Description
Freezing rain is one of the most disruptive forms of wintertime precipitation, impacting air and ground travel, as well as utilities. It was observed that a particular kind of freezing rain event occurs along the coastal plain of southwest Maine and New Hampshire, in which precipitation changes from snow to rain to freezing rain in the presence of synoptic warm air advection across the greater region. Numerical models often missed this progression, which had been noted by local forecasters. This project conducted several case studies, which were then used to build a climatology of events by categorizing freezing rain based on similarities in precipitation type progression from 1988-2018 at KPWM (Portland, ME), and Portsmouth, NH (KPSM) using hourly METAR data. A background on Cold Air Damming (CAD) and local geography is provided, and their role in the development of these events is established. For each of the event categories of interest, sea surface temperature (SST) data from nearby weather buoys, and temperature and dew point data from Bangor, ME (KBGR) were gathered. NARR SLP composites were created for each type of events of interest for KPWM and KPSM. It was shown that snow to rain to freezing rain events were rare, but events of snow to freezing rain were much more common at both KPWM and KPSM, and were still significant. Trends in seasonal, diurnal, and synoptic patterns were established and discussed. Significant differences in the progression of low pressure systems were found to exist between KPWM and KPSM in similar events. The influence of secondary low pressure development offshore proved to be a critical factor in the events, which was discussed in detail. Issues of composite smearing and changes to data collection methods, such as a transition to automated data collection, during the time period were discussed. A framework for future work is established to conduct a more comprehensive upper level analysis.
Identifier
psu-etd-196
