GOES-13 Sounder and Imager water vapor channels (00 UTC, 12 July)

An AWIPS 4-panel display of the three GOES-13 Sounder water vapor channel images along with the single GOES-13 Imager water vapor channel image (above) revealed that a pocket of warm brightness temperatures (denoting dryer air aloft) was in place over much of eastern Virginia and North Carolina around 00 UTC on 12 July 2010.

The corresponding plots of the GOES-13 Sounder (red, green, and blue plots) and GOES-13 Imager (black plot) water vapor channel weighting functions (below, calculated using 00 UTC rawinsonde data from Greensboro, North Carolina) showed a relatively uncommon “bi-modal” structure — this indicated that there were significant contributions from two distinct layers, such that the actual altitude of the features being displayed on the water vapor imagery over that region at that time would be difficult to ascertain.

Greensboro NC GOES-13 Sounder and Imager water vapor weighting function plots

However, 12 hours later, the same AWIPS 4-panel display of water vapor imagery around 12 UTC (below) showed that significant amounts of moisture and cloudiness had moved into the region that was relatively dry at 00 UTC.

GOES-13 Sounder and Imager water vapor channels (12 UTC, 12 July)

With the increased middle and upper tropospheric moisture, note that the 12 UTC  water vapor weighting function plots (below, calculated using 12 UTC rawinsonde data from Greensboro NC) all peaked at significantly higher altitudes — and by the shape of the weighting function plots, it was easier to tell the layer of the troposphere that was being sampled by each of the individual water vapor channels.

Greensboro NC GOES-13 Sounder and Imager water vapor weighting function plots

AWIPS images of the Blended Total Precipitable Water product (below) confirmed that there was a significant increase in total column moisture content over the Greensboro NC region during that 12-hour period. TPW values rose from about 21 mm to around 40 mm over Greensboro during that time.

Blended Total Precipitable Water product

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GOES-11 0.65 µm visible channel images

GOES-11 0.65 µm visible channel imagery (above) indicated that you would have been hard pressed to find a location along the entire West Coast of the US (from California to Washington State) that did not have fog or stratus clouds overhead during the morning hours on 09 July 2010!

During the preceding night-time hours (before visible imagery was available), a comparison of AWIPS images of the 1-km resolution MODIS fog/stratus product and the 4-km resolution GOES-11 fog/stratus product centered over central California (below) demonstrated the value of higher spatial resolution in determining just how far inland some of the fog and stratus features were located at around 06:30 UTC (11:30 pm local time).

MODIS and GOES-11 fog/stratus product images

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MODIS 6.7 µm water vapor image (with and without map overlay)

Under normal atmospheric conditions, the weighting function of most water vapor channels tends to peak at altitudes within the 500-300 hPa pressure range, allowing features within the middle to upper troposphere to be viewed on the water vapor imagery. However, under special conditions — for example, either a very dry or a very cold air mass — the altitude of the water vapor weighting function is shifted downward such that we are able to “see the surface” on water vapor imagery. Such was the case with the MODIS 6.7 µm water vapor image over the Baja California region on 08 July 2010 (above), where the outline of the coast was very obvious on the image.

Even though the water vapor channel was not “seeing the surface” per se, a signal of the strong surface thermal contrast (between the very warm land and the much cooler water) was able to override the weak signal from what little middle-tropospheric water vapor was present. Other cases of strong land/water temperature contrasts have been seen on water vapor imagery, such as with very cold and very dry arctic air masses back in February 2007, December 2006, and January 2004.

However, in this case, the signal of the land/water thermal contrast was not evident on the corresponding GOES-11 6.7 µm / GOES-13 6.5 µm water vapor composite image. Because of the large viewing angle of the geostationary satellites (around 40 degrees for GOES-11 and around 55 degrees for GOES-13 for the Baja California region), the water vapor weighting function was apparently shifted upward to a high enough altitude to preclude detection of the surface land/water thermal signal.

