An AWIPS image of the MODIS Sea Surface Temperature (SST) product (above) revealed that the water temperatures were still quite cool across much of the western Great Lakes on 01 June 2008. Several days later, a northward surge of warm and humid air brought daytime temperatures into the 80s F with dew points into the mid-upper 60s F over a good deal of the region on 06 June 2008. As this warm and humid air flowed over the still-cool waters of Lakes Superior, Michigan, and Huron, dense advection fog formed which lasted into the early morning hours on 07 June 2008.

A comparison of the 4-km resolution GOES-12 IR window, fog/stratus product, and Low Cloud Base product images with the 1-km resolution MODIS fog/stratus product image (below) showed the extensive coverage of fog over the lakes just after 08 UTC (3am local time).

250-meter resolution MODIS true color images from the SSEC MODIS Today site (below) show interesting small-scale structure in the fog over Lake Superior on 06 June and over Lake Michigan on 07 June, including “bow shock waves” where the southerly flow of wind and lake fog was interacting with various islands and coastal features.

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A cold northeasterly flow in tandem with widespread stratus clouds and fog (with some areas of drizzle) to the north of a stationary frontal boundary kept daytime temperatures unusually cool across parts of the Upper Midwest and Great Lakes states on 03 June 2008 — the daytime maximum temperatures of 63º F at Madison, 59º F at Green Bay, and 56º F at Milwaukee were 12, 15, and 17 degrees below normal, respectively. Hourly AWIPS images of GOES derived product imagery (DPI) of the Low Cloud Base product (above) indicated the presence of a large area of cloud bases less than 1000 feet above ground level (aviation Instrument Flight Rules criteria, red enhancement) over parts of southern Wisconsin during the early evening hours, with cloud bases greater than 1000 feet but less than 3000 feet (aviation Marginal Visual Flight Rules criteria, green enhancement) covering much of the remainder of the state. The surface visibility briefly dropped to zero due to dense fog at Kenosha (KENW) in far southeastern Wisconsin. A patch of high cirrus clouds (gray to cyan enhancement) was also seen moving from northern Illinois into far southeastern Wisconsin during that time period (04 to 10 UTC, or 11pm to 5am local time), which was partially obscuring the low cloud features.

A comparison of the 4-km resolution GOES Low Cloud Base product with the 1-km resolution MODIS fog/stratus product around 08 UTC (below) demonstrated the advantage of better spatial resolution for locating the northern edge of the stratus cloud and fog across far northern Wisconsin, the Upper Peninsula of Michigan, and northern Lower Michigan. The spatial resolution of the IR channels on the Advanced Baseline Imager (ABI) instrument aboard the GOES-R satellite (planned to be launched in 2014) will be 2 km, which will provide improved detection of mesoscale features compared to the 4 km IR products now available from the current generation of GOES imagers.

Over far southeastern Wisconsin (below), note that the northern edge of the cirrus cloud shield (gray to cyan on the GOES Low Cloud Base product, and dark gray to black on the MODIS fog/stratus product) appeared to be located slightly farther to the north/northwest on the GOES image (compared to the corresponding MODIS image) — this is due to “parallax error” resulting from the large viewing angle of the geostationary satellite, which is positioned over the Equator.

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A strong cold front moved southward across the Upper Midwest and Great Lakes states on 26 May – 27 May 2008. During the preceding month, temperatures had been colder than normal at many sites across the region (mean air temperature departures for May 2008 included 3.0º F below normal at Milwaukee and 3.1º F below normal at Madison, Wisconsin, 3.2º F below normal at Chicago, Illinois, and 5.1º F below normal at Marquette, Michigan) — as a result, an AWIPS image of the MODIS Sea Surface Temperature (SST) product (above) showed that the water temperatures across much of central Lake Michigan were still in the rather cold 39-45º F range (blue colors). This cold lake water contributed to the formation of a well-defined “pneumonia front” (defined by Behnke (2005) as a lake-modified synoptic scale cold front that results in a rapid air temperature drop of at least 16º F in a 1 hour period) that moved inland across eastern Wisconsin during the evening and night-time hours.

