The 2012-2013 Winter Season is expected to be a busy year, especially the East which had very little snowfall when compared to last year. Last year was also a mild winter for many areas extending from the northern Plains to the Northeast. After a record-breaking March, we stepped into a summer that so far has not let up with intense heat and drought impacting the center of the nation. We believe that these past events will impact the weather for this coming Fall and Winter Season.
For the East, snowfall may average above normal across the mid-Atlantic into southern New England.
We believe that snowfall will average closer to normal for the interior Northeast through northern New England. The Southeast can be wetter than normal with cooler temperatures. The stormtrack may be dominated by the southern branch the first part of the season, until the northern jet increases in strengthen with more opportunities for phasing mid- to late season. This means more widespread rain than snow events early or storms passing off the Southeast coast and out to sea. The question still remains how much blocking sets up this year.
For the Central U.S.
For the northern and central Plains, snowfall is expected to be below normal with near- to above-normal temperatures. With a weak El Nino, there is too much variability to make a call farther east into the Midwest and Ohio Valley. 1977-78 was a snowy season in Chicago with snow amounts over 80 inches, but in 2006 snowfall was in the 20s, both weak El Nino events. Strong El Ninos are drier for the Midwest and Ohio Valley, so we will allow for near normal in this region for now. The southern Plains may end up below normal with occasional shots of cold behind bigger East Coast systems.
For the Rockies and West..
Early start to the season is expected with October and November storms anticipated for the southern and central Rockies. Many weak El Nino Falls showed above-normal snowfall for this area. Also, the Northwest could see normal to above-normal moisture in the Fall, meaning good snow build up in the mountains. However, as the jet splits in the winter, the intensity and frequency of events will lower and so will the amount of snowfall. Cold will surge early south into the Rockies but expected to shift east during the winter.
We are heading into an El Nino Fall and Winter. Signals suggest that this will be a weak El Nino, possibly peaking in the mid- to late Fall. Weak signals of El Nino and La Nina can result in variability. Therefore, up until the time we arrive at the final Winter Season Forecast in the fall, the following points will be researched and addressed which can impact the trend of the winter forecast:
• ENSO- What impact of a weak El Nino compared to a strong El Nino and how peaking in the Fall may impact normal conditions during an El Nino Winter. For example, statistics show variability in snow amounts for Chicago, discussed earlier, but below much below normal in a moderate to strong El Nino.
• Typically in an El Nino winter, a split jet stream pattern develops for most of the season. We feel confident this year that the southern branch will be active, bringing plenty of moisture to southern Rockies, Gulf Coast and the Southeast. But, how fast do we see the northern jet make an impact, transporting colder air into the pattern and leading to phasing? We are leaning toward later in December or January.
• Last year we saw very little blocking develop over the northern Atlantic. This year we feel that blocking will increase, but does this happen in early, mid- or late winter.
• Will drought and heat this summer into the Fall impact the Midwest and north-central Plains? In a more typical and stronger El Nino Winter, these areas are usually drier. Our forecast is for a warm Fall in the Ohio Valley, Lakes and the Northeast with below-normal precipitation away from the coast. Almost perfect conditions would have to set up to have another storm like last October for the Northeast. This year is a low percentage chance for that occurrence.
• Water temperatures are running warmer than normal around the Lakes and Hudson Bay. We’ll this modify colder air masses as they reach the East early in the season. This certainly can happen if the southern part of the jet stream stays stronger than the northern part through November and perhaps into December.
• Warm water temperatures off the New England coast... Could this lead to cyclogenesis and rapidly intense storms. You do not need blocking for this to occur and this can lead to bigger storms along the coast.
• The PNA will be just as important as the NAO this year. The NAO can give us an idea of blocking. A positive PNA can lead to a strong upper ridge in the Northwest or western Canada which increases the northern jet from northwest Canada, southeast into the U.S. with the cold air needed for strong storms and possible big snow events. The European model, right now, shows a positive signal developing in December.
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