Satellite based radar images April 28th tornado outbreak

From: NASA/Goddard Space Flight Center

TRMM Satellite sees massive thunderstorms in severe weather system

The Tropical Rainfall Measuring Mission or TRMM satellite again flew over severe thunderstorms that were spawning tornadoes over the eastern United States on April 28 and detected massive thunderstorms and very heavy rainfall.

3-D Image of Violent Thunderstorms in US Cold Front. Florida to the right. This TRMM radar vertical cross section shows that some of these violent storms reached to incredible heights of almost 17 km (~10.6 miles). Credit: NASA/SSAI, Hal Pierce

TRMM, a satellite managed by both NASA and the Japanese Space Agency, captured the rainfall rates occurring in the line of thunderstorms associated with a powerful cold front moving through the eastern U.S. on April 28. TRMM flew over the strong cold front and captured data at 0652 UTC (2:52 AM EDT) on April 28, 2011. Most of the rainfall was occurring at moderate rates however, there were pockets of very heavy rainfall in Virginia, North Carolina, South Carolina, Georgia and Alabama where rain was falling at a rate of 2 inches (50 millimeters) per hour.

Tornadoes associated with this extremely unstable weather caused the deaths of at least 128 people in Alabama and 15 in Georgia.

The Tropical Rainfall Measuring Mission satellite captured the rainfall rates occurring in the line of thunderstorms associated with a powerful cold front moving through the eastern US on April 28, 2011. The yellow and green areas indicate moderate rainfall between .78 to 1.57 inches per hour. The very small red areas are heavy rainfall at almost 2 inches (50 mm) per hour. Credit: NASA/SSAI, Hal Pierce

TRMM data was also used to generate a 3-D look at the storm. TRMM’s Precipitation Radar (PR) data was used by Hal Pierce of SSAI at NASA’s Goddard Space Flight Center in Greenbelt, Md. to create a 3-D structure of those storms. The image Pierce created is a TRMM radar vertical cross section that shows some of these violent storms reached to incredible heights of almost 17 km (~10.6 miles).


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Alan the Brit

50mm per hour? Although pretty intense, that’s standard practice for rainwater surface run-off design calculations in the UK for soakaways & below/above ground drainage systems, etc. Is there the possibility that the local authorities have not kept sufficient watch on development in the areas affected? I noticed from news items on the Beeb that in any case there appeared to be more wind damage than rainwater damage. My sympathies for all concerned & my sincere condolences, thoughts & prayers, to the families of those who have lost loved-ones.

John Marshall

My sincere condolences to all affected by these storms.
These were not caused by climate change but more probably the meeting of cold northern air masses with the warming air mass from the Gulf of Mexico. Completely natural causes and within natural variation but a rare event for so many tornadoes to form at one time.

charles nelson

I don’t think it’s the quantity of rainfall that’s the issue here.
Nevertheless…it’s this type and quality of information that makes WUWT stand head and shoulders above the herd. Well done once again.

The rainfall rate of 50 mm/hour may have been over a large area. Rates of 100-200 mm/hour occur and are common in hurricanes and frequent in Tstrm downpours. You really don’t want one of those heavy thunderstorms to move slowly overhead, those typically require dirt roads to be rebuilt afterwards.
On Tstrm heights:
From :
Almost all thunderstorm clouds grow to heights above 20,000 feet. With 35,000 feet being typical. The more intense ones continue upwards until they hit the top of the troposphere, called the tropopause. Since penetrating into the stratosphere takes a lot of energy, many cumulonimbus clouds flatten out on the tropopause into the classic anvil shape with the tip streaming off downwind. If the storm is unusually intense, the updraft may punch into the stratosphere in cauliflower-like turrets. These “trop busters” are usually severe storms, with internal updrafts perhaps exceeding 100 mph. At any given place and time the height of the tallest storms is thus controlled by the height of the troposphere. Over the U.S. the tops of the stronger storms range from 40,000 to 65,000 feet from spring through summer and from north to south, respectively. There are some radar reports of echoes exceeding 70,000 feet, but if these reports are correct, this would be a very rare event. In any case, most thunderstorms are high enough that commercial jet traffic does not fly over most storms but rather circumnavigates since there can be “surprises” inside thunderstorm tops including extreme turbulence, hail, lightning, and wind shears.


Yeah, I agree /Alan the Brit — I bet the rainfall rates are underestimated. Several summers ago here in west MD there was a very small (barely a mile in diameter) & isolated but intense Tstorm that moved slowly over my area & got ~ .80 inch of rain in 10 minutes. That’s 4.8 in per hr. Surely these current storms were at least as strong.

I wonder if their algorithms take into account the higher RADAR reflectivity of large hail …
Probably does, but, the question must be asked (and probably already answered in a white paper somewhere).
Another upgrade to the WSR-88D adds dual-polarity capabilities which will include improved hail detection for severe thunderstorm warnings, improved rainfall estimation for flood and flash flood warnings, rain/snow discrimination for winter weather.

Dave Springer

Quantity of rainfall can be very damaging especially in so-called rain-bomb events. One that happened near me in 2007 dropped 19 inches of rain in 6 hours on the small town of Marble Falls, TX causing $100 million in damage.

Frank Ch. Eigler

“some of these violent storms reached to incredible heights of almost 17 km”
That’s not so incredible. Thunderstorms with 55000 ft tops are pretty ordinary in the southern US. Keep an eye on this NOAA web site for storm cell tops. You’ll see numbers larger than 550 on most stormy days.


2″ an hour doesn’t seem like any big deal unless it lasts in one spot for an extended period of time. On April 21, 2011 my Davis weather station recorded a peak rainfall rate of 6.06″ per hour here in Calaveras County but it only lasted for a couple minutes thankfully, as torrents of water were running off the hillsides and it damaged my gravel driveway.

Sam Hall

50 mm/hour isn’t that high.For example, Dallas Texas is predicted to get rain at a rate above 50 mm/hr for 57 minutes every year. Now,that is not in one rain event and not over a wide area.


I hope the NWS had a drop on this…