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Spring 2011 U.S. Climate Extremes - National Climatic Data Center

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  • MikeSar
    [NOAA, National Environmental Satellite, Data, and Information Service] [National Climatic Data Center, U.S. Department of Commerce] DOC
    Message 1 of 1 , Jun 19, 2011
      NOAA, National Environmental Satellite, Data, and Information ServiceNational Climatic Data Center, U.S. Department of Commerce

      Spring 2011 U.S. Climate Extremes

      National Oceanic and Atmospheric Administration

      National Climatic Data Center



      Note: Data in this report are compiled from preliminary statistics

      briefing thumbnail
      Briefing Package presented by Tom Karl, Ed O'Lenic and Harold Brooks on June 15th (PDF)

      Introduction

      The spring (March-May) of 2011, particularly April, brought extreme weather and climate events to many parts of the United States. Tornadoes, flooding, drought, and wildfires ravaged many parts of the country during the period, and each of these extremes broke long-standing records and have been compared to the 'worst such cases' in history. While similar extremes have occurred throughout modern American history, never before have they occurred in a single month. According to the Storm Prediction Center (SPC), there were 875 preliminary tornado reports during April alone, and the confirmed number of tornadoes will approach the all-time monthly record of 542 tornadoes set in May 2003. Record rainfall along the Ohio River Valley, punctuated with snowmelt across the upper Midwest, caused record flooding along the mid and lower Mississippi River, with water levels surpassing the historic floods of 1927 and 1937. Above-normal precipitation and vegetative growth during 2010, followed by dry and windy conditions the first five months of 2011, created ideal wildfire conditions across the Southern Plains where millions of acres of land burned. According to the U.S. Drought Monitor (USDM), the same region experienced Extreme-to-Exceptional [D3-D4] drought following consecutive months that were record to near-record dry.

      April brought an active weather pattern across the contiguous U.S., with strong storms moving through the center of the country, tapping into moisture from the Gulf of Mexico as they matured across the mid-Mississippi Valley. These storms caused widespread severe weather across the Southeast and widespread heavy precipitation across the Ohio Valley. Both the number and magnitude of the severe weather events, as well as the amount of precipitation across the Ohio Valley, broke all-time records, according to preliminary data. Meanwhile, the storm track essentially blocked Gulf of Mexico moisture from entering the Southern Plains.

      Across the Upper Midwest rapid melt of an above-average snowpack during late March through mid-April swelled rivers and caused near record river crests along the Red River in North Dakota and Minnesota. Farther east, across Minnesota and Wisconsin, a significant portion of the snowmelt water found its way into the Mississippi River and moved southward towards the Gulf of Mexico. Meanwhile, the above-average rainfall across the Ohio Valley, combined with snowmelt, caused the Ohio River to swell to near-record levels. At the confluence of the Ohio and Mississippi Rivers, the above-average water flow of each combined to cause the Mississippi River to crest at record to near-record levels from Illinois to Louisiana, flooding hundreds of thousands of acres. After judicial directives, the Army Corps of Engineers opened spillways and destroyed levees, flooding rural areas to save major population centers and infrastructure.

      On a statewide level, during April, above-normal precipitation was widespread across the northern half of the country, while the Southern Plains and Southeast had near- to below-average precipitation. Below-normal precipitation was observed for the previous six months across the southern Plains, exacerbating drought conditions there. At the beginning of May, 73 percent of Texas was experiencing Extreme-to-Exceptional [D3-D4] drought conditions. Texas had its second driest November through April period, third driest January-April, and driest February-April and March on record. The prolonged dryness fueled several large wildfires, which burned 1.79 million acres (0.72 million hectares) nationally during the month, shattering the previous April record.

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      Tornadoes

      The period through the end of May, 2011 was marked by numerous large severe weather outbreaks, causing a record-breaking tornado year for the year-to-date period. Approximately 1,400 preliminary tornado reports were received by the National Weather Service during the January–May period, and 875 of those tornado reports were during the month of April alone.

