Extratropical Highlights

  Table of Indices  (Table 3)

  Global Surface Temperature  E1

  Temperature Anomalies (Land Only)  E2

  Global Precipitation  E3

  Regional Precip Estimates (a)  E4

  Regional Precip Estimates (b)  E5

  U.S. Precipitation  E6

  Northern Hemisphere

  Southern Hemisphere

  Stratosphere

  Appendix 2: Additional Figures

Extratropical Highlights

NOVEMBER 2008

1. Northern Hemisphere

The 500-hPa height pattern during November 2008 featured positive anomalies over western North America , the central North Atlantic , and central Russia , and negative anomalies over Alaska , the eastern U.S. , and southwestern Europe (Fig. E9). The pattern of surface temperature anomalies closely resembled the mid-level circulation, with well above average temperatures across western North America and central/ northern Russia , and below-average temperatures in western Alaska , the southeastern U.S. , southwestern Europe , and northwestern Africa (Fig. E1). The main precipitation signals during November included below average totals in the central and eastern U.S. , and in portions of both southwestern and central Russia (Fig. E3)

a. North Pacific/ North America

The 500-hPa circulation during November featured an amplified wave pattern that extended from Alaska to Europe . Aspects of this pattern included an amplified ridge across western North America. , and amplified troughs over Alaska and the eastern U.S.  (Fig. E9). The associated surface temperatures were above average across western North America , with the largest departures (3˚C – 5˚C) centered in western Canada . In contrast, temperatures were below-average in the southeastern quadrant of the U.S. , with departures in many areas in the lowest 30^th percentile of occurrences (Fig. E1). The pattern of precipitation anomalies also reflected the upper-air circulation, with below average precipitation seen across the central and eastern U.S. in the area upstream of the mean trough axis, and above average precipitation seen in western Canada upstream of the mean ridge axis (Fig. E3). 

           b. Eurasia

The 500-hPa circulation featured extensive areas of positive height anomalies over the central North Atlantic and central Russia , and negative height anomalies over southern Europe (Fig. E9). This overall pattern was associated with a significant poleward transport of heat into northern Europe , and with a pronounced northward shift of the mean jet stream across Scandinavia and Russia . These conditions contributed to a continuation of well above-average temperatures across central and northern Russia , and to a slower-than-normal development of the Siberian snow pack. This reduced snow cover likely contributed further to the anomalous warmth during the last two months.

  2. Southern Hemisphere

    The 500-hPa height field during November featured an anomalous zonal wave-3 pattern, with positive anomalies across the central Ocean basins and negative anomalies across the high latitudes of the North Pacific and southeastern Australia (Fig. E15). This pattern acted to expand equatorward the circumpolar vortex over the North Pacific sector (Fig. S8 middle), contributing to an exceptionally persistent ozone hole (Fig. S8 bottom).

    Land temperatures were generally above average across South America , with the largest departures (exceeding 3˚C) observed in Uruguay and east-central Argentina (Fig. E1). These regions also experienced exceptionally dry conditions during November (Fig. E3). In contrast, precipitation was above average over southeastern Brazil . This dipole pattern of rainfall anomalies was linked to a strong ridge centered off the east coast, which contributed to an extensive onshore flow at 850-hPa into southeastern Brazil (Fig. T20) and at the same time produced strong sinking motion over Uruguay .

    Much of Australia recorded above average precipitation during November, with the largest departures observed in the central and southern parts of the continent (Fig. E3). This enhanced precipitation was related to the anomalous mid-latitude circulation, occurring downstream of the mean upper-level trough and also within the left entrance region of the jet stream (Figs. T21, T22).

    In southern Africa , the rainy season extends from October through April. During November, rainfall was above average for the region as a whole, with area average totals exceeding the 80^th percentile of occurrences (Fig. E4). The most significant surpluses were recorded in the West, particularly in Namibia where totals exceeded the 90^th percentile (Fig. E3). In contrast, rainfall remained well below average in central Mozambique , following a slow start to the 2008-09 rainy season in October.