My Fall and Winter Tornado Forecast (2024-25)

Introduction hey everybody Trey here welcome back to another video the calendar has turned from August to September which means our secondary severe weather season is right around the corner as we know it's been quite the active year tornado wise across the US and a lot of you have asked me if that is expected to continue into the upcoming fall and winter seasons in this video we're going to try to answer that question by analyzing different modulating factors we're going to make a forecast for tornado frequency and distribution across the US for the October 2024 to February 2025 time frame our goal is to figure out which areas of the US might be more or less susceptible than normal to toric activity during the upcoming secondary season as always I'll put links to any Journal articles I mentioned in this video in the description box below so you can do some research on your own so without further Ado let's go ahead and get started as you may recall from our spring tornado forecast we typically look at three main factors that modulate tornado frequency and distribution across the US Global Climate teleconnections sea surface temperature anomalies in the Gulf of Mexico and drought conditions in the elevated mix layer source region now the drought piece is not as big of a factor in the fall and winter months we know that the intensity of drought in the EML source region impacts cap strength during the Spring a decent chunk of tornado events occur on mesoscale days days that don't have a big synoptically evident trough and instead are fueled by smaller scale features such as boundaries subtle short waves Etc that's not so much the case in the second season the vast majority of fall and winter tornado events are are driven by big high amplitude troughs Ascent from these troughs plays a major role in eroding the cap so a stronger cap is not as much of an issue whereas on mesoscale days you're Reliant mostly on Surface Heating and low-level warm injection making it more difficult to erode a strong cap when large scale forcing for a scent is weak that's not to say drought and EML strength don't play a role in the second season a more robust EML can actually Aid in tornado potential particularly in the Southeast where non-optimal thermodynamics often hold events back from reaching their tornado ceiling but drought doesn't play as much of a role in the second season as it does in the spring so we're going to focus on the other modulating factors in this video let's start off with global El Niño Southern Oscillation climate teleconnections perhaps the most influential of these is the elino southern oscillation or Eno we discussed what Eno is and how it works in our spring tornado season forecast so I'll put a link to that video in the description box below if you'd like more in-depth information on Eno as a quick review Eno takes into account sea surface temperature anomalies in the region of the Pacific ocean that lies along the Equator colder than normal Waters in this region represent linia warmer than normal Waters indicate an elino and near average Waters represent the neutral phase you've seen this chart before in my seasonal forecasts on the vertical axis are our equatorial Pacific Sea surface temperature anomalies and on the horizontal axis are our running 3month periods during which those anomalies are averaged July August September August September October September October November and so on plotted are are forecasts from a bunch of different long-term climate models of how Eno might progress through next spring here's where we stand now the average observed sea surface temperature anomaly for the May June July stretch was positive. 25° C and The observed anomaly for July only was positive. 21° C both well within the range for neutral and so beyond that models generally indicate a continued very gradual decrease in these anomalies through early 2025 either remaining in the neutral phase or dipping into a weak linia before perhaps Waters warm slightly by next spring this is supported by the climate prediction Center's probabilities for each Eno phase through next spring with a greater than 70% chance for linia conditions by the October November December time frame probabilities for linia drop below 60% by late winter while chances for neutral conditions increase to 40% we'll have to monitor Eno's progression throughout the second season as a quicker transition into linia conditions may have impacts on tornado frequency and distribution in the US but for now we assume at least weak linia conditions in place for a good chunk of the fall and winter in our spring tornado forecast we used research from Lee ated Al 2016 that suggests that the overall progression of Eno phase throughout the spring is a better indicator of us tornado potential than the individual Eno phase most prevalent during the season unfortunately this method has not been translated to fall and winter tornado activity but there's still ample research linking Eno phase to second season tornado activity in the us both cook it Al 2017 and child's atow 2018 suggest that tornado activity in the US is greater during