      January-May Tornado Counts
      Tornado Reports during January-May 2011

      Tornado activity during April was record breaking. According to data from the Storm Prediction Center (SPC), there were 875 preliminary tornado reports during the month, and the final tornado count will approach the all-time monthly record of 542 tornadoes (May 2003) after all storm surveys are completed. The previous April record was 267 tornadoes, set in April 1974. The 30-year (1981-2010) average for number of April tornadoes is 135. During spring (March-May) 2011 there were several significant tornado outbreaks, mostly across the Southeast, and more information on these individual outbreaks can be found in the State of the Climate report.

      Environmental Conditions

      During the month of April, environmental conditions came together to create the perfect scenario for severe weather across the eastern half of the country. A persistent storm track across the central U.S. allowed frontal systems to interact with Gulf of Mexico moisture and initiate storms across the southeastern quadrant of the nation. During April, seven upper level troughs moved across the country. These upper level troughs provided dynamic forcing that allowed the development several severe weather complexes. Strong jet streams formed along and ahead of these upper level troughs providing diffluence aloft. Diffluence can facilitate rising air within thunderstorms, causing them to become stronger. Along the leading edge of the upper level troughs were surface cold fronts and surface low pressure systems. Southerly winds ahead of the surface cold fronts caused warm and moist air to surge northward. Behind the fronts, cool Canadian air swept across the central part of the country.

      During the two largest outbreaks (April 14th-16th and 25th-28th), there was significant southerly flow ahead of the storm systems. Higher in the atmosphere, the wind tended to be more westerly in direction. This veering of the winds with height created a large spatial extent of vertical wind shear. This shear, under the right circumstances, can fuel long-lived supercell thunderstorms. Also at play was the difference in temperature between the warm southerly flow near the surface and the drier, cooler air aloft associated with the upper level troughs. This scenario is also favorable for severe thunderstorm development when warm moist air near the surface is lifted upwards by the surface cold front into the layer of cooler, drier air, releasing latent heat energy into the storm.

      During the month of April other large scale phenomena played a role in the development of the record-breaking tornado outbreaks. Ahead of the cold fronts, warm and very moist southerly air invaded the eastern half of the U.S. from the Gulf of Mexico. A monthly analysis of winds using reanalysis shows that the southerly component of near surface winds across the Gulf Coast and southeastern U.S. more than 6.7 mph (3 m/s) above the 1971-2000 April average. This indicates that the southerly flow was persistent and strong across during April.

      Another large scale feature which played a role in the development of these severe weather outbreaks was the Gulf of Mexico. Averaged for the month, the sea surface temperatures across the Gulf of Mexico were about 1 degree Celsius (1.8 degree F) above the long-term average. The warm water and atmosphere over the Gulf provided fuel for the severe weather outbreaks. The southerly winds ahead of the storms that moved across the country advected the warm temperatures and Gulf moisture over the continental United States. Many locations across the southern U.S. broke daily temperatures records when these southerly flow regimes set up across the region. The warm sea surface temperatures across the Gulf are a good indicator of the amount of moisture across the region. Warmer temperatures allow the atmosphere to hold more water vapor. The more water vapor in the atmosphere, the more readily storms form and the stronger storms can become.

      Historical Perspective

      Record Annual Tornado Fatalities
      YearFatalities
      1925794
      1936552
      1917551
      1927540
      1896537
      2011
      (through June 7th)
      525
      1953519
      1920499
      1908477
      1909404

      On the January-May timescale, the number of tornadoes and the number of tornado-related fatalities were record breaking. It is likely that the entire country and many states will approach and/or break records for the number of confirmed tornadoes. For the year-to-date period, there were 1,398 preliminary tornado reports nationwide, with the confirmed number likely to be around 900, assuming a confirmation rate similar to the historical average. Nationwide, the previous January-May tornado count record was 1,011 in 2008. The 2011 January-May tornado count will likely rank as the second most since modern records began in 1950. In terms of the number of tornado-related fatalities, there were 525 during the January-May period. When analyzing the number of tornado-related fatalities, there were two separate comparisons — the comparison to the modern (1950-present) tornado record and the non-official (1875-present) record. The 525 fatalities is the most in the 1950-present period,and the sixth in the 1875-present time period.

      The severe weather outbreaks during spring 2011 caused significant property damage across the eastern United States on top of the unfortunate high number of fatalities. According to preliminary numbers from various disaster cost modeling and insurance risk reports, the estimated damage from the spring severe weather outbreaks will approach 12 billion U.S. dollars, with several of the severe weather events likely exceeding one billion U.S. dollars in damage each.

