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]

GOES-16: visible and true-color images of a solar eclipse shadow

February 26th, 2017 |

GOES-16 ABI Visible (0.64 µm) images [click to play animation]

GOES-16 ABI Visible (0.64 µm) images [click to play animation]

GOES-16 — the first of the GOES-R seriesABI visible (0.64 µm) images captured the Lunar Umbra (or solar eclipse shadow) of the “ring of fire” annular eclipse that occurred in the Southern Hemisphere on 26 February 2017. The dark eclipse shadow could be seen moving from west to east, beginning over the southern Pacific Ocean, passing over far southern Chile and Argentina, and finally moving over the southern Atlantic Ocean. GOES-16 will routinely scan the Full Disk every 15 minutes (the current GOES Full Disk scan interval is once every 3 hours), but in a special mode can scan the Full Disk every 5 minutes.

The path of the eclipse shadow (courtesy of EarthSky.org) is shown below.

Path of 26 February 2017 solar eclipse shadow [click to enlarge]

Path of 26 February 2017 solar eclipse shadow [click to enlarge]

True-color GOES-16 Red/Green/Blue (RGB) images are shown below (courtesy of Kaba Bah, CIMSS).

GOES-16 true-color images [click to play animation]

GOES-16 true-color images [click to play animation]

Note: the GOES-16 data posted on this page are preliminary, non-operational data and are undergoing on-orbit testing.

Storm “Doris” affects the British Isles

February 23rd, 2017 |

Meteosat-10 Water Vapor (6.25 µm) images, with hourly surface wind gusts in knots [click to play animation]

Meteosat-10 Water Vapor (6.25 µm) images, with hourly surface wind gusts in knots [click to play animation]

Storm “Doris” affected the British Isles on 23 February 2017, producing strong winds and heavy rainfall. The mid-latitude cyclone rapidly intensified from a central pressure of 1004 hPa at 12 UTC on 22 February to 972 hPa at 12 UTC on 23 February (surface analyses) . EUMETSAT Meteosat-10 Water Vapor (6.25 µm) images (above) exhibited the “scorpion tail” signature of a sting jet (Monthly Weather Review | Wikipedia), and surface wind gusts included 58 knots at Dublin, 64 knots at Wittering and 69 knots at Valley.

The corresponding daylight Meteosat-10 High Resolution Visible (0.8 µm) images (below) revealed better detail of the various cloud structures associated with the storm.

Meteosat-10 High Resolution Visible (0.8 µm) images, with hourly surface wind gusts in knots [click to play animation]

Meteosat-10 High Resolution Visible (0.8 µm) images, with hourly surface wind gusts in knots [click to play animation]

True-color Red/Green/Blue (RGB) images from Terra/Aqua MODIS and Suomi NPP VIIRS visualized using RealEarth are shown below. EUMETSAT posted a natural-color RGB animation here.

Terra MODIS (1039 UTC), Aqua MODIS (1226 UTC) and Suomi NPP VIIRS (1248 UTC) true-color RGB images [click to enlarge]

Terra MODIS (1039 UTC), Aqua MODIS (1226 UTC) and Suomi NPP VIIRS (1248 UTC) true-color RGB images [click to enlarge]

GOES-16: fire detection in Florida

February 20th, 2017 |

GOES-16 (left) and GOES-13 (right) 3.9 µm Shortwave Infrared images [click to play MP4 animation]

GOES-16 (left) and GOES-13 (right) 3.9 µm Shortwave Infrared images [click to play MP4 animation]

Numerous small fires were burning in the Lake Okeechobee area of southern Florida on 20 February 2017. A comparison of GOES-16 ABI (at rapid scan 30 second intervals) and GOES-13 (at routine 15-30 minute intervals) 3.9 µm Shortwave Infrared images (above; also available as a 71 Mbyte animated GIF) showed the “hot spots” — dark black to yellow to red enhancement, with red being the hottest — associated with these fires. Since many of the fires were agricultural sugar cane burns (which tend to be brief, but intense), the vast majority were not detected using the routine operational 15-30 minute scan interval of GOES-13; only the 30-second interval rapid scan GOES-16 images were able to capture these short-lived events. GOES-16 (the first in the GOES-R series) will provide the capability of 30-second or 60-second images within special Mesoscale Sectors.

The improved spatial resolution of the GOES-16 data (2-km at satellite sub-point, vs 4-km for GOES-13) also aided in the detection and characterization of the small and short-lived fires.

Fire detection points from the NOAA Hazard Mapping System for 20 February are shown below.

NOAA Hazard Mapping System fire detection points [click to enlarge]

NOAA Hazard Mapping System fire detection points [click to enlarge]

Note: GOES-16 data shown on this page are preliminary, non-operational data and are undergoing on-orbit testing.