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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

FEBRUARY 2015

1

Extratropical Highlights February 2015

 

1. Northern Hemisphere

The mean 500-hPa circulation during February featured an extensive anomalous wave pattern extending from the western North Pacific to western Asia (Fig. E9). Regional aspects of this pattern included above-average heights across the high latitudes of the North Pacific, western North America, the central North Atlantic, and western Russia. Below-average heights were observed over the central North Pacific, eastern North America, Greenland, and southern Europe.

At 200-hPa, anti-cyclonic streamfunction anomalies in both hemispheres over the central subtropical Pacific reflected eastward extensions of the mean subtropical ridges (Fig. T22). These conditions appear to be linked to enhanced convection over the central equatorial Pacific (Fig. T25).

The main land-surface temperature signals during February included above-average temperatures across Alaska, western North America, Scandinavia, and most of Asia, and below-average temperatures across eastern North America (Fig. E1). The main precipitation signals included above-average totals in the eastern U.S. and southern Europe, and below-average totals in Southern California, the Gulf Coast and Midwestern regions of the U.S., and northeastern Europe (Fig. E3).

 

a. North Pacific/ North America

The mean 500-hPa circulation during February featured a north-south dipole pattern of height anomalies over the North Pacific, and an anomalous ridge-trough pattern across North America (Fig. E9). Over the North Pacific, these conditions were associated with an eastward extension of the east Asian Jet (Fig. T21), which was linked to an eastward extension of the mean subtropical ridge to well east of the date line (Fig. T22). These conditions appear to be coupled to enhanced convection over the central equatorial Pacific (Fig. T25).

Over North America, the 500-hPa circulation featured an amplified ridge in the west and an amplified trough in the east. This pattern was associated with above average surface temperatures across western North America and Alaska, with the largest departures (exceeding +4oC) observed in western Alaska and the west-central U.S. (Fig. E1). The pattern was also associated with exceptionally cold surface temperatures across eastern North America, with much of the eastern half of the U.S. recording departures in the lowest 10th percentile of occurrences.

Monthly precipitation totals in North America (Fig. E3) were above-average in the mid-Atlantic and northeastern regions of the U.S., locations situated downstream of the mean upper-level trough axis. In contrast, monthly totals were below average in southern California and portion of the U.S. Gulf Coast.

Consistent with these conditions, the U.S. Drought Monitor indicated a continuation of exceptional drought in central/ southern California and western Nevada, with extreme drought extending northward into Oregon and southwestern Idaho. Exceptional or extreme drought also continued in north-central Texas and large portions of western Oklahoma.

 

b. Eurasia

The 500-hPa circulation featured an extensive north-south dipole pattern of height anomalies across the North Atlantic and western Russia, with above-average heights in the middle latitudes and below-average heights extending from eastern Canada to central Siberia (Fig. E9). This pattern was associated with an extensive southwesterly flow of milder air into northern Europe for a second straight month (Fig. E10). This warmth contributed to well above-average surface temperatures across all of central Asia, with much of the region recording monthly departures exceeding 5oC (Fig. E1).

 

2. Southern Hemisphere

The mean 500-hPa circulation during February featured an anomalous zonal wave-3 pattern, with above-average heights south of Africa and eastern Australia and also over the high latitudes of the eastern South Pacific (Fig. E15). Below-average heights were observed over much of Antarctica. At 200-hPa, cyclonic streamfunction anomalies were observed east of Australia and across southern Africa (Fig. T22). Over Australia, the resulting amplified wave pattern contributed to an extensive area of descending motion and suppressed precipitation across the eastern half of Australia (Fig. E3).

The South African rainy season lasts from October to April. Rainfall during February was below average for the region as a whole (Fig. E4), with the main deficits recorded across southern Africa (Fig. E3). The suppressed rainfall appears to be linked to an anomalous upper-level trough centered over and west of southern Africa (Fig. T22). To date, the South African rainy season was below average during October- November and January- February. Rainfall was above average in December (Fig. E4).

 

 


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