linia and neutral Falls and Winters than it is during El Nino cook at Al also found that tornado activity during linia periods tends to spread farther north than in other phases particularly during January and February as Illustrated in their figure three this has to do with how Eno modulates the jet stream during El Nino Winters which you see on the top the jet stream is more subdued and shifted farther south leading to stormier conditions along the southern tier of the US whereas in linia Winters as you see on the bottom the jet stream is more Amplified and supports more unsettled conditions from the mid South into the Great Lakes another potential Pacific Decadal Oscillation driver of second season tornado activity in the US is the Pacific decadal oscillation or PDO the PDO involves sea surface temperature anomalies in the interior North Pacific and less importantly along the Pacific coast of the us if we have cooler than normal Waters in the interior North Pacific and warmer than normal Waters along the US West Coast we are in a positive PDO phase as Illustrated on the left and if the opposite is true we are in a negative PDO phase as shown on the right in their 2021 paper norri at Al discussed that a negative PDO is linked to increased tornado frequency in the US versus a positive PDO due to favorable alterations to the jet stream taking a look at a map of current Global sea surface temperature anomalies you'll notice that we have significantly warmer than normal Waters across the interior North Pacific this overrides the conflicting contribution from slightly above average sea surface temperatures along the Pacific coast of the US and thus puts us in a negative PDO in fact this has been the case for quite some time we've been in a negative PDO and often a strongly negative PDO since late 2019 with the expectation that this should persist through at least fall and winter it may be a factor in increased tornado frequency across the US during this secondary season however Nadal 2021 note that the P has a much more limited influence on torn activity in the Southeast compared to areas elsewhere including Texas and the Midwest Eno and Other possible teleconnections (AO, PNA) PDO are good tools to use in forecasting second season tornado activity because they oscillate between phases on a time scale of months to years allowing them to be forecast well ahead of time however there are a couple shorter term teleconnections that are linked to us tornado activity we need to watch for this fall and winter these oscillate between phases on the order of weeks at times so they can't be forecast months in advance but research has shown that they do tend to modulate second season tornado frequency and distribution in the US so they're worth mentioning the first of these is the Arctic oscillation or AO the AO involves a belt of upper level flow that circulates counterclockwise around the Arctic at around 55° north latitude during the ao's positive phase which is Illustrated on the left this belt of flow is stronger which coincides with higher pressure over the Arctic this keeps cold air confined to the Arctic region yielding less cold air intrusions into the US and a more favorable pth pattern for severe weather including tornadoes particularly in the Southeast during a negative AO as Illustrated on the right those winds a loft are weaker and therefore allow cold air to intrude more frequently into the us we head into to fall on the heels of a slightly positive AO but again that may very well change as we head deeper into the season child zal 2018 found that the AO has a slightly stronger relationship with second season tornadoes than Eno does so it definitely Bears watching during the fall and winter the other shorter term connection is the Pacific North American pattern or PNA in the positive phase of the PNA as shown on the left above average pressure is situated from near Hawaii into Western North America and below average pressure exists south of Alaska and over the eastern US the opposite is true during the pn's negative phase as shown on the right lower than normal pressures extend from Hawaii into Western North America while higher the normal pressures are situated south of Alaska and across the eastern US Kim edal 2024 determined that the negative of the PNA is associated with increased second season tornado activity in certain parts of the US thanks to favorable alterations to the jet stream and a more unstable air mass making its way into the eastern half of the us as shown in their figure 4H in longer lived negative periods tornado activity tends to increase in an area from Mississippi and Arkansas into the Upper Midwest centered on the Ohio Valley for example the infamous quad State tornado supercell on December 10th 2021 was linked to a long-lived negative PNA in shorter lived negative periods the increase remains but isn't as widespread focusing on the small area from Arkansas and Western Tennessee into Missouri and Southern Illinois as Illustrated in their figure 4D Kim edal also determined that longer-lived negative PNA is more common in linia periods than in elino like the AO the p is quite volatile oscillating on