Contents of This Report:
The North American 500 mb Maps for September
The upper-air pattern during September consisted of a trough along the Pacific coast, dominant high pressure from the central Rockies to the Mississippi River and a trough over the eastern third of the country.
The Pacific coast trough provided near normal temperatures for the coastal states, although most southern California stations were cooler than normal and coastal Oregon was warmer than normal. The mean upper-level ridge over the West provided warmer than normal conditions for the central and eastern Rockies as well as the central Plains. At the same time, prevalent troughiness from the mid-Mississippi Valley through the Northeast allowed for much cooler than normal temperatures from the Ohio Valley to lower New England and south to Georgia.
| Due to the eastern trough, above normal precipitation was noted from the southern Great Lakes through the Ohio Valley and into the mid-Atlantic states. It was much wetter than normal from Florida through the Carolinas due to tropical storms Gordon and Helene. The mid-continent ridge provided dry conditions from the northern Great Plains, south to Texas, and west to the Great Basin. The prevalent Pacific coastal trough provided wetter than normal conditions for portions of northern California, eastern Oregon and Washington, and areas of the northern Rockies.
|
animation
|
Additional information on hydrometeorological analysis and forecasting can be found at the Hydrometeorological Prediction Center's Web Page. The principles behind the 500 mb flow are briefly explained here.
National Temperature - September
larger image
|
The September 2000 monthly mean temperature averaged across the contiguous United States ranked as the 33rd warmest September since records began in 1895. This information is based on data from the U.S. Historical Climate Network (USHCN) and preliminary data from the Climate Division Database. The preliminary nationally averaged temperature for September 2000 was 66.2° F, 0.8° F above the long-term mean. The rate of temperature increase since 1895 is 0.15° F per century and 1.7° F per century since 1976. The actual September temperature values from 1895 through 2000 are available.
|
| The map to the right, based on approximately 250 airport stations, shows departures from the 1961-1990 normal temperatures for September 2000. Areas of the Ohio Valley, mid-Atlantic, Northeast and interior Southeast were cooler than normal. The Central and Southern Plains and portions of the Southwest were warmer than normal. Most of Alaska was cooler than normal while the Hawaiian stations averaged near normal.
|
larger image
|
larger image
|
The standardized temperature anomalies for September 2000 show abnormal warmth in most of Arizona, New Mexico, western Texas and along the Oregon coast. Warmer than normal conditions prevailed through the central Plains, and portions of the South, Southeast and Far West. Cooler than normal conditions are depicted in a large area east of the Mississippi River and a portion of the northern Rockies. The Piedmont area of North Carolina and Virginia was much cooler than normal. The map animation provided shows the geographical pattern of temperature anomalies for the last 12 months compared to a base period of 1931-1990.
|
National Precipitation - September
larger image
|
Based upon preliminary precipitation data, September 2000 ranked as the 28th driest such month since records began in 1895. This was the first September with below normal precipitation since 1995. The rate of precipitation increase since 1895 is 0.25 inch per century.
|
| The preliminary national standardized precipitation index ranked September 2000 as the 30th driest September since records began.
|
larger image
|
| The map to the right, based on approximately 250 airport stations, shows September 2000 total precipitation as a departure from 1961-1990 station normals. Above to much-above normal precipitation fell in all of Alaska except for the south central portion. September was much drier than normal in the northern Hawaiian stations and averaged near normal in the southern stations.. On the mainland U.S., stations were predominantly wetter than normal in the northern Rockies, and from the southern Great Lakes to the mid-Atlantic region and south through Florida. Stations were drier than normal along the immediate Pacific Coast and from the southern Great Basin to the central Gulf States and northward through South Dakota and Minnesota.
|
larger image
|
National Temperature - January-September 2000
larger image
|
The January-September 2000 mean temperature averaged across the contiguous United States ranked as the warmest such nine-month period since records began 1895. This information is based on data from the U.S. Historical Climate Network (USHCN) and preliminary data from the Climate Division Database. The preliminary nationally averaged temperature for January-September 2000 was 58.3° F, which was 2.4° F above the long-term mean. The rate of temperature increase since 1895 is 1.06° F per century. The last three such year-to-date periods have averaged much above the long term mean. The actual year-to-date data values from 1895 through 2000 are available.
|
| Data collected by NOAA's TIROS-N polar-orbiting satellites and adjusted for time-dependent biases by NASA and the Global Hydrology and Climate Center at the University of Alabama in Huntsville indicate that temperatures in the lower half of the atmosphere (lowest 8 km) were the warmest on record over the U.S. for the year-to-date period (January-September). The average lower tropospheric temperature over the continental U.S. during the January-September 2000 period was 1.5° F above the 1979-1998 long-term mean.
|
larger image
|
National Precipitation - January-September 2000
larger image
|
Based upon preliminary precipitation data, January-September 2000 ranked as the 20th driest such nine-month period since records began in 1895. About 20% of the country was much drier than normal, while about eight percent of the country was much wetter than normal. January-September 2000 is the first such period in five years to average below the long-term mean. The rate of precipitation increase since 1895 is 0.97 inch per century.
|
| The preliminary national standardized precipitation index ranked January-September 2000 as the 22nd driest such nine-month period since records began in 1895.
|
larger image
|
Current data are based on preliminary reports from River Forecast Center stations and First and Second Order airport stations obtained from the National Weather Service (NWS) Climate Prediction Center and real time Global Telecommunications System (GTS) monthly CLIMAT summaries. THE CURRENT DATA SHOULD BE USED WITH CAUTION. These preliminary data are useful for estimating how current anomalies compare to the historical record, however the actual values and rankings for the current year may change as the final data arrive at NCDC and are processed.
The following NCDC datasets are used for the historical U.S. data: the climate division drought database (TD-9640), and the hurricane datasets (TD-9636 and TD-9697). It should be noted that the climate division drought database consists of monthly data for 344 climate divisions in the contiguous United States. These divisional values are calculated from the 6000+ station Cooperative Observer network.
NOAA's National Centers for Environmental Information
