Note: Data in this report are compiled from preliminary statistics
Updated 9 May 2007
The April 2007 Cold Wave occurred across much of the central Plains, Midwest and into the Southeast during the 4th through the 10th. For the month as a whole, April temperatures across the contiguous U.S. were near average ranking 47th coolest, although below average temperatures are apparent in these affected regions. The impacts of this cold air outbreak are extensive and still have yet to be completely quantified. Perhaps the most significant impact of this cold wave is related to the timing and duration of the event in concert with crop emergence and tree blooms. Winter wheat across the central Plains and Midwest and emerged corn and blooming fruits across the southern U.S. were perhaps among the hardest hit agricultural crops.
Several factors made this cold wave more harmful to agricultural interests than similar events in the past. March 2007 was exceptionally warm across a large portion of the U.S. from the northern Plains through the Mississippi Valley and into the Southeast. A dominant ridge of high pressure, entrenched across the contiguous U.S., allowed average monthly temperatures to exceed average conditions by more than 6°F across this region. The prolonged warm spell led to a premature leaf and bloom for many plants and trees across the region. In contrast to the warmth across the Lower 48 states, cold air was entrenched across much of Alaska making it the 3rd coldest March on record for the state.
In early April, a pattern shift brought this cold Arctic air southward into the central and eastern U.S. This record-breaking cold air penetrated much of this region from April 4-10 bringing near-record to record cold temperatures to parts of the central Plains and much of the Southeast. Temperatures in some locations dropped into the teens and lower 20s overnight with many hours of sub-freezing temperatures on multiple and subsequent days. As many as four to five nights of extremely cold temperatures coupled with sustained desiccating winds during the sub-freezing period made this event more harmful for plants and trees and brought extensive losses to agricultural interests.
In northern Alabama, minimum temperatures during this event generally fell into the lower to mid 20s with between 9 and 46 hours of temperatures below 32°F from April 7-10. Visible evidence from satellite shows the browning of vegetation which took place between the 5th and the 8th across the Cumberland Plateau of Tennessee and northern Alabama.
Data from the Climate Reference Network (CRN) across the central Plains and Southeast are shown in the figure below. During the time of the killing freeze, April 4-10, several CRN stations reported minimum temperatures in the teens. These include Batesville, AR (18°F), Manhattan, KS (14°F), Chillicothe, MO (17°F) and Crossville, TN (14°F). The number of hours the minimum air temperature was below 32°F across much of the region was considerable.
When looking at the 20th Century mean for the contiguous U.S., April is warmer than March on average by about 9°F. Comparing March and April temperatures across the central, southern and southeastern portions of the U.S., we see that in many cases, March and April were very similar. Seven of the sixty U.S. Climate at a Glance cities were actually colder in April when compared with March. They include: Amarillo, TX, Birmingham, AL, Dallas, TX, Jackson, MS, Tulsa, OK, Wichita, KA, and Kansas City, MO. Ten additional cities had April average temperatures warmer than March, yet within 1°F of each other.
Statewide temperature averages indicate that April was colder than March across Arkansas, Kansas, Mississippi, Oklahoma, Tennessee and Texas. A comparison of March and April statistics is listed in the table below.
|State||March 07 Avg Temp||April 07 Avg Temp||March Dep (from 20th Century Avg)||April Dep (from 20th Century Avg)|
Between the 4th and 10th there were 1237 broken (321 tied) daily minimum temperature records in the Contiguous United States. (These records are based on the historical daily observations archived in NCDC's TD-3200 data set and preliminary reports from Cooperative Observers and First Order National Weather Service stations, and as such are subject to change.)
