Monthly lunar declination extremes' influence on tropospheric circulation patterns

Short‐term tidal variations occurring every 27.3 days from southern (negative) to northern (positive) maximum lunar declinations (MLDs), and back to southern declination of the moon have been overlooked in weather studies. These short‐term MLD variations' significance is that when lunar declination is greatest, tidal forces operating on the high latitudes of both hemispheres are maximized. We find that such tidal forces deform the high latitude Rossby longwaves. Using the NCEP/NCAR reanalysis data set, we identify that the 27.3 day MLD cycle's influence on circulation is greatest in the upper troposphere of both hemispheres' high latitudes. The effect is distinctly regional with high impact over central North America and the British Isles. Through this lunar variation, midlatitude weather forecasting for two‐week forecast periods may be significantly improved. Key Points Monthly lunar declination deform Rossby longwaves The deformation signal is distinctly regional and high latitude A case study of the Great Storm of 1987 demonstrates effect