WINTER FORECAST 2014-2015 Be sure to Like and Share with your friends! It’s finally here. The winter forecast for the 2014-2015 season from DC Severe Winter Weather has arrived! First, we will go over our overall expectations regarding temperature, snowfall, and precipitation for each month of winter. Last winter, we saw extreme shots of cold air impact the region throughout January into February. The region saw above average snow for the first time in the two years previous. This winter, we expect cold to come with less intensity, but more consistency. This should lead to overall, a very cold winter. We also are forecasting above average precipitation across the region, and above average snow totals, similar to last winter. DETAILED FORECAST: Temperature Departures (How cold it will be compared to average): December : 1 degree colder than average January : 4 degrees colder than average February : 3 degrees colder than average Snowfall (Detailed map below): Reagan National Airport (DCA) : 20” (15.4” average snowfall) BWI : 28” (20.1” average snowfall) Dulles Airport (IAD) 35” (22” average snowfall) We have compiled graphics containing a projected snowfall map, as well as temperature, precipitation, and snowfall departures from average below. Continue reading for a detailed look into the methodology behind our winter forecast, and the variables we used when putting together our outlook. METHODOLOGY: When assessing the upcoming pattern, there are many oceanic and atmospheric cycles we look at to offer clues as to how the atmosphere will behave in the next few months. El Nino Southern Oscillation (ENSO): The first, and most well known cycle is the El Nino/Southern Oscillation, a periodic oscillation of oceanic temperatures and winds in the tropical pacific. This pattern has a major affect on world climate. During the warm phase, known as an El Nino, the DC area tends to be colder and snowier, with the most pronounced type a moderate El Nino. During weak El Nino’s big snowstorms are not as common, but weak El Nino’s rarely yield winters with below average snow. During the cold phase, known as a La Nina, the DC area tends to be warmer with more rain than snow as storm cut to our northwest. However, some weak La Nina’s can still produce snowy patterns. The map below depicts current Ocean temperature anomalies around the world. Notice all the warm water along the equator in the Pacific Ocean. This is a tell-tale sign of an El Nino. El Nino Region 3.4 is currently .8 degrees warmer than normal, within the range of a weak el nino. The Southern Oscillation Index (SOI), a measure of the atmospheric component of ENSO, has also been solidly negative for the past several months, a strong indicator than an El Nino is indeed in the cards for this winter. An Image of the SOI is shown below. This El Nino is likely to remain in the range of weak, although it could push near moderate for a short period of time. Weak El Nino’s are a mixed bunch, not nearly as consistent of a signal for cold and snow as a moderate El Nino would be. That brings us to the second most important part of the forecast, the Arctic Oscillation. Pacific Decadal Oscillation (PDO): The Pacific Decadal Oscillation measures the intensity and location of differences in sea surface temperatures in the North Pacific Ocean. A positive phase often indicates cold and snowy weather across the Mid-Atlantic, while the negative phase usually correlates with our region being warmer. The PDO is measured every month, but we have been in a negative decadal phase for 7 years. However, the PDO has been positive for 9 consecutive months. Not every winter is the PDO guaranteed to be the same as the decadal phase the PDO is in. The graphic below depicts the time series of the PDO phases. Arctic Oscillation (AO) and North Atlantic Oscillation (NAO): The Arctic Oscillation is a measure of height anomalies over the arctic compared with the mid-latitudes. When it is positive, troughing over the arctic allows keeps the cold air out of our region. When the AO is negative, it is more likely that a cold outbreak will occur over the mid-latitudes, including the US. The North Atlantic Oscillation measures these differences in air pressure over the North Atlantic Ocean. A negative AO and NAO tend to be correlated, but this is not always the case. During periods during winter with a -AO, cold and snowy weather becomes more likely, especially when paired with a negative NAO. Predicting the wintertime Arctic Oscillation: Snow Advancement Index/Snow Cover Extent (SAI/SCE) The SAI is a measure of the rate of snow growth south of 60 degrees latitude in Eurasia in the month of October. It has a surprisingly strong correlation to the wintertime AO. The SCE is the greatest snow extent, and is more strongly correlated with actual temperatures than the SAI but less correlated with AO state than the SAI. Due to the vast advancement of Eurasian snowfall so far this fall (this year exceeding every previous year in snow growth), we believe the AO will be strongly negative for a majority of the winter, and the NAO will average negative throughout the winter. This should lead to prolonged cold over much of the country. An Image showing the extent of October Eurasian Snow Cover is shown below. CONCLUSION: Enjoy the winter, it should be cold and fairly snowy. We will keep you covered at all times during this winter. Be sure to like and share this post, so many people will be able to see our forecast! --------------------------------------------------------------------------------------------- All images mentioned above can be found in the photos below. This post was a joint post and contributed to by all members of D.C Severe Winter Weather.
Posted on: Mon, 17 Nov 2014 23:29:58 +0000
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