GOES-12 (left) and GOES-13 (right) visible images

A side-by-side comparison of GOES-12 and GOES-13 visible images (above) shows a well-defined lake-effect cloud band that was oriented generally north-to-south across Lake Michigan on 04 February 2009. This narrow cloud band was producing heavy snow as it moved inland over far northwestern Indiana, with 15-20 inches of storm total accumulation reported. The GOES-12 and GOES-13 images are displayed in their native satellite projections (GOES-12 is positioned over the Equator at 75º West longitude, while GOES-13 is positioned at 105º West longitude).

The improved Image Navigation and Registration (INR)  system on the GOES-13 satellite is immediately obvious, with much less image-to-image “wobble” — and the better navigation of the GOES-13 imagery makes it easier to follow the motion of the ice floes that were drifting over both the western and eastern nearshore waters of Lake Michigan.

Even with the GOES-12 images being re-mapped for display in AWIPS (below), the amount of image-to-image wobble is still obvious. Hourly MADIS winds (or “atmospheric motion vectors”) are also plotted on the visible imagery — these winds are derived by following targets on 3 consecutive satellite images.

AWIPS GOES-12 visible images

A closer view of southern Lake Michigan using 250-meter resolution MODIS true color images from the SSEC MODIS Today site (below) suggests that the ice along the eastern nearshore waters is probably thicker (and likely snow-covered as well).

MODIS true color images

Farther to the north, cold temperatures over the northern Great Lakes region (the morning low on 04 February was -36º F or -38º C at Babbit in northeastern Minnesota, and -28º  F or -33º C at Minong in northwestern Wisconsin) led to increased ice coverage over Lake Superior, as seen in 250-meter resolution MODIS false color imagery from the Terra and Aqua satellites (below). The ice in the lake appears as cyan-colored features, in contrast to supercooled water droplet clouds (which appear as varying shades of white). Note that there are more lake-effect cloud bands over the eastern portion of Lake Superior, where there is much less ice coverage — the ice covering much of the western portion of the lake reduces the amount of heat flux necessary to form the lake-effect cloud bands.

MODIS false color images

Speaking of lakes and their effect on cloud bands and snowfall, there was also an interesting case of “lake-enhanced” snow on this particular day, immediately downwind of Lake Marion and Lake Moultrie in South Carolina (hat-tip to Jon Jelsema at NWS Charleston SC for bringing this to our attention). A MODIS true color image (below, viewed using Google Earth) showed the cluster of cloud bands that were streaming southeastward from the 2 lakes, producing moderate to heavy snow that was reducing visibility as low as 1/4 mile.

MODIS true color image (viewed using Google Earth)

It is interesting to note that a small patch of “transverse band” clouds formed for a brief time, apparently at a slightly higher altitude than the lake-enhanced cloud bands — these transverse bands were more obvious on a NOAA-17 “false color” red/green/blue (RGB) image (below). An animation of GOES-13 visible imagery shows the development of the lake-enhanced cloud bands and the higher-altitude transverse bands — they are both very subtle and appear only briefly, but they are there if you look closely!

NOAA-17 false color RGB image

— 05 FEBRUARY UPDATE —

The surface winds shifted from northerly on 04 February to southerly on 05 February,  which caused the ice that was floating in the nearshore areas of  Lake Michigan to begin drifting northward during the day. This northward drift was clearly seen on GOES-12 and GOES-13 visible imagery (below). You can even see that the “land-fast” ice at the extreme southern end of the lake appeared to break free during the afternoon hours.

GOES-12 (left) and GOES-13 (right) visible images

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MODIS visible + snow/ice images

AWIPS images of the MODIS visible channel and the 2.1 µm near-IR “snow/ice discrimination” channel (above) showed the areal coverage of surface snowfall and ice accrual across much of the southern Plains on 28 January 2009. Many locations across that region received a significant accumulation of ice from freezing rain (1-2 inches of ice were reported in parts of Oklahoma and Arkansas) or sleet (3-4 inches of sleet were reported in parts of Oklahoma), downing trees and powerlines and causing power outages for several hundred thousand people (for more details, see Jesse Ferrell’s WeatherMatrix blog). As the storm departed, it left a light accumulation of snow on top of some of the ice and sleet that was already on the ground.

