1. Northern Hemisphere
During November the 500-hPa
circulation pattern featured positive height anomalies over eastern
, the high latitudes of the North Pacific, the southwestern and central
, and south-central
, and negative height anomalies over western
, and south-central
(Figs. E9, E11).
Over the North Pacific and
, the anomalies reflected the negative phases of the Pacific/ North American
(PNA) and West Pacific (WP) teleconnection patterns (Table E1,
Fig. E7). Over the
, the circulation reflected the ongoing positive phase of the East Atlantic
(EA) teleconnection pattern. This pattern has been a prominent feature of
the circulation since April. In the subtropics, the 200-hPa circulation was
consistent with El Niņo conditions, with anticyclonic streamfunction
anomalies in both hemispheres flanking the regions of enhanced convection
over central and east-central Pacific, and cyclonic streamfunction anomalies
in association with suppressed convection across
The main surface temperature
departures during November reflected warmer-than-average conditions across
, and southeastern
, and cooler-than-average conditions over western
(Fig. E1). The main precipitation anomalies
included above-average totals in the northwestern, mid-Atlantic, and
northeastern states, and below-average totals in the southwestern, Plains,
and Intermountain states, south-central
, and southeastern
(Figs. E3, E5, E6)
In the subtropics, the mean
200-hPa circulation during November was consistent with El Niņo, with
anticyclonic streamfunction anomalies flanking the regions of enhanced
convection over the central and east-central equatorial Pacific (Fig. T22).
In the extratropics the 500-hPa circulation featured a high-latitude
blocking pattern (Fig. E9), which projected
onto the negative phases of both the PNA and WP teleconnection patterns (Table
E1, Fig. E7). The
surface temperature anomaly pattern generally followed the 500-hPa height
anomalies (Fig. E1). Below-average
temperatures were observed downstream of the blocking ridge across eastern
, while above-average temperatures from the southwestern
coincided with a broad area of positive height anomalies.
A strong under-cutting of the
blocking ridge and a persistent downstream trough over western
were present during November. This pattern led to an amplified and
persistent storm track across southwestern
and the Pacific Northwest U.S., resulting in well above-average
precipitation in these regions (Fig. E3).
Monthly totals in the
were above the 90th percentile of occurrences, following four
consecutive months of well below-average precipitation (Fig. E5).
Because the storm track during November was focused in the north, the
Southwestern, Intermountain, and
recorded generally less than 25% of normal precipitation (Fig. E6).
This is the first time since July that monthly precipitation totals were
below average in the Southwest and Intermountain regions.
The 500-hPa circulation
pattern during November featured below-average heights near
and above-average heights over south-central
. Enhanced westerlies south of the mean upper-level trough contributed to
well above-average surface temperatures during November. Monthly
temperatures across the continent generally exceeded the 90th
percentile of occurrences, with the largest departures of 2°-3°C observed
Well above average sea-surface
temperatures were again observed across the high latitudes and tropical
latitudes of the
during November. This pattern is associated with the ongoing warm phase of
the Atlantic multi-decadal mode that began approximately in 1995, and with
the warming trend in global temperatures during the past 100 years.
An anomalous upper-level
trough was again centered over
during November. This feature reflected a weakening of the mean subtropical
ridge and is consistent with the El Niņo-related pattern of suppressed
(Fig. T25). Surface temperatures across
were well above average, with departures in central
exceeding the 90th percentile of occurrences.
2. Southern Hemisphere
The mean 500-hPa circulation pattern during November
featured above-average heights across southern
and south of
, and below-average heights south of
. (Fig. E15). In the subtropics,
anticyclonic streamfunction anomalies extended across the South Pacific
consistent with ongoing El Niņo conditions.
, an enhanced mid-and upper-level ridge contributed to a continuation of
anomalously warm and dry conditions. The temperature departures were
especially significant in the west, where monthly values were in the upper
90th percentile of occurrences. The most significant
precipitation anomalies occurred in the east and northeast, where totals
were in the lowest 10th percentile of occurrences. While these
below average totals are consistent with the El Niņo, they were accentuated
by large-scale subsidence downstream of the upper-level ridge axis.
, surface temperatures were also above average during November, and
precipitation was near average. To date, the 2006-07 South African rainy
season, which extends from October to April, has featured below-average
precipitation in October and near-average totals in November.