Why mild winter 2017

Most of our temperature outlooks have performed pretty well a long-term HSS average of 15 which is greater than 0 going back in time, showing that our forecasters do have skill in this whole seasonal outlook business. Precipitation is usually harder to forecast than temperature, as one big storm can have a large impact on the seasonal totals. This leads to a much noisier observed pattern than temperature. In reality, the western and southeastern regions of the United States observed a drier-than-average winter, while the Missouri and Ohio River Valleys, Great Lakes and western High Plains recorded a wetter than average winter.

Not too bad! If we look at the verification number , the outlook scored a HSS of 23 or a 32 if we only looked at locations with one favored outcome. So, this is a good score for a precipitation outlook when we consider how difficult it can be to predict precipitation. However, on average, both temperature and precipitation have HSS numbers above 0. This outlook had more hits than misses yay! It all sort of depended on where you lived.

That is the nature of these winter outlooks. But in figuring out just how good a winter outlook is overall or whether to trust it , you cannot just look at the one or two times a winter outlook was good or bad. Lots of things. Also active during this winter was the Madden Julian Oscillation. Its influence on the United States was already covered extensively by Michelle last month.

In short, as the MJO moved around the globe, it led to prolonged periods of colder and warmer than average temperatures across much of the country this winter. Though, while this certainly impacted monthly climate, it likely had less impact on climate patterns averaged over the entire winter. Anything else, you ask? Well, there was always the randomness of the weather as well as variability in other atmospheric oscillations like the Arctic Oscillation.

Basically, because it is the one influence that is actually predictable a season ahead of time. We know that other things will impact the winter temperature and precipitation patterns besides ENSO. No one is harder on forecasters than forecasters themselves. For how to truly do justice to the forecast, check out this post. Because there are different ways of treating the areas in the outlook where the chances for all three categories are equal known as Equal Chance or EC.

We can calculate the HSS including EC forecast areas, which are essentially the same as random chance, and we can calculate the HSS for only areas where the outlook favors one outcome more than others. These methods reward different ways of forecasting. The HSS that includes areas with EC can be maximized if a forecaster makes non-EC predictions wherever they think there is a signal, regardless of confidence.

To quantify the effect of warming on the coldest two-week period of the winter in the area, we fitted the series to a Generalised Extreme Value GEV distribution whose mean location is allowed to shift proportionally to the smoothed global mean temperature time series Fig.

That factor is estimated to be about two, indicating that the temperature of the coldest two-week period has increased about two times faster than the global mean temperature rise. This has been explained as a consequence of stronger warming trends in the Arctic, where the cold air originates Screen, ; van Oldenborgh et al, The fit also shows that these two weeks are very unusual in the current climate, with a return time of very roughly years in this region.

The significant dependence of the GEV location on the values of global mean temperature allows us to ask what the return time of such an event was in the climate of a century ago, i. Our estimates indicate that a cold wave like this occurred on average every seventeen years. This means that cold waves like this have become approximately a factor fifteen less frequent due to global warming, as shown in Figure 5. Bottom: return time plot. The blue curves denote the climate of , the red ones the current climate.

We also investigated the possible role of circulation changes on the changes in probability, as there have been suggestions that the probability of cold outbreaks has increased due to the smaller temperature contrast with the Arctic.

This gives rise to the northerly flow that brings Arctic air down over eastern North America. The trend in annual maximum of day averaged pressure at this point has been negative since the late s, contradicting the hypothesis that northerly flows here have increased due to strong Arctic warming. This agrees with reviews of the effect of Arctic warming on the jet stream e. Barnes and Screen, In fact, the temperature of two-week cold waves has increased over all of North America, as expected in a warming world Fig.

We see no evidence of an increased intensity of these cold waves, but rather a faster warming than the mean winter temperature in northern North America. The jet stream also is playing a huge part in the extended warmth.

It travels across Northern California, skimming along the border between the U. So unfortunately or fortunately , it looks as if this pattern is here to stay — along with the pollen. Tree pollen will continue to be on the high side until the region gets some rain. There are moderate drought conditions through a good portion of the area, so some precipitation — any precipitation — is needed.

The good news is that cherry blossoms could peek slightly sooner! The earliest cherry blossom peak date was March 15 back in which was also a very mild winter — see above.

Keep an eye on those blooms and flowers. Actual spring may come a lot quicker than anybody ever thought. Location Help. News Headlines. Customize Your Weather. Privacy Policy. Winter Review Weather. Current Hazards. Rivers and Lakes. Climate and Past Weather.

Current Weather. Forecast Maps. Hour by Hour Forecast.