Precursor Circulation Features for Persistent Extreme Precipitation in Central-Eastern China

Using a composite analysis, the typical precursor circulation configuration from the lower to the upper troposphere responsible for persistent extreme precipitation events (PEPEs) of double-blocking-high type in central-eastern China is identified. The potential of these precursors is further assessed based on the composites of normalized anomalies. The composite results reveal that at 500 hPa, about 2 weeks prior to the onset of PEPEs, a positive height anomaly progresses toward the Ural Mountains region from 30 degrees E and another positive anomaly extends southwest from high latitudes toward the Sea of Okhotsk. Afterward, these two positive anomalies grow in magnitude in situ. The double blocking highs are finally well established with height anomalies of 2.4 and 1.8 standard deviations above normal, respectively. At 850 hPa, an anomalous anticyclone originating from the equatorial western Pacific migrates northwestward 1 week prior to the event occurrence, resulting in a greatly intensified moisture transport toward central-eastern China with a magnitude anomaly over four standard deviations above normal. In the upper troposphere, the eastward-extended South Asia high and the southward-displaced westerlies combine to provide favorable upper-level divergence for PEPEs. These composites of the anomalies and normalized anomalies may offer forecasters some useful clues in recognizing significant weather events about 1-2 weeks in advance of an event.