Subtropical Storm Olga

December 10th, 2007 |

GOES-10 IR images (Animated GIF)

Just as the 2007 Atlantic Tropical Cyclone season started off a bit early (with Subtropical Storm Andrea in early May), it also is ending a bit late with the formation of Subtropical Storm Olga on 10 December 2007. An animation of GOES-10 IR images (above) sourced from the CIMSS Tropical Cyclones site shows the cluster of cold cloud top temperatures (red to white enhancement) associated with Olga, moving just north of Puerto Rico.

GOES-10 IR image + deep layer mean winds

An analysis of the Deep Layer Mean wind field (above) indicated that an upper level low existed just to the south of Olga. The majority of the 00 UTC 11 December 2007 model forecast tracks (below) moved Olga westward toward the Dominican Republic and Jamaica.

GOES-10 IR image + model forecast tracks

“Black stratus” over the Upper Midwest

December 10th, 2007 |

GOES-10 10.7 µm IR images (Animated GIF)

AWIPS images of the GOES-10 10.7 µm IR channel (above) showed a patch of low-level stratus cloud drifting north-northeastward across Iowa, Minnesota, and Wisconsin on 10 December 2007. Note how the tops of the cloud feature appeared warmer (darker gray enhancement) than the adjacent cloud-free (but snow-covered) areas; the term “black stratus” was coined to describe the appearance of these cloud features on grayscale IR imagery. Strong radiational cooling during the night-time hours created a well-defined boundary layer temperature inversion, making the altitude of the stratus cloud tops several degrees C warmer than the surface.

On the comparison of MODIS and GOES-10 “fog/stratus product” images (below), the MODIS image in particular suggested that the leading edge of the stratus cloud feature was notably thicker (orange to red enhancement). This thicker cloud edge may have acted to dramatically slow radiational cooling as the cloud deck moved overhead — in fact, surface temperatures (above) were seen to warm by several degrees F when the cloud feature was overhead.

GOES-10 + MODIS fog/stratus product