      Significant Severe Weather Events

      April 14th–April 16th Tornado Outbreak

      A major severe weather outbreak impacted the southeastern U.S. between April 14th and 16th. A strong upper level low pressure system moved across the central plains, and ahead of the system, very warm and very moist air was advected northward from the Gulf of Mexico. As the associated surface cold front moved into the southeast, a series of severe thunderstorm complexes were initiated across the country. Over the course of the three days, there were 329 preliminary tornado reports across 16 states. NOAA estimates the final tornado count for the outbreak will be around 160 tornadoes, marking one of the largest outbreaks on record, especially for April, which averages 135 tornadoes for the entire month. Although there were a large number of tornadoes, there were 14 tornadoes rated EF-3, and none were rated EF-4 or EF-5. A total of 38 people were killed from the tornadoes, 22 of which were in North Carolina alone. Nationwide, the tornado outbreak break was the deadliest since the 2008 Super Tuesday tornado outbreak that occurred on February 5th and 6th, 2008, when 57 people were killed. The 30 confirmed tornadoes across North Carolina broke the single-storm and single-day tornado outbreak record for the state. The previous record was from the infamous March 1984 Carolina's tornado outbreak when 22 tornadoes killed 42 people in the state.

      Record Daily Tornado Fatalities
      DateFatality Reports
      March 18, 1925747
      March 21, 1932332
      May 17, 1849317
      April 27, 2011314
      April 3, 1974310
      May 27, 1896305
      April 11, 1965260
      April 5, 1936249
      April 25th–April 28th Tornado Outbreak

      Another major and record breaking severe weather outbreak impacted the southeastern U.S. between April 25th and 28th. During the outbreak, there were 434 preliminary tornado reports in 21 states. The NOAA estimate of actual tornadoes for the four day period is 305 (as more complete data become available this number will be revised). The storm scenario was similar to the mid-April outbreak, with a potent upper level low pressure system moving across the Central and Northern Plains, but this low pressure system was a little stronger and had a path more northward. Ahead of the surface cold front, very warm and very moist air infiltrated the southern U.S. from the Gulf of Mexico. Temperatures across the southeast reached into the lower 90s (°F). A strong mid-level jet streak moved into the Tennessee Valley, providing strong shear and dynamic support for severe thunderstorm development. As the storm system moved towards the east, it initiated severe weather each day between the 25th and 28th. The most impressive period of the outbreak was on April 27th, and into the early hours of the 28th, when two severe weather complexes moved across Mississippi, Alabama, Tennessee, and Georgia. NOAA's current estimate is there were 190 tornadoes during that time period. The previous single largest tornado outbreak to impact the U.S. was the April 3-4, 1974 Super Outbreak, when there were 148 tornadoes across the Southeast and Ohio Valley. According to the most recent estimates, there were 3 EF-5 rated tornadoes, 12 EF-4s and 21 EF-3s. There were an estimated 320 tornado related fatalities from the outbreak — approximately 314 of those occurred on the 27th. Alabama alone observed 235 of those fatalities. An EF-5 moved through northern Alabama and killed 78 people, the deadliest of the outbreak. Several major metropolitan areas were directly impacted by strong tornadoes including Tuscaloosa, Birmingham, and Huntsville in Alabama and Chattanooga, Tennessee, causing the estimated damage costs to sore. According to preliminary information, property damages might exceed six billion U.S. dollars. For more information see the monthly U.S. Tornado State of the Climate report.

