First time visitor? Wondering how to read the radar, severe outlook maps and how to understand the weather terms that we use, what it means and how it works? Wonder no longer – you’ve come to the right place! Below you will find everything you need to know about reading the radars, understanding the maps, above, beyond and everything in between on our website.
When rain, snow, flooding or tornadoes threaten our state, we want to help you stay on top of the action! That’s why we offer FIVE Doppler radar imagery sites around the state, covering every inch of Tennessee. But what’s the use of a radar to you if you don’t know how to read it correctly? How would you be able to tell heavy rain from a tornado? What about a narrow band of rain from a gust front? Spotty showers from a flock of birds? (yes, weather radars can even sense birds!)
The “Hook Echo”
A hook echo is a hook shaped radar signature that appears on some supercell thunderstorms. It is almost always found in the lower part of the storm. The signature is often indicative of rotation in a storm and is often seen when a tornado is imminent. Because of this, the National Weather Service may consider the presence of a hook echo as sufficient to justify issuing a Tornado Warning.
A hook echo may develop into a debris ball, a certain sign that a tornado is on the ground and causing damage. A debris ball is caused by the radar reflecting off of debris in a tornado and showing as very heavy reflectivity on radar.
The “Squall Line”
A squall line is a line of thunderstorms that can form along or ahead of a cold front. It
often contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts. Some bow echoes which develop within the summer season are known as derechos, and they move quite fast through large sections of territory. Squall Lines appear on doppler radar as a straight line. Severe, damaging winds are often present along the “leading edge” of a squall line.
The “Bow Echo”
You’ve probably heard this term used on some weather stations – the “bow echo” (as it is commonly referred to). Bow echoes are usually associated with “squall lines” or lines of strong and severe thunderstorms. They can cover a single county or an entire state, and can last for 3-6 hours. These “bow echoes” tend to develop when strong wind shear, or low-level high wind gusts are dominant in a particular area of a storm. Bow echoes usually bring damaging winds and heavy rain, and have the ability to spawn off tornadoes – sometimes even violent tornadoes. Straight-line winds are commonly produced from bowing squall lines. Strong bow echoes are sometimes referred to as “derechos” and have the ability to cause massive and widespread damage. You can find this storm feature on radar imagery by looking for an outward bulge on the front side of a squall line, or long band of strong-to-severe thunderstorms.
“Radar Clutter” is a ring of seemingly light rain surrounding the radar site. Although it looks like rain on radar, it is just the radar picking up on a variety of things: birds, flocks of birds, insects, leaves in the air, tall trees, low-flying airplanes, helicopters, and even sometimes smoke or dust. Radar Clutter is commonly seen at sunrise and sunset.
Severe Weather Outlooks (SPC Outlooks)
Each day, the Storm Prediction Center out of Norman, Oklahoma issues multiple severe weather outlooks, most commonly identified by “Marginal”, “Slight”, “Enhanced”, “Moderate”, and “High” Risks. These risk areas can also be portrayed on a scale of 1 to 5, with 1 being “Marginal” Risk and a low chance for severe weather, and 5 being “High” Risk, with a high chance for severe weather. Keep in mind that severe weather is possible even in a Marginal Risk area. Each SPC Outlook day is characterized by the number of days from the current time. For instance, in SPC terms, today is “Day 1”, tomorrow is “Day 2”, day after tomorrow is “Day 3”, etc. So when you see us post about a severe weather threat for Day 2, it’s just a different way to identify tomorrow.
On Day 1, the SPC has enough knowledge to issue more detailed outlooks, including tornado, hail, and damaging wind outlooks. Anything after Day 1 is “too far out” to accurately portray these, so a generic categorical outlook is released (Marginal, Slight, Enhanced, Moderate, or High Risk for Severe Weather). After Day 3, specifically Days 4-8, it again becomes “too far out” to accurately forecast the Marginal, Slight, Enhanced, Moderate, or High Risks, so a generic risk area is outlined. Severe weather is not forecast by the SPC past Day 8. You can view the Storm Prediction Center’s outlooks by clicking here.
If something important comes up, and we feel that you should know the second that you visit our site, we will post it in our site’s Announcements section. The Announcements section appears at the top of every single page on our website. This can include recent site updates, pre-disaster and post-disaster information, important news from the National Weather Service, FEMA, or any other reputable source, we will post it as quickly as possible to the Announcements section.
Severe Outlook Announcements
Not only do we post the latest news and updates to the Announcements section, we also regularly update the Severe Outlook status for today, tomorrow and the next day. If only one day is indicated to pose a threat of thunderstorms and/or severe weather, we will only post the Severe Outlook update for that day. If there happens to be a threat of thunderstorms and/or severe weather for all three days, then a separate announcement will be posted for each day. Each Severe Outlook announcement is not just a line of text, but it is also a link. Click the text for the corresponding Severe Outlook announcement and you will be directed to a page with the latest Severe Outlook map for that day.
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