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HOME > Expert Assessments > Climate Diagnostics Bulletin > Extratropical Highlights
Extratropical Highlights - January 2007

1. Northern Hemisphere

During January the 500-hPa height pattern featured positive anomalies over the eastern North Pacific, the southeastern U.S. , the Mediterranean Sea , and eastern Siberia , and negative anomalies over Alaska and Scandinavia (Figs. E9, E11). In the subtropics, the 200-hPa streamfunction pattern featured cyclonic anomalies in both hemispheres across the tropical Pacific, indicating no discernible El Niņo signal (i.e., anticyclonic anomalies) on the upper-level circulation (Fig. T22).

The main surface temperature departures during January reflected warmer-than-average conditions across Canada , the eastern half of the U.S. , and nearly all of Eurasia (Fig. E1). For the entire Northern Hemisphere, monthly mean land surface temperatures were ~1.4°C above the 1971-2000 mean, reflecting a continuation of the exceptional warmth observed in December. The main precipitation anomalies during January included above-average totals in the south-central and central U.S. , southern Scandinavia , northeastern Europe , and western Russia , and below-average totals extending from the Mediterranean Sea eastward to Pakistan (Fig. E3).


a. Pacific/ North America

Despite ongoing weak El Niņo conditions, the upper-level circulation during January featured cyclonic anomalies across the eastern subtropical North Pacific (Fig. T22). The presence of strong and persistent positive height anomalies at 500-hPa over the eastern North Pacific is also inconsistent with El Niņo (Fig. E9). Therefore, the continued anomalous warmth across Canada and the eastern U.S. during January cannot easily be attributed to El Niņo.

Instead, enhanced westerlies and strong onshore flow north of the anomalous ridge resulted in exceptionally warm surface temperatures across Canada , with much of the country experiencing temperatures in the upper 70th percentile of occurrences (Fig. E1). The eastern U.S. also experienced above-average temperatures during the month, with departures of 2°-3°C recorded throughout the northeast and Great Lakes region. This anomalous warmth reflected the combination of a persistent upper-level ridge in the southeast, and reduced cold-air advection from Canada .  

The 500-hPa circulation pattern also featured a strong confluent flow over the south-central United States . Large-scale ascending motion in this region contributed to above-average precipitation from eastern Texas northeastward to the southern Great Lakes (Fig. E3). The most significant departures were observed in eastern Texas , where totals were in the highest 90th percentile of occurrences.


  b. North Atlantic / Europe

The 500-hPa circulation pattern during January featured below-average heights over Scandinavia and above-average heights across southern Europe and the Mediterranean Sea (Fig. E9). This pattern reflected a strong negative phase (-2.9) of the Scandinavia teleconnection pattern.  This anomaly pattern was associated with an extensive onshore flow of marine air across northern Europe and southern Scandinavia , which contributed to exceptionally warm surface temperatures and above-average precipitation throughout the region. Farther east, above-average heights and surface temperatures were also observed across central and northern Asia . As a result, temperatures were generally 3°-5°C above average from central Europe to Mongolia , with the largest departures (6°-8°C) recorded in central Russia .

2. Southern Hemisphere

The anomalous 500-hPa circulation pattern during January was fairly weak, with the main features being negative height anomalies over the high latitudes of both the central South Pacific and South Atlantic Oceans (Fig. E15). In the subtropics, cyclonic anomalies were observed across the eastern half of the South Pacific, which is opposite to what is typically found during El Niņo episodes (Fig. T22).

The southern African rainy season extends from October to April. Precipitation during January was well above average, with area-averaged totals in the upper 80th percentile of occurrences (Fig. E4). However, there was a pronounced north-south dipole to the anomaly pattern, with above average totals in northern Mozambique and Tanzania , and below average totals in southern Mozambique and southeastern South Africa (Fig. E3). So far in the 2006-07 rainy season for southern Africa , area-averaged totals were below-normal in October, near-normal in both November and December, and above normal in January (Fig. E4).



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