      April 27th Select Station Dewpoints
      CityApril 27th Hourly Average Dewpoint30-year average April Dewpoint
      Birmingham, Alabama66.2 °F (19.0 °C)49.2 °F (9.5 °C)
      Tuscaloosa, Alabama66.0 °F (18.9 °C)50.9 °F (10.5 °C)
      Huntsville, Alabama61.9 °F (16.6 °C)48.3 °F (9.1 °C)
      Joplin, Missouri Tornado May 22nd
      Record Single Tornado Fatalities
      TornadoFatalitiesDate
      Tri-State
      (Missouri/Illinois/Indiana)
      695March 18, 1925
      Natchez, Mississippi317May 6, 1840
      St. Louis, Missouri255May 27, 1896
      Tupelo, Mississippi216April 5, 1936
      Gainesville, Georgia203April 6, 1936
      Woodward, Oklahoma181April 9, 1947
      Amite, Louisiana/
      Purvis, Mississippi
      143April 24, 1908
      Joplin, Missouri141 (est.)May 22, 2011
      New Richmond, Wisconsin117June 12, 1899
      Flint, Michigan116June 8, 1953

      On May 22nd a severe weather outbreak occurred across the central Plains and the Midwestern United States, and several of the storms generated tornadoes across the region. The most destructive of the storms tracked from southeastern Kansas into southwestern Missouri during the late afternoon. This supercell thunderstorm spawned a strong tornado over Joplin, Missouri, resulting in devastating damage. The National Weather Service rated the tornado an EF-5, with winds in excess of 200 mph (320 km/hr). The tornado was on the ground for approximately 6 miles (9.7km) and had a maximum width of 3/4 mile (1.2 km). The tornado struck the heavily populated southern part of Joplin, resulting in at least 141 deaths and 1,000 injuries. The tornado surpassed the June 1953 tornado which killed 116 people in Flint, Michigan as the deadliest single tornado to strike the U.S. since modern tornado record keeping began in 1950. The deadliest tornado on record for the U.S. was the 'Tri-State Tornado' which killed 695 people across Missouri, Illinois, and Indiana in March 1925.

      Base reflectivity image of Joplin, MO tornado May 22, 2011
      Radial velocity image of Joplin, MO tornado May 22, 2011

      The image on the left shows the base level reflectivity from the Springfield, Missouri NEXRAD radar site of the Joplin, Missouri tornado Sunday May 22, 2011 22:43 GMT (5:43 pm local time). The high reflectivity values occurring over southern Joplin indicate the mostly likely location of the EF-5 tornado.

      The image on the right shows de-aliased storm relative velocity from the Springfield, Missouri NEXRAD radar site of the Joplin, Missouri tornado Sunday May 22, 2011 22:43 GMT (5:43 pm local time). Green colors (negative values) indicate wind moving towards the radar site (located 60 miles [97km] to the east), and red colors (positive values) indicate winds moving away from the radar site. The tight couplet of reds and greens over southern Joplin show the strong rotation occurring within the EF-5 tornado. The large scale green and red couplet indicates the larger scale rotation occurring within the supercell thunderstorm.

      3-D NEXRAD Animation of Joplin Tornado
      Joplin Debris Signature

      Images created with NCDC's Weather and Climate Toolkit and GRLevel2.


      Preliminary* Statewide Torando Records

      Annual Tornado Records
      State2011 Preliminary Tornado Reports*Old Record / Year
      Alabama16094 / 2008
      Kentucky5239 / 1997
      Mississippi136109 / 2008
      North Carolina8967 / 2004
      Tennessee7546 / 2009
      Jan–May Tornado Records
      State2011 Preliminary Tornado Reports*Old Record / Year
      Alabama16072 / 2009
      Arkansas6662 / 2008
      Georgia5649 / 2008
      Indiana4846 / 1990
      Kentucky5234 / 2008, 1974, 2003
      Louisiana7044 / 1990
      Maryland1413 / 2002
      Mississippi13656 / 2008
      Misssouri85-tie85 / 2003
      North Carolina8953 / 1998
      Ohio3128 / 1973
      Tennessee9445 / 2003
      Virginia3833 / 2008
      Wisconsin3533 / 2005
      Entire U.S.13711,224 / 2008
      April Tornado Records
      State2011 Preliminary Tornado Reports*Old Record / Year
      Alabama14035 / 2009
      Arkansas4629 / 1979
      Georgia4625 / 2009
      Kentucky4129 / 1974
      Louisiana3624 / 2000
      Maryland115 / 2002
      Mississippi12126 / 2005
      Misssouri3026 / 1994
      Nevada31 / 2005, 1964, 2001
      New York84 / 1991
      North Carolina8524 / 1996
      Tennessee5042 / 1974
      Texas69 - tie69 / 1957
      Virginia3518 / 2008
      Wisconsin1611 / 1984
      Entire U.S.875273 / 1974

      *2011 numbers reported are preliminary tornado reports. These numbers are subject to change as more up-to-date storm surveys are completed.

