GOES-12 and GOES-13 IR images (Animated GIF)

On the current operational GOES-11 and GOES-12 satellites, data losses occur for several hours each day during the weeks centered around the Spring and Autumn equinox due to (1) Keep-Out Zones (KOZ), and (2) Eclipse. During KOZ, sunlight impinging upon the optical path of the instrument detectors requires the GOES Imager and Sounder to be turned off; during Eclipse, the satellite is in the Earth’s shadow, so the solar panels cannot generate power for the Imager and Sounder instrument packages. On the animation of GOES-12 and GOES-13 10.7 µm IR imagery (above) from 22 August 2008, you can see the period of no data from GOES-12 during such a KOZ — however, data continued to be available using the GOES-13 satellite, due to changes in the spacecraft design that mitigate the KOZ problem.

On AWIPS, data from the GOES-11 (GOES-West) satellite are remapped and used to replace the missing GOES-12 (GOES-East) data during such KOZ and Eclipse periods. During this particular KOZ period, a strong rain band associated with Tropical Storm Fay was moving inland across the Jacksonville, Florida region, creating wind gusts up to 60 mph with heavy rainfall, severe street flooding, and multiple power outages due to downed trees and power lines. On the AWIPS IR images from the KOZ period (below) you can see that the re-mapped GOES-11 data at 05:00 and 06:00 UTC appear somewhat “distorted” due to the large satellite viewing angle (GOES-11 is positioned at 135º W longitude over the Pacific Ocean), and the high-altitude cold cloud top features are shifted significantly eastward due to the associated satellite parallax error.

AWIPS images of GOES IR channel (Animated GIF)

The GOES-13 satellite had recently been brought out of on-orbit storage for a period of operational testing. Real-time GOES-13 images are available here and here; GOES-13 sounder derived products are available under the “GOES-Central” heading.

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AWIPS images of the MODIS + GOES-12 "IR window" channel (Animated GIF)

Areas of low cloudiness (such as stratus and/or fog) at night can be important aviation hazards, but they are sometimes difficult to identify simply by examining standard IR imagery. A comparison of 1-km resolution MODIS 11.0 µm and 4-km resolution GOES-12 10.7 µm “IR window” images (above) does not give the sense that there was widespread fog and stratus clouds in place over much of eastern Colorado during the pre-dawn hours on 20 August 2008. Even with a color enhancement that highlights the warmer range of IR brightness temperatures (below), the edges of the low cloud feature are difficult to pick out unambiguously.

AWIPS images of the MODIS + GOES-12 "IR window" channel (Animated GIF)

There are a variety of satellite products available in AWIPS that can be used to better identify and characterize areas of low cloudiness and fog. In this case, the 1-km resolution MODIS fog/stratus product (below) showed very good details about the edges and structure of the area of low clouds and fog, with the corresponding  4-km resolution MODIS Cloud Top Temperature and Cloud Phase products  indicating that the cloud tops over eastern Colorado were composed of water droplets (blue enhancement) with cloud top temperatures around +5º C (red enhancement). However, note that there was another separate area of supercooled cloud tops farther to the east (located over western Kansas), where the Cloud Top Temperatures were below freezing (yellow enhancement) while the Cloud Phase product still indicated water droplet clouds (blue enhancement) — regions such as this might pose a higher risk for aircraft icing.

AWIPS images of the MODIS fog/stratus + cloud top temperature + cloud phase products (Animated GIF)

Using the GOES-12 satellite, one can examine the 4-km resolution fog/stratus product (below), and also utilize the 4-km resolution Low Cloud Base product along with the 10-km resolution sounder-derived Effective Cloud Amount and Cloud Top Height products to gain additional information about the cloud base height, cloud coverage, and cloud top height.

AWIPS images of the GOES-12 fog/stratus + low cloud base + effective cloud amount + cloud top height products (Animated GIF)

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GOES-12 IR imagery (Animated GIF)

After passing over Key West on 18 August, Tropical Storm Fay made landfall along the Gulf Coast of the Florida peninsula on 19 August 2008. GOES-12 IR imagery from the CIMSS Tropical Cyclones site (above) showed that Fay was moving slowly northward toward a weakness in the deep layer mean flow. GOES-12 IR cloud top temperatures continued to cool as Fay moved inland (IR brightness temperatures near the Florida coast were as cold as -81º C at 08:40 and 09:15 UTC), with an AWIPS image of the MODIS 11.0 µm IR channel (below) showing an eye structure at 16:10 UTC.

