Extratropical Highlights –February
1. Northern Hemisphere
The 500-hPa circulation during February
featured an extensive height anomaly pattern that extended from the western
North Pacific to Europe. Above-average heights were present across the central
North Pacific, the Gulf of Alaska, the eastern U.S., and Europe, and below-average
heights were present over the central subtropical North Pacific, western North
America, the high latitudes of the western North Atlantic, and northeastern
Asia. (Fig. E9).
Over the North Pacific/ North
America region, the anomaly pattern projected onto the strong positive phases
of the West Pacific (+2.1) and Tropical/ Northern Hemisphere (TNH, +1.6)
teleconnection patterns, and also onto the negative phase of the Pacific/ North
American pattern (PNA, -1.7) (Table E1, Fig. E7). These TNH
and PNA phases are opposite to those typically seen during El Niño, and
essentially masked the El Niño signal east of the date line. Nonetheless, the El Niño signal was present over
the western Pacific Ocean, as indicated by anticyclonic streamfunction
anomalies in the subtropics of both hemispheres (Fig. T22) flanking the region
of suppressed equatorial convection (Fig.
The main land-surface temperature signals
during February included above-average temperatures across most of Alaska, the
southeastern U.S., Europe, and portions of northeastern Asia, and below-average
temperatures across the western half of Canada and the northwestern U.S. (Fig. E1). The main precipitation signals included
above-average totals in the western and north-central and eastern U.S., and
below-average totals in western Canada (Fig.
a. North Pacific and America
The 500-hPa circulation during
February featured above-average heights over the Gulf of Alaska and the eastern
U.S., and below-average heights over the central subtropical North Pacific and
western North America. (Fig. E9). These
anomalies are opposite to those typically seen during El Niño. During February,
this pattern was associated with a westward retraction of the Pacific jet
stream (Fig. T21), and reflected an amplification of
the downstream circulation anomalies typically associated with a
This anomalous circulation
contributed to above-average surface temperatures in Alaska and the
southeastern U.S., with departures in the upper 90th percentile of
occurrences in the Southeast (Fig. E1). In contrast, below-average temperatures were
present across western Canada and the northwestern U.S., with most areas recording
temperatures in the lowest 10th percentile of occurrences.
Also, precipitation was well above
average in the western U.S. (Fig. E3), with
area-averaged totals in the upper 90th percentile of occurrences in
the Pacific Northwest, Inter-Mountain, and Southern California regions (Fig. E5). The north-central U.S. also
recorded well above-average precipitation during February (Fig. E3), with area-averaged totals above the 90th percentile
of occurrences in the Midwest, Oho Valley, and Great Lakes regions (Fig. E5).
According to the U.S. Drought
Monitor, the area of severe-to-exceptional drought diminished considerably in
the four-corner region of Utah, Colorado, Arizona, and New Mexico, and also in
b. North Atlantic and Eurasia
The 500-hPa height pattern featured
above-average heights over Europe and below-average heights over the high
latitudes of the western North Atlantic (Fig.
E9). This pattern resulted in above-average
surface temperatures throughout Europe, with most areas recording departures in
the upper 70th percentile of occurrences (Fig. E1).
2. Southern Hemisphere
The mean 500-hPa circulation during
February generally featured above-average heights over Antarctica and
below-average heights in the middle latitudes (Fig. E15). At 200-hPa,
cyclonic streamfunction anomalies over the western
subtropical South Pacific were associated with El Niño (Fig. T22).
Much of northern Australia recorded
below-average precipitation during February, (Fig. E3), in association with a widespread pattern of suppressed
convection over the western tropical Pacific and Indonesia (Fig. T25).
The South African monsoon season
runs from October to April. During February, rainfall was below average for the
region as a whole (Fig. E4). The most significant departures were observed in
the northern portion of the monsoon region, with totals in the lowest 10th
percentile of occurrences in northern Mozambique and central Madagascar (Fig. E3). To
date, the monsoon region has recorded below-average precipitation during
October-December and February, and only slightly above-average totals in