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 2007

       1. Northern Hemisphere  

            The 500-hPa height field during November featured an anomalous zonal wave-3 pattern, with positive anomalies over the western half of the U.S. , the high latitudes of the North Atlantic Ocean, and central Russia , and negative anomalies over the high latitudes of the central North Pacific Ocean, eastern Canada , and eastern Europe (Fig. E9). At 200-hPa cyclonic circulation anomalies were evident in the subtropics of both hemispheres across the eastern half of the tropical Pacific Ocean (Figs. T21, T22). This pattern is consistent with La Niña.

            The main surface temperature departures during November reflected warmer than average conditions in Alaska , the southwestern U.S. , and central Russia (Fig. E1). The main precipitation anomalies included below average totals across much of the United States and portions of eastern China (Fig. E3).  

a. North Pacific/ North America

Regional aspects of the anomalous zonal wave-3 pattern at 500-hPa included below average heights over the high latitudes of the North Pacific, and eastern Canada, and above-average heights across the western half of the United States extending northward into extreme western Canada (Fig. E9).  This pattern was associated with anomalous southerly flow into Alaska , which led to well above-average surface temperatures across much of the state. The largest departures were observed in central Alaska , where temperatures were more than 5°C above average.

In the continental U.S. , the anomalous upper-level ridge contributed to above-average temperatures in the Southwest. Also, a broad area of anomalous upper-level convergence (Fig. T23) and descending motion between the anomalous ridge and the downstream trough axis led to below-average precipitation across large portions of the country (Fig. E3). Area-averaged totals were in the lowest 10^th percentile of occurrences in many regions, including the Pacific Northwest, Inter-Mountain, Great Plains, Midwest , Ohio Valley, Southeast, Gulf Coast , and mid-Atlantic regions (Fig. E5). Ongoing precipitation deficits further exacerbated drought conditions in large portions of the Inter-mountain region and the southeastern U.S.

     2. Southern Hemisphere     

    The 500-hPa height field during November featured an anomalous zonal wave-3 pattern, with above-average heights in the area south of Australia , over the high latitudes of the eastern South Pacific, and over the central South Atlantic, and below-average heights in the area southeast of New Zealand , over the western South Atlantic, and over the central Indian Ocean (Fig. E15). At 200-hPa positive (cyclonic) streamfunction anomalies covered the central and eastern tropical South Pacific Ocean (Fig. T22). This pattern reflected an enhanced mid-Pacific trough consistent with La Niña (Fig. T21).

The South African rainy season extends from October to April, and is often stronger than average during La Niña. During November, above-average totals were observed in the extreme southern and northeastern parts of the monsoon region. Area-averaged totals for the entire monsoon region were in the upper 80^th percentile of occurrences for the second straight month (Fig. E4).