Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images

The first Nor’easter storm of the 2012-2013 winter season (as seen on 07 November 2012 MODIS images) produced snowfall amounts as high as 13 inches in parts of New Jersey and Connecticut (HPC storm summary). After the clouds had cleared in the wake of the departing system, the areal extent of the remaining snow on the ground — which ranged from 1-6 inches at some locations across New Jersey, New York, Connecticut, and Massachusetts — was shown in an AWIPS comparison of 375-meter resolution (re-projected onto a 1-km AWIPS grid) Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images at 17:25 UTC (12:25 PM local time) on 09 November 2012 (above). In the false-color VIIRS RGB image, snow on the ground was enhanced in shades of pink.

Note to National Weather Service forecast offices: as a part of our participation in GOES-R Proving Ground activities, CIMSS is able to provide a limited set of VIIRS imagery for display in your local AWIPS (via LDM feed).

Additional detail could be seen in 250-meter resolution MODIS true-color and false-color RGB images at 18:02 UTC (1:08 PM local time) from the SSEC MODIS Today site (below). In the MODIS false-color RGB image, the snow cover appeared as shades of cyan.

MODIS true-color and false-color Red/Green/Blue (RGB) images

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MODIS Sea Surface Temperature (SST) product with overlay of RTG_SST High-Resolution model SST field

An AWIPS image of the MODIS Sea Surface Temperature (SST) product on 09 November 2012 with an overlay of SST contours from the RTG_SST High-Resolution model valid about 6 hours later (above) showed the residual impact of Hurricane Sandy on the axis of the Gulf Stream, almost 2 weeks after Sandy moved through that area. There were large eddy perturbations seen in the axis of the Gulf Stream, and MODIS SST values of 80º F or higher (darker red color enhancement) that were not captured by the model analysis.

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GOES-15 6.5 µm water vapor channel images (click image to play animation)

McIDAS images of 4-km resolution GOES-15 6.5 µm “water vapor channel” data (above; click image to play animation) showed the development of a series of well-defined mountain waves immediately downwind of the high terrain of the Sierra Nevada mountains in California on 08 November 2012. This mountain wave signature indicates the potential for turbulence — and there were a few pilot reports of light to moderate turbulence in that region between the altitudes of 25,000 and 38,000 feet above ground level (17:02 UTC, 01:00 UTC).

Occasionally the crests of these mountain waves are marked by “rotor clouds” — but they also frequently occur in clear air, which underscores the importance of using water vapor imagery for their detection. AWIPS images of 1-km resolution MODIS 6.7 µm water vapor channel, 0.65 µm visible channel. and 11.0 µm IR channel data at 20:32 UTC (below) showed that there were no cloud features present with some of the mountain waves (or with the entire portion of any given mountain wave).

MODIS 6.5 µm water vapor channel, 6.5 µm visible channel. and 11.0 µm IR channel images

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VIIRS DayNight Band on Suomi/NPP, GOES-R IFR Probabilities and surface observations (Click image to play animation)

The animation above, showing the VIIRS Day/Night Band on Suomi NPP, as well as the GOES-R IFR Probability field that fuses together information from GOES-East and the Rapid Refresh, is offered as testimonial to the use of the Day/Night band in detecting the presence of low clouds. The Day/Night Band (that is “night-time visible”, which band uses reflected moonlight as an illumination source) and the 6.5-µm water vapor imagery and the traditional brightness temperature difference (10.7 µm – 3.9 µm) both show the presence of high-level cirrus over central and southern Florida. This high cloud deck will prevent the traditional fog detection algorithm from returning a useful signal. The comparison between the DayNight Band and the IFR probabilities is especially simple using this simple applet. Where the IFR Probabilities are large in regions free of cirrus, the Day/Night band does suggest the presence of clouds. As with other methods using satellites to detect fog, whether of not the cloud is at the surface is difficult to discern. Note that IFR Probabilities are smaller underneath the cirrus clouds. Both predictors — satellite and Rapid Refresh — must show strong signals for the highest IFR probability to occur, and that cannot happen underneath a cirrus canopy.

More examples of the GOES-R Fog detection algorithm, including a more detailed write-up on this Florida case, can be found at the Fog Blog. A Day/Night band image over the southeast with limited fog over coastal South Carolina and northern Florida is here.

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