Extratropical Highlights – November 2014

 

1. Northern Hemisphere

The 500-hPa circulation during November exhibited two distinct anomalous wave patterns (Fig. E9). The first was a 3-celled pattern extending from the central North Pacific to eastern North America. The second was a 4-celled pattern extending from the central North Atlantic to central Siberia. Regional aspects of this circulation included a highly amplified ridge-trough pattern across North America, and a blocking-type pattern centered over Scandinavia.

The overall height anomalies projected onto a record positive phase of the East Pacific (+3.2) teleconnection pattern, and also onto strong positive phases of the East Atlantic/ Western Russia (+1.1), and Scandinavia (+1.8) teleconnection patterns (Table E1, Fig. E7).

The main land-surface temperature signals during November included above-average temperatures in Alaska and Europe, and below-average temperatures across central Canada and the eastern half of the United States (Fig. E1). The main precipitation signals included above-average totals in the northwestern and southeastern U.S. and southwestern Europe, and below-average totals in the central and northeastern U.S., northeastern Europe, and western Russia (Fig. E3).

 

a. North Pacific/ North America

The mean 500-hPa circulation during November featured an anomalous wave pattern with above-average heights over western North America and below-average heights over the central North Pacific and the eastern half of North America (Fig. E9). These anomalies reflected a record positive phase of the East Pacific (+3.2) teleconnection pattern, which exceeded its previous record strength (+2.1 observed during November 1976) by more than a full standard (Table E1, Fig. E7, ftp://ftp.cpc.ncep.noaa.gov/wd52dg/data/indices/epnp_index.tim).

Regional features of this pattern included an amplified ridge over western North America extending into the polar region, and a very strong Hudson Bay trough. This combination was associated with an extensive and sustained flow of polar air into central North America (Figs. E8, E10), resulting in well below-average temperatures across central Canada and the eastern half of the United States (Fig. E1). The most significant departures were observed in the midwestern U.S., where monthly mean temperatures were in the lowest 10^th percentile of occurrences.

The precipitation patterns across the North America also reflected the strength and position of the mean ridge-trough axes, with above-average totals observed in the southeastern U.S., and below-average totals recorded in Alaska, western Canada, and the central and northeastern U.S. (Fig. E3).

According to the U.S. Drought Monitor, a massive area of exceptional drought continued in central/ southern California and western Nevada, with extreme drought extending northward into Oregon. Exceptional or extreme drought was also observed in northeastern Texas and south-central Oklahoma.

 

b. Europe/ Russia

The 500-hPa circulation featured an anomalous wave pattern extending from the eastern North Atlantic to central Russia, and included a blocking ridge over Scandinavia and amplified troughs over the eastern North Atlantic and central Russia (Fig. E9). This pattern projected onto the positive phases of the East Atlantic/ Western Russia (+1.1) and Scandinavia (+1.8) teleconnection patterns (Table E1, Fig. E7)

This pattern impacted surface temperatures and precipitation Europe and western Russia. For example, the associated enhanced southwesterly flow of mild marine air across Europe contributed to well above-average surface temperatures, with many parts of Europe recording departures in the upper 90^th percentile of occurrences (Fig. E1). Central and southern Europe were situated downstream of the mean trough axis, and recorded above-average precipitation with departures in the upper 70^th percentile of occurrences (Fig. E3). In contrast, monthly precipitation totals were well below average in northeastern Europe and western Russia, regions located downstream of the mean ridge axis.

 

2. Southern Hemisphere

The mean 500-hPa circulation during November featured above-average heights over southeastern Australia, the high latitudes of the central South Pacific, and south of Africa, and below-average heights across the high latitudes of the Indian Ocean and in the vicinity of New Zealand (Fig. E15).

In eastern Australia, the amplified ridge led to a continuation of well above average surface temperatures, with much of the region recording departures in the upper 90^th percentile of occurrences (Fig. E1). Most of southeastern and eastern Australia also recorded a continuation of exceptionally dry conditions in response to anomalous sinking motion downstream of the mean ridge axis (Fig. E3).

The South African rainy season lasts from October to April. Rainfall for the region as a whole was below average during October and November 2014(Fig. E4), with the largest deficits recorded in the northeast including northern Mozambique and Madagascar (Fig. E3).

The Antarctic ozone hole typically develops during August, reaches its peak aerial extent in September and October, and dissipates by early December. Overall, the 2014 ozone hole was slow to develop during August, was near the 2004-2013 mean size during September through November, and dissipated at the end of November (Fig. S8, top). This near-average size follows two consecutive years in which ozone hole was smaller than average.