Snow and ice on the ground are strong absorbers at the 2.1 µm wavelength, so those surface features appear darker on the MODIS Snow/Ice image — and since ice is an even stronger absorber, a surface accrual of ice appears even darker than a layer of snow on the ground. In contrast, supercooled water droplet clouds appear as brighter white features on the Snow/Ice image. Also, note that Oklahoma (where there was only 1-2 inches of snow on the ground) appeared significantly darker on the MODIS Snow/Ice image than areas in the far northern portion of the image (where there was 5-10 inches of snow cover). One rather curious feature on the imagery: the thin mesoscale streaks of snow on the ground across northern Missouri, oriented almost exactly west-to-east.

A comparison of the 1-km resolution MODIS Snow/Ice image with the 1-km resolution MODIS Land Surface Temperature product and the 10-km resolution GOES-12 sounder Skin Temperature product (below) revealed the effect that the snow and ice were having on keeping the ground (surface) temperatures down. While the MODIS LST product indicated that the vast majority of Oklahoma was at or below freezing at that time (darker green color enhancements), the corresponding GOES-12 sounder Skin Temperature product suggested that much of the western half of Oklahoma had surface temperatures that were a few degrees above freezing.

A closer view of the MODIS Snow/Ice image and the MODIS Land Surface Temperature product (below) showed a swath of colder LST values (darker green colors) across southwestern, central, and northeastern Oklahoma, roughly corresponding to the areas with a more significant accrual of ice (darker enhancement on the Snow/Ice image). Note from the surface METAR reports that the air temperatures appeared to be a few degrees F colder within the swath of colder MODIS LST values — presumably due to the fact that there was a thicker ice accrual (or ice covered with snow) on the ground in that region.

MODIS Snow/Ice image + Land Surface Temperature product (with surface reports)

A false color RGB composite image using MODIS channel 01 (visible), channel 06 (near-IR), and channel 31 (IR window) is shown below, which gives another depiction of the coverage of the snow and ice on the ground. The brightest pink areas are those which had the thickest accrual of ice (with a light layer of snow on top of the ice).

McIDAS MODIS "false color RGB image" (using channels 01, 06, and 31)

False color red/green/blue (RGB) composite images using MODIS channel 01 (visible), channel 06/07 (near-IR), and channel 31 (IR window) generated using McIDAS imagery (above) and AWIPS imagery (below) gives another depiction of the coverage of the snow and ice on the ground. The brightest pink areas in Texas and Oklahoma are those which had the thickest accrual of ice (with a light layer of snow on top of the ice).

AWIPS MODIS "false color RGB image" (using channels 01, 07, and 31)

With the enhanced graphics capabilities of the next generation of AWIPS (“AWIPS-2” or “AWIPS Migration”), these kinds of RGB composite images will hopefully be easy to create on a routine basis.

— 30 JANUARY UPDATE —

AWIPS MODIS "false color RGB image"

Following the storm, sunshine and warmer temperatures began to melt some of the snow cover and ice cover on the ground. An AWIPS MODIS “false color RGB image (above) shows the extent of the ice and snow (pink-colored features) that remained on the ground on 30 January 2009.

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GOES-13 visible images

GOES-13 visible channel images (above) displayed a beautiful example of ducted internal gravity wave clouds over parts of Iowa, Wisconsin, Illinois, and Michigan during the daylight hours on 27 January 2009. The main linear “wave train” feature became obscured by a veil of high cirrus clouds later in the day, but other smaller/shorter wave features were seen to the north (over far northeastern Iowa and southern/central Wisconsin).

AWIPS images of the 1-km resolution MODIS visible, 3.7 µm “shortwave IR”, 6.7 µm “water vapor”, and 11.0 µm “IR window” channels (below) revealed the following points: (1) a strong component of solar reflection on the shortwave IR image (brightness temperature values were as warm as +25º to +35º C, darker gray color enhancement) suggested that the cloud billows were composed of supercooled water droplets, (2) the upward/downward gravity wave motions were also evident on the water vapor imagery, and (3) the IR window brightness temperature values were generally in the -20º to -29º C range (cyan to dark blue color enhancement).

