Heavy Rains over southern California

February 28th, 2017 |

GOES-15 Water Vapor (6.5 µm) images [click to play animation]

GOES-15 Water Vapor (6.5 µm) images [click to play animation]

The GOES-15 Water Vapor animation, above, shows a potent cold front moving through southern California late on 27 February. This front that passed through San Diego at 0500 UTC on 28 February (9 PM PST) was accompanied by abundant precipitation, the heaviest rainfall in 13 years at the San Diego airport (link), with widespread 2+-inch rains that caused power outages and flooding. The image below (from this site), shows the 24-hours precipitation ending at 1200 UTC on 28 February 2017. Values in excess of 6″ occurred in the mountains east of San Diego.

Accumulated Precipitation for 24 hours ending 1200 UTC on 28 February 2017 [click to enlarge]

Accumulated Precipitation for 24 hours ending 1200 UTC on 28 February 2017 [click to play animation]

Hourly MIMIC Total Precipitable Water estimates for the 72 hours ending 1400 UTC on 28 February 2017 [click to enlarge]

Hourly MIMIC Total Precipitable Water estimates for the 72 hours ending 1400 UTC on 28 February 2017 [click to play animation]

Satellite estimates of Total Precipitable Water (TPW) suggested that heavy rains were likely. MIMIC total precipitable water plots, above (source), show a moisture source that tapped the rich moisture of the Intertropical Convergence Zone. NOAA/NESDIS Blended Precipitable Water Percent-of-Normal plots (source, at this site), shown below, show values exceeding 200% of normal over southern California. Both MIMIC and Blended TPW products offer excellent situational awareness.

NOAA/NESDIS Blended Total Precipitable Water Percent-of-Normal, times as indicated [click to play animation]

NOAA/NESDIS Blended Total Precipitable Water Percent-of-Normal, times as indicated

An interesting aspect of the GOES-15 Water Vapor animation, at the top of this post, is the appearance of land features. The spine of the mountains over Baja California appears throughout the animation, for example, as does the Front Range of the Rockies from Colorado southward to New Mexico. Should land features be visible in water vapor imagery? An answer to that lies in computed weighting functions, shown below (from this site), that describe from where in the atmosphere energy at a particular wavelength is being detected by the satellite.

At the start of the water vapor animation, near 0000 UTC, thick clouds cover southern California (and the sounding from San Diego shows saturated conditions); dry layers in the sounding appear by 1200 UTC. The 7.4 µm weighting function shows that information is detected by the satellite from lower down in the atmosphere; energy detected at 6.5 µm comes from higher in the atmosphere. This difference arises because of the better absorptive qualities of water vapor gas for 6.5 µm radiation vs. 7.4 µm radiation. By 1200 UTC, sufficient drying has occurred that the 7.4 µm Sounder Channel is detecting radiation that emanates from sea level. Note also at 1200 UTC that each individual moist layer influences the weighting function — but there is insufficient moisture at 1200 UTC in those moist layers that they are opaque to energy at either 6.5 µm or 7.4 µm.

Note: GOES-R Series satellites, including GOES-16, have ‘water vapor’ channels at 6.2 µm, 6.9 µm and 7.3 µm.

Water Vapor Weighting Functions at 72293 (San Diego) for GOES Imager (6.5 µm) (Black Line) and GOES Sounder (7.4 µm) (Red Line) at 0000 UTC 27 February (Left) and 1200 UTC 28 February (Right). The Sounding for San Diego is also indicated [click to enlarge]

Water Vapor Weighting Functions at 72293 (San Diego) for GOES Imager (6.5 µm) (Black Line) and GOES Sounder (7.4 µm) (Red Line) at 0000 UTC 27 February (Left) and 1200 UTC 28 February (Right). The Sounding for San Diego is also indicated [click to enlarge]

Atmospheric river events bring heavy precipitation to California

January 13th, 2017 |

MIMIC Total Precipatable Water product [click to play MP4 animation]

MIMIC Total Precipatable Water product [click to play MP4 animation]

A series of 3 atmospheric river events brought heavy rainfall and heavy snowfall to much of California during the first 10 days of January 2017 (NWS San Francisco/Monterey | WeatherMatrix blog). Hourly images of the MIMIC Total Precipitable Water product (above; also available as a 33 Mbyte animated GIF) showed the second and third of these atmospheric river events during the 06 January11 January 2017 period, which were responsible for the bulk of the heavy precipitation; these 2 events appear to have drawn moisture northeastward from the Intertropical Convergence Zone (ITCZ)..

