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Tuesday, June 15, 2010

Jeff Masters Wunder Blog: Heaviest 1-day rain in Oklahoma City history; 92L fizzles

Heaviest 1-day rain in Oklahoma City history; 92L fizzles
by Jeff Masters, Wunder Blog, June 15, 2010

Oklahoma City's rainiest day in history brought rampaging floods to the city and surrounding areas yesterday, as widespread rain amounts of 8-11 inches deluged the city. Fortunately, no confirmed deaths or injuries have been blamed on the mayhem, though damage is extensive. Oklahoma City's Will Rogers Airport received 7.62" of rain yesterday, smashing the record for the rainiest day in city history. According to the National Climatic Data Center, the city's previous rainiest day occurred September 22, 1970, when 7.53 inches fell. Some rivers continue to rise due to all the rain, and the Canadian River east of downtown Oklahoma City is four feet over flood stage, with major flooding expected today. You can track the flooding using our wundermap with the USGS Flood layer turned on.

Figure 1. Radar-estimated precipitation for the period June 14-15, 2010, during the Oklahoma City floods. A large swath of 8-10 inches of rain (dark red colors) was indicated, from Oklahoma City northeastwards.
An inordinate number of major U.S. floods this year
We've had an inordinate number of severe floods in the U.S. so far this year. The worst was the May Tennessee flood, which killed 31 people -- the highest death toll from a non-tropical cyclone flooding event in the U.S. since 1994, and the most devastating disaster in Tennessee since the Civil War. The Tennessee floods were rated as a 1000-year flood for Middle Tennessee, West Tennessee, South Central and Western Kentucky and northern Mississippi. Two-day rain totals in some areas were greater than 19 inches. Last Friday's disastrous flash flood in Albert Pike Recreation Area, Arkansas, killed twenty people. That flood was triggered by 8+ inches of rain that fell in just a few hours over the rugged mountains west of Hot Springs. And in March, record rains from a slow-moving and extremely wet Nor'easter triggered historic flooding in Rhode Island and Southeastern Massachusetts, with several rivers exceeding their 100-year flood levels. The 16.32" of rain that fell on Providence, Rhode Island, made March that city's wettest month in recorded history.

All of these flooding events were associated with airmasses though brought record-breaking warm temperatures to surrounding regions of the country. For example, during the overnight hours when the June 11 flood in Arkansas occurred, fifty airports in the Southern and Midwestern U.S. had their highest minimum temperatures on record. During the 1000-year flood in Tennessee, 51 warm minimum temperatures records were set in the eastern half of the U.S. on May 1, and 97 records on May 2. Rhode Island's record wettest March also happened to be its record warmest March. And the air mass that spawned yesterday's Oklahoma City floods set record warm minimum temperatures at 22 airports across the central and Eastern portions of the U.S. on Monday. All this is not surprising, since more moisture can evaporate into warmer air, making record-setting rainfall events more likely when record warm temperatures are present. The total number of airports in the U.S. considered for these comparisons is around 500, so we're talking about significant portions of the U.S. being exposed to these record-breaking warm airmasses this year. For the spring months of March-May, it was the 21st warmest such period in the 116-year record, according to the National Climatic Data Center. At the 500 or so largest airports in the U.S., daily high temperature records outnumbered low temperature records by about a factor 2.5, 1200 to 508. Record high minimums this spring outnumbered record low maximums by 1163 to 568. So far in June, record daily highs have outpaced record lows by 176 to 13, and record high minimums have outpaced record low maximums, 419 to 62.

