Rapid melting-layer erosion diagnosed from observations and WRF simulations during a rain-to-snow transition in Northeast China

Abstract Precipitation-phase transitions in winter storms remain difficult to predict because they depend sensitively on the depth and evolution of near-0 °C stratification in the lower troposphere. This study examines a rapid rain-to-snow transition over Liaoning Province, Northeast China, during 5–6 November 2023 using surface observations, the 08:00 Beijing Time (BJT) upper-air sounding, ERA5 reanalysis, and high-resolution Weather Research and Forecasting (WRF) simulations. The event featured a northwest-to-southeast progression of observed precipitation-phase changes and a brief sleet (mixed rain–snow) stage at Shenyang. Synoptic analyses revealed the eastward progression of an upper-level vortex and the northeastward development of a deepening surface cyclone, providing a favorable circulation background for the transition. WRF broadly reproduced the precipitation distribution and near-surface thermal evolution, although biases remained in precipitation amount, temperature, and humidity. A temperature-tendency budget identified contributions from horizontal temperature advection, vertical temperature transport, and a composite residual thermodynamic term to rapid low-level cooling. The simulated cooling was accompanied by the descent of the 0 °C isotherm from approximately 750 hPa before 05:00 BJT to 900–925 hPa around 05:30–06:00 BJT, indicating rapid erosion of a shallow melting layer. The WRF Single-Moment 6-class (WSM6) simulation showed the downward extension of snow and graupel, together with weakening low-level liquid hydrometeors. The WSM6–Thompson comparison revealed substantial differences in simulated snow and graupel distributions despite similar low-level 0 °C-isotherm evolution. These findings highlight the importance of vertical thermal structure, melting-layer erosion, and model-dependent hydrometeor responses in understanding rapid rain-to-snow transitions.