The transition to Winter across southern Wisconsin

January 2nd, 2008 |

MODIS true color images (Animated GIF)

A sequence of MODIS true color images (from the SSEC MODIS Direct Broadcast site) covering the period from 27 November 2007 to 02 January 2008 (above) shows the transition from predominantly bare ground (with only isolated patches of thin snow cover) at the end of November to widespread deep snow cover across all of southern Wisconsin during the month of December 2007. Madison, Wisconsin (located at the center of the images) experienced its second snowiest December on record, with 33.5 inches falling during the month. The maximum snow depth at the Madison airport was 12 inches (on both 12 and 16 December), but NWS Cooperative Observers in the Madison metro area reported snow depths as high as 16 inches; across southern Wisconsin, a maximum snow depth of 22 inches was reported at Germantown and Jackson.

While the official temperature at the Madison airport did get as low as -10ºF on 06 December, the month as a whole was only 1.8ºF below normal (average temperature: 21.2ºF); as a result, the lakes in the Madison area froze within about a week of their median freeze dates. The images above show that several of the more shallow lakes southeast of Madison were the first to freeze, with the largest of the Madison lakes (Lake Mendota) appearing totally frozen and white with deep snow cover on the final 02 January 2008 true color image. Contrast this to the previous winter season, when Lake Mendota did not freeze until 20 January 2007 (the second latest freeze date on record!).

Meso-vortex and lake-effect snow band over Lake Michigan

January 2nd, 2008 |

GOES-12 3.9µm IR + visible images (Animated GIF)

An animation of GOES-12 3.9 µm shortwave IR (nighttime) and visible channel (daytime) images (above) shows a well-defined meso-vortex and single lake-effect snow (LES) band moving southward across the southern portion of Lake Michigan on 02 January 2008. This narrow (but intense) LES band and meso-vortex contributed to impressive storm total snowfall amounts that included 26.0 inches at Hudson Lake, Indiana (located about 15 miles west of South Bend, Indiana — station identifier KSBN) and 18.5 inches at Buchanan, Michigan (located about 10 miles northwest of KSBN) — however, it appears that the majority of those storm total snowfall amounts were due to synoptic-scale snow and lake-enhanced snow processes during the preceding 24-48 hours.

Mid-lake convergence played a role in the formation and maintenance of the LES band, as seen in an AWIPS image of the MODIS visible channel with CIMSS GOES Mesoscale Winds overlaid (below).

AWIPS MODIS visible + mesoscale winds

An AWIPS 4-panel display of MODIS images (below) shows the visible channel (upper left panel), 2.1 µm near-IR “Snow/Ice” channel (upper right panel), Cloud Top Temperature product (lower left panel), and Cloud Phase product (lower right panel) at 16:45 UTC (10:45 am local time). The darker appearance of the thickest (eastern) portion of the LES band on the MODIS “snow/ice” image suggested that part of the cloud band had glaciated and was composted primarily of ice crystals at that time (snow and ice are strong absorbers at the 2.1 µm wavelength, and appear much darker than supercooled water droplet clouds on the MODIS Snow/Ice channel imagery); this idea was further supported by corresponding MODIS Cloud Top Temperatures in the -15ºC to -20ºC range (cyan to dark blue enhancement, lower left panel) and “mixed phase” pixels on the MODIS Cloud Phase product (dark gray enhancement, lower right panel).

AWIPS MODIS 4-panel image