Drought - April 2009


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Contents Of This Report:
Map showing Palmer Z Index

Top of Page National Overview



Top of Page Detailed Drought Discussion


The weather patternweather pattern for April consisted of a generally westerly flow in the atmosphere. Strong low pressure systems and associated fronts, embedded in this west-to-east circulation, brought rain and snow to areas of the country, with heavy precipitation falling over parts of the Plains, Midwest, and South. Rain or snow especially benefited the drought areas of the southern Plains, intermountain West, Southeast, and mid-Atlantic states. The precipitation largely missed the Southwest, parts of California, southern Texas, the southern half of Florida, and parts of the Northeast, with drought or abnormally dry conditions expanding in these areas (April 28 USDM versus March 31 USDM).

U.S. precipitation anomalies, April 2009 April 28, 2009 U.S. Drought Monitor

The month was drier than normal across the eastern half and northern coast of Puerto Rico, with a generally dry pattern for the southeastern half and northwestern corner of the island for the year-to-date and last 180 days. The Hawaiian Islands were generally drier than normal for April and the last 3 months, but a mixed pattern dominated for the last 12 months. The precipitation pattern for Alaska was generally drier than normal in the southeastern half and wetter than normal in the northwestern half for April and the last 3 months, but mixed for the last 12 months. The seasonal precipitation pattern resulted in a May 1st snowpack that was below average in some southern Alaska locations but mostly average or above.

By the end of April, the core drought areas included:
  • the southern Plains, with moderate to extreme drought;
  • south central Texas, where widespread extreme to exceptional drought was entrenched;
  • the southern half of Florida, with worsening moderate to extreme drought;
  • the southern Appalachians, where moderate hydrologic drought lingered;
  • portions of the northwestern Great Lakes/Upper Mississippi Valley, where moderate to severe drought persisted;
  • parts of the West, with moderate to severe drought; and
  • Hawaii, where moderate to severe drought continued across the central and eastern islands.
For the last week in April, according to USDM statistics, moderate to severe drought affected 43 percent of Hawaii, 25 percent of the West, and 8 percent of the Midwest; moderate to extreme drought affected 15 percent of the Southeast; and moderate to exceptional drought affected 32 percent of the South.

A number of drought indices and impact indicators are used to assess drought conditions. Soil moisture conditions are estimated by several models (LDAS surface layer, LDAS deeper layer, CPC U.S. soil moisture, CPC North America soil moisture) and by USDA observations (topsoil conditions, compared to 5-year mean, compared to 10-year mean). The LDAS ensemble soil moisture analyses (surface layer, deeper layer) and CPC soil moisture analysis revealed significantly dry soil moisture in southern Florida, south Texas, and parts of the West, and soils were drying out in parts of the Northeast. These models, and the soil moisture model by the Midwest Regional Climate Center (surface layer, deeper layer), showed how dry soils lingered in southeast Minnesota and western Wisconsin, especially at the deeper layers. USDA reports indicated nearly 60 percent to over 80 percent of topsoil moisture in Texas, New Mexico, and Florida was rated very short to short, with topsoil drier than average in parts of the Northeast, Upper Mississippi Valley, and Washington state. The dry soils adversely impacted agriculture, pasture and range land, and natural vegetation in the Southwest, southern Plains, Florida, and parts of the Northeast. About 60 percent of the pasture and range land was rated in very poor or poor condition in Florida and California by early May. April 30, 2009 top 1 meter soil moisture percentile from the LDAS ensemble model

April 26, 2009 USDA topsoil moisture short-very short compared to 10-year mean

May 3, 2009 USDA observations of pasture and range land in poor or very poor condition

Maximum number of consecutive dry days for April 1-30, 2009, as analyzed by the USGS and NOAA

April 2009 USGS mean streamflow
As of April 30, large parts of the Southwest and parts of the Northwest had gone 2 or more weeks without significant rainfall. The maximum consecutive number of dry days in April was especially troublesome for parts of the Upper Mississippi Valley, Florida, and southern Texas. Streamflow levels (both modeled and observed) were significantly low in parts of Florida, the Upper Mississippi Valley, and the Northeast and below normal across parts of the West and southern Plains. Data from the USGS network of wells indicated lingering groundwater impacts across the Southeast, worsening groundwater conditions across parts of Florida, and below-normal groundwater levels in southern Alaska.