Flooding and global warming
Groisman et al. (2004) found that in the U.S. during the 20th century, there was a 16% increase in cold season (October-April) "heavy" precipitation events (greater than 2 inches in one day), a 25% increase in "very heavy" precipitation events (greater than 4 inches in one day), and a 36% rise in "extreme" precipitation events (those in the 99.9% percentile -- 1 in 1000 events.) A sharp rise in extreme precipitation is what is predicted by global warming models in the scientific literature Hegerl et al. (2004). According the landmark 2009 U.S. Climate Impact Report from the U.S. Global Change Research Program, "the amount of rain falling in the heaviest downpours has increased approximately 20 percent on average in the past century, and this trend is very likely to continue, with the largest increases in the wettest places." Most of this increase came since 1970, due to the approximate 1 °F increase in U.S. average temperature since 1970. That 1 °F increase in temperature means that there is 4% more moisture in the atmosphere, on average. 

Dr. Joe Romm over at has an excellent interview with Dr. Kevin Trenberth of the National Center of Atmospheric Research on the subject of heavy precipitation events and global warming. Dr. Trenberth is the world's leading expert on water vapor in the atmosphere, and he comments that "since the 1970s, on average, there's about a 4% increase in water vapor over the Atlantic Ocean, and when that gets caught into a storm, it invigorates the storm so the storm itself changes, and that can easily double the influence of that water vapor and so you can get up to an 8% increase, straight from the amount of water vapor that's sort of hanging around in the atmosphere. This is reasonably well established." 

Dr. Trenberth further comments, "Now the physical cause for this is very much related to the water vapor that flows into these storms. And these kinds of storms, well all storms for that matter, reach out on average--this is very much a gross average--about 4 times the radius or 16 times the area of the region that's precipitating, the rain. And for these kinds of storms a lot of the moisture is coming out of the sub-tropical Atlantic and even the tropical Atlantic; some of it comes out of the Gulf of Mexico. And so the moisture actually travels about 2000 miles where it gets caught up in these storms and then it rains down. And the key thing is, that in the tropical and sub-tropical Atlantic the sea temperatures are at very high levels and in fact they're the highest on record at the moment right in the eastern tropical Atlantic. It's going to be interesting to see what that does for this hurricane season coming up."

We cannot say that any of this year's flooding disasters were definitely due to global warming, and part of the reason for this year's numerous U.S. flooding disasters is simply bad luck. However, higher temperatures do cause an increased chance of heavy precipitation events, and it is likely that the flooding in some of this year's U.S. flooding disasters were significantly enhanced by the presence of more water vapor in the air due to global warming. We can expect a large increase in flooding disasters in the U.S. and worldwide if the climate continues to warm as expected.

Figure 2. A portable classroom building from a nearby high school floats past submerged cars on I-24 near Nashville, TN on May 1, 2010. One person died in the flooding in this region of I-24. Roughly 200-250 vehicles got submerged on this section of I-24, according to wunderphotographer laughingjester, who was a tow truck operator called in to clear out the stranded vehicles.

Funding issues threaten hundreds of streamgages
According to the USGS web site, river stage data from 292 streamgages has been discontinued recently, or is scheduled for elimination in the near future due to budget cuts. In Tennessee, 16 streamflow gages with records going back up to 85 years will stop collecting data on July 1 because of budget cuts. Five gages in Arkansas are slated for elimination this year. Hardest hit will be Pennsylvania, which will lose 30 of its 258 streamgages. With over 50 people dead from two flooding disasters already this year, now hardly seems to be the time to be skimping on monitoring river flow levels by cutting funding for hundreds of streamgages. These gages are critical for proper issuance of flood warnings to people in harm's way. Furthermore, most of the northern 2/3 of the U.S. can expect a much higher incidence of record flooding in coming decades. This will be driven by two factors: increased urban development causing faster run-off, and an increase in very heavy precipitation events due to global warming.

Figure 3. Streamgages that have been discontinued or are being considered for discontinuation or for conversion from continuous record discharge to stage-only stations. Funds for these 292 threatened streamgages are from the U.S. Geological Survey and other Federal, State, Tribal, and local agencies. For those streamgages that have already been discontinued, extensive efforts were made to find another funding source; however, when no funding was made available the streamgages had to be discontinued. If you have questions about specific streamgages, click on the state of concern on the USGS web page of threatened stream gages.

