01/16/2016
The Mid-Atlantic’s Strong El Nino Winter
The impact of a strong El Nino on the weather in the mid-Atlantic is often not that significant. South of us tends to be wetter, north of us dryer but being in the middle we still get a little bit of everything. Unlike the very predictable waves of moisture hitting the west coast the precipitation impact for us—rain, snow, nothing--still depends on the exact track a given storm. The North Atlantic Oscillation (NAO) actually has the biggest impact on our weather. A negative NAO means the regular west to east air flow in the upper atmosphere over the north Atlantic gets blocked which sends cold air from Canada plunging down along our Atlantic coast. A negative NAO combined with moisture out of the Gulf of Mexico or out of the Atlantic (a Nor’easter) give us our biggest storms. Unfortunately the NAO is very hard to predict more than a few days out and doesn’t seemed to be directly impacted by El Nino.
What does seem to be happening in our area so far this winter is mild temperatures interspersed with brief periods of bitter cold, regular precipitation which usually arrives when the temperatures are mild and strong winds which often follow the precipitation. This pattern has its pluses and minuses. First plus: the regular precipitation is falling in moderate amounts when the ground isn’t frozen so the roots of evergreen trees and shrubs can use that moisture to keep hydrated and the soil isn’t being left soggy which could cause the roots of deciduous plants to rot. Second plus: strong winds, which can be very damaging to evergreens, have been arriving after the rain which has hydrated the evergreens mitigating the negative impacts of the wind. Third plus: we’ve had very brief periods of severe cold. Long durations of severe cold can freeze top soil down several inches resulting in fine root damage to all plant material particularly when the ground is not protected by fallen leaves or mulch.
Now the bad news! Dramatic fluctuations in air temperature are very hard on all types of plant material. In the fall deciduous plants drop their leaves and evergreens harden off preparing for winter. Unfortunately, after we’ve had at least one significant cold spell plants are programed to respond to warming temperatures as an indication of the arrival of spring. That’s why you see crocuses and daffodils shooting up out of the ground. It’s also why some Cherry trees and Forsythia are blooming as well as some Daphnes and Camellias. What you aren’t seeing is that all plants are responding to the warmer weather by getting ready to leaf out, bloom, put on new growth. This takes energy stored in the plants roots, energy that will have been wasted when the plant realizes it was a false alarm spring has not arrived and the plant will waste more energy getting back in winter mode. Most plants will survive this temperature fluctuation just fine but there will be residual effects. Blooming and putting out the first flush of leaves in the spring may be slow or weaker than normal because both take a large amount of stored energy. In extreme temperature changes some evergreen plants like Nandinas and Daphnes will drop their leaves and it will be well into the spring before they are able to re-leaf out. Deciduous plants like Japanese Maples, Redbuds and Hydrangeas are likely to have more dead branches once they do start growing in the spring.
What can you do? Most important thing is NOT to prune or fertilize. Pruning and fertilizing stimulate growth in any plant that is not dormant so this winter both should wait until spring has definitely arrived. Other suggestions would be to check your drainage to make sure plants aren’t sitting in water and make sure there is sufficient mulch around plants that are particularly sensitive or exposed. Beyond that come spring be patient with your plants and give them a little extra time to get looking their best.
Let me know if you have questions?