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      Flooding

      During the spring of 2011, persistent rainfall combined with melting snowpack caused historical flooding in some of the United States' major rivers, including the Ohio, the Mississippi, and the Missouri. A relentless storm track pattern provided nearly 300 percent of normal precipitation amounts in the Ohio Valley. As the Ohio, Missouri, and Mississippi River experienced historical crests, dams and levees were breached. Those that were not breached were significantly tested throughout the enduring event. Smaller towns and farmland were intentionally flooded to save larger, more populated towns. While the slow-moving disaster provided extra lead time for the residents to prepare their homes and businesses, hundreds of thousands of acres of farmland from an area south of the Great Lakes to the Gulf Coast were swimming in 20 feet (6 m) of water for weeks.

      The Lower Mississippi Basin begins at the confluence of the Ohio and Upper Mississippi Rivers in Cairo, Illinois. According to the U.S. Army Corps of Engineers, 4 million people reside within the 35,000 square mile Lower Mississippi watershed. After a massive flood overwhelmed the southernmost stretch the river in 1927, the Army Corps of Engineers built a 2,200-mile system of earthen levees, floodwalls and other controls along the Mississippi, Arkansas, and Red Rivers. The flood control system has been tested over the years, especially in 1973 and 1993 when extremely wet conditions swelled the rivers to comparable historical levels. In 2011, extreme amounts of precipitation led to unprecedented flooding in several locations along the major rivers.

      The extreme amounts of precipitation was set up by a large-scale weather pattern during April which consisted of high pressure, which typically results in warm dry air, over the South and Southwest U.S. This high pressure was associated with a ridge which inhibited systems from entering the region deflecting storms into the Ohio River Valley region. The persistence of this pattern during the season exacerbated the magnitude of the precipitation amounts and subsequent flooding.

      Precipitation Records

      During the month of April, over 1,300 daily precipitation records were broken across the Midwest and South - 197 in Kentucky alone. For the month, 72 locations reported their wettest day in any April on record and 5 of these stations set a new all-time record for the wettest 24-hour period for any month. Rainfall totals for April exceeded 13 inches (330 mm) in cities along the Ohio River. At Louisville International Airport, the 13.97 inches (355 mm) surpassed the previous record of 11.10 inches (282 mm) set in 1970. A monthly record of 13.52 inches (343 mm) of precipitation was also a record in Cincinnati. Further inland, the 15.91 inches (404 mm) of precipitation in Paducah, Kentucky was also an April record. The 12.7 inches (329 mm) that was measured in Lexington surpassed the 1970 record of 9.3 inches (236 mm). Columbus, Ohio received 7.14 inches (181 mm) of precipitation which was also a record. The 6.89 inches (175 mm) that fell in Cleveland broke the 1961 record of 6.61 inches (168 mm). From March-May, departures were at least 150 percent of normal in an area that stretched from the Ohio Valley to the Middle Mississippi Valley.

      Spring Record Precipitation Amounts
      LocationRecordAmountPrevious Record (year)
      Northwest Climate RegionMost March–May Precipitation10.10"9.39" (1993)
      WashingtonMost March–May Precipitation13.67"12.85" (1997)
      WyomingMost March–May Precipitation6.69"6.41" (1906)
      IndianaMost March–May Precipitation19.38"18.05" (1933)
      OhioMost March–May Precipitation17.47"16.22" (1964)
      KentuckyMost March–May Precipitation23.70"22.08" (1935)
      West VirginiaMost March–May Precipitation18.19"17.11" (1967)
      PennsylvaniaMost March–May Precipitation18.62"15.48" (1983)
      New YorkMost March–May Precipitation16.14"14.35" (1983)
      VermontMost March–May Precipitation17.18"16.94" (1983)

      Flooding

      Mississippi River

      In order to protect heavily populated cities from flooding, the Army Corps of Engineers opened several spillways along the Lower Mississippi River. On May 2 officials intentionally breached part of the Birds Point-New Madrid Levee near the confluence of the Ohio and Mississippi Rivers to protect the small Illinois town of Cairo, population of 2,800. The two-mile opening allowed water to pass through at a rate eight times that of Niagara Falls, flooding the Birds Point New-Madrid Floodway - which is 130,000 acres of Missouri farmland in addition to about 100 residences. The move was challenged in courts, but overturned, preventing devastating flooding in Cairo and elsewhere downstream. The Corps estimated it will take up to two months for the water to recede from the floodway and another month for the land to dry out.

