Snow streaks across the Great Lakes region

November 18th, 2008 |
MODIS true color and false color images

MODIS true color and false color images

MODIS true color and false color images from the SSEC MODIS Today site (above) displayed a number of mesoscale snow streaks across parts of the Great Lakes region on 18 November 2008. The snow on the ground (as well as any clouds) appear as white features on the true color imagery — on the false-color imagery,  any snow cover on the ground (as well as ice crystal clouds aloft) appear as cyan-colored features  (in contrast to supercooled sater droplet clouds, which appear as varying shades of white). Many of the snow streaks across parts of Wisconsin, Michigan, Indiana, and Ohio were on the order of 10 miles (19 km) or less in width.

A surge of cold arctic air on the previous day helped to initiate widespread snow showers across much of the Great Lakes region, which produced the narrow snowfall streaks. There was also significant lake-effect snowfall to the lee of the Greak Lakes –  snowfall amounts were as high as 22.0 inches at Trenary in the Upper Peninsula of Michigan, 10.5 inches at Gile in far northern Wisconsin, and 9.8 inches at Moorestown in the southwestern part of Lower Michigan. Extensive snow cover can be seen across far southwestern Lower Michigan and far northern Indiana on the MODIS images, along with an elongated lake-effect cloud band stretching north to south across Lake Michigan.

GOES-12 visible images

GOES-12 visible images

AWIPS images of the GOES-12 visible channel (above) showed that many of the snow streaks began to melt during the late morning and early afternoon hours.

Remnants of Hurricane Paloma

November 14th, 2008 |
GOES-12 visible and 3.9 µm shortwave IR images

GOES-12 visible and 3.9 µm shortwave IR images

GOES-12 visible (daytime) and 3.9 µm shortwave IR (night-time) images (above) showed a distinct swirl of clouds drifting northward across the Gulf of Mexico on 13 November14 November 2008. This cloud swirl was actually the remnants of Hurricane Paloma, which had intensified to a Category 4 hurricane and made landfall over Cuba on 08 November. Note that there were a few weak convective bursts forming near the center of the swirl, but these were fairly short-lived.

AWIPS images of the 1-km resolution MODIS visible, 11.0 µm IR window, and 3.7 µm shortwave IR images (below) indicated that the swirl was comprised of primarily low-level clouds at 18:54 UTC, with IR brightness temperatures considerably warmer  than -20º C — in fact, the MODIS Cloud Top Temperature product displayed values that were generally in the 0º C to +10º C range.

MODIS visible + 11.0 µm IR + 3.7 µm IR images

MODIS visible + 11.0 µm IR + 3.7 µm IR images

The MIMIC Total Precipitable Water product (below) showed that the remnants of Paloma (which initially had drifted back southwestward over Cuba on 12 November) were embedded within a plume of higher precipitable water (30-45 mm, or 1.2-1.8 inches) as it moved northward across the eastern Gulf of Mexico.

MIMIC Total Precipitable Water

MIMIC Total Precipitable Water

As the remnants of Paloma reached the coast of the Florida panhandle on the morning of 14 November, explosive convective development was seen. This convection actually displayed a well-defined “enhanced-v” storm top signature on the GOES-12 10.7 µm IR imagery (below). Some back-building of the convection was also evident on the IR imagery — this convection produced a swath of heavy rainfall and flash flooding across parts of the Florida panhandle region, with a report of 9.25 inches of rain at Bloxham (located to the southwest of Tallahassee), and 2.61 inches falling at Tallahassee (setting a new rainfall record for the date). Radar-estimated storm total precipitation exceeded 14 inches.

GOES-12 10.7 µm IR images

GOES-12 10.7 µm IR images

A comparison of 1-km resolution NOAA-18 and 4-km resolution GOES-12 IR images (below) demonstrated the superior enhanced-v detection capability of higher spatial resolution data. The enhanced-v “delta-t” value (the difference between the coldest overshooting top and the warmest portion of the downstream warm wake) was an impressive 22.8º C, which would be a large delta-t value for a tornado or hail-producing supercell over the Great Plains region! This convection was also producing a good deal of cloud to ground lightning, as was noted on the early morning NWS Tallahassee Area Forecast Discussion:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
410 AM EST FRI NOV 14 2008

…SCATTERED SHOWERS AND THUNDERSTORMS HAVE BEEN DEVELOPING OVER OUR AREA…WITH A FEW OF THESE STORMS ALREADY EXHIBITING MARGINAL ROTATING UPDRAFTS AND IMPRESSIVE CLOUD TO GROUND LIGHTNING. THE LATEST RUC INDICATES MUCAPE FROM 350 J/KG OVER CENTRAL GA TO 1500 J/KG ALONG THE FL GULF COAST. THIS IS RATHER IMPRESSIVE FOR THIS TIME OF YEAR…

GOES-12 10.7 µm + NOAA-18 10.8 µm IR images

GOES-12 10.7 µm + NOAA-18 10.8 µm IR images

A blog post by Stu Ostro at the Weather Channel raises the interesting question of whether the energy associated with the remnants of Paloma played a role in the additional development of deadly tornadoes across North and South Carolina about 24 hours later?

