The 2020 tornado season thoughts.

Well it’s April 1^st, which means severe season for us in the Northeast will be here soon. It’s already gotten off to a fast start across the Plains, Southern States into the Midwest; these areas have seen several cluster outbreaks of tornadoes over the last few weeks. Not only has the early spring been active, but the winter was active as well.  January and February saw several severe outbreaks, especially in the south and southeast, that brought increased tornado activity; even Maryland saw a record breaking five tornadoes on February 8^th.

Springtime and tornadoes

April is considered the start of the most dangerous three months for tornado activity across the CONUS. The reason tornadoes are more common in the spring is because conditions that lead to tornadogenesis come together more frequently during the spring.  Tornadoes are most likely to form, when the northern jet stream dips south into the CONUS. The trough brings cold dry into direct contact with warm moist air provided by the Gulf of Mexico. Tornadoes need four ingredients: lift, windshear, moisture, and instability. That dip in the jet stream helps provide for the windshear. The colder dry air is pushed over the top of the warm moist air; this creates instability, with the warm air rising up through the colder air aloft causing updraft. If things combine just right, a tornado can form. These conditions are more commonly found in the spring of the year. 

   

What is considered tornado season in the Northeast and northern Mid-Atlantic?

Severe/tornado season for New York State, New England, and Delaware, is generally June through August. While Pennsylvania and Maryland are generally May through July. But our peak time is usually end of May into the first part of July.   But we have to remember tornadoes can occur any month of the year, if conditions are favorable.

Tornadoes can also happen at any time of the day or night, But the most likely time for tornadoes to occur are during the afternoon into the evening, 3 P.M. to 9 P.M.

The US averages 1,239 tornadoes every year, based on the 20-year average from 1998 to 2017. Almost 60% of these occurred over that April through June time-frame.

For more information on the New SPC Convective Outlook, click here.

For more information on thunderstorms and tornadoes, click here   

For more information on tornadoes, click here. 

For more information on non tornadic severe weather, click here.

This seasons pattern:

Last year was  a very active tornado year, second only to 2011. 2011 was extremely active with nearly 1700 recorded tornadoes. Last year saw 1,422 tornadoes, based on the SPC inflation adjusted count. The question is what about 2020?

As I said above, winter 2019-2020 was quite active severe wise. The same pattern that brought the warm winter, is also likely to bring an active spring severe season.

Models are nowhere near sophisticated enough to use for tornado forecasting. So we have to use statistical methods instead.

Studies have shown tornado occurrence is linked to pressure anomalies near the Rocky Mountains, dry lines, the North American low-level Jet, the Madden-Julian Oscillation, the El Nino Southern Oscillation, North Atlantic Oscillation, and Sea Surface Temperature Anomalies SSTA in the Gulf of Mexico (GOM).  There is a strong linkage between SSTA in March and April, emergence of the PNA, and year to year tornado activity.  These teleconnections are what control the troughing/ridging placement, Jet Stream Position, and moisture laden flow from the GOM.

SST Map is from WeatherBell

Over the winter we had a very persistent positive Arctic Oscillation (AO) and positive North Atlantic Oscillation (NAO).  Those who follow my post, know this keeps most of the cold air and the active storm track locked up in Canada and Arctic. The resulting jet stream cutting through the CONUS helped the warmer southern air to surge northward. Add in the negative Pacific North American Pattern and the mainly positive Eastern and Western Pacific Oscillations and you have the reason winter 2019-2020 was so warm.

Given that the same pattern we had during the winter is still with us. The likelihood it will extend through this Spring and into Summer 2020 is quite high. So, the same pattern that caused the strong and active southeast ridge, is also going to have a big impact on our spring into summer severe weather possibilities. By and large the overall teleconnection pattern during December into March is still with us.   So, it seems reasonable to assume that we will see the jet bring storm systems farther south, bring cold dry air into contact with the warm moist are out of the GOM due to the southeast ridge. Given the pattern, an above average tornado season is likely in 2020. April could end up with a lot of severe weather including tornadoes.  The increased threat for severe weather will continue to ramp up for May and June. But while the overall pattern looks quite favorable for tornado production. That doesn’t guarantee that it will actually end up producing more tornadoes.

What about the Northeast and northern Mid Atlantic?

Pennsylvania, the Mid Atlantic into the Northeast saw above average activity in 2019. New York State and New England have seen an uptick in severe weather over the last few years.  This is in part due to the warmer SSTA off the coast. On my Facebook weather page, I mentioned that the SSTA in the GOM and along the Eastern Seaboard are 3-6 weeks ahead of schedule.  During March we saw how severe weather overachieved in terms of the severity of the setup. The reason for that is likely the very warm SSTAs. So, with all of this in mind, I think the Mid Atlantic and Northeast will see an above average severe year. But severe thunderstorms produce more than just tornadoes, so regardless of how many tornadoes we end up with, there will be an increased risk for large hail, flooding downpours, damaging wind gust and downburst.

Trying to forecast tornadoes is very difficult, trying to forecast tornado development weeks and months ahead of time is virtually impossible. So, all I can do is show the overall setup that looks to be in place and try to draw some conclusions from similar setups. There is no way I can tell where or when tornadoes will form, how many outbreaks we will see, or how strong the tornadoes will be.  So instead, make sure you have a severe weather plan in place. Practice that plain with your family, so everyone knows where to take shelter and what to do to try and be safe. By doing this you’ve taken a major step in assuring your family has a safe severe weather season.  Always obey warning issued by the NWS. Also buy a NOAA weather alert radio. 

For more information on severe weather safety, click here.  

Well that is it…..