      One week later on May 9, the Bonnet Carre' Spillway was opened, allowing flood waters to flow into Lake Pontchartrain. When all 350 bays are opened in that spillway, it diverts 250,000 cubic feet (7,079 cubic meters) of water per second into Lake Pontchartrain and on into the Gulf. The last time all Bonnet Carre' bays were opened was in 1983. Farther upstream, a portion Morganza Spillway was opened on May 14. This move alleviated stress on the Old River Control Structure upstream and the levees which protect New Orleans downstream. The only prior time the Morganza Spillway had been opened was in 1973 and this marked the first time in history that all three spillways have been opened simultaneously.

      Mississippi River Historical Crests
      Mississippi River Historical Crests

      Image Credit: US Army Corps of Engineers

      Even with all the precautions taken, the populated cities and rich farmland along the riverside, which are normally protected by the system of levees, were flooded. The massive wall of water drifted slowly southward, overtopping its banks along the way. In Memphis, Tennessee on May 10, the Mississippi River crested at 47.9 feet (14.6 m), the highest level reached at Memphis since 1937 (48.7 feet or 14.8 m). In Greenville, Mississippi, the river crested on May 16, about one foot below the historical crest of 65.4 feet (19.9 m) set in 1927. The 2011 flood set a record in Vicksburg, Mississippi, cresting on May 18 at 57.1 feet (17.4 m) , besting the previous record of 56.2 feet (17.1 m) set in 1927. The flooded Mississippi also caused the Yazoo River to backfill, flooding out Yazoo City, Mississippi where some of the worst flooding occurred. Flood stage is 29 feet (8.9 m), but the crest reached 38.7 feet (11.8 m), just a few feet shy of the record set in 1927 of 43.4 feet (13.2 m).

      Natchez, MS Hydrograph
      Natchez, MS Hydrograph

      Image Credit: US Army Corps of Engineers

      Another stage height record was set farther downstream in Natchez, Mississippi on May 19. The crest was nearly 4 feet (1.2 m) higher than the previous record of 58.04 feet (17.7 m) set in 1937. To the south of Baton Rouge is the Atchafalaya Basin which, according to the U.S. Geological Survey, is the largest swamp in the United States. When the Morganza Spillway was opened as much as 1.2 million gallons of water per second flooded into the basin encroaching upon Morgan City which is perched on the banks of the Atchafalaya River. The river gauge at the riverside city, home to nearly 13,000, experienced its maximum peak at 10.35 feet (3.2 m) on May 29, just shy of the record of 10.53 feet (3.2 m) set in 1973.

      Due to drastic steps of the Army Corps of Engineers that sacrificed farmland and less populated cities, major flooding was averted in the more populated cities along the southernmost sections of the Mississippi River. While the slow surge of water had dispersed some by the time it made it to Baton Rouge (flood stage is 35 feet or 10.7 m) and New Orleans (flood stage is 17 feet or 5.2 m), low-lying areas were still affected. The crest at Baton Rouge was more than 3 feet (0.9 m) below its record level and it was 5 feet (1.5 m) below the record level in New Orleans.

      Missouri River

      Additional flooding occurred later in the spring and into the summer along the Missouri River. The Missouri River is the longest river in North America and one of the largest tributaries of the Mississippi. Its headwaters begin in Montana and flow through several major cities including: Great Falls, Montana; Williston and Bismarck, North Dakota; Omaha, Nebraska and Kansas City, Missouri before joining with the Mississippi in St Louis, Missouri.

      Record amounts of precipitation and melting snowpack contributed to historical flooding along the Missouri and its tributaries. The average rainfall across the state of Wyoming, which hosts several tributaries of the Missouri, was the most for any spring, based on records that data back to 1895. In eastern Montana, precipitation was 300 percent of normal for the month of May. The Missouri River basin experienced its fourth wettest spring and its third wettest May on record.