Another “small ice crystal” mountain wave event

November 12th, 2008 |
GOES-12 10.7 µm and 3.9 µm IR images

GOES-12 10.7 µm and 3.9 µm IR images

GOES-12 10.7 µm “IR window” and 3.9 µm “shortwave IR” images (above) showed a large area of mountain wave clouds to the lee of the spine of the Rocky Mountains, spreading eastward across parts of Alberta and Montana on 12 November 2008. Note how quickly the 3.9 µm IR brightness temperatures increased once  the reflection of solar radiation commenced — the wave clouds almost seem to “disappear” on the 3.9 µm imagery as the daytime sun angle increased, even as 10.7 µm IR brightness temperatures as low as -60º to -70º C (red to black color enhancement) persisted.  While this case was in the same general region as another mountain wave event observed on 03 November, the mountain wave cloud was much larger in this case.

AWIPS images of 1-km resolution MODIS 11.0 µm “IR window”, 3.7 µm “shortwave IR”, 1.3 µm near-IR “Cirrus detection”, 6.7 µm “Water vapor”, and Visible channels (below) allowed a more detailed look at the mountain wave clouds around 19:50 UTC. The coldest 11.0 µm IR brightness temperature over western Montana was -71º C (black enhancement), which corresponded to the 39,200 foot (200 hPa) level according to the Great Falls, Montana rawinsonde data. However, the 3.7 µm brightness temperatures in that same area were around +22º C (about 90º C warmer!), due to the strong reflection of solar radiation by the very small ice crystals that comprised the mountain wave cloud.

MODIS 11.0 µm IR, 3.7 µm IR, Cirrus, Water vapor, and Visible images

MODIS 11.0 µm IR, 3.7 µm IR, Cirrus, Water vapor, and Visible images

The MODIS cirrus detection image with an overlay of MADIS atmospheric motion vectors (below) confirmed the presence of strong winds aloft over the region, with wind speeds of greater than 100 knots (with one target as high as 186 knots over northwestern Montana). The MODIS cirrus image also helped to highlight some subtle cloud-top striations that were present.

MODIS cirrus image + MADIS atmospheric motion vectors

MODIS cirrus image + MADIS atmospheric motion vectors

Power plant plumes in Minnesota

November 10th, 2008 |
MODIS + GOES-12 fog/stratus product images

MODIS + GOES-12 fog/stratus product images

AWIPS images of the 1-km resolution MODIS fog/stratus product and the 4-km resolution GOES-12 fog/stratus product (above) showed the value of the higher spatial resolution MODIS data for detecting subtle power plant plumes in the stratus clouds over northern Minnesota on 10 November 2008.  These plumes likely originated at large coal-fired power plants (or paper mills?) located across that region — emissions from these industrial sources may have acted as cloud condensation nuclei, causing a higher concentration of smaller supercooled cloud droplets downwind of the plants.

The MODIS Cloud Top Temperature values in the region were around -13º C (below, darker green color enhancement), and the MODIS Cloud Phase product indicated that the stratus clouds were composed of supercooled water droplets (blue color enhancement).

MODIS fog/stratus, IR, Cloud Top Temperature, and Cloud Phase images

MODIS fog/stratus, IR, Cloud Top Temperature, and Cloud Phase images

GOES-12 Low Cloud Base product indicated that the stratus clouds had bases below 1000 feet (below, green color enhancement), while the GOES-12 Cloud Top Height product suggested that the tops of the stratus clouds were around 13,000 feet (lighter green color enhancement).

MODIS fog/stratus, GOES low cloud base, GOES cloud top height products

MODIS fog/stratus, GOES low cloud base, GOES cloud top height products

It is interesting to note that similar power plant plumes were also seen on the MODIS fog/stratus product on the previous day (below), but without a stratus cloud deck over the region.

MODIS fog/stratus product images (09 and 10 November)

MODIS fog/stratus product images (09 and 10 November)