MODIS visible + shortwave IR + water vapor + IR window images

The MODIS Cloud Phase and Cloud Top Temperature products (below) supported  the idea of predominantly supercooled water droplet clouds (blue color enhancement), with minimum Cloud Top Temperature values of -22º C along the Wisconsin/Illinois border region.

MODIS visible + cloud phase + cloud top temperature images

A MODIS visible image with an overlay of CIMSS Mesoscale Winds and pilot reports of turbulence (below) showed that the winds in the middle to upper troposphere were fairly strong from the southwest (several wind speeds of 160-200 knots were indicated between the pressure levels of 250 and 337 hPa), and there were a handful of pilot reports of light to moderate turbulence (with one report at an altitude of 37,000 feet over extreme northern Illinois, near the gravity wave feature).

CIMSS GOES mesoscale winds

The rawinsonde data from Davenport, Iowa (below) a few hours after the gravity wave features were seen on the satellite imagery showed a pronounced temperature inversion between the 450-500 hPa pressure levels — the air temperatures in that layer were in the -21 to -26º C range,  in agreement with the MODIS IR brightness temperature and Cloud Top Temperature values associated with the main gravity wave feature. According to the GOES-12 sounder Cloud Top Height product, the tops of these cloud features were within the 12,000-15,000 feet range (which seemed a bit on the low side, judging from the rawinsonde data).

Davenport, Iowa rawinsonde data

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MODIS 11.0 µm IR + GOES-12 10.7 µm IR + GOES-12 sounder Skin Temperature

Much of the central and southern Florida peninsula experienced temperatures at or below freezing on the morning of 22 January 2009. Surface air temperatures were as cold as 15º F at Archbold in the Tampa NWS County Warning Area (CWA), 16º F at Plymouth in the Melbourne CWA, and 23º F at Palmdale in the Miami CWA. A comparison of AWIPS images of the 1-km resolution MODIS 11.0 µm IR window channel, the 4-km resolution GOES-12 10.7 µm IR window channel, and the 10-km resolution GOES-12 sounder Skin Temperature product (above) showed that IR brightness temperatures and sounder skin temperature values of 32º F and colder (cyan to blue to purple colors) extended well south of Lake Okeechobee at 07:15 UTC (3:15 AM local time). The coldest MODIS IR / GOES-12 IR / GOES-12 Skin Temperature values at that time were -11.5º C (11.3º F) / -9.0º C (15.8º F) / -5.5º C (22.1º F), respectively.

An AWIPS image of the 1-km resolution MODIS Land Surface Temperature (LST) product over central Florida  (below) revealed that the coldest LST values of 17.3 º F (purple color enhancement) were found just southwest of Leesburg (station identifier KLEE), along the border of Lake county and Sumter county.

MODIS Land Surface Temperature product (central Florida)

The MODIS Land Surface Temperature product over southern Florida (below) showed that LST values of 32º F and colder (darker blue color enhancement) were found as far south as the area east of  Naples (station identifier KAPF). Note the relative warmth of Lake Okeechobee, were LST values of 55-56º F (red color enhancement) were seen.

MODIS Land Surface Temperature product (southern Florida)

An animation of the GOES-12 10.7 µm IR window imagery (below) showed the southward progression of below-freezing surface IR brightness temperatures during the night-time hours, as well as the warming of the Florida peninsula after sunrise on 22 January.

GOES-12 10.7 µm IR images

GOES-12 water vapor and IR images

The air mass over Florida was dry enough to allow the 7.4 µm water vapor channel on the GOES-12 sounder to actually sense the surface (above; animation) — in this case, the weighting function (below) for the 7.4 µm water vapor channel (red plot) peaked at a very low altitude, allowing the thermal signal of the contrast between cold land and warm ocean to reach the satellite.

GOES-12 weighting functions (calculated using Miami rawinsonde data)

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