronounce gradient in moisture established over middle Tennessee by 0400 UTC on 21 August, and the amount of moisture is very large!

The rain that fell is analyzed below (data source: MRMS). The heavy rain caused drastic (and record-setting) stream flows and water heights on the Big Piney River. The flooding also closed I-40 temporarily.

MRMS Radar Estimates of Radar, 1400 UTC 20 August – 1400 UTC 21 August 2021 (click to enlarge), from WFO OHX.

The animation below shows the GOES-16 Low-level water vapor imagery. A pronounced boundary is apparent near the region where the flooding rains developed. (Band 8 imagery — upper-level water vapor infrared (6.19 µm) imagery — shows a gradient in the same region as well)

GOES-16 Low-Level water vapor infrared (Band 10, 7.3 µm) imagery, 2001 UTC 20 August 2021 – 1251 UTC on 21 August 2021 (Click to enlarge)

GOES-16 Band 13 Clean Window infrared (10.3 µm) imagery, below, overlain on top of the Level 2 Total Precipitable Water (TPW) product document the development of the training thunderstorms along the TPW gradient. The motion of the storms is along the gradient. Numerous blog entries at the Hazardous Weather Testbed discuss how convective development is favorable along gradients, and in this case the developing thunderstorms maintain access to the moisture.

GOES-16 Clean Window infrared (Band 13, 10.3 µm) imagery, 0001 UTC 21 August 2021 – 0956 UTC on 21 August 2021 (Click to enlarge)

Derived Motion Winds can be used to estimate the winds surrounding the developing convection, and the animation below, from 0000 to 0956 UTC, show primarily northwesterly flow, so if the storms are moving with the ambient flow — and there’s no guarantee that that’s happening — you can infer their motion. Derived motion winds in the vicinity of the developing storms are primarily northwest and north-northwest. That might help a forecaster anticipate training with convection.

GOES-16 ABI Band 13 Infrared (10.3 µm) and Derived Motion winds at 350-450 mb (yellow), 450-600 mb (green) and 600-775 mb (orange) from 0001 – 0956 UTC on 21 August 2021 (Click to enlarge) Note that Derived Motion Wind Vectors are computed every 15 minutes.

How do you know when anticipated thunderstorms within a primed region are ready to erupt — especially at night when visible imagery are unavailable (except for Day Night Band imagery; with Suomi-NPP (flying over at 0641 UTC and NOAA-20, flying over at 0720 UTC you can get a 50-minute animation in the middle of the night, shown here, with data from VIIRS Today). The animation below, of the GOES-16 Night Time Microphysics RGB, follows an example discussed here by Carl Jones, WFO FGF. The appearance of red values in the RGB over west-central TN around 0501 UTC heralds the development of deeper convection. This should also be the time when GLM lightning observations develop. See the second animation below.

GOES-16 Night time microphysics RGB, 0001 – 0951 UTC 21 August 2021 (click to enlarge)
GOES-16 Night time microphysics RGB, 0501 – 0601 UTC on 21 August 2021 (click to enlarge)

It turns out the relationship between color change in the RGB and lightning initiation isn’t quite so clear-cut. The stepping animation below shows the Night Time Microphysics and the GOES-16 Cloud Phase product. It is a challenge to relate a cloud phase to a particular color. GLM observations are occurring in regions where ice clouds are present. However, there are also regions where ice clouds are diagnosed and lightning is not happening.

GOES-16 Night time microphysics RGB (upper left), Level 2 Cloud Phase product (upper right), GOES16 Band 13 infrared (10.3 µm) imagery (lower left) and GOES-16 Band 13 infrared (10.3 µm) imagery overlain with GLM Minimum Flash Area observations (lower right). Animation is from 0501 – 0756 UTC on 21 August 2021 (Click to enlarge)

The Weather Prediction Center (WPC) had two Mesoscale Discussions on this event, here and here.


