Well it’s
April 1st, 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 8th.
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.
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.
For more information on severe weather safety, click here.
Well that is
it…..
Tornado activity in California in April. Historically what does this look like? I was not aware of this.
ReplyDeleteCentral California, especially near and in the Central Valley is what is considered a locally enhanced zone. Central California can and does see increased tornado activity in April. Over the last 12 years both the Sacramento and the San Joaquin Valleys have had a big uptick in tornado warnings.
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