During the year one of the most common questions I get asked is how I come up with all of the different topics I discuss. Usually it s fairly simple and straightforward since our region sees some of the most active weather in the world. I also receive questions about different aspects of the weather and climate that I love to try and answer, so I encourage anyone to email me questions.
Every once in a while, though, it does become a little tough to come up with new things to discuss when no new questions have come in, or when our weather has been relatively quiet. With a couple of exceptions the weather across much of the Prairies has been relatively quiet this past couple of weeks. There have been a few storm systems that have brought snow cover to most regions (check out the snow cover map), but nothing in these storms has been unusual and our snow cover is pretty much average.
One of the two fairly noteworthy weather events across the Prairies this past couple of weeks has been the unusually mild temperatures over most of the Prairies, at least up until this was written last week. With a forecast for bitterly cold weather and lots of snow this winter, we have so far seen pretty much the opposite. All of the major centres across the Prairies have seen well-above-average temperatures so far this month, with highs on most days making it above 0 C, and several centres and days seeing high temperatures near or even above 10 C! We did see a short cold snap centred on the 18th of the month, where overnight lows dropped into the -20 C range, but as quick as the cold air moved in, it moved out again. The second event was the high winds which rocked a good portion of southern and western Alberta with wind speeds of over 140 km/h reported.
High pressure continues
What is causing all of these warm temperatures and the high winds? Well, believe it or not, the weather pattern responsible appears to be an extension of the weather pattern we saw for much of the summer across the Prairies. Strong areas of high pressure have been continuously redeveloping over the western United States. These highs are not only surface based, but extend well into the upper atmosphere. This results in plenty of sinking air, which usually means plenty of sunshine and warm temperatures.
We have definitely seen the warm temperatures, although sometimes we ve been lacking in the sunshine department. The reason for this is that the sinking air under the high can trap moisture near the ground. Combine this with the cooler temperatures we naturally see at this time of the year and you will often get plenty of low clouds and/or fog. While this will keep temperatures from really heating up during the day, cloud cover at night during the winter will almost always result in warmer temperatures.
Along with the warm temperatures there have been some strong differences in pressure between the southwestern high and areas of low pressure moving through central and northern Canada. It was this situation that brought the extremely high winds on the 23rd of November.
The two big questions, I guess, are what is causing this particular pattern, and how long is it going to last? Both of these questions are tough ones. The first question, as to what causes this particular pattern, is difficult to answer since there does not appear to be any direct driving force for it. In fact, any of the current long-term driving forces are still pointing toward colder-than-average conditions.
Could it be the low ice cover we have been seeing in the Arctic? Well, new research shows there appears to be a connection between the low ice cover and a northward movement in the position of the jet stream. With a more northerly position of the jet stream it is possible that the usual southern upper high could be allowed to drift farther north than what normally happens. Since the jet stream is the location where most main storm systems will travel, it is not surprising that we have not seen much in the way of significant snow or rainfall so far this winter.
The argument or question around all of this is: What is driving what? Is the upper high simply pushing the jet stream farther north, or is the northern movement of the jet stream allowing the high to move north? We don t really know the answer, and likely won t at least not for a number of years.
If the pattern starts to show up more and more often, then it s probably the drop in sea ice driving the change. The other big question is, how long will this weather continue? My first response is, Who knows?
If we actually take a look at the medium-range weather models that forecast out to about Dec. 10, they lean toward an overall continuation of this pattern. We are moving deeper and deeper into winter and the amount of solar energy is continuing to decline. This means that not only are we getting less energy and are continually cooling off, but over the Arctic, cold air is continuing to build. This will mean it will be increasingly difficult to maintain mild temperatures and it will also become harder and harder for the southern ridge of high pressure to keep the cold Arctic air at bay.
Personally, until I see a definite shift in the weather models to a different pattern, I would say that we should expect warmer-and drier-than-average conditions to last well into December.
For those of you who are superstitious, I guess I just blew it, and we ll probably now see temperatures come crashing down soon.
Infact,anyofthe currentlong-term drivingforcesare stillpointingtoward colder-than-average conditions.