very short time scales but with Eno forecast to shift into a weak linia by this winter we'll have to keep an eye out for periods of negative PNA which could bring enhanced tornado activity to the eastern half of the us Gulf of Mexico SST anomalies our other main driving factor for fall and winter tornado activity in the US is Gulf of Mexico sea surface temperature anomalies as described in Molina at Al 2018 warmer than normal Waters in the Gulf of Mexico lead to a more unstable air mass that can be transported farther northward into the US which is favorable for severe weather including tornadoes in their figure 2f kimal 2024 note a broad area from the Gulf Coast to the Midwest that sees increased tornado AC ity when Gulf of Mexico waters are warmer than average on the other hand a cooler than normal Gulf yields a less unstable air mass that can be eved northward which is not as optimal for severe weather currently the waters across nearly the entire Gulf of Mexico are quite a bit warmer than average based on model forecasts this is expected to persist through at least late 2024 into early 2025 which is plausible given how high Gulf sea surface temperature anomalies are currently and a lack of tropical Cyclone activity to disturb these warm Waters we'll have to monitor how things progress throughout the second season but for our purposes we'll assume average to above average sea surface temperatures across the Gulf of Mexico for fall and winter all right let's take Current forecast products a look at what some of our current forecast products are saying here are the climate prediction Center's next several 3-month precipitation outlooks beginning with the October November December period green shading indicates probabilities for above normal precipitation and brown indicates probabilities for below average precipitation with darker shading indicating higher probabilities in each category you'll notice that chances for below average precipitation creep in quickly across the Southern Tier of the country to start the fall with the highest likelihood of subnormal precipitation situated from New Mexico and Texas into the Gulf Coast through the fall and winter probabilities for above average precipitation start off across the Northeast and slowly inch west and south with time including the region from the Great Lakes into the mid South by early 2025 now of course precipitation doesn't necessarily correlate to toric activity but it can be a look at how active the background pattern might be overall in addition let's analyze some model forecasts of 500 M geop potential height anomalies for this upcoming second season as a refresher geop potential height is the height of a constant pressure surface in this case 500 mbars above mean sea level in general lower Heights are associated with troughs which can drive severe weather and higher Heights are associated with ridges on these Maps yellows oranges and reds indicate above normal Heights whites indicate near average heights and blues indicate below normal Heights notice how the entire us is entrenched in above normal Heights from October to January this could indicate a fairly quiescent background pattern that's not entirely conducive for consistent severe weather by winter we do see some decrease in height anomalies over Canada and the northern us but above average heights remain over most of the country Discussion of analogs begins all right now let's look at some analoges I went through and looked for Falls and Winters since 1950 that had similar configurations of Eno PDO and Gulf of Mexico sea surface temperatures compared to what we're expecting for the October 2024 to February 2025 period this includes Eno transitioning from El Nino to start the year into a neutral or weak linia phase during the fall and winter a negative PDO and generally above average sea surface temperatures in the Gulf of Mexico there weren't a ton of great matches but I did find a couple that fairly closely resembled our current proges the first is Analog: 1966-67 1966-67 1966 started out with a moderate El Nino that transitioned into a neutral phase by Spring this persisted through fall and winter nearly dipping into a weak Lao by early 1967 PDO was negative for the entire fall and winter albeit a bit less negative than what we're expecting this season unfortunately the sea surface temperature anomaly archive I use only goes back to 1982 so we'll have to ignore Gulf of Mexico se- surface temperature anomalies for this particular analog 1966-67 featured an active fall before tornado activity went relatively quiet during the winter activity was heavily centered on the Midwest in particular Iowa Missouri and Illinois with a few strong to Violent tornadoes mixed in including an F5 in Northern Iowa on October 14th 1966 and a couple f4s on January 24th 1967 in addition a smattering of activity occurred from the Gulf Coast States into the Eastern Seaboard another Analog: 2016-17 decent analog is 201617 2016 also saw a strong El Nino transition into a neutral or weak linia phase by fall but we dipped into a weak linia a bit more quickly than what we've seen this year PDO was also somewhat variable oscillating