1. Northern Hemisphere
The 500-hPa height pattern
during June featured positive anomalies over the high latitudes of the
central North Pacific,
Greenland
, the polar region, and
Mongolia
, and negative anomalies in the
Gulf of Alaska
, across the central
North Atlantic
, and western
Russia
(Figs. E9, E11).
At 200-hPa, cyclonic streamfunction anomalies were evident across the
subtropical
Pacific Ocean
in both hemispheres. This pattern reflected a weakening of the mean
subtropical ridges over the western Pacific and a strengthening of the mean
mid-Pacific troughs in both hemispheres (Fig. T22).
These conditions are consistent with suppressed convection across the
equatorial Pacific during the month (Fig. T25).
The main surface temperature
departures during June reflected above-average temperatures in the eastern
United States
,
Europe
, and most of eastern
Asia
, and below-average temperatures in northwestern and central
Russia
(Fig. E1). The main precipitation anomalies
included above average totals in the central
U.S.
and northwestern
Europe
, and below average totals across the northeastern
U.S.
and eastern
Mongolia
(Fig. E3).
a.
North America
The 500-hPa circulation
pattern during June featured an enhanced ridge over the southwestern
United States
and a broad trough over the
Gulf of Alaska
. The anomalous ridge appears to partly reflect a downstream response to the
very persistent and amplified mid-Pacific trough at 200-hPa centered near
Hawaii
(Fig. T22). This overall pattern was
associated with enhanced precipitation in western
Canada
(Fig. E3), and with above-average
temperatures across the southwestern
United States
(Fig. E1).
Farther downstream, the mean
upper-level trough position was shifted eastward to the western
North Atlantic
(Figs. E9, E11),
resulting in anomalous upper-level convergence and descending motion across
the mid-Atlantic and northeastern
United States
(Fig. T23). In both regions, area-averaged
totals were in the lowest 20th percentile of occurrences for the
second straight month (Fig. E5). Although
the southeastern
U.S.
recorded near-average totals during June, long-term precipitation deficits
in that region meant a continuation of extreme drought from
Mississippi
to western
Georgia
and across the southern half of
Tennessee
.
In contrast the southern
Plains states recorded well above-average precipitation for the second
straight month. For the
Great Plains
region as a whole, area-averaged totals have been above the 90th
percentile of occurrences in five of the last seven months.
b.
Eurasia
The 500-hPa circulation
pattern during June featured a north-south dipole of height anomalies across
the
North Atlantic
, with positive anomalies at high latitudes and negative anomalies farther
south (Fig. E9). This pattern reflected a
strong high-latitude blocking ridge, and a southward shift of the mean
upper-level westerlies to central and southern
Europe
. Farther downstream, a broad ridge spanned eastern Europe and an anomalous
trough was centered over northwestern and central
Russia
. The surface temperature anomaly patterns reflected these circulation
features, with temperatures in the upper 90th percentile of
occurrences across eastern Europe and temperatures in the lowest 30th
percentile of occurrences in portions of northwestern and central
Russia
(Fig. E1).
In
Asia
, a persistent pattern of positive height anomalies at 500-hPa was
associated with well above-average temperatures across eastern
Mongolia
and northern
China
, as monthly departures exceeding the 90th percentile of
occurrences in many regions. Much of this region also recorded above-average
temperatures in May.
2. Southern Hemisphere
The 500-hPa height
anomaly pattern during June featured a pronounced zonal wave-3 pattern, with
positive anomalies south of
Australia
, over the central South Pacific, and south of
Africa
,
and negative anomalies across
Australia
, most of the central
South Atlantic Ocean
, and the central
Indian Ocean
(Fig. E15). The
circulation across
Australia
featured a ridge in the southwest and a strong trough
in the southeast. This pattern contributed to below-average precipitation in
the southwest and above-average precipitation along the eastern seaboard (Fig.
E3). This circulation, in combination with the
strong ridge south of the continent, was also associated with an anomalous
southerly flow of cool marine air at 850-hPa into southeastern and
south-central
Australia
(Fig. T20). As a
result, much of central and eastern Australia recorded well below-average
temperatures(2°-3°C below average), with large interior portions of the
continent recording values in the lowest 10th percentile of
occurrences (Fig. E1).
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