Severe convection developed in the warm sector of a cyclone that was moving through the mid-Mississippi River Valley region, producing widespread reports of heavy rain, damaging winds, hail, and tornadoes on the evening of 03 April 2008 (SPC storm reports | NWS Little Rock AR report). An AWIPS image of the MODIS 11.0µm IR channel (above) shows the surface frontal positions and mean sea level pressure analysis at 03 UTC (10 PM local time).

AWIPS images of the GOES-12 10.7µm “IR window” channel (above) shows that a well-defined “enhanced-V signature” developed in the vicinity of Hot Springs, Arkansas (station identifier KHOT) after 01:15 UTC (8:15 PM local time) — hail of 1.75 inches in diameter was reported at Bonnerville (located just southwest of Hot Springs) around 01:10 UTC (8:10 PM local time). Heavy rain (6.44 inches) fell at Glenwood (also located southwest of Hot Springs). This enhanced-v storm then continued to move northeastward toward the Little Rock area (station identifier KLIT), where it produced tornadoes that damaged parts of Little Rock during the 02:50-03:10 UTC (9:50-10:10 PM local time) period — one tornado actually forced the staff of the National Weather Service Forecast Office at North Little Rock Airport to take cover for a short time while the storm moved close to the facility. The second-highest wind gust on record (64 mph) was also recorded at North Little Rock Airport during this event.

Cloud to ground (CG) lightning strikes plotted on the GOES-12 IR imagery (above) revealed that a cluster of CG strikes was associated with the vertex of the enhanced-v signature on satellite imagery. As is typically the case, this storm was negative strike dominant, with positive strikes making up less than 10% of the total cloud to ground lightning strikes.

A comparison of 4-km resolution GOES-12 IR imagery with 1-km resolution NOAA-17 AVHRR IR imagery (above) demonstrates the improved storm top temperature detection capability of the polar-orbiting AVHRR instrument. In particular, a closer view of the developing enhanced-v signature near the Arkansas/Missouri border region (below) shows finer detail in the temperature fields and the magnitude of the enhanced-v cold/warm cloud top temperature couplet (-81ºC/-61ºC on the AVHRR image, versus -75ºC/-64ºC on the GOES-12 image).

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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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