Fog over the southeast US

November 5th, 2012 |
VIIRS DayNight Band on Suomi/NPP, GOES-R IFR Probabilities and surface observations (Click image to play animation)

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.

GOES-14 is no longer sending images

November 3rd, 2012 |
GOES-14 0.62 µm Visible Image

GOES-14 0.62 µm Visible Image

GOES-14 came out of storage in mid-August for an annual north-south maneuver and for GOES-R Testing. While in normal mode, GOES-13 suffered an anomaly, and GOES-14 replaced GOES-13 temporarily as GOES-East before GOES-13 returned to service.

After operating in SRSO-R mode for Hurricane Sandy, GOES-14 was switched off after the 1845 UTC image on 1 November 2012 (above). It will remain in stand-by mode until recalled because of anomalies with GOES-West (GOES-15) or GOES-East (GOES-13). For more information on the future plans for GOES-14, click here.

Strong storm in the Gulf of Alaska

November 2nd, 2012 |
POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images

POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images

A strong storm (with a central pressure near 950 hPa or 28.05″) had been intensifying over the Gulf of Alaska on 02 November 2012, and eventually began to enhibit a classic tightly-wrapped signature of a cyclone that had reached the occluded stage on POES AVHRR 0.86 µm visible channel and 12.0 µ IR images at 19:05 UTC (above) and also on MODIS 0.64 µm visible channel and 11.0 µm IR channel images at 21:00 UTC (below). This storm was producing widespread storm-force winds, with some gusts to hurricane force over the western Gulf of Alaska.

MODIS 0.64 µm visible channel and 11.0 µm IR channel images

MODIS 0.64 µm visible channel and 11.0 µm IR channel images

High-elevation snow cover remaining from “Superstorm Sandy”

November 2nd, 2012 |
MODIS 0.65 µm visible channel and false-color Red/Green/Blue (RGB) images

MODIS 0.65 µm visible channel and false-color Red/Green/Blue (RGB) images

Cold air and upslope flow on the western side of Hurricane Sandy contributed to some very impressive snowfall totals across parts of the central Appalachian Mountains in the eastern US (HPC storm summary)| HPC snowfall contour map). Once some of the cloud cover began to clear from the region on 02 November 2012, a comparison of AWIPS images of visible channel data and false-color Red/Green/Blue (RGB) composites from MODIS at 16:09 UTC or 12:09 PM local time (above) and again at 17:55 UTC or 1:55 PM local time (below) revealed the extent of the remaining high-elevation snow cover. On the false-color RGB images (created using the 2.1 µm “snow/ice channel” on MODIS, and the 1.61 µm “snow/ice channel” on VIIRS as the Green and Blue components of the image composites), snow cover appeared as the darker red features (which also appeared white on the corresponding visible images).

Data from the National Operational Hydrologic Information Center (observed snow depth | model-derived snow depth) indicated that some sites still had a snow depth in excess of 20 inches on on the morning of 02 November.

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

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