Oklahoma Hail

Hail

Data Limitations

Hail data are not of sufficient quality to robustly determine historical trends and is of poorer quality than even the tornado dataset. This can be attributed to the increases in non-meteorological factors such as population and storm spotter coverage over time, as well as the uncertainty in reported hail size. However, the recent acknowledgement to assess the number of hail days instead of individual hail reports has mitigated some of the biases.

Definition and Description

Hail
Definition

Showery precipitation in the form of irregular pellets or balls of ice more than 5mm (0.2 inches) in diameter, falling from a cumulonimbus cloud (NWS 2009).

Description

Hail forms by the collision of supercooled drops – raindrops that are still liquid even though the air around them is below freezing. The hailstone grows, supported by the updraft, until it is too heavy to remain aloft. Stronger updrafts generally produce larger hail size. Because obtaining large hail sizes requires a strong updraft, the timing of large hail is related to the lifecycle of large cumulonimbus clouds, which peak in intensity during late afternoon and evening hours. Updrafts may also be supported by vertical motion along a boundary, such as a front or mountains.

Hail severity is rated by the diameter of the largest hailstones in a storm. Hail of 1-inch diameter or greater is considered severe.

Historical Data

Severe Hail Days Per Year

(1986-2015) NOAA/National Weather Service Storm Prediction Center

This map shows the average number of days per year in which severe hail reports were received in your area during the period noted. The map gives you a sense of the approximate number of days each year that you can expect to see severe hail (1-inch or greater in diameter) in your area. The 2- inch or greater map is also available for viewing.

1. Click on the link below to go to the website 2. Select 1.00-Inch Hail Days or 2.00-Inch Hail Days.

Severe Hail Reports

Hail: (1955-present) Southern Regional Climate Center

This interactive tool shows you the historical record for individual severe hail reports in your area. It can be used to determine hail events that have impacted your area or close to your area.

1. On left side of screen, click on Search with Radius. 2. Choose the diameter of the area of which you want to investigate (25 or 50 miles). 3. Select Hail (de-select Tornado and Wind). 4. Pan, zoom, and then click on the map area of interest. 5. Reports are displayed on the map and in two tables below the map.

Map: Mouse over individual storm reports for details.

Tables: There are two tables, Recent Storm Data and Historical Storm Data. Click on column header to sort by column of interest. For example, to view the dates in which the largest hail occurred, click on the Scale column headers to sort by the largest hail values.

Storm Events Database

Hail: (1955-present)NOAA National Centers for Environmental Information

This interactive tool shows you the historical record for individual severe hail reports by county. It can be used to determine hail events that have impacted your area or close to your area.

1. On the bottom left, under Select State or Area, choose Oklahoma → then Search 2. From top to bottom, select a specific Begin and End Date, as well as County of interest. 3. Under Event Type(s), select Hail. 4. Under Advanced Search and Filter OptionsHail Filter, select hail size of interest. 5. Press Search. Summary results are presented in a table. Note: This tool can be used to analyze a variety of additional hazards with various time periods, and hail data goes as far back as 1955.

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