A Slow Start To Severe Season So Far.
March is when severe weather season typically ramps up in the United States. This year things have been a little slow to get going though. This is of course good news for everyone other than bored storm chasers, but why has it been so quiet and does that mean it’s going to continue?
It’s been no surprise to many that so far March has been downright COLD. In fact, as I write this a good chunk of the nation from Colorado to the east coast is under some form of winter weather advisory as an unusual March snowstorm lays down a heavy corridor of snow south of I-80. While random cold days, and even snow aren’t unheard of in March, the persistence we have seen this year is. In Chicago for example, March’s average temperature has been just 33.4 degrees. That is colder than December, January and February! Chicago is not alone, the persistent chill has many residents in the north and east half of the nation begging for spring.
We can thank a stubborn blocking pattern over Greenland for all of this. Basically what has happened is the cold airmass that typically sits over that region as well as the arctic has managed to switch places with the more mild airmass the US would typically expect this time of year. The dome of warm air is now “stuck” up there and hasn’t been able to make its way back south. This pattern has been cleverly named “The Greenland Block.” It is not the first time this pattern has shown up either. A similar pattern gave much of the country a very cool summer and slow severe weather season in 2009. The picture below illustrates what is going on.
So the burning question on all our minds is just how long will this last? Blocking patterns are stubborn and take awhile to break down, but there do appear to be some signs of spring. First and foremost is simple climatology. We are moving into April, and longer days plus a higher sun angle mean it can’t stay cold forever. Those looking for something more than just that will have to dig deeper into forecasting techniques. One indicator is called the NAO (North Atlantic Oscillation) and without getting too technical, it’s basically an ocean parameter that correlates to the general weather pattern. When the value is positive we generally have warmer and stormier weather. When the value is negative, we have cooler weather. As you can see, we’ve been negative for all of March, but the forecast direction is heading back towards positive territory.
Some of the models do indeed pick up on this trend and are showing more typical temperatures further out. Such as this run of the GFS (Global Forecast System) for April 5th
The folks at the Climate Prediction Center have also been observing some of these long range trends, and have their outlook indicating warmer than average temperatures for much of the country from April through June.
So winter weary residents need not worry. Warmer weather IS coming. We just have to be patient this year. What does that mean for severe weather? It is way too hard to predict when and where storms will form, but what I do know is with warm weather comes more instability, and where there is instability there can be violent weather. Just because we are off to a slow start, doesn’t mean mother nature won’t flip the switch and suddenly we will find ourselves immersed in a very active pattern. That is why it is always important to be prepared, and stay weather alert no matter how slow things get.