Ben's Weather Blog

After Thursday, this week has been quite cold. Temperatures have gone down quite a lot, and snow is here as well. Today when the sun was up, the temperature varied from -17.2 to -15.7. A high of -15.7 is definitely quite abnormally low. Current forecasts suggest this is only the beginning.

Here are the current temperatures, with a bunch of numbers sprayed all over it so you make sense of it:

Those -40s up at the top are a big mass of cold air anchored there. Winds are sweeping this air across the country. The 5s and 10 you see in the bottom left are an area of upper-level ridging. If you take a close look, you can see winds coming out of that area currently extending all the way to the eastern edge of the Rocky Mountains.

As we can see here, we somewhat have a battle of warm and cold: Warm air is trying to move north from the ridge, and cold air is trying to move south from the mass of it in YK/NT/NU. The actual systems that are moving that cold air down are the lows on the very active storm track we currently have. This is expected to be the pattern for the next little while for southern Alberta and BC. Warmer, but when a low moves through, temperatures drop. Thus, an alternation of above and below normal. We, however, are far enough north that the warmth is not the dominant factor. For us, it more of an alternation of mildly below normal and record territory. Yes, record territory.

This brings me to the forecast. The actual large-scale system behind this is pretty boring, basically a continuation of what I just explained in the last paragraph. For the forecast for specifically us, things get quite interesting. To start, here’s Environment Canada:

Like I said, a wave of mildly below normal (Sun/Mon), and record territory (Thu/Fri). Those highs are definitely record territory, but a low of -28 isn’t. Other forecasts have -30s for Wednesday night-Friday night.

Now let’s look at an ensemble model:

This is the Canadian one, GEPS. Ensembles wash things out as they go on, so I’ve drawn arrows for the likely temperature patterns. It has the 25-75 percentile actually getting quite close to -35 Thursday night. Even ensembles amplify temperature events as they near, so we might have a shot at getting it. -35 is definitely record territory.

Operational models also have extreme cold, and the most extreme of them, ECMWF, has us getting within a few degrees of -40. I would say we have good chances at both a minimum low and minimum high records, with temperatures to beat being around -35 and -25.

The very interesting thing about this cold wave is that we will still stay active, and the semi-clippers that we have (semi because they are tracking over us quite slow, then speed up as they exit Alberta) will continue to ring good amounts of snow repeatedly.

One more thing, we have no idea when this cold wave will end. The best thing I can say is that there is about a 90% chance of us still being in it in 10 days.

Starting Monday, a large pattern change will occur and we will dive to quite possibly well below normal temperatures.

To begin, we’ll talk about why. For the last many months low pressure has dominated the first 1000 kilometres off the west coast of Canada and the US, but now that is changing.

Here’s now:

Here’s a week from now:

Right now, low pressure dominates in the eastern Pacific, but a large transition will take place around the weekend, where a ridge takes that place. At this time of year, a ridge in the eastern Pacific will disturb the polar vortex (especially when it is weak, like right now), and cause it to rebound just east. This means a sudden shot of cold air. The Pacific ridge will strengthen fast over next week, and keep cold in place for quite a while.

So it was pretty simple why, so next we have to investigate the structure of the cold wave. I would guess starting Monday, temperature will begin to drop, but it wont be very fast. Only a gradual decrease of 3-5 degrees a day. Temperatures will likely stabilize around Wednesday, and stay stable for the rest of the work week.

From the 29th on, models currently diverge considerably, but the main pattern is still on most. Expect a quick ~2 day shot of even colder air, probably bringing the coldest of the cold wave, before a very rapid warmup, staying warm for about another two days, and then a possible return to cold. The exact timing of all this currently varies from starting the 29th to starting the 1st.

During the shot of even colder air, current model differences are generally between -15 and -30 for a lowest temperature.

Now finally, the snow. The begin the cold wave it seems we will have a system move pretty much straight across the entire prairies from west to east. Another system will also come up form the US and interact with it. Here is a map, to help you make sense of this:

These two lows will interact and possibly merge. If they do, the prairie low will get stalled before, and give us a lot of heavy snow. If they don’t get close enough to each other, then the low will more act as an Alberta clipper, and only give us a dusting of snow. Right now, model differences generally put down between 1 and 10 cm of snow mainly Monday morning through Monday night.

For right now, that is all you need to know. Be prepared for the cold!

After a pretty average weekend, temperatures are expected to get back up to above normal, but not by much.

It will start around midnight tonight, when a warm front will come through:

This will raise temperatures by a few degrees, and bring in a warmer airmass. There might be precipitation along the front, but most likely we won’t get anything.

For the next few days, expect highs around 13-15 and lows around 3-5, with the exception of tomorrow night, when we may actually reach the negatives.

On Wednesday night, a low will pass over southern Alberta, and some precipitation may reach here. Here’s another map:

After that, expect a quite warm Friday, with a high getting into the high teens. After Friday, it seems we may end up diving into a cold wave.

But what is the reason for all this? Well, it’s going to involve many more maps:

First of all, let’s start with right now; the first image. The upper-level flow has been very active lately, with rounds of lows circumnavigating the globe. As you can see, we can find 5 on the scope of the map. On the second map, now for tomorrow’s forecasted conditions, we can find low #2 has dissipated, while #1 has strengthened. As this low continues to strengthen, ridging begins on the west coast and quickly balloons to what we can see on the third map, for Wednesday. This is the usual pattern for North America; if there is a low in the Gulf of Alaska and nothing is blocking ridging on the west coast, it will happen.

This ridge isn’t strong though, so the heat won’t be as well. In the fourth picture, now for Thursday, we also find a weak subtropical jet is trying to form. We can also see the main jet stream seems to be breaking up a lot at the top of the ridge, which is normal for weak, tall ridges that are starting to decay.

As we get to image 5, for Saturday, we see the very small hint of a subtropical jet stream is gone, but another weak bit of flow connecting the bottom points of the ridge are connecting a bit. The jet extension (strong, zonal flow) from Siberia is pushing the stuck low over to here, and temperatures will drop quickly after the end of the work week.

Some of you may be wondering what all the red and blue dashed lines on the maps are, so here’s an explanation. They are contour lines for the distance between the surface and the altitude at which the pressure reaches about half of that. It is generally warmer when that value is higher, and vice versa. If you look very closely, you may be able to see some numbers on the lines, which is a value at the contour in decametres. The thick blue line at 540 is approximately where rain will change over to snow.

Well, that’s it for today! No posts tomorrow, but I’ll be back Wednesday.