between weekly negative and positive Gulf of Mexico sea surface temperature anomalies were an excellent match however with warmer than normal Waters persisting across the gulf throughout the entire fall and winter these conditions led to a well above average second season in terms of tornado activity with 370 tornadoes across the US from October to February a time period that usually sees around 200 250 fall began on the quiet side before an active stretch to end November activity ramped up significantly in January and February including a rare SPC high-risk Center on Georgia and Florida on January 22nd and a significant outbreak across the Midwest on February 28th overall the gulf coast states featured heavily in 201617 along with a decent amount of activity from the central plains into the Midwest in Ohio River Valley Analog: 1970-71 19771 was also a decent analog 197 didn't start out with as strong of an El Nino as we saw at the beginning of 2024 and we eventually transitioned into a Lenin that was quite a bit stronger than what's expected going forward into 2025 however PDO was moderately to strongly negative throughout the entirety of the fall and winter which closely matches our expectation for p this upcoming second season again our sea surface temperature archive only goes back to 1982 so we'll have to ignore Gulf of Mexico anomalies for this analog 176 tornadoes occur during fall 1970 and winter 1971 the fact that this number comes close to our modern average for tornadoes during the secondary season suggests that it may have actually been above average given less effective tornado reporting practices back then the bulk of the activity occurred from the Southern Plains into the Gulf Coast with scattered activity across the Midwest including a few rare December tornadoes in Wisconsin the 19771 season was bookended by active months the Southern Plains in southeast led the way in October and February saw abundant activity in the Gulf Coast dates with a few violent tornadoes mixed in the middle portion of the season was relatively quiet outside of these three Other (weaker) analogs analoges I couldn't find any other good matches 1983 84 1992 93 and 1995 96 were all decent matches for Eno but they each featured generally positive PDO and cold anomalies in the Gulf of Mexico still these Seasons all featured average to above average tornado activity a good chunk of which occurred in the region from the Gulf Coast States into the Eastern seab board so with all of this My fall/winter tornado forecast in mind what do I think is going to happen tornado wise this fall and winter this forecast is a tough one as we have some conflicting factors in a scarcity of good analoges Eno is expected to be generally favorable with neutral to weak linia conditions in the forecast and our persistent negative PDO should continue through the second season Waters in the Gulf of Mexico should remain warmer than normal as well however our current forecast products show elevated chances for a dry fall and winter across the Southern Tier of the country country but this was the case going into the second season in 201617 and we still ended up with an above average fall and winter tornado wise given a generally favorable background pattern I expect an average to slightly above average second season in the tornado Department continuing the trend from this past spring I think the Midwest into the Ohio Valley and Midsouth will be a relative Hot Spot thanks to a more Amplified jet stream via the forecast lenia and negative PDO and a farther northward advance of favorable warm sectors from the warmer than average Gulf of Mexico tornado activity won't be as frequent as what we saw in the spring here but we should see a few events across this region to help bolster the tornado count into above average territory in addition we should see a good amount of tornado activity in the Gulf Coast states particularly from East Texas into Alabama and Georgia this is pretty typical during the fall and winter as evidenced by our analoges but the tornado count may be slightly enhanced across this region relative to normal in part due to a warm Gulf of Mexico weather toric activity will be front loaded backloaded or evenly dispersed throughout the second season remains a bit of a question mark given a Darth of evidence suggesting one progression or another but there should be a few notable events sprinkled throughout the fall and winter to help bring the tornado count up to average or slightly above there are some wild cards that we'll need to watch out for if we see tropical Cyclone activity finally increase in the back half of this hurricane season any landfalling storms could boost the tornado count in addition as we discussed before prolonged stretches of positive AO and negative p a May set the stage for an increase in tornado activity in certain areas of the us but we just can't forecast those months in advance all in all the fall and winter tornado season looks to continue what has been a very active year across the US and I'm interested to see how things play out as we close out 2024 and roll into 2025 thanks for watching and we'll see you in the next video