1-month Standardized Precipitation Index, April 2009 2-month Standardized Precipitation Index, April 2009 3-month Standardized Precipitation Index, April 2009

The dryness in April was a continuation of prolonged dryness in some parts of the country. In parts of the Northeast and mid-Atlantic states, the first four months of 2009 were dry, but the latter months of 2008 were wet. Parts of Florida and southern Texas have been persistently dry for the last 6 months or longer. In other parts of the Southeast and southern Plains, wet conditions during the last few months have eased drought conditions which can be traced back several months. In the Upper Mississippi Valley and parts of the West, dry conditions can be traced back 12 months or longer.

6-month Standardized Precipitation Index, April 2009 9-month Standardized Precipitation Index, April 2009 12-month Standardized Precipitation Index, April 2009

January-April 2009 statewide precipitation ranks While April did not have any record dryness on a statewide level, the year to date has been very dry in some areas. New Jersey had the second driest January-April on record and New York had the third driest January-April on record. Several other states (Connecticut, Delaware, New Mexico, Pennsylvania, Vermont) ranked as tenth driest, or drier, for the year to date. Arizona had the eleventh driest January-April on record and New Hampshire ranked twelfth driest. The Northeast region, as a whole, had the fourth driest January-April on record, and for the contiguous U.S., 2009 had the twelfth driest January-April in the 1895-2009 record.

New Jersey precipitation, January-April, 1895-2009 New York precipitation, January-April, 1895-2009

Record dry conditions have occurred in Deep South Texas and central to southern Florida. Texas climate division 10 (Lower Rio Grande Valley) had the driest December-April and October-April in the 1895-2009 record. North Central Florida (climate division 3) had the driest November-April and September-April, while Florida climate division 5 (Everglades and Southwest Coast) ranked driest for January-April and February-April. Even though this is normally the dry season, much-drier-than-normal weather has dominated most of central to southern Florida during the last several months, giving the region the driest November-April and December-April and second driest January-April, February-April, October-April, and September-April. Precipitation for central and southern Florida, November-April, 1895-2009

Texas Lower Rio Grande Valley precipitation, October-April, 1895-2009 North Central Florida precipitation, September-April, 1895-2009

Beneficial rain and snow fell over parts of the West during April, especially from the intermountain basin to the central and northern Rockies. But much of the Southwest, Pacific Northwest, and California had below-normal precipitation during the month. Long-term deficits remained across much of the West. For the last 12 months, California had the eighth driest May-April and Oregon ranked twelfth driest. This year marks the third consecutive year that California has had a very dry May-April.

Snowpack and snow water content remained below average across parts of the West. Reservoir levels were above average in Arizona, Colorado, Washington, and Wyoming but below average across many other states. According to the Palmer Drought Index, about 54 percent of the region was in moderate to extreme drought at the end of the month, while the USDM estimated the statistics at about 25 percent in moderate to exceptional drought and about 66 percent experiencing abnormally dry to exceptional drought conditions. The differences between the Palmer and USDM statistics are due to the extreme seasonality of precipitation in the West and other hydrologic components in the drought calculations.
24-month Standardized Precipitation Index, April 2009
May 2008-April 2009 statewide precipitation ranks

California statewide precipitation, May-April, 1895-2009 Percent area Western U.S. in moderate to extreme drought and wet spell, based on Palmer Drought Index, January 1996-present

A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.



SOUTHEAST DROUGHT

According to the Southeast Regional Climate Center, much of the region had below normal precipitation totals for April, especially the Carolinas, southern Virginia, and the southern three-quarters of Florida. Monthly precipitation totals were less than 50 percent of normal across much of southern Florida. In contrast, monthly precipitation totals across most of Georgia and small portions of Alabama and South Carolina were above normal. Prodigious monthly precipitation totals over southern Georgia and western Florida were associated with multiple mesoscale convective systems that tracked across the region in association with the approach of two cold fronts between the 1st and 3rd of the month. Most of Puerto Rico experienced below normal precipitation totals for the month.

