New Upgrades to the Des Moines Radar

A new software upgrade has been installed at the Des Moines WSR-88D radar that will enable the radar to obtain low level scans more frequently in severe weather events. Previously, the WSR-88D scanned the atmosphere at progressively higher angles to create a 3D profile of a storm. These scans would begin at 0.5 degrees above the horizon (the lowest angle possible) and end at a maximum angle of 19.5 degrees. These scans form what is known as a Volume Coverage Pattern, or VCP. This maximum angle can vary depending on the distance the storms are from the radar. Last year, a feature called AVSET (Automatic Volume Scan Elevation Termination) was installed that allows the radar to automatically restart a VCP if the radar beam travels above the storms.

With this latest upgrade, a new feature called SAILS (Supplemental Adaptive Intra-Volume Low‐Level Scan) will enable the radar to insert an additional 0.5 degree scan in the middle of a VCP. See the illustrations below for more details.

Why is this Important?

When it comes to severe weather, frequent low-level radar scans are crucial to observe the development of tornadoes, which can form in a matter of seconds. Thus, with SAILS the NWS to be able to observe rapidly changing weather phenomenon with a greater degree of precision and issue more timely severe weather warnings. Currently, the WSR-88D radar completes its lowest scan in 3 to 4.5 minutes (during severe weather), depending on the range of the storms from the radar (AVSET). With SAILS, the radar will now perform this low-level scan every 1.8 to 2.5 minutes, giving us low-level data almost twice as fast as before.

Other New Features

This upgrade will also bring several new enhancements besides SAILS. One new addition will be a radial noise filter, which will greatly reduce the “spikes” seen on the radar image at sunrise and sunset (see example from the Minneapolis radar below). Another new feature will enable the radar to automatically determine the best settings for viewing velocity data for the strongest storms in the radar’s coverage area.

A “sun spike” removed from the Minneapolis radar while radars to the north and south (which had not been upgraded yet) still contain these spikes.

(Courtesy of the Minneapolis NWS)

Click here for technical details on SAILS

Iowa Heat Awareness Day – June 5, 2014

The Iowa Homeland Security and Emergency Management Division, and the National Weather Service have declared June 5, 2014 as Heat Awareness Day in Iowa. Extreme heat is a seasonal hazard in Iowa which is often underestimated. Did you know that heat is the number one weather-related killer? Understanding heat safety is important and can save lives.

Summertime in Iowa means two things: heat and humidity. These two weather parameters combine to create the Heat Index (Apparent Temperature), which is an accurate measure of how hot it really feels when relative humidity is combine with the actual air temperature. The combination of extreme heat and humidity conspire to tax the human body beyond its natural cooling abilities. Heat related deaths account for many deaths and injuries each year.

Vehicle Safety

HotCar

Above: Thermometer set in car to record temperature
Bottom: High temperature recorded in car

Just how hot can the interior of a car become? To find out, last year we placed a thermometer inside a car parked outside in the sun during a full work day. The high temperatures on the day we conducted our experiment only reached 80°F. However! The interior temperature in the car reach 117°F! A car with the windows cracked showed a similar temperature rise. Even on a relatively mild day, the interior of a car can become dangerously hot for children or pets left unattended. Never leave children or pets unattended in a car, even for short periods of time. Remember: Beat the Heat, Check the Back Seat!

backseatboy2

What is the Heat Index?

The Heat Index (HI) is sometimes referred to as the “apparent temperature” and is a measure of how hot it feels outside to the human body. The HI includes the influence of both the actual air temperature and relative humidity. The body dissipates almost 90% of its heat through sweat but sweating by itself does nothing to cool the body unless the water is removed by evaporation, and high relative humidity hinders evaporation.

heatindex

To figure out the HI, reference the Heat Index Chart and find the intersection of the air temperature and relative humidity. The shaded zones on the chart correspond to the probabilities of developing heat-related disorders. Heat disorders are generally a result of the body’s inability to shed excess heat by sweating or a chemical (salt) imbalance caused by too much sweating. When heat gain exceeds the level the body can remove, or when the body cannot compensate for fluids and salt lost through perspiration, the temperature of the body’s inner core begins to rise and heat-related illness may develop. The table explains the risk to the body from continued exposure to excessive heat and is color coded to match the HI chart shown.

HeatDisorders

 

More information can be found:
Heat and Heat Safety (pdf)
NWS Des Moines Heat Safety
NWS Heat Safety (Español)