Extratropical Highlights –January 2016

 

1. Northern Hemisphere

The 500-hPa circulation during January featured above-average heights across the polar region and across both the subtropical North Pacific and Atlantic Oceans and Africa. The circulation also featured below-average heights across the central North Pacific and Atlantic Oceans and Europe (Fig. E9). This overall anomaly pattern projected strongly onto the positive phase of the Pacific/ North American teleconnection pattern (PNA, +1.9) and also onto the negative phase of the Polar/ Eurasia Pattern (-2.6) (Table E1., Fig. E7). A positive PNA pattern is a typical response to El Niño.

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 eastern half of the subtropical North and South Pacific, straddling the region of enhanced convection (Fig. T25), along with cyclonic anomalies at higher latitudes of the North Pacific. This pattern was associated with an eastward extension of the wintertime 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 January included above-average temperatures across Canada, western Europe, and eastern Siberia (Fig. E1). The main precipitation signals included above-average totals in the northwestern U.S., the Gulf Coast region of the U.S., western Europe, and eastern China. Below-average totals were recorded across central U.S. and north-central Russia (Fig. E3).

 

a. North Pacific/ North America

At 500-hPa, the circulation during January featured above-average heights across the subtropical North Pacific Ocean and western Canada, and below-average heights over the central and high latitudes of the North Pacific and the southeastern U.S. (Fig. E9). At 200-hPa, the circulation featured anticyclonic streamfunction anomalies across the subtropical eastern North Pacific in association with El Niño, along with negative anomalies over the high latitudes of the North Pacific (Fig. T22). This pattern was associated with an eastward extension of the wintertime East Asian jet steam to well east of the date line. It was also associated with enhanced westerly winds throughout the troposphere in the western U.S. (Figs. T20, T21). These conditions reflected a strong positive PNA pattern and contributed to increased storminess in the western U.S., both of which are typical of El Niño.

This circulation contributed to anomalously warm surface temperature across most of Canada, with many areas again recording departures in excess of +5^oC and in the upper 90^th percentile of occurrences (Fig. E1). It also contributed to above-average precipitation in the northwestern and Gulf Coast regions of the U.S., and to below-average precipitation in the central U.S. (Fig. E3).

According to the U.S. Drought Monitor, drought conditions were lessened in Washington, Oregon, and Idaho, while exceptional drought continued across central California and western Nevada. Severe drought persisted in south-central and eastern Oregon, while extreme drought persisted in western Montana.

 

b. North Atlantic

The 500-hPa circulation during January featured above-average heights over northern Africa and below-average heights across the eastern North Atlantic and Europe. These conditions were associated with an exceptionally strong southwesterly flow of jet stream winds and low-level winds into western Europe, which resulted in anomalously warm and wet conditions in the region (Figs. E1, E3, E4).

 

c. China

Well above-average precipitation was recorded in eastern China during January (Fig. E3), with totals reaching near-record levels (1971-present record) for the third straight month (Fig. E4). The continued surplus precipitation was again linked to an amplified 200-hPa trough over China (Fig. T22).

 

2. Southern Hemisphere

The mean 500-hPa circulation during January featured above-average heights south of Australia, south of Africa, and over the high latitudes of the eastern South Pacific. The circulation also featured below-average heights over the central South Pacific and throughout the polar region (Fig. E15). At 200-hPa, a significant El Niño response was evident in the ongoing pattern of anticyclonic streamfunction anomalies across the eastern half of the South Pacific Ocean (Fig. T22).

The main precipitation signals during January included above-average totals across southern Australia, with departures exceeding the 90^th percentile of occurrences in both the southwest and southeast (Fig. E3).

Consistent with El Niño, below-average precipitation was again observed in the South African monsoon region (Fig. E4). The South African rainy season lasts from October to April. To date, the region has received well below-average precipitation in every month from October-January.