Severe drought (D2) conditions persisted across portions of central and southern Florida, and a small region of southwestern Florida was upgraded to the extreme drought classification (D3). Drought conditions in northeast Georgia and northwest South Carolina showed continued improvement early in the month in response to plentiful rainfall in late March and early April. The small area of severe drought (D2) in northwest South Carolina was downgraded to the moderate drought (D1) classification. This was tied to a reduction of the size of the D1 region, which occupied only a small portion of northeastern Georgia and western North Carolina by the middle of the month. Moderate drought conditions across northern Virginia lessened to abnormally dry conditions during the month. Dry conditions over the last 4 months contributed to the development and rapid spread of a wildfire near Myrtle Beach, South Carolina on the 22nd that burned nearly 20,000 acres and destroyed 76 homes. Additionally, on the 23rd of the month, lightning sparked a brush fire in the drought-stricken Everglades of southern Florida forcing the closure of Interstate 75.

SOUTHERN REGION DROUGHT

As noted by the Southern Regional Climate Center, the month of April had variable precipitation for the Southern Region. Large areas of the region experienced above normal monthly totals, while other large areas received below normal precipitation. Precipitation totals in Mississippi were generally below 75 percent of normal. Totals were 25-50 percent of normal in the coastal areas of Mississippi and in southeastern Louisiana, specifically the Florida parishes of the state. There was also a second dry belt that extended from north eastern Louisiana, through central Mississippi to northeastern Mississippi. Along this belt, monthly totals ranged from 25 to 50 percent of normal. The driest areas of the Southern Region consisted of the western Texas panhandle and the southern tip of Texas where precipitation totals were mostly below 25 percent of normal. Many stations in Texas Climate Divisions 5 (Trans Pecos) and 10 (Lower Valley) reported little to no precipitation for the month. Conversely, the wettest portions of the Southern Region included south eastern Texas, west central Texas, north central Texas, and south central Oklahoma. These areas all experienced precipitation totals that ranged from 200 to 400 percent of normal.

The spatially variable pattern of April precipitation led to both improvements and deteriorations in drought conditions within the Southern Region. Near normal precipitation led to improved conditions in eastern Tennessee. Similarly, normal rainfall for the month in southern Arkansas resulted in the removal of abnormally dry conditions. Heavy precipitation totals in Oklahoma allowed for a great improvement throughout the state. Drought conditions were improved by one category along the Oklahoma panhandle. Last month, this area was categorized as moderate to severe drought. In Texas, the northern Texas panhandle experienced a two category improvement from moderate drought to drought-free conditions. There were also significant improvements in the eastern portions of the state, where precipitation totals for the month were well above normal. In the southernmost counties of Texas, dry conditions (continued from last month) led to a slight expansion of exceptional drought.

MIDWEST DROUGHT

As explained by the Midwest Regional Climate Center, April was a wet month with nearly all the region receiving above-normal precipitation. Minnesota, northwest Iowa, northwest Wisconsin, and eastern Ohio were below normal for the month, but elsewhere precipitation was above normal.

HIGH PLAINS REGION DROUGHT

As noted by the High Plains Regional Climate Center, showers and thunderstorms during April helped erase the D2, D1, and much of the D0 (severe drought to abnormally dry) conditions in Kansas. However, areas across north central Kansas and eastern Nebraska missed out and D0 (abnormally dry) conditions spread by the end of the month. Drought conditions improved across Wyoming and parts of Colorado, but abnormally dry conditions developed in western North Dakota in mid April. By the third week of April, more than 10 percent of North Dakota was under abnormally dry conditions. Divide, Burke Williams, Mountrail, McKenzie, Billings and Golden Valley counties were so dry, the National Weather Service put out Fire Danger statements during the second and third week covering most of the Bismarck County Warning Areas.

