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Climate Diagnostics Bulletin
Climate Diagnostics Bulletin - Home Climate Diagnostics Bulletin - Tropics Climate Diagnostics Bulletin - Forecast

 

  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 2013

1

Extratropical Highlights November 2013

 

1. Northern Hemisphere

The 500-hPa circulation during November featured below-average heights throughout the polar region, and a zonal wave-3 pattern of height anomalies in the middle latitudes (Figs. E9, E11). This wave-3 pattern reflected above-average heights over the high latitudes of the North Pacific, the eastern North Atlantic and central Russia, and below-average heights over eastern North America, Europe and Japan.

The main land-surface temperature signals during November included well above-average temperatures across eastern Europe and central Asia, and below-average temperatures in the eastern U.S. (Fig. E1). The main precipitation signals included above-average totals in the southern U.S. and Mexico, and below-average totals in the northwestern U.S., Europe, Scandinavia and southwestern Russia (Fig. E3).

 

a. North Pacific/ North America

The mean 500-hPa circulation during November featured above-average heights over the high latitudes of the North Pacific, and below-average heights over eastern Canada and the north-central U.S. (Fig. E9). The circulation also featured positive streamfunction anomalies at 200-hPa across the southeastern U.S. and Gulf of Mexico (Fig. T22).

Over the central and eastern North Pacific, this overall circulation pattern reflected three main features. First, it reflected a complete disappearance of the mean Aleutian Low and a corresponding northward shift of the mean jet core, with the mean jet axis entering North America in the vicinity of west-central Canada (Fig. E10). Second, it reflected an amplification of the mean Hudson Bay trough, along with enhanced northwesterly flow across Canada and the north-central U.S. Third, it reflected an enhanced ridge and strong confluent flow across the southeastern U.S., which put that region in the right-entrance region of the jet stream.

This overall circulation pattern contributed to below-average temperatures across the eastern one-third of the U.S., with much of the region recording departures in the lowest 30th percentile of occurrences (Fig. E1). It also contributed to above-average precipitation in the southern U.S., Mexico, and Gulf of Mexico (Fig. E3).

In the southwestern U.S., well above-average precipitation during the past three months (Fig. E5) has helped to considerably lessen the severity of ongoing drought conditions. However, much of that region still recorded moderate or severe drought at the end of November. Also, moderate or severe drought persisted across large portions of the upper Midwest, including Iowa, Minnesota, Illinois, western Wisconsin, and northern Missouri.

 

b. North Atlantic/ Eurasia

The mean 500-hPa circulation featured above-average heights over the eastern North Atlantic and central Russia, and below-average heights over Greenland/ Scandinavia and the Mediterranean Sea (Fig. E9). This pattern was associated with a pronounced spilt-flow configuration north of Great Britain. The northern branch of this split flow brought milder Atlantic air across northern Europe and well into northern Russia (Fig. E10), while the southern branch brought a southwesterly flow of Mediterranean air into south-central Russia. This combination contributed to well above-average temperatures across central Asia, with many areas recording departures (exceeding +5oC) in the upper 90th percentile of occurrences (Fig. E1).

The southern branch of flow also brought sinking motion and below-average precipitation to large portions of Europe (Fig. E1). November marks the fifth consecutive month of below-average precipitation for both northern and southern Europe (Fig. E4).

 

2. Southern Hemisphere

The mean 500-hPa circulation during November featured a zonal wave-1 pattern of height anomalies over Antarctica, and above-average heights in the middle latitudes extending from the south of Australia to South America (Fig. E15).

Over eastern Australia, the 200-hPa circulation featured cyclonic streamfunction anomalies and an amplified trough (Fig. T22). This pattern was associated with well below-average precipitation in southeastern Australia, which was situated upstream of the mean trough axis (Fig. E3). In the north and northeast, above-average precipitation during November followed six consecutive months of below-average totals and three straight months with totals in the lowest 20th percentile of occurrences (Fig. E4).

The South African rainy season lasts from October to April. During November 2013, rainfall for the region was below average (Fig. E4), and many interior areas recorded totals in the lowest 30th percentile of occurrences (Fig. E3). Last month, the region recorded slightly above-average totals.

The Antarctic ozone hole typically develops during August, reaches its peak aerial extent in September and October, and dissipates rapidly during November. The 2013 ozone hole dissipated in mid-November, after being smaller than the 2003-2012 average during August-October (Fig. S8). This marks the second straight year with a below-average size of the ozone hole.

 


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