To clarify the precipitation forecast skills of climate forecast operations in the flood season in Liaoning Province of China, this study examines the forecast accuracies of China’s national and provincial operational climate prediction products and the self-developed objective prediction methods and climate model products by Shenyang Regional Climate Center (SRCC) in the flood season in Liaoning. Furthermore, the forecast accuracies of the main influencing factors on the precipitation in the flood season of Liaoning are assessed. The results show that the SRCC objective methods have a relatively high accuracy. The European Centre for Medium-Range Weather Forecasts (ECMWF) sub-seasonal forecast initialized at the sub-nearest time has the best performance in June. The National Climate Center (NCC) Climate System Model sub-seasonal forecast initialized at the sub-nearest time, and the ECMWF seasonal and sub-seasonal forecasts initialized at the nearest time, perform the best in July. The NCC sub-seasonal forecast initialized at the sub-nearest time has the best performance in August. For the accuracy of the SRCC objective method, the more significant the equatorial Middle East Pacific sea surface temperature (SST) anomaly is, the higher the evaluation score of the dynamic–analogue correction method is. The more significant the North Atlantic SST tripole is, the higher the score of the hybrid downscaling method is. For the forecast accuracy of the main influencing factors of precipitation, the tropical Atlantic SST and the north–south anti-phase SST in the northwest Pacific can well predict the locations of the southern vortex and the northern vortex in early summer, respectively. The warm (clod) SST in China offshore has a good forecast performance on the weak (strong) southerly wind in midsummer in Northeast China. The accuracy of using the SST in the Nino 1+2 areas to predict the north–south location of the western Pacific subtropical high is better than that of using Kuroshio SST. The accuracy of predicting northward-moving typhoons from July to September by using the SST in the west-wind-drift area is better than using the SST in the Nino 3 area. The above conclusions are of great significance for improving the short-term climate prediction in Liaoning.

The influence of mid-high latitude intraseasonal variability (ISV) on the occurrence frequency of Northeast China cold vortex (NCCV) in early summer was examined through statistical analysis and thermal-dynamical diagnostic. Multi-variable empirical orthogonal function (MVEOF) was employed to extract the thermal-pressure coupled ISV mode. Our results show that the geopotential height and air temperature over the NCCV active region exhibit a statistically significant intraseasonal periodicity of 20–60 day. The dominant ISV mode features a westward propagated zonal dipole pattern, which is generated over the Lake Baikal region and triggered by intraseasonal wave energy accumulation. By dividing the ISV cycle into 8 phases, it is found that more NCCVs with a large scope occur in phases 5 to 8 than those in phases 1 to 4. The positive (negative) geopotential height and air temperature tendencies in phases 1 to 4 (5 to 8) act to suppress (facilitate) the NCCV activity. The thermo-dynamical tendency budget and scale decomposition reveal that when an anomalous intraseasonal cyclonic circulation propagates westward from Lake Baikal to Ural Mountains, the anomalous southwesterly transports mean negative vorticity from the north side of the Tibetan Plateau to Northeast Asia, and transports mean warm air temperature from low latitude to high latitude, leading to the positive geopotential height and air temperature tendencies and thereby restraining the NCCV activity. The opposite is also true for the facilitation of NCCV modulated by the negative geopotential height and air temperature tendencies.

A large-scale persistent fog event occurred over the Yellow Sea of China from April 27 to May 4, 2015. In this study, we used satellite remote sensing data, ground meteorological observed data, global sounding data, and reanalysis data from the National Centers for Environmental Prediction (NCEP) and sea surface temperature (SST) data from the National Oceanic and Atmospheric Administration (NOAA) to analyze the evolutionary characteristics, the boundary-layer marine meteorological characteristics, and the development mechanism of the sea fog event. The results show that the sea fog event was a warm advective fog process. The Yellow Sea was at the rear of the warm high and the front of the continental low (circulation situation with high in the east and low in the west). The southerly and southeasterly winds transported warm and moist air from the Northwest Pacific northward to the Yellow Sea which served as the water vapor source. A thermal turbulence interface was formed during the sea fog development. The weak vertical wind shear below the interface was conducive to the maintenance and development of sea fog in the area of the temperature inversion in the boundary layer and the formation of a certain thickness of sea fog. The sea fog occurred in the area with water vapor convergence, where the 2-m dew point was slightly higher than the SST. The area with a relative humidity greater than 90% and an air–sea temperature difference from 0 to 2 °C overlapped with the sea fog area, and these two values indicate the extent of the sea fog.