Terra MODIS Visible (0.65 µm) and Near-Infrared

Terra MODIS Visible (0.65 µm) and Near-Infrared “Snow/Ice” (2.1 µm) images [click to enlarge]

A relatively cloud-free day on 13 January provided a good view of the Sacramento Valley and San Francisco Bay regions. A comparison of Terra MODIS Visible (0.65 µm) and Near-Infrared  “Snow/Ice” (2.1 µm) images (above) showed that snow cover in the higher terrain of the Coastal Ranges and the Sierra Nevada appeared darker in the Snow/Ice band image (since snow and ice are strong absorbers of radiation at the 2.1 µm wavelength) — but water is an even stronger absorber, and therefore appeared even darker (which allowed the areas of flooding along the Sacramento River and its tributaries to be easily identified). A similar type of 1.6 µm Near-Infrared “Snow/Ice” Band imagery will be available from the ABI instrument on the GOES-R series, beginning with GOES-16.

Better detail of the flooded areas of the Sacramento River and its tributaries was seen in 250-meter resolution false-color Red/Green/Blue (RGB) imagery from the MODIS Today site — water appears as darker shades of blue, while snow appears as shades of cyan (in contrast to supercooled water droplet clouds, which appear as shades of white). In the corresponding MODIS true-color image, rivers and bays with high amounts of turbidity (tan shades) were evident; the offshore flow of sediment from a few rivers could also be seen.

Terra MODIS true-color and false-color RGB images [click to enlarge]

Terra MODIS true-color and false-color RGB images [click to enlarge]

 

Heavy rainfall and high-elevation snowfall in Hawai’i

December 2nd, 2016 |

GOES-15 Water Vapor (6.5 µm) images, with overlays of GFS model 500 hPa geopotential height [click to play animation]

GOES-15 Water Vapor (6.5 µm) images, with overlays of GFS model 500 hPa geopotential height [click to play animation]

6-hour interval GOES-15 (GOES-West) Water Vapor (6.5 µm) images with overlays of GFS model 500 hPa geopotential height (above) showed middle to upper tropospheric moisture that was being drawn northwestward toward Hawai’i by the circulation of a closed low centered southwest of the state during the 01-02 December 2016 period.

A closer view using 15-minute interval GOES-15 Water Vapor images (below) showed 2 distinct pulses of moisture moving across the eastern portion of the island chain. Due to the prolonged flow of moisture and the variable terrain, Flood Warnings and Winter Storm Warnings were issued for the Big Island of Hawai’i (as shown using RealEarth).

GOES-15 Water Vapor (6.5 µm) images, with hourly surface reports [click to play MP4 animation]

GOES-15 Water Vapor (6.5 µm) images, with hourly surface reports [click to play MP4 animation]

Hourly images of the MIMIC Total Precipitable Water (TPW) product (below) showed the large plume of moisture, which had its roots within the Intertropical Convergence Zone (ITCZ). Maximum TPW values in the vicinity of Hawai’i were in the 50-55 mm (2.0-2.2 inch) range. 24-hour rainfall amounts were as high as 6.27 inches on the island of Hawai’i and 3.67 inches on the island of Kauai.

MIMIC Total Precipitable Water product, with tropical surface analyses [click to play animation]

MIMIC Total Precipitable Water product, with tropical surface analyses [click to play animation]

===== 03 December Update =====

GOES-15 Visible (0.63 µm) images (below) provided glimpses of the snow-covered peaks of Mauna Kea and Mauna Loa (circled in red) on the Big Island of Hawai’i early in the day on 03 December.

