A Foehn gap over California, and very strong jet stream winds over the Southwest US

March 31st, 2010
MODIS water vapor. IR, and visible images

MODIS water vapor. IR, and visible images

AWIPS images of the 1-km resolution MODIS 6.7 µm water vapor channel, the 11.0 µm IR channel, and the 0.65 µm visible channel (above) showed a pronounced “Foehn gap” immediately downwind of the highest terrain of the Sierra Nevada mountain range on 31 March 2010.

A comparison of the 1-k resolution MODIS 6.7 µm water vapor image with the corresponding 8-km resolution 6.7 µm water vapor image from GOES-11 (below) demonstrates the ability to detect such features with better spatial resolution.

1-km resolution MODIS and 8-km resolution GOES-11 water vapor images

1-km resolution MODIS and 8-km resolution GOES-11 water vapor images

Strong southwesterly winds aloft with speeds of 70-110 knots were creating this Foehn gap — but the core of a very strong jet stream was located a bit farther to the south and east. According to the RUC model, the highest wind speeds at the level of maximum Wind Speed was in excess of 140 knots over far northwestern Arizona and far southwestern Utah. However, there were a number of MADIS Atmospheric Motion Vectors (AMVs) that indicated wind speeds as high as 161 knots, 167 knots, 170 knots, and 179 knots (below).

MODIS water vapor image + RUC winds speeds + MADIS AMVs

MODIS water vapor image + RUC winds speeds + MADIS AMVs

MODIS water vapor image + RUC wind speeds + MADIS AMVs

MODIS water vapor image + RUC wind speeds + MADIS AMVs

MODIS water vapor image + RUC wind speeds + MADIS AMVs

MODIS water vapor image + RUC wind speeds + MADIS AMVs

MODIS water vapor image + RUC wind speeds + MADIS AMVs

MODIS water vapor image + RUC wind speeds + MADIS AMVs

Fatal tornadoes in the Bahamas

March 29th, 2010
GOES-12 10.7 µm IR images + cloud-to-ground lightning strikes

GOES-12 10.7 µm IR images + cloud-to-ground lightning strikes

Strong convection moving eastward from Florida and across the Bahamas produced at least two tornadoes on the island of Grand Bahama on 29 March 2010 — according to media reports, there were fatalities at the Grand Bahama Container Port located at the western end of the island, where several large cranes were toppled. There were also tornadoes reported in Florida a few hours earlier. AWIPS images of GOES-12 10.7 µm IR channel data with an overlay of negative (cyan) and positive (violet) cloud-to-ground lightning strikes (above; also available as a QuickTime animation) showed several clusters of convection moving across Grand Bahama Island (located in the center of the images; station identifier MYGF is Freeport). In particular, note the storms with the highest density of negative cloud-to-ground lightning strikes moving across the island during the 15:15 – 15:45 UTC time period — this is likely the convective cell that produced the tornadoes. The coldest IR brightness temperatures over the Bahamas on the 4-km resolution GOES-12 images was -66º C (darker red color enhancement).

The Blended Total Precipitable Water (TPW) product (below) indicated that TPW values were in excess of 50 mm or 2.0 inches (darker purple color enhancement) along and ahead of a cold frontal boundary that was approaching from the west. These TPW values were 150%-200% above normal. In addition, the presence of a pre-frontal trough may have played a role in helping to enhance surface convergence in the vicinity of the Bahamas.

Blended Total Precipitable Water product

Blended Total Precipitable Water product

A closer view using 1-km resolution MODIS 11.0 µm IR channel data at 15:52 UTC (below) revealed greater detail in the overshooting top structure of the convection as it was moving over the eastern portion of the Grand Bahama Island. The coldest MODIS IR brightness temperatures near the island were -70º C (black color enhancement).

MODIS 11.0 µm IR image

MODIS 11.0 µm IR image

The CLAVR-x POES AVHRR Cloud Type product (below) indicated a number of “Overshooting Top” category clouds (violet color enhancement) associated with the stronger convective clusters.

POES AVHRR Cloud Type product

POES AVHRR Cloud Type product

The POES AVHRR Cloud Top Height product (below) showed that the highest cloud tops over the Bahamas were around 15 km or 49,000 feet (cyan color enhancement).

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Top Height product

A MODIS Sea Surface Temperature (SST) product from the following day (below) revealed that there was a very strong SST gradient between Florida (where SST values were primarily in the mid 60s F, green colors) and the Bahamas (where SST values were in the mid 70s F, orange colors). Perhaps the significantly warmer SST values of the Gulf Stream may have also played a role in the intensification of the convection as it approached the Bahamas?

MODIS Sea Surface Temperature product

MODIS Sea Surface Temperature product

Blowing dust in New Mexico and Texas

March 26th, 2010
GOES-12 visible images

GOES-12 visible images

McIDAS images of the GOES-12 0.65 µm visible channel data (above) showed the development of a large plume of blowing dust across parts of southern New Mexico and western Texas late in the day on 26 March 2010. Surface winds gusted to 84 mph at El Paso in Texas, with the blowing dust temporarily reducing the surface visibility to 0.1 mile.

