I thought that it would be a good idea to talk about thunderstorms, risks for severe weather and watches versus warnings.
Types of Thunderstorms
A lot of us had experienced annoying inconveniences, thank to thunderstorms. Some situations include getting out of a pool when a clap of thunder is heard, watching a car become dented due to baseball-sized hail, and being woken up by lightning in the middle of night. Even though they can be fascinating or inconvenient, understanding the basics of thunderstorms can help understand the forecasts for severe weather.
All thunderstorms have these characteristics: lightnings, precipitation (to some degree), updraft, and downdraft. They experience cumulus, mature, and dissipating stages. All of them require these ingredients: moisture, lift, and instability. Yet, the severe thunderstorms often require wind shear. However, none of thunderstorms are alike. Some are garden variety, and others are immensely powerful. Some don’t produce as much rain as other. Personally, I have seen a whole spectrum of thunderstorms: a nearly stationary supercell that produced very large hail and barely any rain; very weak summer pop up storm; and a fast-moving squall line passing through in winter.
Ordinary Thunderstorm- Garden variety, doesn’t continue very long (around 30 minutes or so), typical summertime pop up storms, very rarely can become marginally severe
Mult-Cell Clusters- Group of individual cells clustered together, all in different stages of development, can occasionally become severe, can become problematic if they stay over one spot because they could drop so much rain in one area causing flooding
Squall Lines- Thunderstorms in lines, updraft located in front, typically severe hail and winds, sometimes weak tornadoes, can sustain for several hours, intense lines may be classified as derecho in rare cases
Supercell- Most powerful type, rotating updraft that stays separated from downdraft, can sustain for several hours, usually in high shear environments, well known for tornadoes, especially EF-2+, usually produce very large hail and strong winds
Severe Weather Risks
These are risk levels used by Storm Prediction Center to show how widespread and/ or intense the thunderstorms would be. The higher risk is, more serious the situation can be in regard to severe weather. I have seen a lot of different scenarios with these risk levels, so I had listed them with corresponding risk levels to give you ideas what they look like.
General Thunderstorm – Lowest grade used by SPC, denotes sub-severe thunderstorms, most commonly seen in forecasts. Marginally severe thunderstorms still occur, but it’s rare.
Typical scenarios: summertime pop up thunderstorms, rainy days with thunderstorms
Marginal- Second lowest risk level used by SPC, just above General Thunderstorms, small risk of severe thunderstorms. Thunderstorms usually tend to be sub-severe and marginally severe (60 mph winds and quarter-size hail). Common.
Typical Scenarios- landfalling hurricanes/ tropical storms producing few tornadoes, few marginally severe pop up storms
Slight- Higher chance of severe weather than Marginal, but lower than Enhanced. Most diverse scenarios. Can occasionally see significant severe weather (80+ mph winds, strong tornadoes, 2+ inches hail), but usually marginally severe thunderstorms. Somewhat common.
Typical scenarios: Several marginally severe thunderstorms, low-end squall lines, a stray supercell producing softball-sized hail, landfalling hurricanes/ tropical storms producing tornadoes
Enhanced- Higher than Slight Risk. Denotes more widespread severe weather and/ or few intense storms. Uncommon.
Typical Scenarios: Few supercells, squall line with more widespread wind or more intense squall lines
Moderate- Second highest level used by SPC. Intense thunderstorms expected (80+ mph winds, strong to violent tornadoes, and/or 2+ inches hail). Few times per year.
Typical scenarios: Tornado outbreaks/ multiple supercells with significant hail and wind, derechos/ intense squall lines
High- Highest level used by SPC. Similar to Moderate Risk except for more widespread and sometimes longer time. We have not seen one in 2018 so far, but we still have until the end of this year to see one. Yet, we can hope to steer clear of seeing a high risk day…
Typical Scenarios: Major tornado outbreaks, very intense derechos in late spring/ summer.
Watches vs Warnings
Watch- Large areas (several counties), issued by SPC, keep your eyes peeled for warnings
Warning- Smaller areas (one or few counties), issued by local NWS offices, take actions (go to safe room/ get in shelter)
Rarely, there will be PDS (particularly dangerous situations) watches and warnings. PDS indicates that there are intense storms in the area, and unsurprisingly, they are usually seen on moderate or high risk days. When PDS tornado (or more rarely severe thunderstorms) watch is issued, the SPC is not joking about the intensity of storms.
What I saw before while tracking severe weather is that there are several instances of warnings with PDS wordings. they’re meant to be taken very seriously. Few examples are:
- Tornado emergency (one of most serious warnings)
- Tornado warnings indicating confirmed tornado on ground
- Severe thunderstorms with 80+ mph wind and/or hail at least size of baseballs (Saw a few that mention 90+ mph and giant hail)
Thunderstorm types: https://www.weather.gov/jetstream
Risk categories and watches: https://www.spc.noaa.gov/misc/about.html
Watch vs warnings: https://www.weather.gov/safety/tornado-ww
I am a trained NWS spotter, and this blog is meant to be informative about weather-related topics with some light humor and commentaries.