1. Northern Hemisphere
The 500-hPa circulation during May 2003 featured a persistent pattern of
positive height anomalies over the central North Pacific, Mexico, and
across the low latitudes of the North Atlantic extending eastward to
Turkey, and negative height anomalies over the high latitudes of the
eastern North Atlantic and the polar region (Figs. E10,
E12). The prominent temperature anomalies
during May included warmer-than-average temperatures across the southern
United States, eastern Canada, Europe, and both western and central Russia,
and cooler-than-average conditions across the northern United States (Fig.
E1). Prominent precipitation anomalies during the month (Fig.
E3) included above-average totals over the eastern United States
and Scandinavia, and below-average totals over the Gulf Coast region of the
United States, northeastern Canada, and portions of southern Europe (Fig.
a. Pacific/North America
The upper-level circulation during May featured above-average heights
across the western and central North Pacific, in association with a strong
negative phase of the North Pacific teleconnection pattern (Table
E1). These positive anomalies extended across the eastern Pacific
during the first half of the month (Figs. E13, A2.1),
followed downstream by an amplified trough over the western U.S. and
above-normal heights across the southeast (Fig.
These anomaly patterns were reversed during the second half of May, as
indicated by a transition from the negative phase to the strong positive
phase of the Pacific/ North American (PNA) teleconnection pattern (Fig.
E8). During this latter period the mean upper-level ridge was
located over the southwestern states, and an amplified upper-level trough
was centered over the eastern states.
For the month as a whole these circulation patterns contributed to well
above-average rainfall across the eastern United States, with totals
exceeding the 90th percentile in the Southeast, Mid-Atlantic,
and Ohio Valley regions, and exceeding the 80th percentile in
the Great Lakes and Midwest regions (Figs. E3, E5).
Significantly below-average rainfall was recorded in the Gulf coast region,
with totals below the 10th percentile observed over southeastern
Texas and southern Louisiana. The largest positive surface temperature
anomalies during May were observed across the South (+1°
to +2°C), with and the largest negative
anomalies (-1°C) were observed in the
The upper-level circulation during May featured a persistent trough at
high latitudes of the eastern North Atlantic and an amplified ridge
extending across the subtropical North Atlantic to the Caspian Sea (Fig.
E10). This circulation contributed to a warmer than average
conditions across Europe, with temperatures exceeding the 90th
percentile in southeastern Europe and exceeding the 70th
percentile elsewhere (Fig. E1).
2. Southern Hemisphere
In the Southern Hemisphere the 500-hPa circulation during May featured
above-average heights across the central latitudes of the South Pacific,
and in the areas south of the three continents, and below-average heights
over the high latitudes of the South Pacific and the central Indian Ocean (Fig.
E16). Surface temperatures were near normal across southern Africa
and most of Australia during May, and generally above average over southern
South America (Fig. E1).
Most of extratropical South America experienced well above-average
precipitation during May, with totals exceeding the 90th
percentile over much of Argentina (Fig. E3).
Eastern Australia experienced a continuation of below-average rainfall
during May, with drier-than-average conditions also observed over most of
the southern half of the continent.