Skip Navigation Links 
NOAA logo - Click to go to the NOAA home page National Weather Service   NWS logo - Click to go to the NWS home page
Climate Prediction Center

HOME > Expert Assessments > Climate Diagnostics Bulletin


Extratropical Highlights - March 2000

1. Northern Hemisphere

The circulation during March featured above-average heights across the east-central North Pacific, over the polar region, and in the area extending northeastward from the eastern half of North America to northern Europe (Fig. E9). The circulation also featured below-average heights across the high latitudes of the North Pacific, over the lower latitudes of the central North Atlantic and over eastern Europe/ western Russia.

In the subtropics, there was again considerable symmetry of the upper-level circulation anomalies in both hemispheres (Fig. T22, bottom). The most notable aspect of this anomaly pattern has been a persistent pattern of anticyclonic circulation anomalies extending eastward in the Northern Hemisphere from the Atlantic Ocean to Asia and in the Southern Hemisphere from the Atlantic Ocean eastward to Australia. This pattern was also prominent throughout 1999 in association with ongoing La Niņa conditions, and is a leading mode of atmospheric variability on both the interannual and interdecadel time scales.

a. North America

Above-average heights covered the eastern half of the United States during March, in association with an overall weakening and eastward shift of the mean Hudson Bay Trough. This trough typically extends southward from Hudson Bay to the Great Lakes region of the United States at this time of the year. These conditions were associated with anomalously zonal flow across the United States, and with a markedly reduced strength of northwesterly flow over the north-central U.S. and Canada. As a result, surface temperatures were well above-average across Canada and most of the United States during the month (Fig. E1), with values exceeding the 90th percentile over large portions of central Canada and the northeastern quadrant of the United States (Fig. E1, bottom). Elsewhere, temperatures averaged above the 70th percentile over most of the remaining portion of Canada, and throughout the United States east of the Continental Divide. Anomalously warm temperatures also covered most of Mexico during the month.

The eastern half of the United States also recorded below-average rainfall during the month (Fig. E3), with large portions of this area having recorded below-normal rainfall since last summer. During this 9-month period exceptionally dry conditions have prevailed in the Great Plains region, the Midwest, and the Great Lakes area (Fig. E5). The Midwest and Great Lakes regions have recorded below-average rainfall in every month since July 1999. Considerable dryness has also prevailed in the Gulf Coast, the mid-Atlantic and Northeast regions since November 1999, with longer-term precipitation deficits in these latter two regions also extending back to July 1999. In the Great Plains area, March was the first month since July 1999 in which near-average rainfall was recorded.

b. Europe/ Asia

Most of Europe experienced milder-than-average temperatures during March (Fig. E1), with surface temperatures averaging above the 70th percentile across Europe. In northwestern France and portions of Great Britain temperatures averaged above the 90th percentile during the month. This anomalous warmth was associated with an overall northward shift of the main belt of westerlies (Fig. E11, left) and main storm track (Fig. E13, left) to southern Scandinavia.

2. Southern Hemisphere

The Southern Hemisphere circulation during March (Fig. E15) featured above-normal heights over southeastern Australia and New Zealand, over the middle latitudes of the central South Pacific and central Indian Ocean, and over the high latitudes of the central South Atlantic. It also featured below-normal heights over the high latitudes of the South Pacific and Indian Ocean. Much of the central latitudes have experienced above-average heights for over a year, in association with an extremely persistent pattern of anticyclonic circulation anomalies in both hemispheres extending from the Atlantic ocean eastward to Australasia (See Northern Hemisphere Highlights above).

In recent months southeastern Africa has recorded significantly above-average rainfall in association with this anomalous circulation. This excessive rainfall has occurred during the region’s rainy season, and has resulted in large-scale flooding across much of central Mozambique. A Tropical Cyclone also impacted Mozambique during the month, which exacerbated flooding conditions in that area. A second Tropical Cyclone (TC Hudah) also impacted the coastal areas of central and northern Mozambique in early April. This system made a direct hit on northeastern Madagascar in early April, destroying the towns of Antalaha and Cap Est.

The above-average rainfall during January-March in southeastern Africa was associated with an anomalous large-scale circulation pattern that featured 1) enhanced low-level easterly winds across the central Indian Ocean in association with an amplification and poleward shift of the Mascarene High (Fig. T20, bottom), 2) an anomalous low-level circulation center over south-central Africa, with anomalous westerly winds across southern Africa between 10°-20°S, and 3) anomalous upper-level easterly winds in association with a poleward extension of the subtropical high (Fig. T22) and a corresponding poleward shift of the main upper-level westerly winds to south of the continent (Fig. T21).Overall, these conditions were associated with low-level confluence extending southwestward along the Mozambique coast, and with anomalous large-scale convergence across southeastern Africa and the Mozambique Channel. Collectively, these conditions represented an enhanced monsoonal circulation over southeastern Africa.

NOAA/ National Weather Service
NOAA Center for Weather and Climate Prediction
Climate Prediction Center
5830 University Research Court
College Park, Maryland 20740
Page Author: Climate Prediction Center Internet Team
Page last modified: August 24, 2007
Information Quality
Privacy Policy
Freedom of Information Act (FOIA)
About Us
Career Opportunities