Examining surface temperature data from Milwaukee and Madison in Wisconsin, Behnke (2005) documented 25 cases of pneumonia fronts during the period 1948-2003. It was found that reduced roughness over the north-south oriented Lake Michigan allowed for stronger impact of the pneumonia fronts over the southern portions of the lake and shoreline, and colder lake temperatures in the north helped to increase the nearshore temperature gradient and frontal propagation. Topography appeared to have little influence on pneumonia front generation and maintenance — the associated temperature falls were strongly dependent on diurnal landmass heating and Lake Michigan surface water temperatures.

The inland progression of the “pneumonia front” boundary was clearly evident on Milwaukee (KMKX) base reflectivity radar data (above; QuickTime animation). Note that a sequence of 3 distinct boundaries could be seen: Boundaries 1 and 2 were likely the primary cold front (moving south-southeastward across south-central Wisconsin), and an initial “weak pulse” of lake-cooled air moving southward (roughly perpendicular to the lakeshore), respectively; then, Boundary 3 (the true “pneumonia front”) raced rapidly inland from east to west, with surface air temperatures quickly dropping from the 70s F to the 40s F across far eastern Wisconsin. At Milwaukee (KMKE, where the daytime maximum temperature was 81º F), the air temperature later dropped from 78º F to 49º F in one hour, with northerly winds gusting to 38 mph; even as far inland as Madison (KMSN, where the daytime maximum temperature was 82º F), the temperature later dropped from 64º F to 55º F in one hour, with northeasterly winds gusting to 24 mph as the pneumonia front passed.

An extensive area of post-frontal stratus clouds could be seen moving southward and southwestward on 4-km resolution GOES-12 3.9 µm IR images (above), but the leading edge of the stratus clouds became masked by a veil of high cirrus clouds streaming eastward from convection across Iowa and Missouri. The 1-km resolution MODIS fog/stratus product (below) was more helpful in accurately locating the leading (southern) edge of the stratus clouds around 04:32 UTC (11:32 PM local time).

Additional reference:

Synoptic and Local Controls of the Lake Michigan Pneumonia Front, C. Behnke and P. Roebber, 16th Annual U.S./Canada Great Lakes Operation Meteorology Workshop, Milwaukee, WI, Sep. 5-7, 2007.

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AWIPS images of the GOES 10.7 µm IR channel (above) showed the development of severe thunderstorms across parts of Colorado, Wyoming, Nebraska, and Kansas on 22 May 2008 (see also: CIRA RAMMB Satellite Case Study). According to the SPC storm reports, a number of tornadoes were produced by these storms (one tornado-related fatality was reported near Greely, Colorado), along with large hail (up to 2.75 inches in diameter near Windsor, Colorado and 3.00 inches in diameter near Grinnell, Kansas).

A closer view using the 1-km resolution MODIS 11.0 µm IR channel (above) from around 17:57 UTC (11:57 am local time) revealed a rather diffuse “enhanced-v” signature just east/northeast of Fort Collins, Colorado (station identifier KFNL). This storm went on to produce tornadoes and large hail in southeastern Wyoming, with one tornado doing extensive damage in the Laramie area.

Another MODIS IR image from around 19:34 UTC (1:34 pm local time) displayed impressive detail in the overshooting top structure of the storms developing over western Kansas and far southwestern Nebraska (below), with the coldest cloud top brightness temperatures in the -70º to -80º C range (black to while enhancement).

The GOES sounder derived Convective Available Potential Energy (CAPE) product (below) indicated that the pre-convective environment across northeastern Colorado during the morning hours was becoming unstable, with CAPE values in the 2000-4000 J kg-1 range (yellow to red enhancement) at 16:00 UTC (10 am local time). The air mass south of the warm front and east of the dryline (from southern Kansas into Texas) was also very unstable, with CAPE values in some areas over 4000 J kg-1 (purple enhancement).

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