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.

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.

View only this post Read Less

AWIPS images of the 1-km resolution MODIS 11.0-3.7 µm fog/stratus Brightness Temperature Difference (BTD) and the 4-km resolution GOES-12 fog/stratus BTD (above) showed the value of higher spatial resolution MODIS data for detecting power plant plumes embedded within the stratus clouds over northern Minnesota on 10 November 2008.  These plumes originated at large coal-fired power plants (or paper mills?) located across that region — emissions from these industrial sources acted as cloud condensation nuclei, causing a higher concentration of smaller supercooled cloud droplets downwind of the plume source.

The MODIS Cloud Top Temperature values in the plume region were around -13ºC (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).

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).

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

View only this post Read Less

GOES-12 10.7 µm IR imagery (above) showed Category 4 Hurricane Paloma just south of Cuba on 08 November 2008. A well-defined eye was present, surrounded by cold cloud top temperatures in the -70º to -80º C range (as cold as -81º C at 16:25 UTC). GOES-12 visible images from the CIMSS Tropical Cyclones site (below, with an overlay of QuikSCAT winds on the initial image) also displayed a nice eye structure during the morning hours.

A plot of the CIMSS Advanced Dvorak Technique tropical cyclone intensity estimate (above) indicated that Hurricane Paloma experienced a period of rapid intensification late in the day on 07 November — apparently the tropical cyclone was moving over a tongue of high Ocean Heat Content (below), which may have aided such intensification. On 08 November, Hurricane Paloma became the second strongest November hurricane on record (behind Hurricane Lenny in 1999) — and it is also interesting to note that 2008 now becomes the only year on record with a major hurricane occurring in 5 separate months (Bertha in July, Gustav in August, Ike in September, Omar in October, and Paloma in November).

View only this post Read Less

AWIPS images of the GOES-12 6.5 µm “water vapor channel” (above) displayed 3 impressive storms during the 05 November – 06 November 2008 period: a powerful blizzard in the northern Great Plains states, a strong “gale force” storm along the US East Coast, and Tropical Storm Paloma in the western Caribbean Sea. The Plains blizzard produced wind gusts to 85 mph at Rapid City and snowfall amounts as high as 45.7 inches at Deadwood in western South Dakota; the East Coast storm was responsible for wind gusts in excess of 58 mph and waves greater than 18 feet at the Diamond Shoals buoy off the coast of North Carolina; and Tropical Storm Paloma was showing signs of entering a period of rapid intensification.

Note the presence of abnormally dry air on the water vapor imagery over southern Georgia, northern Florida, and the adjacent offshore waters of the western Atlantic — water vapor brightness temperatures were as warm as -10ºC (darker orange color enhancement) early in the day on 06 November. GOES-12 water vapor channel weighting functions (below) showed that the altitude of the layer being detected within the dry air mass in place over Jacksonville, Florida was at a significantly lower altitude (centered near the 500 hPa pressure level) compared to what would be detected in a more “normal” US Standard Atmosphere (centered near the 325 hPa pressure level).

Taking a closer look at the Great Plains blizzard, AWIPS images of the MODIS 6.7 µm water vapor channel (below) revealed an intensifying dry slot that was moving northward across Nebraska and South Dakota on 05 November. CRAS model fields of the 850-700 hPa layer equivalent potential temperatures (red contours) suggested that a Trough of Warm Air Aloft (TROWAL) was in the process of forming over central South Dakota, which was helping to fuel a line of new convective development around 19 UTC.

Several hours later, the GOES sounder Total Column Ozone product (below) revealed a tongue of higher ozone values (around 350 Dobson Units, green colors) surging northward from Nebraska into central South Dakota.

This higher-ozone feature was apparently associated with a potential vorticity (PV) anomaly (below), with the dynamic tropopause (taken to be the pressure of the 1.5 Potential Vorticity Unit surface, red contours) being brought downward to near the 500 hPa pressure level over north-central South Dakota at 06 UTC on 06 November. The approach of this PV anomaly may have played a role in further intensification of the blizzard later that day.

Around this time, the NWS forecast office at Rapid City noted that the TROWAL (below, as seen in GFS model 300-310 K layer equivalent potential temperatures, red contours) was also becoming better defined, stretching southwestward across  North Dakota into western South Dakota:

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
229 AM MST THU NOV 6 2008

.DISCUSSION…DEEP CYCLONE CENTERED ACROSS CENTRAL SOUTH DAKOTA WITH WIDESPREAD BLIZZARD CONDITIONS ACROSS WESTERN SOUTH DAKOTA.
WINDS GUSTING TO 78 MPH IN THE RAPID CITY AREA. MOST OTHER LOCATIONS GUSTING TO 60-65 MPH…EVEN IN CUSTER. TROWAL WRAPPED ACROSS NORTH DAKOTA INTO WESTERN SOUTH DAKOTA…AIMED AT THE BLACK
HILLS.

Finally, Tropical Storm Paloma: GOES-12 IR images with an overlay of ASCAT winds from the CIMSS Tropical Cyclones site (below) showed a series of convective bursts having cold cloud temperatures along with a well-defined wind field associated with the intensifying tropical cyclone.

View only this post Read Less