Last week saw eight straight days with temperatures at or above 80 degrees – our longest warm stretch since last August. It might even seem like a well-deserved treat after a cold winter. Consider the case of the temperature milestones so far this year.
With our proximity to the mild Atlantic Ocean, it’s not uncommon to see a warm reprieve during the winter. Recall February of 2008, when a long stretch of 60 and 70 degree weather convinced the trees on the Brickyard that it was time to flower. That’s not to say that 2009-2010 will go down as a particularly cold winter (our early-January arctic blast aside). We didn’t break any record lows, and our seasonal snowfall total was unremarkable. The active jet stream pattern created by El Niño meant ‘Snowpocalypse’ for the Northeast but only frequent clouds and rain in our area. This resulted in cooler-than-normal daytime highs. As the chart indicates, temperatures throughout most of January and February remained below average.
By early March, we had just scraped away our last inch of snowfall. Within a week, the cold weather pattern eased its icy grip on the East Coast and allowed our temperatures to finally exceed 70 degrees on March 9. Ordinarily, 70-degree weather is not a big deal for North Carolina. Most notable was how long the warm weather stayed away this winter. Between December 9, 2009 and March 9, 2010 – one quarter of the calendar year – temperatures never reached 70.
To put it in perspective, Raleigh’s average date for the first 70-degree weather is normally around January 30, and it historically ranges between January 1 and March 14. In other words: the 70s had a very late start this year.
Our first 80-degree day came on April 1, which was very nearly average compared with the climate data. It wouldn’t be long until Raleigh saw its first 90-degree day of the year, on April 6. In the sixty-two year history of official weather observations at RDU airport, that’s the third earliest date on the calendar year that we’ve reached the 90 degree mark. In an average year, the first 90-degree day is around May 19.
So we went from having the second-latest start of the seventies to the third-earliest start for the nineties in one month’s time. Between March 7 and April 11, the daily high temperatures were an average of seven degrees above normal. During the same time period, nighttime lows were about five degrees above normal. What is responsible for the rapid warm up? Over the past few weeks, an area of high pressure remained stationary off the Southeast coast of the U.S., which is a very typical pattern for summer. Because winds around a high flow clockwise, the prevailing winds have been from the south or southwest, bringing north unseasonably warm air from the tropics. The sudden warm up is also the likely culprit for the terrible allergy season, as several species of trees released their pollen all at once.
If you are a fan of summer-like weather, you probably love that it has arrived sooner rather than later. How long will it stay? As you’ve already noticed, temperatures are not nearly as hot this week. The long term forecasts from the Climate Prediction Center believe that the temperatures in North Carolina will stay close to average for the next few weeks, with a major heat wave or cold snap unlikely. Average temperatures for mid-April tend to be in the lower- to mid-70s. Past that, the one month outlook implies that we may see a warmer than usual May with average precipitation. By the first of June, meteorological summer begins for good.
In the next column, I examine yet another meteorological phenomenon that roared back to life this spring after an unusually long absence.