      In Wyoming and Montana, for the month of May, a total 14 locations set precipitation records and seven locations set a new all-time record for the wettest 24-hour period for any month on record. In Glasgow, Montana, the monthly precipitation amount of 6.97 inches (177 mm) was a record in addition to the seasonal snowfall record of 108.6 inches (276 cm). This shattered the previous snowfall record of 70.7 inches (180 cm) set in 2006/2007. During the July 1 - June 30 snow season, Williston, North Dakota received a record 107.2 inches (272 cm) of snow. The previous record was 94.7 inches (241 cm) set during the 1895-1896 season. Record to near-record snowpack in the Northern Rockies and High Plains during the winter and spring contributed to high levels of runoff. The runoff quickly filled all six of the rivers reservoirs forcing the Corps of Engineers to release them. The swollen river breached levees, forcing mandatory evacuations downstream. Additional damaging flooding is expected to continue through early summer.

      Lake Champlain

      Flooding was not confined to just rivers and streams. Water levels at Lake Champlain, which straddles New York, Vermont, and Canada, also experienced historical crests. At Rouses Point, Vermont, water levels rose to 102.8 feet (31.3 m) on May 10 and remained at or near historical levels for several weeks. The previous record lake level was 102.1 feet (31.1 m) set in 1869 and the normal for this time of year is about 97 feet (29.6 m). Record amounts of rainfall and melting of winter snowpack in the state exacerbated the flooding. It was the wettest Spring on record in Vermont. In Burlington, it was the wettest May on record with 8.67 inches (220 mm) of precipitation - besting the previous record of 7.10 inches (180 mm) set in 2006. Warmer-than-normal spring temperatures also increased the melting and runoff of snowpack. In Burlington, 128.4 inches (236 cm) of snow fell this season, 45.3 inches (115 cm) more than normal.

      Historical Perspective

      The prolonged flooding during the spring of 2011 that affected the Ohio, Mississippi and Missouri River Valleys draws comparisons to the great floods during the early 20th century. During the fall of 1926, record precipitation amounts resulted in major flooding along the lower Mississippi in the spring of 1927. During the three-month period (March-April), Arkansas, Illinois, and Missouri each had their wettest such period in 117 years of record keeping. It was reported that the flood of 1927 submerged more than 165 million acres, drowning 246 people. Economic losses were estimated at 2.8 billion in 2010 dollars.

      During the winter 1937, excessive precipitation during an 11-day period (January 13-24) contributed to flooding along the Ohio River. The state of Kentucky experienced a record 16.13 inches (410 mm) of precipitation in January. Individual locations had as much as 23 inches (584 mm) of precipitation during the month. From January 1-24 percent of normal precipitation in the area was approximately 600 percent of normal. Due to the copious amounts of precipitation, the Ohio River crested in Louisville at 85.4 feet (26 m). The Louisville flood stage is 51 feet (15.5 m). Further downstream in Paducah, the flood stage is 39 feet (11.9 m), but the river crested at 60.6 feet (18.5 m). It was reported that 3.3 billion in 2010 U.S. dollars worth of damage was done from the event.

      As a result of a series of heavy snows in the Upper Midwest during the winter of 1972/1973 punctuated by heavy springtime rains in the South, the Mississippi swelled, overtopping its banks during the spring of 1973. Both Tennessee and Wisconsin had their wettest March-April period. Additionally, nearly every state east of the Rockies experienced above normal precipitation. Damages came to an estimated 256 million in 2010 U.S. dollars.