A 250-meter resolution Aqua MODIS true color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below) revealed that at the time of the Aqua satellite overpass (20:24 UTC), plumes of blowing sand were already beginning to stream northeastward from the White Sands National Monument and Missile Range in southern New Mexico — the blowing sand had already reached the partially snow-covered Sacramento Mountains located to the east of Alamogordo. At that time, the surface visibility at Alamogordo was 5 miles…but within 3 hours the visibility there dropped to 0.5 mile.

Aqua MODIS true color image (viewed using Google Earth)

Aqua MODIS true color image (viewed using Google Earth)

With the approach of darkness, the GOES-12 (GOES East) visible channel imagery could no longer be utilized to track the location and movement of the thick airborne dust — however, the older GOES-11 (GOES West) satellite imager instrument still retains a 12.0 µm channel that is helpful for creating a simple 10.7 – 12.0 µm (channel 04 – channel 05) IR temperature difference product that is useful for tracking airborne dust (and also volcanic ash) at night. Such a sequence of GOES-11 10.7 – 12.0 µm images (below) showed that the dust plume (yellow to cyan color enhancement) continued to move eastward and northeastward across Texas and into southwestern Oklahoma during the hours after sunset.

GOES-11 10.7-12.0 µm IR temperature difference images

GOES-11 10.7-12.0 µm IR temperature difference images

A few hours later, a similar MODIS IR difference product created by subtracting the brightness temperatures of the 11.0 µm and 12.0 µm channels (below) showed that the leading edge of the dust (yellow color enhancement) had moved as far as northern Oklahoma and extreme southern Kansas. Note the “cleaner” appearance of the MODIS IR difference product, a result of the higher spatial resolution (1 km) and improved spectral response of the IR channels on the MODIS instrument compared to the GOES imager.

Aqua MODIS 11.0-12.0 µm IR temperature difference product

Aqua MODIS 11.0-12.0 µm IR temperature difference product

The ABI instrument aboard the GOES-R satellite will mark the return of the 12.0 µm channel on the GOES imager, which will allow such phenomena to be more easily identified and tracked.

Fire and Ice in northern Minnesota

March 26th, 2010
MODIS true color and false color images

MODIS true color and false color images

A comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a large fire (perhaps a prescribed burn?) in a remote area of the Red Lake Indian Reservation, just to the west of the Upper and Lower Red Lakes in far northern Minnesota on 26 March 2010. On the false color RGB image, the fire hot spot shows up as a large bright red feature — note the rapid increase in areal coverage of the burn area between the time of the 17:04 UTC Terra satellite overpass and the 18:50 UTC Aqua satellite overpass. The still-frozen lakes appear as varying shades of cyan, while unfrozen bodies of water show up as a much darker blue color. On the true color RGB image, the hazy-looking smoke plume can be seen drifting northward (advected by surface winds from the south that were gusting as high as 29 knots).

MODIS 3.7 µm, POES AVHRR 3.7 µm, and GOES-12 3.9 µm shortwave IR images

MODIS 3.7 µm, POES AVHRR 3.7 µm, and GOES-12 3.9 µm shortwave IR images

AWIPS images of the 1-km resolution MODIS 3.7 µm, the 1-km resolution POES AVHRR 3.7 µm, and the 4-km resolution GOES-12 3.9 µm shortwave IR channel data (above) shows some important differences in both the location of the hottest pixels (GOES-12 has the fire located farther to the west, in far eastern Pennington county) as well as the intensity of the hot spots: the 18:42 UTC MODIS image registered a maximum IR brightness temperature value of 46.5º C, and the 18:48 UTC POES AVHRR image registered a value as high as 54.5º C. At that same time, the cursor readout for the 18:45 UTC GOES-12 image read “NO DATA” — thus demonstrating the value of the 1-km resolution MODIS and POES AVHRR imagery for identifying the exact location of the hottest portion of the fire.

An animation of the 4-km resolution GOES-12 3.9 µm shortwave IR images (below) did show that the fire hot spot was gradually growing in size, and briefly began to exhibit IR brightness temperature values as high as 37.5º C at 17:45 UTC and 48.0º C at 18:15 UTC — but then the fire intensity exceeded the AWIPS temperature threshold and “NO DATA” was indicated by the AWIPS cursor readout before the fire hot spot eventually became obscured by a dense cirrus cloud canopy drifting overhead from the southwest..

GOES-12 3.9 µm shortwave IR images

GOES-12 3.9 µm shortwave IR images

The shortwave IR channels on the ABI instrument aboard the GOES-R satellite will have a spatial resolution of 2 km, which should produce images that more closely resemble the 1-km resolution MODIS and POES AVHRR images shown above (further enhancing our fire detection capabilities in the future).