Selected U.S. City and State Extremes for April.
|Record Monthly Lows|
|Date||City||New/Tie Record||Old Record||Old Date|
|April 7, 2007||Asheville Regional Airport, NC||20||22||April 1, 1987|
|April 8, 2007||Savannah Airport, GA||28||32||April 8, 1962|
|April 8, 2007||Augusta Regional Bush Field. GA||26||26||April 7, 1982|
|April 8, 2007||Alma, GA||30||31||April 8, 1987|
|April 8, 2007||Columbia Metro. Airport, SC||26||26||April 20, 1983|
|April 8, 2007||Greenville-Spartanburg Airport, SC||24||25||April 20, 1983|
|April 8, 2007||Charlotte Douglas Intl. Airport, NC||21||24||April 1, 1923|
|April 8, 2007||Jacksonville, FL||31||34||April 8, 1987|
|Record Daily Lows|
|Date||City||New/Tie Record||Old Record||Old Year|
|April 6, 2007||Danville, VA||28||28||2004|
|April 6, 2007||Salisbury, MD||23||26||2002|
|April 7, 2007||Greenville-Spartanburg Airport, SC||28||28||1950|
|April 7, 2007||Columbia Metro. Airport, SC||30||30||1982|
|April 7, 2007||Asheville Regional Airport, NC||20||25||1982|
|April 7, 2007||Charlotte Douglas Intl. Airport, NC||25||27||1950|
|April 7, 2007||Wilmington, NC||32||34||1950|
|April 7, 2007||Northwest AL Regional Airport Muscle Shoals, AL||26||30||1982|
|April 7, 2007||Huntsville Intl. Airport, AL||25||27||1950|
|April 7, 2007||Atlanta, GA||28||29||1982|
|April 8, 2007||Salisbury, MD||25||27||1990|
|April 8, 2007||Washington National||29||29||1982|
|April 8, 2007||Danville, VA||22||26||1961|
|April 8, 2007||Lynchburg, VA||22||24||1970|
|April 8, 2007||Bluefield, VA||21||22||1972|
|April 8, 2007||Elizabeth City, VA||27||29||1982|
|April 8, 2007||Norfolk, VA||33||33||1972|
|April 8, 2007||Charleston Airport, SC||30||34||1950|
|April 8, 2007||Downtown Charleston, SC||38||43||1972|
|April 8, 2007||Columbia Metro. Airport, SC||26||31||1971|
|April 8, 2007||Greenville-Spartanburg Airport, SC||24||32||1990|
|April 8, 2007||Florence, SC||26||34||1971|
|April 8, 2007||N. Myrtle Beach, SC||29||30||1950|
|April 8, 2007||Asheville Regional Airport, NC||22||26||1994|
|April 8, 2007||Raleigh-Durham Intl. Airport, NC||27||28||1975|
|April 8, 2007||Piedmont Triad Intl. Airport, NC||25||28||1990|
|April 8, 2007||Charlotte Douglas Intl. Airport, NC||21||30||1961|
|April 8, 2007||Wilmington, NC||29||33||1972|
|April 8, 2007||New Bern , NC||30||31||1950|
|April 8, 2007||Northwest AL Regional Airport Muscle Shoals, AL||26||30||1939|
|April 8, 2007||Huntsville Intl. Airport, AL||26||28||1958|
|April 8, 2007||Mobile Regional Airport, AL||38||39||1990|
|April 8, 2007||Pinson, AL||25||27||1990|
|April 8, 2007||Jacksonville, FL||31||37||1971|
|April 8, 2007||Pensacola Regional Airport, FL||39||41||1939|
|April 8, 2007||Gainesville, FL||35||38||1950|
|April 8, 2007||Brunswick, GA||37||38||1950|
|April 8, 2007||Alma, GA||30||34||1950|
|April 8, 2007||Athens, GA||27||32||1990|
|April 8, 2007||Atlanta, GA||30||32||1886|
|April 8, 2007||Macon, GA||28||30||1990|
|April 8, 2007||Augusta Regional Bush Field. GA||26||32||1971|
|April 8, 2007||Savannah Airport, GA||28||35||1950|
|April 9, 2007||Savannah Airport, GA||31||36||2000|
|Record Daily Lowest Maximums|
|Date||City||New/Tie Record||Old Record||Old Year|
|April 7, 2007||Roanoke, VA||39||45||1982|
|April 7, 2007||Bluefield, VA||27||36||1982|
|April 7, 2007||Savannah Airport, GA||56||62||1950|
|April 7, 2007||Downtown Charleston, SC||56||57||1982|
|April 7, 2007||Columbia Metro. Airport, SC||51||53||1907|
|April 7, 2007||Asheville Regional Airport, NC||38||48||1973|
|April 7, 2007||Huntsville Intl. Airport, AL||45||50||1939|
|April 7, 2007||Northwest AL Regional Airport Muscle Shoals, AL||46||48||1958|
