A strong inter-hemispheric symmetry of upper-level
circulation features was again evident during July (Fig. T22).
This pattern featured positive streamfunction anomalies across much of the middle
latitudes of the Northern Hemisphere, and across the subtropical latitudes of the Southern
Hemisphere from Australia westward to South America. It also featured anomalous cyclonic
circulation anomalies across the low latitudes of both hemispheres over the central
Pacific. These conditions are consistent with the ongoing pattern of tropical rainfall and
tropical convective activity, which featured an amplified Southeast Asian monsoon system (Fig. T25), and above-normal rainfall across the Sahel region of
northern Africa and over large portions of the equatorial Indian Ocean.
a. North America
During July the western United States and Canada were situated downstream of an
upper-level trough, while most of eastern North America remained under the influence of an
amplified upper-level ridge (Fig. E9). This circulation
contributed to below-normal temperatures over large portions of the western United States
and Canada (Fig. E1) and to above-normal monsoonal rains in
the southwestern United States (Figs. E3, E5).
Farther east, extremely warm temperatures again dominated eastern North America during
the month, with values in some regions exceeding the 90th percentile. Extreme
dryness accompanied this warmth over much of the eastern seaboard of the United States,
with record low area-averaged totals observed in the Northeast. In fact, record low
rainfall has been observed in the Northeast during five of the last nine months (Fig. E5). Record low accumulated rainfall totals for the
April-July period have also been observed in portions of the mid-Atlantic region, where
severe drought conditions prevailed during July.
b. North Atlantic, Eurasia
An anomalous anticyclonic circulation again prevailed across southern Europe and
northern Africa during July, resulting in a continuation of extremely warm temperatures
(exceeding the 90th percentile) over much of the region (Fig.
E1). Abnormally warm temperatures (2°-4°C above normal) were also observed in
eastern Europe and western Russia during the month, as well as over most of eastern
Siberia. This warmth was consistent with the persistence of the anomalous anticyclonic
circulation at upper levels extending eastward from the North Atlantic to the western
Over southern and eastern China and the adjacent ocean waters, significantly
above-normal rainfall was observed during July. Since 1 June 1999, 550 mm to 1050 mm has
fallen across much of the region, which is 140 mm to 690 mm above the long-term mean. This
rainfall was aided by increased typhoon activity, and by strong intraseasonal (MJO)