      In the summer of 1993 frequent and excessive rainfall in the northern Plains southeastward into the central U.S. saturated soils, filling streams and rivers to capacity. For the summer period, record precipitation fell in Iowa, Illinois, Minnesota, Montana, Nebraska, and the Dakotas. Observed river crests in Iowa and Missouri easily surpassed previous record amounts by several feet. In St. Louis, at the confluence of the Missouri, Illinois and Mississippi rivers, the old record of 43.3 feet (13.2 m) set in 1973 was shattered on August 1, 1993 (49.7 feet or 15.1 m). The Missouri River also inundated towns. In Kansas City, the river set a new stage height of 48.9 feet (14.9 m), topping the old record of 46.2 feet (14.1 m) set in 1951. A total of 20 river gauges set all-time records. The devastating floods of 1993 are currently the costliest flooding disaster in the U.S. as damages neared 23 billion in 2010 U.S. dollars. In addition to the cost, more than 50 people were killed and at least 15 million acres of farmland were flooded. Other effects of the 1993 floods were: halted shipping on the Mississippi and Missouri for nearly two months, ten airports were flooded, all rail traffic in the Midwest was ceased, and both the 1993 and 1994 harvests were lost.

      Impacts

      The impacts of the 2011 flooding are far reaching, affecting economic sectors such as: agriculture, fishing, shipping, insurance, refineries, and tourism. Economic losses will take years to recoup. Hundreds of thousands of acres of farmland were flooded, creating a nightmare at a time of year when the growing season is just beginning for many crops. In Tennessee, corn planting has been delayed and the winter wheat crop, which is typically harvested in June, was damaged. It was reported that nearly 900,000 acres of farmland in Mississippi was flooded - roughly 10 percent of all farmland in the state. In Arkansas, it is estimated that the flood waters wiped out 1 million acres of farmland - a staggering number when you consider that the agriculture industry generates 16 billion dollars annually in Arkansas. In all, the floods washed out more than 3.5 million acres of farmland within the Lower Mississippi River Valley.

      The dangerous floodwaters shut down river commerce, which would have also caused additional stress on the levees. In addition to river commerce, in eastern Arkansas a 23-mile section of Interstate-40, a major east-west thoroughfare, was closed. Businesses and homes were closed or swept away, leaving many without a job or personal belongings. As the event continues to unfold, estimated economic losses are mounting. Overall, total insured losses currently amount to approximately 2-4 billion dollars.

      Selected Estimated Economic Losses
      AmountType
      $800 millionAgriculture in Mississippi
      $500 millionAgriculture in Arkansas
      $320 millionDamage in Memphis, Tennessee
      $317 millionAgriculture and property in Missouri's Birds Point-New Madrid Spillway
      $80 millionFirst 30 days of flood fighting efforts in Louisiana

      Farming was not the only economic sector in the South that was heavily damaged. The amount of fresh water flowing into the Gulf of Mexico caused an imbalance in the ecosystem wiping out the oyster beds which need the salt water to keep their metabolisms in check. The large amounts of fresh water saturated with fertilizers, pesticides and other farming chemicals is expected to flow into the gulf causing a "dead-zone" according to Lt. Col. Mark Jernigan, deputy commander of the New Orleans District of the U.S. Army Corps of Engineers. A dead zone is as area with low oxygen levels caused by the increase of fertilizers which fuels the growth of algae.

      It is too early to be able to give an exact figure of the damages done and economic loss of the 2011 flooding. However, we do know that it will take years to recover from the 6.8 million acres that were flooded. The flooding that occurred across the United States in Spring of 2011 will be one of the worst flooding disasters in modern American history.

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      Drought and Wildfire

      During March and April, drought and wildfires were the main headline across the Southern Plains of Oklahoma, Texas, and New Mexico. The track of storms from the Rockies into the Central and Northern Plains essentially cut off the Southern Plains from the Gulf of Mexico moisture source. The strong cold fronts and dry lines associated with the upper level troughs, which moved through the center of the country, brought strong winds and dry air into the region. The combination of warm, dry, and windy conditions worsened drought across the region and flamed out-of-control wildfires. The amount of precipitation during April across the Southern Plains stood in stark contrast to the record precipitation across the Ohio Valley, the record floods along the Lower Mississippi River, and the severe weather outbreaks across the Southeast.

      Environmental Conditions

      Starting in March, and lasting into April, a strong ridge of high pressure consistently setup across the Southern Plains, essentially blocking storms systems from entering the region. This led to Oklahoma and New Mexico having their top ten driest March, and Texas to have its driest March, on record. April brought continued dryness, with below-average precipitation for New Mexico, and Texas had its 5th driest April on record. The abnormally dry conditions stretched back to October 2010 for the region, with the March-April 2011,

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