AWIPS MODIS IR image

The appearance of the eye structure continued to improve on GOES-12 visible imagery (below) even as Fay remained over land during the day, and QuikSCAT winds indicated that tropical storm force winds extended out across the adjacent offshore waters of both the Gulf of Mexico and the Atlantic Ocean.

GOES-12 visible image + QuikSCAT winds

The GOES-12 satellite was placed into Rapid Scan Operations (RSO), allowing images at 5-10 minute intervals (below) as the center of Fay grazed Lake Okeechobee in southern Florida. Winds gusted to 78 mph at Moore Haven along the western shore of Lake Okeechobee (MODIS image in Google Earth). It is interesting to note that MODIS Sea Surface Temperatures in Lake Okeechobee on Sunday 17 August were as warm as 91.8 F — this large body of warm water may have acted as an additional source of  evaporation and sensible heat to help fuel convection around the eye of Fay.

Note that Fay almost seemed to exhibit a slight amount of trochoidal oscillation on the GOES-12 images (though nothing like that seen with Hurricane Wilma back in 2005). However, a comparison of GOES-12 and GOES-13 RSO visible images revealed that this apparent “eye wobble” was due to irregularities in satellite navigation (the image-to-image navigation is significantly improved on the newer GOES-13 satellite, due to changes in the spacecraft design).

GOES-12 RSO visible images (Animated GIF)

Due to the aforementioned weak deep layer mean flow regime, the future motion of Fay was very uncertain, as could be seen by the large spread of model forecast tracks (below).

GOES-12 water vapor imagery + model forecast tracks

Even though Fay was not a particularly strong tropical cyclone, the slow forward motion meant an increased threat for heavy rainfall over the southeastern US; the Hydrometeorological Prediction Center 5-day total  precipitation accumulation forecast (below) suggested that rainfall could approach 15-20 inches in parts of Florida and Georgia.

HPC 5-day total precipitation accumulation forecast

** 29 AUGUST UPDATE **

The Melbourne, Florida NWS office received a storm total of 19.62 inches of rain, with  an amazing 27.65 inches reported 8 miles northwest of Melbourne (below).

Total rainfall from Fay (courtesy of NOAA HPC)

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250-m resolution MODIS true color image

Moderate to extreme drought conditions across much of North Dakota during the Spring and Summer of 2008 had caused the water levels at Long Lake (a small  alkaline lake located east-southeast  of Bismarck) to become very low — as a result, bright white “salt flats” began to grow in size, becoming large enough to be seen on 1-km resolution GOES-12 visible imagery as well as on 250-meter resolution MODIS true color imagery from the SSEC MODIS Today site (above) on 18 August 2008. This feature could also be seen on MODIS true color imagery from the previous day (below, viewed using Google Earth).

MODIS true color image (viewed using Google Earth)

AWIPS images of the MODIS visible channel, Land Surface Temperature (LST) product, and Normalized Difference Vegetation Index (NDVI) product from 17 August (below) revealed that LST values were significantly cooler over the high albedo areas of the white “salt flats” (in the upper 70s to low 80s F, compared to 100-110 F over the surrounding areas), and NDVI values were very low over the dry lake bed (less than 0.1, compared to 0.4 to 0.6 in the surrounding areas).

AWIPS images of MODIS visible, LST, and NDVI (Animated GIF)

** 20 AUGUST UPDATE **

Strong southerly winds on 20 August (gusting to 40 mph at Mobridge SD, 44 mph at Jamestown ND, and 36 mph at Bismarck ND) were creating a plume of “blowing dust” off the dry lake bed of Long Lake. A comparison of GOES-12 and GOES-13 Rapid Scan Operations (RSO) visible imagery at 5-10 minute intervals (below) shows the extent of the plume. This image comparison also serves to highlight the improved navigation on the newer GOES-13 satellite — note the excellent image-to-image navigation on the GOES-13 images on the right, compared to the notable wobble on the GOES-12 images on the left.

GOES-12 + GOES-13 RSO visible images (Animated GIF)

MODIS true color imagery (below, viewed using Google Earth) showed that the plume extended northward  to the Turtle Mountain plateau (the darker green feature) along the North Dakota/Canada border! A forecaster from Rapid City SD spoke to his nephew via telephone, who was driving an agricultural combine harvester south of Martin and west of Harvey in central North Dakota — this location appeared to be right in the middle of the plume — and the nephew reported 2-3 miles visibility, but no apparent smell or odor. 

MODIS true color image (viewed using Google Earth)

Hat-tip to Lee Czepyha, Meagan Holm, and Matthew Bunkers of the National Weather Service forecast office at Rapid City, SD for first noting this interesting feature and bringing it to our attention (and getting ground truth reports)!

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