Lee-side frontal gravity waves are occasionally seen to the east of the Rocky Mountains, moving southward across the High Plains of the central US (for example, see  03 April 2007, 07 April 2000, and 12 January 1998). However, a satellite signature of what appeared to be a similar type of feature was observed along the US East Coast on 02 April 2008. AWIPS images of the GOES-12 6.5 µm “water vapor channel” (above) showed the positions of a cold frontal boundary at 3 hour intervals on that day, while more frequent GOES-12 water vapor images viewed using McIDAS (below) revealed the subtle “gravity wave” feature as it propagated southward off the coast of Virginia and North Carolina during the day. Several coastal stations in Virginia and North Carolina reported northerly to northeasterly surface winds of 30 mph (13 meters per second) or greater after the passage of the gravity wave, with offshore buoy and ship reports as high as 38 mph (17 meters per second).

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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.

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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.

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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.

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.

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