GOES-11 6.7 µm + GOES-13 6.5 µm water vapor composite (with and without map overlay)

Surprisingly, not even the GOES-11 sounder 7.4 µm water vapor channel image (below) was able to detect the strong surface thermal signal — the weighting function of this channel often peaks much lower in the troposphere (usually around 850-700 hPa). Again, perhaps the large geostationary satellite viewing angle was a factor. With the MODIS instrument flying directly overhead, there was no corresponding upward shift in the water vapor channel weighting function.

GOES-11 sounder 7.4 µm water vapor image (with and without map overlay)

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GOES-13 0.63 µm visible images

A stagnant area of high pressure situated over the Northeast and Mid-Atlantic states contributed to a prolonged heatwave over that part of the US, with widespread temperatures over 100º F (38º C) for several days — including 106º F (41º C) at Williamsburg, Virginia and Frederick, Maryland on 06 July 2010. McIDAS images of GOES-13 0.63 µm visible channel data (above) showed a large area of very hazy sky conditions covering much of the Northeast and Mid-Atlantic regions on that particular day — and corresponding MODIS Aerosol Optical Depth values were also quite high within the hazy areas seen on visible imagery, with surface Air Quality Index values deteriorating into the “Moderate” to “Unhealthy for Sensitive Groups” categories.

An AWIPS image of the MODIS Land Surface Temperature (LST) product (below) revealed that while many air temperatures (measured in an instrument shelter about 5 feet above the surface) were only as warm as about 100º F at 18:05 UTC (2:05 pm local time), the “skin temperature” of the ground surface was much warmer — with many areas exhibiting LST values in the 120-130º F range (darker orange to red color enhancement). The warmest LST value seen at that time was 136º F in southeastern Pennsylvania. As an aside, MODIS Sea Surface Temperature values were as warm as 87º F in the southern portion of Chesapeake Bay.

MODIS Land Surface Temperature product + surface METAR reports

Other notable features seen on the GOES-13 visible imagery above included (1) the development of a line of severe thunderstorms along a frontal boundary from Nebraska and South Dakota, which produced a number of tornadoes and large hail up to 2.75 inches in diameter, (2) a extensive area of cloudiness over the Yucatan Peninsula of Mexico, which eventually developed into Tropical Depression #2 over the Gulf of Mexico on the following day, and (3) the dissipation of fog and stratus along the California coast during the late morning and afternoon hours (with convection developing further inland over the Sierra Nevada mountain range).

In terms of the coastal fog and stratus in southern California, GOES-15 0.63 µm visible channel images (below) showed how slow these features were to burn off in some areas. In fact, a number of locations in the San Diego, California area experienced record low maximum temperatures for the date — including a daily high temperature of only 65º F at San Diego International Airport (labeled SAN on the images), which was 10 degrees below the normal high temperature (75º F) for San Diego on 06 July. It is also interesting to note that heating of the higher terrain of some of the offshore islands appeared to help initiate the earlier clearing of the marine layer stratus cloud deck.

GOES-15 0.63 µm visible channel images

A 250-meter resolution MODIS true color Red/Green/Blue (RGB) image (created using Bands 1/4/3) from the SSEC MODIS Today site (below) shows even greater detail in the structure of the coastal fog/stratus features at 21:23 UTC (2:23 pm local time).

MODIS true color RGB image (created using bands 1/4/3)

===== 10 JULY UPDATE =====

The large pocket of haze seen on the GOES-13 visible imagery over the Northeast US on 06 July slowly migrated southward along the East Coast during the next several days. An animation of hourly GOES-13 visible images (below) showed that the haze was concentrated over the Mid-Atlantic states on 07 July, but then moved further south to settle along and off the coast of the North and South Carolina, Georgia, and Florida during the 08/09/10 July period. A large cyclonic circulation over the far western Atlantic Ocean was largely responsible for helping to draw the hazy air mass southward.

GOES-13 0.63 µm visible images (06 July - 10 July)

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