Dry air disrupting 92L
Invest 92L, which yesterday was a remarkably well-developed African tropical wave for so early in the season, has fizzled, due to dry air. Infrared satellite loops show the disturbance has lost nearly all of its heavy thunderstorms, and water vapor satellite loops show that the storm has wrapped a large amount of dry air to the west into the storm's center of circulation. With the storm continuing to track west-northwest to northwest into dryer air, the prospects for 92L developing into a tropical depression appear dim. With wind shear expected to rise from its current levels of 10-15 knots to 20-25 knots on Wednesday, the combination of shear and dry air should be able to pretty much destroy 92L on Wednesday. Shear values will likely increase to 30-40 knots by Friday, when 92L will move into the northern Lesser Antilles Islands. There is a window of opportunity this afternoon for 92L to fend off the dry air and organize into a tropical depression. One advantage the storm has it that it has developed a well-formed surface circulation. The low-level center of circulation is easy to spot on satellite imagery, since wind shear due to strong upper-level winds from the west have exposed the center to view. The National Hurricane Center is giving 92L a moderate (30% chance) of developing into a tropical depression by Thursday morning. I would put the chances a bit lower, at 20%. Even if 92L does develop into a tropical depression, it is highly unlikely to cause any trouble for the Lesser Antilles Islands, since wind shear and dry air will probably destroy the system before it can reach the islands.

Figure 4. Morning satellite image of Invest 92L. The low-level circulation is easy to spot on satellite imagery, since wind shear due to strong upper-level winds from the west have exposed the center to view. A small clump of heavy thunderstorms is located just east of the exposed center of circulation.

Elsewhere in the tropics
None of the reliable computer models is calling for tropical cyclone development in the Atlantic over the next seven days. There is a small swirl of low clouds visible in satellite imagery at 8N, 22W, just off the coast of Africa, associated with a tropical wave. This circulation is under wind shear of about 20 knots, which is probably too high for such a small circulation to survive in.

Oil spill wind and ocean current forecast
Light, predominantly southwesterly to westerly winds of 5-10 knots will blow in the northern Gulf of Mexico most of this week, according to the latest marine forecast from NOAA. The more westerly wind direction is expected to maintain a slow (0.5 mph) eastward-moving surface ocean current that will transport oil eastwards along the Florida Panhandle coast, according to the latest ocean current forecast from NOAA's HYCOM model. These winds and currents may be capable of transporting oil as far east as Panama City, Florida, by the end of the week. Oil will continue to threaten the coasts of Louisiana, Alabama, and Mississippi for the remainder of the week as well, according to the latest trajectory forecasts from NOAA and the State of Louisiana. The long range 8-16 day forecast from the GFS model indicates a typical summertime light wind regime, with winds mostly blowing out of the south or southeast. This wind regime will likely keep oil close to the coastal areas that have already seen oil impacts over the past two weeks.

NOAA has lauched a great new interactive mapping tool that allows one to overlay wind forecasts, ocean current forecasts, oil location, etc.

Oil spill resources
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA has lauched a great new interactive mapping tool that allows one to overlay wi
nd forecasts, ocean current forecasts, oil location, etc.
Gulf Oil Blog from the UGA Department of Marine Sciences
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Synthetic Aperture Radar (SAR) imagery from the University of Miami

"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4 p.m. EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog. You can also email the questions to me today before the show: Be sure to include "Hurricane Haven question" in the subject line. Some topics I'll cover today on the show:

1) Why did 92L die so quickly?
2) Is the formation of 92L a harbinger of an active hurricane season?
3) What damage could a hurricane do to oil drilling platforms and underwater pipes at the bottom of the Gulf of Mexico?

Today's show, will be 1/2 hour, and you can tune in at The show will be recorded and stored as a podcast.


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