Climate Summary

Temperature and Precipitation by climate division
Departures from Normal for April 2011
Based on Preliminary Data

April 2011 in North Carolina brought warm temperatures, heavy rain to western NC, and the worst tornado outbreak in 20 years. Indeed, April 2011 was one of the most active months on record for severe thunderstorms and tornadoes across the southern US.

Temperatures were warm overall, ranking April 2011 as the 11th warmest April on record. This warmth was most evident in the minimum temperatures, not in maximum temperatures. Most locations across NC had average maximum temperatures that ranked in the top 30 warmest Aprils, but most stations had average minimum temperatures that ranked in the top 10 warmest on record. A few locations, including Asheville, Wilkesboro, Raleigh, and Elizabeth City, had average minimum temperatures in April 2011 that ranked as the top 5 warmest.

Rainfall was heaviest along the mountains and foothills, but strong thunderstorms also produced heavy rainfall across parts of the piedmont and coastal plain.

Precipitation for April 2011
Based on estimates from NWS Radar
Data courtesy NWS/NCEP

Precipitation for April 2011: Percent of Normal
Based on estimates from NWS Radar
Data courtesy NWS/NCEP

Impacts to Agriculture and Water Resources

With precipitation amounts across central NC a bit closer to normal for March and April, drought conditions improved. By the end of April, severe hydrological drought (D2) conditions were no longer observed, and moderate drought (D1) had retreated from the northern Piedmont region.

While streams and reservoirs improved, there is still concern that with low groundwater levels, severe drought conditions could return if we experience a drier summer. The groundwater supply acts as a giant reservoir beneath our feet to provide base-flow to streams and reservoirs. Indeed, high groundwater supplies in the spring of 2010 helped to maintain streams and reservoirs during the dry summer of 2010. A similarly dry summer in 2011 would likely mean more water supply concerns. While we aren’t able to predict if the summer will be wet or dry, the NC Drought Management Advisory Council and the State Climate Office continue to keep a watchful eye on conditions with meetings each week.

US Drought Monitor for North Carolina
Courtesy NC DENR Division of Water Resources

April 16 Tornado Summary – A Climate Perspective
by Corey Davis and Bradley McLamb

The April 16, 2011, tornado outbreak will go down as one of the most significant in North Carolina history. The unusually destructive tornadoes that ravaged parts of the Tar Heel State were the result of a powerful storm system that passed well to our north. This placed North Carolina in the crosshairs of the storm’s strong cold front and high vertical wind shear, which were the catalysts that allowed numerous supercells -- severe thunderstorms capable of producing strong, long-track tornadoes -- to form over central and eastern North Carolina. The environment that produced these storms is much more common in the Central Plains of the U.S. than in our neck of the woods, but this event will stand as evidence that it is possible in North Carolina as well.

In terms of the number of tornadoes reported and the number of fatalities, this tornado outbreak ranks as one of the worst in North Carolina history. The National Weather Service reported five EF-3 tornadoes, eight EF-2 tornadoes, nine EF-1 tornadoes and eight EF-0 tornadoes, for a total of 30 separate tornadoes that resulted in 24 fatalities across the state. It is important to remember that some of the tornadoes came from the same supercell thunderstorm. In other words, a tornado may have touched down, lifted up, and then touched down again later along the path of one supercell.

The 30 reported tornadoes is the greatest one-day total in North Carolina, replacing the previous record of 20 tornadoes on April 7, 1998. Other days with many tornadoes reported include:

• April 15, 1996 when 18 tornadoes impacted parts of eastern North Carolina,
• September 15, 1999 with 17 tornadoes reported during the landfall of Hurricane Floyd, and
• March 28, 1984 with 14 tornadoes reported across the western coastal plain, including four tornadoes with F-4 magnitudes.

The 1984 event still ranks as the deadliest on record in North Carolina, with 41 fatalities attributed to the tornadoes on that day. The 24 confirmed fatalities from this year's event ranks second in terms of fatalities.

SCO Agricultural Products

Growing Degree Days
The growing degree days product is an interactive tool that plots user-defined growing degree day accumulations across the Southeast. This tool allows users to view accumulations for various weather stations across the Southeast after inputting a given date range and base temperature. Information is displayed spatially in Google Maps so that users can quickly compare GDD accumulations for their specific location to those over their entire region. Users can also download an Excel spreadsheet of the data.

http://www.nc-climate.ncsu.edu/products/ag/gdd

Reference Crop Evapotranspiration
Our reference crop evapotranspiration product includes tools that allow users to retrieve reference crop evapotranspiration values for stations across the southeastern U.S. These data are estimated using the FAO56 Penman-Monteith method, which incorporates observations of solar radiation, temperature, wind speed, and relative humidity. Two products use Google Maps for displaying:

• Daily ET estimates for the given date, which includes a graph of the daily time series upon clicking on a station
• Daily or monthly averages as a historical climate tool, where users can view an annual bar chart upon station click

http://www.nc-climate.ncsu.edu/et

Peanut Decision-Support Tools
The peanut decision-support tools developed by our office allow for county extension agents to receive daily peanut advisories via email for dissemination to growers. These advisories use hourly weather observations combined with modeling capabilities to determine if the diseases leaf spot or Sclerotinia blight are favorable for development based on recently observed conditions, as well as forecasted conditions over the next 72 hours. As such, chemical applications for disease prevention can be more appropriately timed for when environmental conditions favor disease onset.

http://www.nc-climate.ncsu.edu/products/ag/peanuts

Turfgrass Irrigation Management
The turfgrass irrigation product was designed to help those with grass minimize their outdoor water use while simultaneously maintaining a beautiful lawn. This online decision support tool uses information about irrigation rates and the type of grass grown, as well as recent precipitation amounts and evaporation rates to provide a precise amount of water a user would need to apply to ensure a healthy lawn without wasting water.

http://www.turffiles.ncsu.edu/TIMS

Cucurbit Downy Mildew Forecasting
The cucurbit downy mildew products allow users to see where reports of the disease have been issued, including detailed information regarding dates of disease symptoms, the type of plant affected, and the current report status. Visual forecasts are also included to compliment the text forecast discussions provided by the ipmPIPE team, which show areas of low, moderate, or high risk for cucurbit downy mildew.

http://cdm.ipmpipe.org

CRONOS API

CRONOS, our database of high quality climate data from the Southeast, was launched in 2003. Since then, it has become the foundation for most climate services that we offer. However, the data access needs of some of our clients are beginning to change. More people are writing their own analysis software and using GIS. For these users, manually visiting CRONOS and clicking through the pages can become tedious.

We are pleased to announce the full launch of the CRONOS API, which is designed for programmers and research scientists. It enables direct access to CRONOS without having to go through a web interface. It requires no specialized knowledge of database or query structure, SQL or any particular programming language. The CRONOS API is already being used by staff scientists and several external partners.

More details about the CRONOS API including documentation:
http://cirrus.meas.ncsu.edu/projects/api/wiki/apiref

Please contact the State Climate Office for more information or to request access to the CRONOS API.