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National Oceanic and Atmospheric Administration

Climate of 1998
Annual Review:
Month-by-Month Variability in U.S.

National Climatic Data Center, Asheville, NC
January 8, 1999
U.S. Annual Temperature, 1895-1998
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Temperature and precipitation conditions varied considerably across the United States during 1998.

    The year started out wet on a national scale, with more than 20% of the country experiencing extremely heavy monthly precipitation totals during January, February, and March. Extremely dry conditions affected over 10% of the country during each month from April-June, but on a national scale these dry areas were offset by other equally-large areas with extremely wet conditions. This balancing act continued through much of the rest of the year. October was a wet month with over a fourth of the country extremely wet.
    U.S. Monthly Precipitation, January-December 1998
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    The Animated Palmer Z Index maps show the geographical pattern of short-term (i.e., monthly) wetness and dryness for each month, January-December 1998. As seen in the maps, the West Coast, Southeast, and Eastern U.S. were unusually wet (green shading) for much of the late winter. Spring (April-May) brought extremely dry conditions (red shading) to the Southern Plains and Gulf Coast, and also to the Northern Plains to Great Lakes region. The dryness continued in parts of the South during the summer and fall, spreading up the Atlantic Coast and into the Midwest and Great Lakes. Wet conditions predominated in the West for much of the year, occurred in the central parts of the country during much of the spring and summer, and spread into the Northeast during early summer.
    Animated Palmer Z Index Maps
    Animated Map

    The Animated Palmer Drought Index maps show the geographical pattern and progression of long-term drought and wet spell conditions for January-December 1998. These maps illustrate very well how the extremely dry spring and summer changed the long-term conditions in the South and East from severe wet spell (green shading) to severe drought (red shading). They also show the persistent wetness in the West. The Palmer Drought Index is best used as a drought/wet spell indicator for reservoir and groundwater applications.
    Animated Palmer Drought Index Maps
    Animated Map

    The Palmer Crop Moisture Index is computed on a weekly basis and is useful for following the impact of precipitation anomalies on agriculture. The Animated Crop Moisture Index maps show the rapid onset of drought in Texas and Florida during the spring and its rapid expansion across much of the Southeast.
    Animated Palmer Crop Moisture Index Maps
    Animated Map

    The year was characterized by unusual warmth on a national scale. More than 20% of the country experienced unusually warm monthly mean temperatures during January and February, May through September, and again in November. The heat was widespread in September, when nearly two-thirds of the contiguous United States averaged much warmer than normal. Areas of unusually cool weather occurred during late spring and early summer, with nearly 20% of the country (mostly in the Far West and Northern Plains) averaging much cooler than normal in June.
    U.S. Monthly Temperature, January-December 1998
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    The Animated Temperature Index maps show the geographical pattern of monthly temperature anomalies for each month, January-December 1998. As seen in the maps, warm temperature anomalies (red shading) predominated across the Southern Plains to Far West, and from the Ohio Valley to the Northeast, in January. The anomalously warm area shifted to the northern half of the country in February. The southern tier of states averaged colder than normal (blue shading) in April, while the northern tier averaged warmer than normal. Unusually cold conditions in the Far West in May expanded across the Northern Plains in June. Much of the country east of the Rockies averaged unusually warm in May. Hot conditions covered the Southern Plains and Southeast during June and July, and persisted through much of the rest of the year. The Western U.S. was dominated by warm anomalies for much of the last half of the year, beginning in July. Temperatures averaged much warmer than normal in September across most of the country, from the Gulf Coast to the Canadian border and from the Atlantic to Pacific Coasts. November saw a return to unusually warm anomalies, this time stretching from Florida to the Northern Rockies.
    Animated Temperature Index Maps
    Animated Map



For further information, contact:

    Mike Changery
    NOAA/National Climatic Data Center
    151 Patton Avenue
    Asheville, NC 28801-5001
    fax: 828-271-4328
    email: mchangry@ncdc.noaa.gov
-or-
    David Easterling
    NOAA/National Climatic Data Center
    151 Patton Avenue
    Asheville, NC 28801-5001
    fax: 828-271-4328
    email: david.easterling@noaa.gov
-or-
    Rob Quayle
    NOAA/National Climatic Data Center
    151 Patton Avenue
    Asheville, NC 28801-5001
    fax: 828-271-4328
    email: rquayle@ncdc.noaa.gov

NCDC / Climate Research / Climate of 1998 / Annual / U.S. Month by Month / Search / Help


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