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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

APRIL 2016

1

Extratropical Highlights –April 2016

 

1. Northern Hemisphere

The 500-hPa circulation during April featured above-average heights across the subtropical North Pacific Ocean, the western U.S., the high latitudes of the North Atlantic, and the Mediterranean Sea (Fig. E9). The circulation also featured below-average heights across the high latitudes of the North Pacific, eastern Canada, and the eastern North Atlantic.

At 200-hPa, a significant El Niño response continued in the streamfunction (Fig. T22) and wind (Figs. T21) fields. This response featured anticyclonic anomalies over the central subtropical North and South Pacific straddling the region of enhanced convection (Fig. T25), along with cyclonic anomalies at higher latitudes of the North and South Pacific. This pattern was associated with an eastward extension of the East Asian jet steam to well east of the date line. This jet stream pattern represents major dynamical and kinematic changes in the mid- and upper-level circulation during El Niño, and it also represents a fundamental manner in which El Niño’s circulation impacts are communicated downstream.

The main land-surface temperature signals during April included a continuation of above-average temperatures across much of North America and central Asia (Fig. E1). The main precipitation signals included above-average totals in the U.S. Plains and Gulf Coast states, southwestern Europe, and China (Fig. E3).

 

a. North Pacific/ North America

At 500-hPa, the circulation during April featured above-average heights across the subtropical North Pacific Ocean and western North America, and below-average heights over the high latitudes of the North Pacific (Fig. E9). At 200-hPa, the circulation featured anticyclonic streamfunction anomalies across the subtropical central North Pacific in association with El Niño, along with cyclonic anomalies over the high latitudes of the North Pacific (Fig. T22). This pattern was associated with an eastward extension of the East Asian jet steam to well east of the date line, along with an amplified jet exit region upstream of the western U.S. (Fig. T21). This anomalous jet exit region is indicated by the combination of southwesterly wind anomalies upstream of California north of the mean jet axis and northwesterly/ northerly wind anomalies upstream of Mexico south of the mean jet axis.

This overall circulation was associated with an extensive onshore flow of marine air into Canada and Alaska, and with increased storminess across the central and southern U.S. These conditions were associated with well above-average surface temperatures in Alaska and western Canada (Fig. E1), and with well above-average precipitation in the U.S. Great Plains and Gulf Coast states (Fig. E3). Area-averaged precipitation totals in the Great Plains were the largest for April in the 1979-present record. Area-averaged totals in the Gulf Coast region were above the 80th percentile of occurrences for the second straight month (Fig. E5).

According to the U.S. Drought Monitor, exceptional or extreme drought continued across central California during April, while extreme drought persisted in western Nevada. However, the spatial coverage of these drought areas continued to decrease during April. Also, moderate drought persisted in southeastern Oregon, and in the southern half of both New Mexico and Arizona.

 

 

b. Eurasia

The 500-hPa circulation during April featured above-average heights over central Siberia and a broad trough over China (Fig. E9). These conditions were associated with a continuation of well above-average surface temperatures in central Asia (Fig. E1). They were also associated with well above-average precipitation in China, with much of central and southern China recording totals above the 70th and 90th percentile of occurrences (Fig. E3). Above-average totals in China were the largest in the 1979-present record for April (Fig. E4).

 

2. Southern Hemisphere

The mean 500-hPa circulation during April featured above-average heights over the high latitudes of the eastern South Pacific, eastern Australia and New Zealand, across the South Atlantic, and over the eastern Indian Ocean (Fig. E15). At 200-hPa, the El Niño response was evident in the ongoing pattern of anticyclonic streamfunction anomalies across the central subtropical South Pacific Ocean, and with cyclonic anomalies over the central South Pacific (Fig. T22).

The main surface temperature signals during April included significantly above-average temperatures in southern Africa, Madagascar, and eastern Australia (Fig. E1). The main precipitation signals during April included well above-average totals in southern South America, and below-average totals in eastern and northern Australia (Fig. E3).

The South African rainy season extends from October to April. During April, the area as a whole recorded near-normal precipitation (Fig. E4). Overall, the 2015-16 South African rainy season was below normal, which is typical of El Niño. Below-average precipitation was recorded from October-February, above-average precipitation was recorded in March, and near-normal precipitation was recorded in April.

 

 

 


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