Monitor Thunderstorms Yourself! Nexrad 101
Tired of those rebellious thunderstorms that happen in between TV weather broadcasts? Want more information about your exact location that TV weather cannot cover? Do you want an idea whether you are going to get rain and how much? Do you want a way to see if weather warnings will hit or miss your location? Learning how to use Wunderground’s Nexrad can help you do it. Wunderground was the first online weather service, and has a reputation for being the most accurate. It was bought by the Weather Company (Weather Channel) in July 2012.
Nexrad works best on a PC’s and laptops. If you have a smartphone, consider downloading the appropriate Weather Underground App for your type of phone.
What do I use?
Use this Nexrad link here or in the Tulare SD Top Info section on our main page! Next Generation Radar (Nexrad) uses high-resolution S-band Doppler. Always monitor National Weather Service (NWS) watch and warning statements at the same time you are using Nexrad. Watches, warnings, and statements will be posted as they are in effect on the main Wunderground page for Tulare SD. Remember to refresh the main webpage periodically!
How do I use Nexrad?
Once you go to the Nexrad page, click the Animate button to see the direction of storms.
Change the Base Reflectivity bar above the radar pic to either One Hour Rainfall or Storm Total. The One Hour option lets you see what people are getting right before it gets to you! The Storm Total option gives you an estimate of total rainfall after it is done. Storm Total will be available up to 12 hours later.
If a storm or rain clouds are nearing this area, draw a small box around Tulare to zoom to where you see small rectangles in the clouds/cells. These rectangles are about the size of a section of land. Drawing: Hold the mouse button down while drawing the small box around Tulare, then let go. If you want to zoom back out, change the zoom option on the top-right of the radar pic back to 100%.
Change the Storm Tracks to show All. The Storm Tracks option is just under the radar pic. You will notice when there are storm cells, the radar may show a tiny black square, yellow triangle, yellow square, or purple triangle next to the 2 character Doppler cell name. You may want to change the Frame Delay to Medium, so you can read cell ID names better. A yellow square on the cell represents possible hail. A yellow triangle represents a possible mesocyclone which means a rotating thunderstorm as it moves forward, and a purple triangle means the possibility of a tornado vortex signature (unless the cloud top is low elevation). Most tornado cells and bad hail have echo tops over 30,000 feet.
Look at the bottom of the Nexrad page for a specific cell ID name (2 characters) where it will show more info for the cell, such as echo top elevation and hail information. Both dBZ and VIL can tell heavy rainfall. The dBZ scale goes up to 75. Light rain usually begins at 20 dBZ, and higher numbers in the 60’s will be heavy rainfall and/or hail. VIL is used to estimate the size of the hail. VIL’s above 35 can be larger hail.
Change the Base Reflectivity bar above the radar pic to One Hour Rainfall. Make sure you are animating the radar. It should say “Stop” instead of “Animate”. Make sure to draw a very small box around your location. You should be able to see the rainfall level that is heading toward you. However, some cells may slightly intensify, dissipate, or change directions right before getting to you. Zoom out to see rain further out, then draw another box to zoom back in.
Always monitor National Weather Service (NWS) watch and warning statements at the same time you are using Nexrad. Watches and warnings will be posted as they are in effect on the main Wunderground webpage for Tulare SD or from several other sources such as the phone app. Remember a “watch” means possible and a “warning” means spotted nearby. A phone app is important if the power goes out.
Tornadoes are not an exact science yet, but often happen on the southeast corner of a cell in this region, especially with systems from the west. However, they can also be on the backside and other parts of the cell. More intense tornadoes (wedges) can happen on the backside of the cell.
Most tornadoes and funnel clouds need heavy rain in part of the cell or from a nearby cell. The heavy rain in another part of the cell or at the rear of the cell causes a downdraft of moist air that is called a rear flank downdraft (RFD). When this is combined with a nearby updraft of warm air from below (nearby where rain hasn’t cooled the air), this can cause a mesocyclone to be pulled downward to form a wall cloud. The downdraft and updraft cause the mesocyclone/wall cloud to rotate. A rotating wall cloud may produce a funnel cloud anywhere from 5-30 minutes after the rotating wall cloud is formed.
Nexrad can help offer information when it is dark or heavy rain. Many times, Nexrad will first show a mesocyclone (yellow diamond), which means the cell is rotating. Nexrad will show a purple triangle when it detects a tornado vortex signature, which is usually a strong mesocyclone, but can represent a funnel cloud or tornado. We have seen several purple triangles in this area that never become a funnel cloud or tornado, but should be watched carefully, plus NWS warnings should be monitored.
Low clouds without much moisture will also show up as mesocyclones and even tornado vortex signatures, but are normally harmless. It is important to monitor the cell’s echo top elevation, and dBZ and VIL (for moisture). A mesocyclone or tornado vortex signature should be watched if the cell has a very high echo top elevation, high dBZ and high VIL (heavy rain).
There are several other tools to use for monitoring tornadoes:
Tulare SD on the Map:
You will notice Tulare is placed on the radar map (and most other maps) being two miles from highway 281. We believe you should monitor the the area between the symbol for Tulare and the highway for actual Tulare radar information, not directly on the symbol.