Criteria for Forecasting Cold Surges Associated with Strong High Pressure Areas over Thailand during the Winter Monsoon

Abstract

At present, the arrival of a 1020 hPa isobar at the border of Thailand is assumed to define a strong high pressure area over the country associated with a cold surge. Using this definition, with the National Centers for Environmental Prediction (NCEP) analysis data, twenty-four strong high pressure cases were found in the five winters (October-February) from 2002 to 2006. The 24 cases were studied using the Advanced Research WRF (ARW) Modeling System in order to determine the extent to which they were cold surges as defined by a mean sea level pressure (MSLP) rise, a sudden increase in wind speed, and sharp drops in surface air temperature and dew point temperature. The 24-hour changes of meteorological elements for five days at Udon Thani station during the strong high pressure cases were examined to find detailed criteria for forecasting cold surges in Thailand. It was found that the indicators of a cold surge are an increase in wind speed of at least 2.6 m/s, a rise in MSLP of at least 1.8 hPa and drops in surface air temperature and dew point temperature of at least 1.7°C and 2.1°C, respectively, at Udon Thani station.