This event was discussed at an FDTD Webinar (link) led by Matt Reagan and Brendan Schaper from the Nashville forecast office. (Storyboard Link)

Heavy rainfall and flooding associated with Tropical Cyclone Seroja

April 4th, 2021 |

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

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

The incipient circulation of Cyclone Seroja moved very slowly across the island of Timor in Indonesia during the 03 April – 04 April 2021 period — and the MIMIC Total Precipitable Water product (above) depicted very high values over that area (just northwest of Australia).

At Kupang’s El Tari Airport, precipitation amounts included 547 mm (21.5 inches) during the 48 hours ending at 00 UTC on 05 April — with the heaviest amounts of 106 mm (4.2 inches) in 6 hours and 80 mm (3.1 inches) in 3 hours occurring during the 00-06 UTC period on 04 April when the pressure was falling as Cyclone Seroja began to slowly organize and intensify (below). Flash flooding affected much of the island, with multiple deaths being reported.

Time series plot of surface observations at El Tari Airport, Kupang [click to enlarge]

Time series plot of surface observations at El Tari Airport, Kupang, Indonesia [click to enlarge]

JMA 2.5-minute interval rapid scan Himawari-8 “Clean” Infrared Window (10.4 µm) images (below) revealed a few convective bursts — with cloud-top infrared brightness temperatures of -90ºC and colder (yellow pixels embedded within darker shades of purple) — in the vicinity of Kupang (station identifier WATT) between 04 UTC on 04 April and 00 UTC on 05 April.

JMA Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play animation | MP4]

JMA Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play animation | MP4]

A NOAA-20 VIIRS Infrared Window (11.45 µm) image at 0550 UTC visualized using RealEarth (below) showed one lone -90ºC pixel within a convective burst centered just north of Kupang.

NOAA-20 VIIRS Infrared Window (11.45 µm) image at 0550 UTC on 04 April [click to enlarge]

NOAA-20 VIIRS Infrared Window (11.45 µm) image at 0550 UTC on 04 April [click to enlarge]


CMORPH estimates of 7-day precipitation (available in RealEarth) over the region show 300-400 mm over West Timor, and values exceeding 700 mm (!!) over the adjacent ocean.

7-day CMORPH accumulation of precipitation ending 0000 UTC 5 April 2021 (Click to enlarge)

Flooding in Tennessee

March 28th, 2021 |

GOES-16 “Clean” Infrared Window (10.35 µm) images, with hourly Precipitation Type plotted in cyan [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with hourly Precipitation Type plotted in cyan [click to play animation | MP4]

GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm) images centered on Nashville (above) displayed multiple clusters of thunderstorms that moved across Tennessee during the 27 March – 28 March 2021. The coldest overshooting top infrared brightness temperatures were in the -70 to -79C range. Precipitation ended and clouds cleared as a cold front moved eastward across the state on 28 March.

Hourly images of the MIMIC TPW product (below) showed the northward surge of moisture from the Gulf of Mexico beginning early on 27 March, providing an environment conducive to heavy rainfall.

MIMIC TPW product [click to play animation | MP4]

MIMIC TPW product [click to play animation | MP4]

Plots of rawinsonde data from 00 UTC and 12 UTC on 27 March [click to enlarge]

Plots of Nashville rawinsonde data from 00 UTC and 12 UTC on 27 March [click to enlarge]

Plots of Nashville rawinsonde data from 00 UTC and 12 UTC on 27 March (above) and 28 March (below) illustrated the rapid increase in moisture on 27 March, followed by the gradual decease in the wake of the cold frontal passage.

Plots of rawinsonde data from 00 UTC and 12 UTC on 28 March [click to enlarge]

Plots of Nashville rawinsonde data from 00 UTC and 12 UTC on 28 March [click to enlarge]

 

 


CMORPH estimates of accumulated precipitation (available in RealEarth) are shown below, with 24-hour totals ending 23:59 on 27 March (left) and 28 March (right).  The darker purple region denotes totals of >100 mm in 24 hours.

24-hour precipitation totals ending 23:59 on 27 March (left) and at 23:59 28 March (right) 2021 (Click to enlarge)