|April 7, 2007||Tallahassee, FL||58||59||1898|
|April 8, 2007||Tallahassee, FL||58||61||1899|
|April 8, 2007||Savannah Airport, GA||59||61||1982|
|Record Daily Snow|
|Date||City||New/Tie Record||Old Record||Old Year|
|April 7, 2007||Baltimore, MD||0.2||0.2||1972|
|April 7, 2007||Greenville-Spartanburg Airport, SC||T||0||-|
|April 7, 2007||Raleigh-Durham Intl. Airport, NC||T||0||-|
|April 7, 2007||Asheville Regional Airport, NC||1.2||1||1989|
|April 7, 2007||Elizabeth City, VA||T||0||-|
|April 7, 2007||Richmond, VA||1||0.2||1990|
|April 7, 2007||Salisbury, MD||1.2||1||1990|
|Provided by William Schmitz, Southeast Regional Climate Center|
The April 2007 Cold Wave brought significant crop losses across the central Plains, Midwest, and into the Southeast. Although the extent of damage has not been fully assessed, losses may total billions of dollars in the affected states.
The event brought extensive losses mainly due to the anomalous warmth during the month of March which helped induce an earlier spring blossom, in some cases two weeks prior to crop development in 2006. Over the weekend of 6-9 April, average low temperatures across the south were on average 24°, 20°, 16°, and 18°F, each of those days respectively; all temperatures below the critical threshold of 28°F. If mean temperatures are below that critical temperature developing fruit and blossoms are likely to suffer damage. At 25°F, agricultural officials said, farmers can expect to lose about 90 percent of their crop.
According to Virginia's Department of Agriculture and Consumer Services peaches and apples were the most affected in Virginia, with apple losses varying from 5% to 90% and peach losses varying from 80% to 100%, depending on the area. Meanwhile, North Carolina's Department of Agriculture and Consumer Services reported a preliminary estimate of at least $112 million in crop losses.
The following table provides a summary of Very Poor to Poor crop conditions for the period prior to and after the cold wave. The information found below was provided by U.S. Department of Agriculture / National Agricultural Statistics Service.
|Winter Wheat||14% (04/01)*||36% (04/22)|
|Winter Wheat||6% (04/01)||64% (04/23)|
|Corn||16% (04/08)||58% (04/22)|
|Pastures||15% (04/01)||25% (04/22)|
|Corn||3% (04/01)||26% (04/22)|
|Pastures||34% (04/01)*||49% (04/22)|
|Apples||0% (04/01)||99% (04/22)|
|Peaches||5% (04/01)||83% (04/22)|
|Tobacco||0% (04/01)||30% (04/22)|
|Winter Wheat||9% (04/01)||29% (04/23)|
|Red Clover||NR||32% (04/22)|
|Winter Wheat||12% (04/01)||30% (04/22)|
|Winter Wheat||4% (04/01)||41% (04/22)|
|Winter Wheat||8% (04/01)||64% (04/23)|
|Pastures||17% (04/01)||39%% (04/22)|
|Winter Wheat||3% (04/01)||39% (04/23)|
|Truck Crops||2% (04/01)||35% (04/22)|
|Irish Potatoes||6% (04/01)||30% (04/22)|
|Rye||1% (04/01)||58% (04/22)|
|Barley||1% (04/01)||55% (04/22)|
|Oats||0% (04/01)||31% (04/22)|
|Winter Wheat||26% (04/01)**||27% (04/22)|
|Apples||8% (04/08)||60% (04/22)|
|Peaches||12% (04/08)||70% (04/22)|
|Winter Wheat||1% (04/01)||50% (04/22)|
|Corn||1% (04/01)||46% (04/22)|
|Pastures||11% (04/01)||25% (04/22)|
|Cucumbers||0% (04/01)||70% (04/22)|
|Snapbeans||0% (04/01)||70% (04/22)|
|Cantelopes||0% (04/01)||45% (04/22)|
|Watermelons||0% (04/01)||43% (04/22)|
|Oats||1% (04/01)||41% (04/22)|
|Winter Wheat||3% (04/01)||84% (04/22)|
|Apples||0% (04/08)||91% (04/22)|
|Pastures||31% (04/01)*||32% (04/22)|
|Peaches||2% (04/01)||86% (04/22)|
NR = Not Reported
* Due to drought
** Due to wetness
Information provided by U.S. Department of Agriculture / National Agricultural Statistics Service
