500-hPa height pattern during July 2008 featured positive anomalies over the
high latitudes of the central North Pacific, eastern
, and negative anomalies over
, and the eastern
(Fig. E9). Over the central
, the subtropical circulation at 200-hPa reflected a lingering La Niņa signal,
with cyclonic anomalies in both hemispheres flanking the suppressed convection
over the central equatorial Pacific (Fig. T22).
main surface temperature departures during July reflected warmer than average
conditions in the southwestern
, and portions of
, and below-average temperatures in
and extreme western
(Fig. E1). The main precipitation
anomalies included above average totals in the
regions of the
(Fig. E5), portions of northern and eastern
, and eastern
, and below-average totals in the Pacific Northwest U.S. (Fig. E3).
a. North Pacific/
though La Niņa has dissipated, as measured by the Niņo 3.4 SST index, there
remained a complete disappearance of tropical convection from the central
equatorial Pacific (Fig. T25).
Impacts from this anomalous convection continued to be reflected in cyclonic
streamfunction anomalies over the central subtropical Pacific of both
hemispheres (Fig. T22).
500-hPa height pattern during July featured amplified troughs over
, and a persistent ridge over the southwestern US. This
overall pattern was associated with a continuation of below-average
precipitation in northern
(Fig. E5). In northern
many locations have recorded almost no rainfall since late March, which set the
stage for numerous (1781) uncontrolled wildfires that burned over 702,000 acres
during June and early July.
regions of the
recorded above-average precipitation during July. Both
regions have seen well above-average precipitation since February (Fig.
, the eastern flank of the normal Asian monsoon ridge at 200-hPa was weaker than
average for the second straight month (Fig.
T22). This pattern has favored well
above-average precipitation, with totals during both June and July in the upper
90th percentile of occurrences.
2. Southern Hemisphere
The 500-hPa height
field during July featured large areas of above-average heights centered south
, and below-average heights located over the eastern South Pacific and over the
(Fig. E15). In the subtropics, ongoing
positive 200-hPa streamfunction anomalies over the central
indicated an anomalous cyclonic circulation consistent with a lingering La Niņa
signal (Fig. T22).
The main surface
temperature anomalies during July reflected exceptionally warm conditions over
, where departures exceeded the 90th percentile of occurrences (Fig.
E1). This region was situated downstream of the
mean upper-level trough, and also experienced anomalous poleward flow at 850-hPa
(Fig. T20). These conditions were
associated with a poleward shift of the mean cold frontal boundary, and with an
anomalous southward incursion of mild air into central