The determination of observed atmospheric differences between heavy and light precipitation events in New Jersey, USA

Robert Harnack, Kirk Apffel, Matei Georgescu, Shaun Baines

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The climatology of a limited sample of heavy precipitation events occurring in New Jersey, USA, is studied via statistical averaging and frequency histograms of environmental conditions at the event location. Also, the spatial distribution of related circulation features is examined. In addition, statistical differences between conditions accompanying the heavy (HEAVY) and a selected sample of light (LIGHT) precipitation events is determined. A large number of surface, standard level, stability and wind shear variables are employed as well as synoptic-scale circulation features. Variables that are identified as statistically significant, after a Student's t-test is applied to a sample mean and standard deviation are listed by season. In addition, scatter plot and composite maps are produced to illustrate conditions concurrent with the onset of heavy precipitation. In general, there are only slight differences between values obtained for the HEAVY sample and the LIGHT sample. However, the differences are large enough for some variables in some seasons that the forecaster may be able to use these results to advantage. In particular: (i) a significantly warmer and moister atmosphere at selected levels is indicated for the HEAVY sample for Autumn and Winter but not for Spring and Summer; (ii) upper-tropospheric divergence is significantly greater in all seasons except Summer; and (iii) wind shear is significantly larger in all seasons except Summer. There is much similarity in the mean position of examined synoptic features such as troughs, vorticity maxima, jet axes and jet streaks for the two samples. However, the amplitude of circulation in the troposphere is much larger for the HEAVY sample, especially in the lower troposphere. In addition, the 850-hPa wind maximum axis (low-level jet indication) is much more often oriented from south to north and located within 300 km of the event location for the HEAVY cases. There was surprisingly no significant sample difference found for static stability and precipitable water in any season. Based on the results reported here, the forecaster is particularly advised to examine the tropospheric circulation amplitude and the position of low and upper-level jet axes and jet streaks before forecasting heavy precipitation in the mid-Atlantic region of the USA.

Original languageEnglish (US)
Pages (from-to)1529-1560
Number of pages32
JournalInternational Journal of Climatology
Issue number12
StatePublished - Oct 2001
Externally publishedYes


  • Heavy precipitation forecasting
  • New Jersey climate
  • Quantitative precipitation forecasting
  • Synoptic climatology

ASJC Scopus subject areas

  • Atmospheric Science


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