The Direct Broadcast antenna at the UW-Madison CIMSS can receive information over much of the contiguous United States. This includes the NOAA-20 overpass that acquired data around 0910 UTC over southern California during a frontal passage. NOAA-20 supports both the Visible Infrared Imaging Radiometer Suite (VIIRS) and the Advanced Technology Microwave Sounder (ATMS) instruments. Microwave imagery from ATMS, above, at 21.3 and 36.5 GHz, (from this temporary site) show the narrow stream of moisture flowing into southern California. Note the very cold brightness temperatures south of Baja California. In this region, clear skies are allowing information from the ocean surface to reach the satellite, but ocean water has very low emissivity at microwave frequencies/wavelengths; as a consequence, the computed brightness temperature (computed assuming a blackbody emission) is very cold.

Weighting Functions for ATMS Bands 18-22, below (source), show that Band 22 receives information from higher in the atmosphere and Band 18 received information from lower in the atmosphere. All five frequencies are within a region where microwave energy is strongly absorbed by water vapor (as shown in this absorption spectrum figure from here). You can infer from the weighting functions that Band 22 is a region where water vapor absorption is strongest of the 5 channels, and Band 18 is in a region of the spectrum where water vapor absorption is weakest of these 5 channels.

ATMS Brightness Temperatures for channels 18-22 are shown below. All show cooler temperatures over southern California (and in a band extending to the southwest of southern California). This suggests that water vapor is either more abundant in this region, or at higher altitudes (or both). These images give qualitative estimates of moisture. As noted above, the moisture band is fairly narrow.

MIRS software that is part of CSPP (software that is used at direct broadcast sites to process the signal from ATMS or VIIRS) can be used to create horizontal fields of temperature and dewpoint from the microwave information. These quantitative fields are shown below. The dewpoint fields show higher dewpoints that are especially concentrated at about 500 mb. A sharp northern edge to the moisture is also apparent.

MIRS temperature fields in the mid- to lower-troposphere, below, suggest a fairly sharp temperature gradient associated with the northern edge of the moist plume.

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The I05 image (11.45 µm), below, from VIIRS, shows infrared information over southern California. The front affecting southern California is manifest as a relatively narrow band of cloudiness. Skies are mostly cloud-free south of Baja California. It’s easier to interpret the microwave imagery above if you have access to visible and infrared imagery at the same time. Of course, VIIRS and ATMS will both sample at the same times because they’re on the same satellite. It’s a good practice to use data from the visible (when available), infrared and microwave to better characterize atmospheric features.

CMORPH-2 estimates also give information about rainfall. They are available at RealEarth (where you can search for CMORPH) or here. The animation below suggests steady rains from the Pacific into the San Gabriel/San Bernardino mountains.

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Many locations in the Los Angeles basin had record rainfall on 5 February: Los Angeles airport: 2.57″ ; Burbank: 2.19″ ; Downtown Los Angeles: 2.93″ ; Long Beach: 2.57″. Rainfall totals from JAXA’s GsMAP site, below, show the concentration of heavy rain over Los Angeles.

CMORPH-2 estimates of 24-hour precipitations (from RealEarth), below, also show a concentration of heavy rain over Los Angeles.

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1-minute Mesoscale Domain Sector GOES-18 (GOES-West) “Clean” Infrared Window (10.3 µm) images (above) displayed a period of convective bursts near and over the American Samoa island of Tutuila on 04 February 2024 — which produced heavy rainfall (leading to flash flooding and landslides; during the 6-hour period ending at 1200 UTC, Pago Pago recorded 3.92 inches of rain), strong winds (gusting to 38 kts or 44 mph at Pago Pago, with wind gusts elsewhere estimated to 50 mph) and power outages across parts of the island (Local Storm Reports). The coldest cloud-top infrared brightness temperatures were in the -90 to -93ºC range (shades of purple embedded within brighter white regions) — which indicated that the stronger overshooting tops were ascending past the local tropopause, according to Pago Pago rawinsonde data.

These convective bursts developed as Tropical Disturbance TD06F was slowly approaching American Samoa (Fiji Meteorological Service surface analyses: 0300 UTC | 0600 UTC | 1200 UTC); TD06F continued to organize and intensify, eventually becoming Tropical Storm Nat at 1200 UTC on the following day (see this blog post for more information).

