Actinae in the North Pacific Ocean

March 29th, 2008

AVHRR false color images (Animated GIF)

AVHRR false color imagery (above; viewed using Google Earth) and GOES-11 visible channel imagery (below) revealed a family of cyclonic vorticies  propagating westward across the eastern North Pacific Ocean on 29 March 2008. The radially-banded cloud features that form such cloud “swirls” are known as actinae or actinoform clouds, and they are seen occasionally in the marine stratocumulus cloud field over the Pacific Ocean (for example, other similar cases were observed in March 2007 and June 1997). This type of cloud pattern was first observed on TIROS V imagery way back in August 1962 and October 1962.

GOES-11 visible images (Animated GIF)

More snow in the Upper Midwest

March 28th, 2008

MODIS true color images (Animated GIF)

The winter of 2007/2008 has already produced record snowfall (100.7 inches at Madison, Wisconsin, and 76.2 inches at Dubuque, Iowa) or near-record snowfall (107.0 inches at Grand Rapids, Michigan, and 98.9 inches at Milwaukee, Wisconsin) over portions of the Upper Midwest region;  on 27 March 2008, another 2-6 inches of snow fell across parts of eastern Iowa (4.4 inches at Dubuque), southern Wisconsin (5.7 inches at Palmyra), northern Illinois (3.0 inches at Hebron), southern Michigan (4.0 inches at Hastings), and northern Indiana (2.6 inches at Valparaiso). “Before” and “after” MODIS true color images from the late morning hours on 26 March and 28 March (above, viewed using Google Earth) showed the change in snow cover over the affected areas; the tight gradients and mesoscale structure of the resulting streaks of snow cover help to illustrate the difficulty of predicting snowfall amounts for any given location. Also note that many of the lakes in southern Wisconsin were still frozen (appearing white on the true color imagery).

An animation of GOES-12 visible images (below) reveals the power of the late-March high sun angle — even though surface air temperatures remained in the 30s F, some of the bands of fresh snow cover melted very quickly during the morning hours on 28 March.

GOES-12 visible images (Animated GIF)

Warm air ahead of a cold frontal boundary

March 27th, 2008

MODIS visible images (Animated GIF)

A cold frontal boundary was moving southward across the central and southern Plains on 27 March 2008. AWIPS images of the MODIS visible channel (above) showed that the leading edge of the front was generally cloud-free as it moved through the Oklahoma and Texas panhandle regions.

AWIPS images of the GOES-12 3.9µm shortwave IR channel (below) revealed a well-defined “warm air wedge” (darker gray to black colors) out ahead of the advancing cold frontal boundary; a line of convection was seen to form along the leading edge of the front from eastern Oklahoma into Arkansas and Missouri. Also note that there were several “hot spots” (black pixels) due to scattered fire activity that was burning briefly across the region; winds of 20-40 mph behind the front created an environment favorable for fire growth.

GOES-12 3.9µm IR images (Animated GIF)

The effect of this “wedge” of warm air along and ahead of the cold front was very evident on AWIPS images of the MODIS Land Surface Temperature product (below) — a curved band of warmer land surfaces (100-115º F, darker red to black colors) showed up over parts of northeastern New Mexico, the Texas panhandle, and southwestern Oklahoma. Note that the MODIS LST values are surface “skin temperatures”, which can be several degrees warmer than the shelter air temperatures which are measured 5 feet above ground level — afternoon air temperatures reached 94ºF at Wichita Falls, Texas (KSPS) and 93ºF at Frederick, Oklahoma (KFDR) before the cold front passed those locations.

MODIS Land Surface Temperature images (Animated GIF)

Springtime flooding in the central US

March 20th, 2008

MODIS false color image

A MODIS false color image from the SSEC MODIS Today site (above) shows the extent of river flooding across much of the Mississippi River and Ohio River valley regions in the central US on 20 March 2008. This image is a 3-channel Red/Green/Blue (RGB) combination using MODIS band 7 (2.1µm), band 2 (0.8µm), and band 1 (0.7µm) — healthy vegetation appears as varying shades of green; water appears dark blue to black; supercooled water droplet clouds appear as white; ice crystal clouds as well as snow or ice on the ground appear as varying shades cyan.

Comparisons of MODIS false color images “before flooding” (29 November 2007; sourced from the NASA MODIS Rapid Response site) and “after flooding” (20 March 2008) appear below, covering the northcentral and the southcentral US — note the swollen appearance of many the rivers on 20 March, due to a combination of springtime snowmelt and recent heavy precipitation (widespread reports of 5-10 inches of rainfall in a 7-day period, which was 400-600% above normal). A total of 16.93 inches of rainfall was reported at Clearwater, Missouri, and Cape Girardeau, Missouri set a new 48-hour precipitation record with 11.48 inches falling from 18-19 March.

MODIS false color images - northcentral US (Animated GIF)
MODIS false color images - southcentral US (Animated GIF)

In the comparison of MODIS “true color” and “false color” images (below), note how many of the flooded areas across southern Illinois and Indiana show up very unambiguously (as medium to dark shades of blue) on the false color image, while they appear more vague (as lighter brown colored areas, due to their high sediment content) on the true color imagery. Even though it was the first full day of the Spring season, much of Minnesota, Wisconsin, and Michigan still had a significant snow cover remaining on the ground, and a number of lakes and rivers were still frozen; small patches of lake ice could still be seen in southern Lake Michigan (both along the southern shore, and floating near the center of the lake).

MODIS true color + false color images (Animated GIF)

The CIMSS MODIS Imagery in D-2D project makes one component of the MODIS RGB false color imagery (the 2.1µm Band 7 or “snow/ice” channel) available on AWIPS via LDM subscription. AWIPS is restricted to 8-bit displays, so it cannot create the type of 24-bit “true color” and “false color” imagery shown above, but a simple comparison of the MODIS visible channel (Band 1) and snow/ice channel (Band 7) images (below) does help to highlight which of the rivers and tributaries were experiencing flooding on 20 March (water shows up as a very dark feature on the snow/ice channel imagery).

AWIPS MODIS visible + snow/ice images (Animated GIF)

A hydrograph for the Meramec River near St. Louis (below) highlights the magnitude of this particular flooding event: the previous record floodstage of 39.7 feet is forecast to be exceeded at that location on 22-23 March.

hydrograph for Meramec River