Using a combined LEO/GEO approach, ABI and VIIRS retrievals are used to estimate flooding from a satellite perspective. Individual flood products from VIIRS and ABI (or AHI, depending on location) are blended to create the NOAA LEO/GEO Flood Mapping Product.

An example is shown below over the Sacramento, California region. Recent rains in California caused flooding in much of the state, including regions near the state’s capital, Sacramento, particularly along the Sacramento River. RealEarth provides a 14-day archive of the NOAA LEO/GEO Flood Mapping Product (listed as River Flood: Joint ABI/VIIRS), which is available on a daily basis. The product is an estimate of surface flooded water fractions, and can be obstructed by cloud cover as seen in the frame from 1-29-2023. While the area looks heavily flooded, it is important to note that many of these regions are actually agricultural rice farms that intentionally flood surface areas.

A flood gauge monitored by the USGS shows a decline in water levels over the past week in Sutter County, CA, just north of Sacramento and along the Sacramento River.

You can generate the RealEarth LEO/GEO Flood Product animation on your own or investigate other flood sites by visiting the RealEarth webpage.

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SAR data are being acquired over American Samoa for the next several weeks. SAR data from a Sentinel-1A overpass at 0553 UTC on 31 January, shown above (from this website), shows mostly light winds, mostly less than 10 m/s. The Normalized Radar Cross Section (NRCS) data can be used to view any ice contamination in the wind speed image. Ice can cause very strong reflection of the SAR signal that will be misinterpreted as strong winds. If significant ice is present in any convective tower, it will have a feathery appearance in the NRCS data.

SAR netcdf files can also be imported into AWIPS, and the toggle below compares GOES-18 Band 13 imagery and SAR data at the same time. On this day it is challenging to relate the small increases in wind apparent in the SAR imagery to Band 13 satellite imagery.

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MetopB overflew the Samoan Islands shortly after 0900 UTC (link), and Advanced Scatterometer (ASCAT) winds from that platform also show weak winds. MetopC ASCAT winds from 0831 and 1011 UTC show light winds as well.

Thanks to the NOAA Office of Observations and NOAA/NESDIS/STAR SMCD and SOCD for arranging these observations.

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The Special Collection actually started on 30 January, and two RADARSAT collections occurred, one at 0544 (Wind Analaysis is here; NRCS is here) and one at 1647 UTC (Wind Analysis ; NRCS). Toggles of the two image pairs are shown below.

The 1647 UTC wind speed analysis includes regions where contamination by thick ice in clouds is likely occurring. That is, those very strong wind values (nearly 50 knots!) centered near 16.25 S and 171.5 W are not true surface winds speeds, but arise because of strong reflection from thick ice within convective clouds in that vicinity. (The ice features have a feathery look in the NRCS fields). GOES-18 Band 13 imagery over that region, below, shows abundant deep convection. The GOES-18 Cloud Phase product (here) indicated ice clouds over the convection, but only within certain regions of the convection was the ice thick enough to reflect enough SAR radiation to affect the derived wind speeds.

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GOES-16 (GOES-East) “Red” Visible (0.64 µm) images which include plots of GOES-16 Derived Motion Winds within the Suface-900 hPa layer (above) showed the eastward transport of several ice floes from the northern portion of Green Bay into Lake Michigan on 30 January 2023. Surface wind gusts and Derived Motion Wind speeds were generally in the 15-20 knot range during much of the day.

VIIRS True Color RGB and False Color RGB images from NOAA-20 and Suomi-NPP (below) confirmed that these features were ice floes (snow and ice appear as shades of cyan in the False Color RGB images). The VIIRS data were downloaded and processed by the SSEC/CIMSS Direct Broadcast ground station.

The emergence of ice floes into Lake Michigan can also be seen in a comparison of RADARSAT Synthetic Aperture Radar (SAR) wind data (source) at 1208 UTC and 2332 UTC (below). Ice features are very reflective in SAR wind data, and appear as brighter shades of yellow to red in these 2 images.

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An animation of the Day Cloud Type RGB over Lake Superior on 30 January 2023, above, shows two prominent features: persistent lake-effect bands oriented west-northwest to east-southeast over the western four-fifths of the Lake (station KCMX on the Keewenaw peninsula, for example, observed heavy snow during this animation), and a more north-south oriented convergence band that extends from the eastern Upper Peninsula of Michigan towards Marathon, ON. Note the northeast wind observation on Caribou Island in eastern Lake Superior.

Advanced Scatterometer (ASCAT) winds from Metop-B (that had a timely descending overpass to view Lake Superior), shown below, neatly show the convergent wind field. (Imagery from this website). A 1500 UTC surface analysis (here) shows a trough of low pressure over extreme eastern Lake Superior consistent with the region of northeast winds.

Note that the RGB used above is the Day Cloud Type RGB (rather than the perhaps more well-known Day Cloud Phase Distinction). In very cold airmasses, the ‘red’ band of the Day Cloud Phase Distinction RGB loses the ability to discriminate between the cold ground and higher cloud tops that might have a temperature similar to the Earth’s surface. The Day Cloud Type RGB uses Band 4 (the so-called ‘Cirrus Band’) rather than Band 13. The toggle below compares Day Cloud Type and Day Cloud Phase Distinction RGBs at 1736 UTC. Day Cloud Type is doing a better job on this day in discriminating between the different cloud tops in the Lake-Effect bands and in the convergence band.

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Thanks to Paul Ford, ECCC, for drawing our attention to this interesting convergent band over Lake Superior!

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