DEEP: Coastal Hazards Primer - Precipitation

Coastal Hazards Primer - Precipitation
Coastal Hazards Primer
 Introduction   Precipitation
 Flooding    Tropical Storms and Hurricanes 
 Erosion   Winter Storms 
Precipitation generally takes the form of rain, freezing rain, snow, sleet, and hail.  The NOAA National Weather Service (NWS) defines these as follows:17
  • Rain: Liquid precipitation that falls to earth in drops more than 0.5 mm in diameter.
  • Freezing Rain: Rain that freezes into a glaze upon contact with the ground.
  • Snow: Precipitation in the form of ice crystals, mainly of intricately branched, hexagonal form and often agglomerated into snowflakes, formed directly from the freezing of water vapor in the air.
  • Sleet: Pellets of ice composed of frozen or mostly frozen raindrops or refrozen partially melted snowflakes. These usually bounce after hitting the ground or other hard surfaces..
  • Hail: Showery precipitation in the form of irregular pellets or balls of ice more than 5 mm in diameter, falling from a cumulonimbus cloud.

All forms of wintry precipitation, such as sleet, freezing rain, snow, and hail can create hazardous conditions on roads and walkways, and damage infrastructure like power lines, buildings and trees from the weight of ice of snow.  Non-wintery precipitation is a frequent contributor to flooding events. These are familiar to anyone who lives in Connecticut, not just coastal residents. 

Coastal storms can be unique, however, because precipitation is often accompanied by other hazards, such as high winds, flooding, or coastal erosion.  The coastal devastation of the 1938 hurricane was the product of many factors including the coincidence of high tide, high winds, and a storm surge.  However, much of the flooding in inland areas resulted from three days of continuous rain that preceded the hurricane’s arrival, saturating soils to the point where rivers and stream were filled to their banks.  The rain subsequently delivered by the hurricane thus exacerbated the previous situation. 

A 2002 University of Connecticut publication, Precipitation in Connecticut is an authoritative summary of data from 73 precipitation gauges across the state and adjacent portions of New York, Rhode Island, and Massachusetts.  The record at many begins in 1948, but several have records dating back to the late 19th century. The publication presents the following results:

  • The average annual precipitation over the last 100 years shows a generally increasing trend, with high year-to-year variability;
  • When averaged over the period of record, total precipitation is distributed evenly throughout the year with slightly higher amounts in the summer than in the winter;
  • The proximity of the ocean moderates the snowfall in Connecticut, especially along the coast. The average snowfall in is about 30 inches along the coast, 40 inches inland and 60 inches in the northwest corner;
  • Connecticut has four precipitation regions, two of which include the coastline (Greenwich to Stratford and Milford to Stonington). The regions were created by statistically comparing the extreme precipitation records, grouping those with the least statistical differences and minimizing the distance between them. Each region has a unique set of precipitation characteristics defined by:
    • Spatial Distribution of Extreme Events
    • Intensity-Duration-Frequency graphs for 2yr, 5yr, 10yr, 25yr, 50yr, and 100yr storms
    • Weekly Distribution of 1hr, 6hr, and 24hr Extreme Events
The NOAA National Climate Data Center provides a searchable index for weather observation station records.  You can find precipitation data for various stations in Connecticut for 15 minute, hourly, daily, and monthly intervals.
In Summary
What can you do when it comes to the threat of precipitation events in Connecticut?
Content Last Updated January 3, 2012