This is the forecast for the Arctic Oscillation (AO) during the winter of 2014-2015.
(From the Official winter forecast) The above image shows a pretty daunting image of the stratosphere, so let's decipher it. The red line shows observed temperatures at the 70 millibar level of the stratosphere, between the 65N and 90N latitude lines. The dashed green line illustrates average temperatures for any given time, while the gray outlines give an indication of the record high and low stratospheric temperatures for any given time period over the past few decades of records.
Gazing over the image above, specifically around the most recent records of temperatures, we find ourselves on the above-normal side, with that red line bursting up into above-normal territory more than once in the last few weeks. This year's warmth at the 70mb level looks to be a bit more prevalent than that of last year, as you can see just to the left of the center of this image.
Why is this important to the coming winter? Above-normal temperatures in the stratosphere allow for a higher threat for persistent high pressure to form over the Arctic Circle, and general upper-latitude area. The polar vortex, a strong low pressure system of cold air located across the troposphere and stratosphere, can be strengthened during times when the stratosphere is colder than normal, and weakened when warmth prevails.
When this warmth prevails, strong bodies of high pressure can punch north from the lower latitudes into the Arctic, disrupting the polar vortex. When this happens, fragments of the vortex can break off and be sent to the lower latitudes (as was seen last winter), or the whole vortex can be shunted down south. If the high pressure sticks around in the Arctic for long periods of time, it can be referred to as "blocking" high pressure, for the way it "blocks" the pattern from flowing east to west around the globe, since the high pressure remains stagnant and backs everything up.
If the stratosphere is to remain warmer than normal this winter, the polar vortex may fragment, leading to increased risks for cold air outbreaks in North America.
The above image shows anomalies of the October Pattern Index over the last several days, since the start of October. The OPI, the concept of which was brought about by a group of Italian scientists, says that monitoring of the atmosphere during the month of October can yield great hints at what the coming winter will bring. October is a month well-known for big winter-predictors showing their cards for the coming cold season (i.e. the LRC, and Judah Cohen's Snow Advance Index (SAI)), but it may interest many to know that the OPI may be one the best, if not the best predictor of the upcoming winter season out of the three mentioned above.
The explanation page of the OPI tells of the index's incredible accuracy, around 90%, of being able to predict the December-January-February Arctic Oscillation. In the winter, a negative phase of the Arctic Oscillation (AO) means the polar vortex is weak and is more prone to sending cold outbreaks to the mid-latitudes, while a positive AO indicates a strong polar vortex, hence a warmer winter increases in probability.
Though we aren't to the middle of October yet, early indications are that the OPI is sustained in a negative phase, today plummeting to around -2, as shown above. If the OPI stays in that negative territory for the rest of October, chances are the winter may have a negative Arctic Oscillation. The AO doesn't define the winter in terms of cold overall, but it can give a good hint at the temperature pattern for the coming winter.
Based on the OPI, the stratosphere, solar conditions, as well as my analog years, the Arctic Oscillation is expected to be negative this winter.
Andrew
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| CPC |
Gazing over the image above, specifically around the most recent records of temperatures, we find ourselves on the above-normal side, with that red line bursting up into above-normal territory more than once in the last few weeks. This year's warmth at the 70mb level looks to be a bit more prevalent than that of last year, as you can see just to the left of the center of this image.
Why is this important to the coming winter? Above-normal temperatures in the stratosphere allow for a higher threat for persistent high pressure to form over the Arctic Circle, and general upper-latitude area. The polar vortex, a strong low pressure system of cold air located across the troposphere and stratosphere, can be strengthened during times when the stratosphere is colder than normal, and weakened when warmth prevails.
When this warmth prevails, strong bodies of high pressure can punch north from the lower latitudes into the Arctic, disrupting the polar vortex. When this happens, fragments of the vortex can break off and be sent to the lower latitudes (as was seen last winter), or the whole vortex can be shunted down south. If the high pressure sticks around in the Arctic for long periods of time, it can be referred to as "blocking" high pressure, for the way it "blocks" the pattern from flowing east to west around the globe, since the high pressure remains stagnant and backs everything up.
If the stratosphere is to remain warmer than normal this winter, the polar vortex may fragment, leading to increased risks for cold air outbreaks in North America.
The above image shows anomalies of the October Pattern Index over the last several days, since the start of October. The OPI, the concept of which was brought about by a group of Italian scientists, says that monitoring of the atmosphere during the month of October can yield great hints at what the coming winter will bring. October is a month well-known for big winter-predictors showing their cards for the coming cold season (i.e. the LRC, and Judah Cohen's Snow Advance Index (SAI)), but it may interest many to know that the OPI may be one the best, if not the best predictor of the upcoming winter season out of the three mentioned above.
The explanation page of the OPI tells of the index's incredible accuracy, around 90%, of being able to predict the December-January-February Arctic Oscillation. In the winter, a negative phase of the Arctic Oscillation (AO) means the polar vortex is weak and is more prone to sending cold outbreaks to the mid-latitudes, while a positive AO indicates a strong polar vortex, hence a warmer winter increases in probability.
Though we aren't to the middle of October yet, early indications are that the OPI is sustained in a negative phase, today plummeting to around -2, as shown above. If the OPI stays in that negative territory for the rest of October, chances are the winter may have a negative Arctic Oscillation. The AO doesn't define the winter in terms of cold overall, but it can give a good hint at the temperature pattern for the coming winter.
Based on the OPI, the stratosphere, solar conditions, as well as my analog years, the Arctic Oscillation is expected to be negative this winter.
Andrew
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