A GOES-18 Infrared image at 0710 UTC (below) included cursor sampling of the associated Level 2 derived product Rain Rate, Cloud Top Phase and Cloud Top Height — the derived Rain Rate at that cold (-92ºC) overshooting top was 3.94 inches per hour.

A larger-scale view during the 3-day period from 02-04 February is shown below. Clusters of deep convection first affected the islands of Western Samoa, before later forming over American Samoa. The South Pacific Convergence Zone (SPCZ) remained in the vicinity of the Samoan island chain during that time (1200 UTC surface analyses: 02 Feb | 03 Feb | 04 Feb), helping to focus convective development..

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All 4 components of the GOES-16 (GOES-East) Fire Detection and Characterization Algorithm (FDCA) (above) showed the diurnal variability of thermal signatures associated with a large and deadly wildfire complex near Viña del Mar and Quilpué in the Valparaíso District — located along the central coast of Chile — from 02-04 February 2024 (maximum Fire Power values occasionally reached 2200-2300 MW). After the wildfires began around 1510 UTC on 02 February, they spread northward rather quickly (due to strong southerly winds) — until an influx of cooler and more moist Pacific air early on 04 February helped to suppress the fire behavior. The METAR site plotted in the imagery is Santiago International Airport (where daytime air temperatures rose into the 90s F on 02/03 February).

A larger-scale animation of the FDCA products (below) indicated that additional wildfires were active farther to the south in Chile — with notable fires to the west of Curicó (the southernmost METAR site plotted in the imagery), which continued burning into the daytime hours on 04 February.

GOES-16 daytime True Color RGB and Nighttime Microphysics RGB images from the CSPP GeoSphere site revealed dense smoke plumes from the Viña del Mar and Valparaiso area that were transported northward — and clusters of hot fire pixels (darker shades of purple to blue) that persisted well after sunset — on 02 February (above) and 03 February (below).

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The four-panel animation below covers the initiation of the fires. The fire temperature RGB shows that most of the surface is red, because surface temperatures are very warm: Land Surface Temperatures from GOES-16 show values exceeding 120^o F during the warmest part of the day, cooling to the mid-90s by 2300 UTC. Initiation of the fires shows up as a brighter red point that quickly turns more yellow and whitish as the fires intensify.

===== 05 February Update =====

A 30-meter resolution Landsat-9 Natural Color RGB image at 1440 UTC on 05 February (above) revealed the burn scar from the wildfire complex that destroyed portions of Viña de Mar and Quilpué.

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GOES-18 (GOES-West) and GOES-16 (GOES-East) True Color RGB images from the CSPP GeoSphere site (above) showed hazy plumes of blowing dust lofted by Tehuano gap winds that emerged from the south coast of Mexico — which spread out across the Gulf of Tehuantepec and the adjacent waters of the Pacific Ocean on 27-30 January 2024 (long, narrow rope clouds delineated portions of the gap wind boundary on 28/29/30 January). Most Tehuantepec Wind events tend to last 24 or perhaps 48 hours — so the 3+ day duration of this particular episode was fairly unusual.

GOES-16 “Red” Visible (0.64 µm) images on 30 January (below) included plots of Metop ASCAT winds (with several red Gale Force wind vectors over the Gulf of Tehuantepec) and plots of surface/buoy/ship reports (with notable ship reports of 35 knot winds at 1400 UTC, and Blowing Dust at 1800 UTC). The cold front responsible for this Tehuano wind event moved rapidly southward across the western Gulf of Mexico and entered the Isthmus of Tehuantepec on 27 January (surface analyses) — and reached its southernmost position across southern Nicaragua on 30 January.

GOES-16 “Red” Visible (0.64 µm) images with an overlay of the Dust Detection derived product at 4 different times from 28-30 January (below) showed examples of Medium Confidence dust detection.

Surface wind speeds derived using Metop-B/C ASCAT and GCOM-W1 AMSR2 data (source) showed portions of the Tehuano wind field as it spread out across the Gulf of Tehuantepec and the Pacific Ocean during 28-30 January (below).

As a result of the strong gap wind flow, Significant Wave Heights derived from Jason-3 on 29 January and Sentinel-3A on 30 January (below) reached maximum values of 13-17 ft.

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