The most important responsibility of
any NWS field office is the timely issuance of severe weather warnings. The
WSR-88D Doppler radar has dramatically helped in this task. Our radar tower is
located next to our parking lot outside our front door. AWIPS has been
configured so that radar monitoring and warning issuance are performed at any of
our AWIPS workstations.
How we issue a severe storm warning:
Radar surveillance is always part of the job. On a day-to-day basis, both forecasters are performing this function while completing their other duties. However, in active weather, this is a much more time-consuming process. Therefore, at least one meteorologist is solely assigned this task. After interrogating a storm, if the radar meteorologist determines that a warning is required, he/she clicks on an icon that's in the upper right corner of the AWIPS graphic screen. This activates the warning program. A cursor pops up on the screen, along with a dialog box (seen to the right). The cursor is moved to the storm of concern on the current radar image, and a radar image from 10 to 15 minutes prior. This is so the computer can calculate storm movement. The meteorologist then makes sure the proper items are clicked in the box, including warning type, valid time, and any appropriate instructions, and then clicks an icon at the bottom of the screen to compose the warning. AWIPS then composes the warning, and includes the names of communities in the path of the storm, and the time they will be first affected. The meteorologist has a chance to make any necessary additions or adjustments on a text workstation before issuing the warning.
The advantage of Doppler radar is its ability to not just detect where the precipitation is falling, but also determine movement of particles within the storm. In the image below left, the areas colored green depict movement toward the radar (which is off the image to the right), and the areas colored red depict movement away from the radar. From this, one can infer rotation at this location since fairly strong winds are depicted in opposite directions side by side. However, this accounts for the wind field at just one level. We have the ability to view radar data at a number of levels. Thus, if a similar scenario is found at the same location at different, adjacent levels, this is a rotating column of air, which is a precursor of tornado development.
This was the case in this image, when there was an
F4 tornado on the ground near Frostburg, MD. This tornado occurred during the
tornado outbreak on June 2, 1998. A reflectivity image from this storm at the
same time can be seen to the right. More details of the June 2, 1998 outback can
We also have the ability to dial to other radars to get a different view of storms. That feature was useful in this instance, as the storm was moving away from the WSR-88D radar in Pittsburgh, PA out of Garret County, Maryland and into the County Warning Area of our neighboring office just outside of Washington DC (Sterling, VA ). It also serves as good backup coverage. In other words, if the radar were to develop mechanical difficulties, we can always obtain radar data from surrounding sites, and maintain surveillance. AWIPS makes this task much easier since the data gathering is done automatically.
As indicated above, the radar can view storms at multiple levels. Instead of viewing the data in each "slice" along the Earth's surface, it is also possible to view the data with respect to height. The image below is such a cross section. With AWIPS, the starting and ending points of the cross section can be placed anywhere and in any orientation.. We can determine if there is hail inside a thunderstorm as its return is much stronger than that of water particles.
The radar's computer can also estimate rainfall based on the intensity of the returns, and is able to display maps like the velocity image above with 1 hour totals, 3 hour totals, and storm total rainfall. The software can also assist us with hail detection, and determining the size of potential hail stones.
Our radar is very sensitive and at times it picks up non-weather features. In the picture below the doughnut shaped feature on the left hand side are actually birds taking off from nearby lakes shortly after sunrise.