WESTERN DROUGHT

As summarized by the Western Regional Climate Center, precipitation was below normal across most of the western and southern portions of the region. Interior areas of the Great Basin, the Wasatch, parts of the Central and Northern Rockies, and the plains of Montana, along with isolated pockets of southern Arizona were wetter than normal. Parts of Wyoming, Montana and Colorado had an exceptionally wet and snowy April. Great Falls, Montana tied their all-time snowiest month ever with 35.4 inches (89.9 cm). Bozeman, Montana also recorded their snowiest month of all time with 49.6 inches (126 cm). The large snow event along the Front Range of Colorado on the 17-19th produced 56.3 inches of snow (143 cm) in Rollinsville.

Mountain snowpack remained mostly healthy in the Pacific Northwest and Intermountain region with snowpack on May 1st near or slightly above normal. The Southwest and California remained well below normal. Snowmelt inflow to Lake Powell on the Colorado River was expected to be near average. California snowmelt runoff was again expected to be well below average for the third consecutive year.

California: As noted by California and NOAA officials, the precipitation of recent months has improved reservoir levels along the Sierra Nevada from where they were earlier this year, although several reservoirs to the north and west still had low levels. The end-of-April 2009 overall statewide reservoir storage was approximately at the same level as April 30, 2008. In northern California, Shasta county experienced early May rains which have improved short-term conditions. However, long-term conditions remained dry. According to local reports, multiple consecutive low rainfall years have dropped the water table causing agricultural wells to go dry.

Alaska: According to National Weather Service reports (from information compiled and provided by Audrey Rubel at NOAA NWS Alaska Region Headquarters), precipitation for the month showed a pattern of discontinuity with drier-than-normal conditions in eastern Alaska and wetter than normal in the west. Due to the gradual warm-up taking place during April with lengthening daylight hours, the seasonal snowpack disappeared or was significantly reduced at many locations.

NORTHEAST DROUGHT

As noted by the Northeast Regional Climate Center, April 2009 was the third consecutive month with above-normal temperatures in the Northeast and the fourth month in a row with below-normal precipitation. The regional average was 3.24 inches (8.23 cm) or 91 percent of the normal April precipitation amount. This represented a range of values from 66 percent of normal in Vermont to 141 percent of normal in Delaware. The general weather pattern this month kept the bulk of the precipitation in the southern three states and along the coast, leaving interior sections of the Northeast quite dry.

Above-normal rainfall in the southern third of the Northeast improved drought conditions in West Virginia and Maryland from moderate drought to abnormally dry, according to the April 28, 2009 USDM. Most of western West Virginia improved to normal conditions. Below-normal precipitation in the central portion of the Northeast resulted in abnormally dry conditions in Delaware, New Jersey, Pennsylvania, southern New York and western Massachusetts and Connecticut.



Top of Page State/Regional/National Moisture Status


A detailed review of drought and moisture conditions is available for all contiguous U.S. states, the nine standard regions, and the nation (contiguous U.S.):

STATES:
Alabama Arizona Arkansas California Colorado Connecticut
Delaware Florida Georgia Idaho Illinois Indiana
Iowa Kansas Kentucky Louisiana Maine Maryland
Massachusetts Michigan Minnesota Mississippi Missouri Montana
Nebraska Nevada New Hampshire New Jersey New Mexico New York
North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania
Rhode Island South Carolina South Dakota Tennessee Texas Utah
Vermont Virginia Washington West Virginia Wisconsin Wyoming


REGIONS:
Northeast Region East North Central Region Central Region
Southeast Region West North Central Region South Region
Southwest Region Northwest Region West Region
Map showing the nine U.S. standard regions
NATIONAL:
Contiguous U.S.




Top of Page Pre-Instrumental Perspective


There is no April 2009 Paleoclimatic Perspective.

Citing This Report

NOAA National Climatic Data Center, State of the Climate: Drought for April 2009, published online May 2009, retrieved on July 30, 2014 from http://www.ncdc.noaa.gov/sotc/drought/2009/apr.