In addition to the extensive crop losses discussed above, there are indications that losses in vegetative cover resulted in other impacts beyond the immediate damages. Scientists in NOAA's Air Resources Laboratory, Atmospheric Turbulence and Diffusion Division, have observed a decline of carbon dioxide uptake by the forest ecosystems as well as an impact on the energy budget of the region. Content for this section was provided by Dr. Tilden Meyers at ATDD.
The early green up resulting from the unusually warm temperatures in March is clearly depicted from in-situ observations from two of NOAA's Surface Energy Balance Network (SEBN) towers located on the Walker Branch Watershed and Chestnut Ridge towers in Oak Ridge, Tennessee. As shown in the figure below, the Normalized Difference Vegetation Index (NDVI), an indicator of plant canopy green leaf area, clearly shows the early green-up relative to last year with the sharp rise occurring about 3 weeks earlier than in 2006. The dramatic impact of the widespread and intense spring freeze is clear from the sharp drop in the NDVI value on day 98 (April 8). The NDVI is only 25% above the winter baseline at a time when it should be at a maximum. The recovery of the vegetation is beginning, but the pace and extent to which the vegetation recovers will become evident in the coming weeks.
The increase in carbon dioxide (CO2) uptake by tree and plant life that normally occurs as forests leaf out in the spring has also been impacted by the record cold. The graph below depicts the consequent decline of CO₂ uptake by the forest ecosystems (blue line - 2007; red line - 2006, typical pattern of increasing carbon dioxide uptake in the spring season). As of May 3, for the daytime period, the average integrated CO₂ flux did not yet show a sink (negative fluxes; uptake of CO₂ from the atmosphere), when under normal conditions it would be showing a maximum daily uptake. (While human and animal life breath in oxygen and exhale carbon dioxide, healthy forests take in carbon dioxide and release oxygen.) Negative CO₂ fluxes (net uptake of carbon dioxide) would be evidence of a healthy forest ecosystem.
The lack of normal amounts of vegetative cover is resulting in more of the sun's energy being used for heating the atmosphere instead of evaporating water from trees and plant life. The evapotranspiration from the canopy (transfer of moisture from vegetation and the Earth's surface to the atmosphere) is ¼ of what is normally expected for early May. Conversely, sensible heat flux is much higher, which results in more of the sun's energy being used to heat the air near the Earth's surface. These conditions are somewhat analogous to conditions in the desert, where radiation from the sun acts to raise the temperature of the air instead of evaporating moisture from vegetation and the ground.
The resulting warmer air temperatures and reduced moisture in the atmosphere have the potential to exacerbate drought conditions in the region. In early May, severe to extreme drought covered an area that stretched from western North Carolina, southern Tennessee and northern Georgia to eastern Missisippi. Severe to extreme drought was also present in southern Georgia, where the largest wildfire on record for the state continued to burn in early May. Drought also affected parts of Florida, the Southwest US, and areas of the northern Rockies, northern High Plains, and northern Minnesota. Additional drought information is available in the April US Drought report.
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