What does December's weather look like? | Weather
Welcome to our News 10NBC weather blog where our team will post occasional meteorological musings about projected future weather patterns while also addressing other pertinent topics such as the global warming theory and astronomical goings-on.
This blog will, at times, address patterns in much greater depth than can be done on the TV. With that in mind, I have noted below the definitions of a few key factors that that we consider in assessing longer range forecasting. These factors are called “teleconnections” as they tend to impact and link to large segments of jet streams to one another.
There are strong signs of a shift in the jet stream pattern over North America for the period December 5 to December 15.
We will enter a neutral to positive PNA pattern (see below) which will favor the coldest air of the season to date arriving in the Great Lakes and Northeast. This cold air, while robust, will not be anything that unusual for December and it will be spread out in two or three surges.
Additionally, since only modest high latitude blocking is foreseen for the next 10 to 12 days (ie: a neutral or positive NAO, also see below), we aren’t about to become too bullish on intense and enduring cold.
Snow and ice chances in Rochester and the Finger Lakes between December 5 and December 15 will hinge primarily on two factors: moisture pooling on the front end of these arctic incursions, in association with developing low pressure, as well as from lake effect. The details are not at all clear as of this writing, but it seems likely that Old Man Winter will be making his presence felt here in the not too distant future.
Meanwhile, on the global warming front, here is a link to a fact check put together by meteorologist Joe D’Aleo, one of the brightest minds in the profession:
Finally, in terms of the night sky, several planets are visible this month. Here is a site I sometimes refer to for the latest night sky happenings:
Keep Looking Up!
MORE THOUGHTS ON DECEMBER AND THE COMING WINTER...
Here are a few more thoughts relative to the longer range outlook:
We in the weather office have been doing some research over the past few days, trying to better assess where we are heading this winter…a winter of conflicting data in the global indicators.
We were inspired by a recent research that showed that the AO was so strongly positive in November so as to rank among the top two on record.
With that kind of powerful signal we decided to start there and then look at some of the other trends in global teleconnectors to see if a relationship could be found.
What we discovered, using data points with strongly positive AO’s, negative PDO’s and weak La Nina’s was one season really stood out: the winter of 1994-95.
To test our findings, we pulled Rochester data to see if there were local congruities. Here is what we found: November of 1994 had an average temperature of 45.8 degrees which was 5 degrees above normal. November of 2011 had an average temperature of 45.8 degrees (yes, identical which is eye-catching). November of 1994 had a snowfall of 2.8 inches compared to a normal of 7 inches. November of 2011 had a snowfall of 0.3 inches.
AO: Arctic Oscillation. This refers to changes in pressure patterns in the Artic region. A positive mode means lower than normal pressure and this corresponds to a generally milder pattern from the Northeast U.S. into western Europe. A negative mode means higher pressure in the arctic and colder than normal conditions from the Northeast U.S. to western Europe.
NAO: North Atlantic Oscillation. This is a subset of the AO, focusing on pressure patterns in and around Greenland and Iceland. Like the AO, a positive NAO refers to lower than normal pressure in these areas and correspondingly milder conditions from the Northeast U.S. to western Europe. Last year and the year prior, the NAO was severely negative, overwhelming other forcing mechanisms, and consistently driving arctic air into the Great Lakes and Northeast. While the NAO is a hugely important climate driver, it defies consistent long range prediction (unfortunately).
PDO: Pacific Decadal Oscillation. An oscillation of both sea surface temperatures and air pressure that occurs over a time span of decades across the central and north Pacific. A warm (positive phase) tends to be associated with El Nino’s (see below). The PDO was warm since the late 70’s likely accounting for slight global warming, but has recently entered the negative phase suggesting a world-wide cooling is ahead.
ENSO: El Nino/La Nina Southern Oscillation. Natural shifts in surface sea water temperatures and surface pressures in the Equatorial Pacific Ocean. El Nino refers to warmer waters reaching Central America and is correlated with a strong, sub tropical jet stream which brings above normal cool season precipitation to the southern U.S. from California to Florida. La Nina means that the prevailing jet stream is the Polar jet which is much farther north and correlates to above normal cool season precipitation from the Pacific Northwest to the Great Lakes. (We will be in a La Nina this winter.)
MJO: Madden-Julian Oscillation. Shifts in tropical convection over and near the Indian Ocean have been shown to impact the jet stream circulation over North America.
PNA: Pacific North American Oscillation. The positive mode of this jet stream regime gives a ridge in the western states and a trough in the eastern states and is typically the regime in place during the bigger winter weather events of the eastern half of the country. The negative mode favors heavier winter precipitation and colder air in the western states to the Midwest, and above normal temperatures in much of the east, especially the southeast.
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