GOES-15 Visible (0.63 µm) images, with hourly surface reports [click to play animation]

GOES-15 Visible (0.63 µm) images, with hourly surface reports [click to play animation]

Hurricane Matthew: heavy rainfall and flooding across the Southeast and Mid-Atlantic US

October 9th, 2016 |

MIMIC Total Precipitable Water product, from 06 October/04 UTC to 08 October/16 UTC [click to play MP4 animation]

MIMIC Total Precipitable Water product, from 06 October/04 UTC to 08 October/16 UTC [click to play MP4 animation]

Copious amounts of moisture associated with Hurricane Matthew resulted in heavy rainfall (map | text list) and widespread flooding across the Southeast and Mid-Atlantic US during the 07 October to 09 October 2016 period. Hourly images of the MIMIC Total Precipitable Water (TPW) product (above; also available as a 22 Mbyte animated GIF) showed the high TPW values that spread from Florida to the Mid-Atlantic states; all-time record high TPW values were measured via rawinsonde at Jacksonville, Florida and Charleston, South Carolina, with a record high value for the month of October at Newport/Cape Hatteras, North Carolina (Tweet). For more details, see the Weather Underground blog.

Track of Matthew, from 28 September at 12 UTC to 09 October at 18 UTC

Track of Matthew, from 28 September at 12 UTC to 09 October at 18 UTC

Matthew set numerous records for intensity, longevity, and landfall (summary) — an animation of hourly GOES-13 Water Vapor (6.5 µm) images covering the 11-day period from 12 UTC on 28 September to 12 UTC on 09 October is shown below (also available as a large 113 Mbyte animated GIF). The CIMSS Tropical Cyclones site posted GOES-13 Visible (0.63 µm) animations from the individual days of 03 October, 04 October, 05 October, 06 October, 07 October, and 08 October.

GOES-13 Water Vapor (6.5 µm) images [click to play MP4 animation]

GOES-13 Water Vapor (6.5 µm) images [click to play MP4 animation]

The combination of high winds and flooding led to widespread power outages, with over 2 million homes and businesses without power. A comparison of nighttime Suomi NPP VIIRS Day/Night Band (0.7 µm) images from 28 September (before Mattthew arrived) and 09/10 October (after the passage of Matthew) showed a notable reduction in the glow of city lights in areas with no power (below; images courtesy of William Straka, SSEC). Note that the presence of patchy clouds on all 3 images tended to diffuse or even obscure the appearance of city lights below, depending on the thickness of the cloud layer(s).

Suomi NPP VIIRS Day/Night Band (0.7 µm) images on 28 September, 09 October and 10 October [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) images on 28 September, 09 October and 10 October [click to enlarge]

As clouds cleared in the wake of Hurricane Matthew on 09 October, a Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image at 1859 UTC, viewed using RealEarth (below), revealed patterns of turbidity in the offshore waters of the Atlantic Ocean from Florida to North Carolina; this increased turbidity was a result of high amounts of particles suspended in the water due to a combination of mixing from prolonged high winds and runoff from inland flooding.

Suomi NPP VIIRS true-color image [click to enlarge]

Suomi NPP VIIRS true-color image [click to enlarge]

About 8 hours later, a Terra MODIS Sea Surface Temperature (SST) product image at 0243 UTC on 10 October (below) showed a large eddy of warm Gulf Stream water (with a maximum SST value of 85.2º F, darker red color enhancement) surrounding a pocket of cooler water (with a minimum SST value of 78.5º F, darker blue color enhancement) off the coast of South Carolina.

Terra MODIS Sea Surface Temperature product [click to enlarge]

Terra MODIS Sea Surface Temperature product [click to enlarge]

The VIIRS Instrument on Suomi NPP provides data that are used in a River Flood Product (discussed previously on this blog). The product uses three reflective bands (I01, I02, and I03 at 0.64 µm, 0.86 µm and 1.61 µm, respectively) and the infrared window band I05 at 11.45 µm. The image below (courtesy of Sanmei Li at George Mason University) identifies many flooded regions over North Carolina. In particular, the flooding near Goldsboro and Lumberton is identified.

snppviirs_floodmap_south_north_carolina_usa_11oct_2016_18_17

JPSS River Flood product produced with Suomi NPP data, 1817 UTC on 11 October 2016 (Click to enlarge)

A sequence of 1 pre-Matthew (06 September) and 3 post-Matthew (09, 10 and 12 October) Terra/Aqua MODIS false-color RGB images from the SSEC MODIS Today site (below) also helped to highlight areas of flooding (darker shades of blue, especially notable along river valleys) that resulted from the heavy rainfall.

Terra and Aqua MODIS false-color images, from 06 September and 09, 10 and 12 October 2016 [click to enlarge]

Terra and Aqua MODIS false-color images, from 06 September and 09, 10 and 12 October 2016 [click to enlarge]